Showing papers on "Ferromagnetism published in 2013"
TL;DR: This work directly confirms the DW chirality and rigidity by examining current-driven DW dynamics with magnetic fields applied perpendicular and parallel to the spin spiral and resolves the origin of controversial experimental results.
Abstract: In most ferromagnets the magnetization rotates from one domain to the next with no preferred handedness. However, broken inversion symmetry can lift the chiral degeneracy, leading to topologically rich spin textures such as spin spirals and skyrmions through the Dzyaloshinskii-Moriya interaction (DMI). Here we show that in ultrathin metallic ferromagnets sandwiched between a heavy metal and an oxide, the DMI stabilizes chiral domain walls (DWs) whose spin texture enables extremely efficient current-driven motion. We show that spin torque from the spin Hall effect drives DWs in opposite directions in Pt/CoFe/MgO and Ta/CoFe/MgO, which can be explained only if the DWs assume a Neel configuration with left-handed chirality. We directly confirm the DW chirality and rigidity by examining current-driven DW dynamics with magnetic fields applied perpendicular and parallel to the spin spiral. This work resolves the origin of controversial experimental results and highlights a new path towards interfacial design of spintronic devices.
1,591 citations
TL;DR: In this article, the spin Hall magnetoresistance effect in ferromagnetic insulator/platinum and non-ferromagnet hybrid structures was investigated and quantitatively analyzed.
Abstract: We experimentally investigate and quantitatively analyze the spin Hall magnetoresistance effect in ferromagnetic insulator/platinum and ferromagnetic insulator/nonferromagnetic metal/platinum hybrid structures. For the ferromagnetic insulator, we use either yttrium iron garnet, nickel ferrite, or magnetite and for the nonferromagnet, copper or gold. The spin Hall magnetoresistance effect is theoretically ascribed to the combined action of spin Hall and inverse spin Hall effect in the platinum metal top layer. It therefore should characteristically depend upon the orientation of the magnetization in the adjacent ferromagnet and prevail even if an additional, nonferromagnetic metal layer is inserted between Pt and the ferromagnet. Our experimental data corroborate these theoretical conjectures. Using the spin Hall magnetoresistance theory to analyze our data, we extract the spin Hall angle and the spin diffusion length in platinum. For a spin-mixing conductance of 4×1014 ??1m?2, we obtain a spin Hall angle of 0.11±0.08 and a spin diffusion length of (1.5±0.5) nm for Pt in our thin-film samples
457 citations
TL;DR: The first experimental verification of the spin gapless magnetic semiconductor Mn(2)CoAl, an inverse Heusler compound with a Curie temperature of 720 K and a magnetic moment of 2 μ(B) is reported.
Abstract: Recent studies have reported an interesting class of semiconductor materials that bridge the gap between semiconductors and half-metallic ferromagnets. These materials, called spin gapless semiconductors, exhibit a band gap in one of the spin channels and a zero band gap in the other and thus allow for tunable spin transport. Here, we report the first experimental verification of the spin gapless magnetic semiconductor Mn(2)CoAl, an inverse Heusler compound with a Curie temperature of 720 K and a magnetic moment of 2 μ(B). Below 300 K, the compound exhibits nearly temperature-independent conductivity, very low, temperature-independent carrier concentration, and a vanishing Seebeck coefficient. The anomalous Hall effect is comparatively low, which is explained by the symmetry properties of the Berry curvature. Mn(2) CoAl is not only suitable material for room temperature semiconductor spintronics, the robust spin polarization of the spin gapless semiconductors makes it very promising material for spintronics in general.
399 citations
TL;DR: The findings suggest the use of chemically amenable phenalenyl-based molecules as a viable and scalable platform for building molecular-scale quantum spin memory and processors for technological development.
Abstract: When molecules of a phenalenyl derivative, which has no net spin, are deposited on a ferromagnet, they develop into a magnetic supramolecular layer with spin-filtering properties; this could be the basis for a new approach to building molecular magnetic devices. Various types of molecular magnets carrying high localized spin have been studied as potential devices for information processing and storage, but it remains a considerable challenge to electronically couple to these spin centres. Moodera et al. have designed a phenalenyl derivative, essentially a graphene fragment, with the potential to act as an interface for the exchange of magnetic spin information in molecular spintronic devices. The graphene fragment has no net spin itself, but when deposited as a layer on a ferromagnet it transforms to produce a supramolecular magnetic film. The resulting nanoscale magnetic molecules, or memory 'bits', can be manipulated by external stimuli, and the resulting device exhibits an unexpectedly large magnetoresistance of 20% near room temperature. The use of molecular spin state as a quantum of information for storage, sensing and computing has generated considerable interest in the context of next-generation data storage and communication devices1,2, opening avenues for developing multifunctional molecular spintronics3. Such ideas have been researched extensively, using single-molecule magnets4,5 and molecules with a metal ion6 or nitrogen vacancy7 as localized spin-carrying centres for storage and for realizing logic operations8. However, the electronic coupling between the spin centres of these molecules is rather weak, which makes construction of quantum memory registers a challenging task9. In this regard, delocalized carbon-based radical species with unpaired spin, such as phenalenyl10, have shown promise. These phenalenyl moieties, which can be regarded as graphene fragments, are formed by the fusion of three benzene rings and belong to the class of open-shell systems. The spin structure of these molecules responds to external stimuli11,12 (such as light, and electric and magnetic fields), which provides novel schemes for performing spin memory and logic operations. Here we construct a molecular device using such molecules as templates to engineer interfacial spin transfer resulting from hybridization and magnetic exchange interaction with the surface of a ferromagnet; the device shows an unexpected interfacial magnetoresistance of more than 20 per cent near room temperature. Moreover, we successfully demonstrate the formation of a nanoscale magnetic molecule with a well-defined magnetic hysteresis on ferromagnetic surfaces. Owing to strong magnetic coupling with the ferromagnet, such independent switching of an adsorbed magnetic molecule has been unsuccessful with single-molecule magnets13. Our findings suggest the use of chemically amenable phenalenyl-based molecules as a viable and scalable platform for building molecular-scale quantum spin memory and processors for technological development.
373 citations
TL;DR: It is shown that the Dzyaloshinskii-Moriya interaction can be adjusted to stabilize either left-handed or right-handed Néel walls, or non-chiral Bloch walls by adjusting an interfacial spacer layer between the multilayers and the substrate.
Abstract: Contacting ferromagnetic films with normal metals changes how magnetic textures respond to electric currents, enabling surprisingly fast domain wall motions and spin texture-dependent propagation direction. These effects are attributed to domain wall chirality induced by the Dzyaloshinskii-Moriya interaction at interfaces, which suggests rich possibilities to influence domain wall dynamics if the Dzyaloshinskii-Moriya interaction can be adjusted. Chiral magnetism was seen in several film structures on appropriately chosen substrates where interfacial spin-orbit-coupling effects are strong. Here we use real-space imaging to visualize chiral domain walls in cobalt/nickel multilayers in contact with platinum and iridium. We show that the Dzyaloshinskii-Moriya interaction can be adjusted to stabilize either left-handed or right-handed Neel walls, or non-chiral Bloch walls by adjusting an interfacial spacer layer between the multilayers and the substrate. Our findings introduce domain wall chirality as a new degree of freedom, which may open up new opportunities for spintronics device designs.
347 citations
TL;DR: In this paper, the authors demonstrate that ultrathin ferromagnetic Pt/Co/Pt films with perpendicular magnetic anisotropy exhibit a sizable Dzyaloshinskii-Moriya interaction (DMI) effect.
Abstract: We demonstrate here that ultrathin ferromagnetic Pt/Co/Pt films with perpendicular magnetic anisotropy exhibit a sizable Dzyaloshinskii-Moriya interaction (DMI) effect. Such a DMI effect modifies the domain-wall (DW) energy density and consequently, results in an asymmetric DW expansion driven by an out-of-plane magnetic field under an in-plane magnetic field bias. From an analysis of the asymmetry, the DMI effect is estimated to be strong enough for the DW to remain in the N\'eel-type configuration in contrast to the general expectations of these materials. Our findings emphasize the critical role of the DMI effect on the DW dynamics as the underlying physics of the asymmetries that are often observed in spin-transfer-related phenomena.
341 citations
TL;DR: In this paper, the authors employ ab-initio electronic structure calculations to study 60 LiMgPdSn-type quaternary Heusler compounds, including half-metals, spin-gapless semiconductors, and 9 semiconductor types.
Abstract: We employ ab-initio electronic structure calculations to study 60 LiMgPdSn-type (also known as LiMgPdSb-type) quaternary Heusler compounds. All compounds obey the Slater-Pauling rule with diverse electronic and magnetic properties. 41 compounds are found to be half-metals, 8 spin-gapless semiconductors, and 9 semiconductors. CoVTiAl and CrVTiAl compounds are identified as ferromagnetic and antiferromagnetic semiconductors, respectively, with large energy gaps in both spin directions. All magnetic compounds are expected to have high Curie temperatures making them suitable for spintronics/magnetoelectronics applications.
329 citations
TL;DR: Optical manipulation of magnetic order by femtosecond laser pulses has developed into an exciting and still expanding research field that keeps being fueled by a continuous stream of new and sometimes counterintuitive results, which may also potentially revolutionize data storage and information processing technologies.
Abstract: This review discusses the recent studies of magnetization dynamics and the role of angular momentum in thin films of ferrimagnetic rare-earth-transition metal (RE-TM) alloys, e.g. GdFeCo, where both magnetization and angular momenta are temperature dependent. It has been experimentally demonstrated that the magnetization can be manipulated and even reversed by a single 40 fs laser pulse, without any applied magnetic field. This switching is found to follow a novel reversal pathway, that is shown however to depend crucially on the net angular momentum, reflecting the balance of the two opposite sublattices. In particular, optical excitation of ferrimagnetic GdFeCo on a time scale pertinent to the characteristic time of the exchange interaction between the RE and TM spins, i.e. on the time scale of tens of femtoseconds, pushes the spin dynamics into a yet unexplored regime, where the two exchange-coupled magnetic sublattices demonstrate substantially different dynamics. As a result, the reversal of spins appears to proceed via a novel transient state characterized by a ferromagnetic alignment of the Gd and Fe magnetic moments, despite their ground-state antiferromagnetic coupling.Thus, optical manipulation of magnetic order by femtosecond laser pulses has developed into an exciting and still expanding research field that keeps being fueled by a continuous stream of new and sometimes counterintuitive results. Considering the progress in the development of plasmonic antennas and compact ultrafast lasers, optical control of magnetic order may also potentially revolutionize data storage and information processing technologies.
305 citations
TL;DR: Spectroscopic investigations of the magnetism using element-specific techniques, including X-ray magnetic circular dichroism andX-ray absorption spectroscopy, are reported, finding direct evidence for in-plane ferromagnetic order at the interface with Ti(3+) character in the dxy orbital of the anisotropic t2g band.
Abstract: A number of recent transport and magnetization studies have shown signs of ferromagnetism in the LaAlO3/SrTiO3 heterostructure, an unexpected property with no bulk analogue in the constituent materials. However, no experiment thus far has provided direct information on the host of the magnetism. Here we report spectroscopic investigations of the magnetism using element-specific techniques, including X-ray magnetic circular dichroism and X-ray absorption spectroscopy, along with corresponding model calculations. We find direct evidence for in-plane ferromagnetic order at the interface, with Ti(3+) character in the dxy orbital of the anisotropic t2g band. These findings establish a striking example of emergent phenomena at oxide interfaces.
292 citations
TL;DR: In this paper, proximity-induced ferromagnetism was demonstrated in a topological insulator, combining a ferromagnetic insulator EuS layer with Bi(2)Se(3), without introducing defects.
Abstract: An exchange gap in the Dirac surface states of a topological insulator (TI) is necessary for observing the predicted unique features such as the topological magnetoelectric effect as well as to confine Majorana fermions. We experimentally demonstrate proximity-induced ferromagnetism in a TI, combining a ferromagnetic insulator EuS layer with Bi(2)Se(3), without introducing defects. By magnetic and magnetotransport studies, including anomalous Hall effect and magnetoresistance measurements, we show the emergence of a ferromagnetic phase in TI, a step forward in unveiling their exotic properties.
289 citations
TL;DR: A large spin Hall angle in Py, determined from Py thin films of different thicknesses, indicates many other ferromagnetic metals may be exploited as superior pure spin current detectors and for applications in spin current.
Abstract: The inverse spin Hall effect (ISHE) has been observed only in nonmagnetic metals, such as Pt and Au, with a strong spin-orbit coupling. We report the observation of ISHE in a ferromagnetic permalloy (Py) on ferromagnetic insulator yttrium iron garnet (YIG). Through controlling the spin current injection by altering the Py-YIG interface, we have isolated the spin current contribution and demonstrated the ISHE in a ferromagnetic metal, the reciprocal phenomenon of the anomalous Hall effect. A large spin Hall angle in Py, determined from Py thin films of different thicknesses, indicates many other ferromagnetic metals may be exploited as superior pure spin current detectors and for applications in spin current.
TL;DR: A new metallic 2D material with high electrical conductivity (1×10(3) S m(-1)) consists of VSe2 ultrathin nanosheets with 4-8 Se-V-Se atomic layers with intrinsic room-temperature ferromagnetism.
Abstract: A new metallic 2D material with high electrical conductivity (1×10(3) S m(-1)) consists of VSe2 ultrathin nanosheets with 4-8 Se-V-Se atomic layers. This is the first 2D transition-metal dichalcogenide with intrinsic room-temperature ferromagnetism. The nanosheets increase the charge-density-wave transition temperature to 135 K by dimensional reduction.
TL;DR: In this paper, a short review is given of the recent work on single-phase crystals that are ferroelectric and ferromagnetic at or near room temperature, focusing on copper oxide, perovskite oxides with mixed B-site occupancy (such as Pb(Fe1/2Ta 1/2)x(ZryTi1−y)1−xO3 and related Nb and W compounds), Fe-, Co-, and Mn-based Aurivilius-phase oxides and hexaferrites.
Abstract: A short review is given of the recent work on single-phase crystals that are ferroelectric and ferromagnetic at or near room temperature. BiFeO3 is mentioned only briefly, because it has been reviewed in detail elsewhere very recently; emphasis instead is on copper oxide, perovskite oxides with mixed B-site occupancy (such as Pb(Fe1/2Ta1/2)x(ZryTi1−y)1−xO3 and related Nb and W compounds), Fe-, Co-, and Mn-based Aurivilius-phase oxides and hexaferrites. Seven years ago, Wilma Eerenstein, Neil Mathur and Jim Scott published a Venn diagram (above) showing the overlap of piezoelectricity, ferroelectricity (green circle), ferromagnetism (black circle), and magnetoelectricity (blue hatched center circle); and soon thereafter Manuel Bibes put into each sector the crystals which were thought to belong. The overlap region between green and black are multiferroic ferromagnetic-ferroelectrics. Not all were correct; BiMnO3 is NOT ferroelectric. Of these materials, only Cr2O3 and BiFeO3 function at room temperature (or are magnetoelectric, and the former is neither a ferromagnet nor ferroelectric). Today’s review is an update on the new multiferroic and/or magnetoelectric materials that function at or near ambient temperatures and pressures: Cupric oxide (not actually magnetoelectric), iron magnesium hexaferrites, and perovskite oxides based upon PbTiO3.
Multiferroics combine two properties not typically found together: ferroelectricity and ferromagnetism. With complex structures and properties, such materials are undeniably intriguing. James F. Scott reviews single-phase multiferroics that exhibit the magnetoelectric effect — whereby magnetic polarization is induced by applying an external electric field or, conversely, an electric polarization is induced through a magnetic field — at or near room temperature. In particular, four classes of materials — copper oxides, perovskite oxides, ‘Aurivillius-phase’ layered oxides and manganese hexaferrites — are discussed. Multiferroic magnetoelectrics have potential data storage applications and should ideally combine properties desirable for both magnetic and ferroelectric random-access memory. Various limitations such as low operational temperatures, small polarizations, and possibly slow switching speeds (still unmeasured for most new materials) had hindered their use, but these are likely to be overcome in future. The materials reviewed here seem very promising, advances in processing may improve the properties of multiferroic magnetoelectrics, and these compounds could also prove suitable for other memory devices.
TL;DR: N nanometre-sized ferromagnetic platelets suspended in a nematic liquid crystal can order ferromagnetically on quenching from the isotropic phase, and may find use in magneto-optic devices.
Abstract: More than four decades ago, Brochard and de Gennes proposed that colloidal suspensions of ferromagnetic particles in nematic (directionally ordered) liquid crystals could form macroscopic ferromagnetic phases at room temperature. The experimental realization of these predicted phases has hitherto proved elusive, with such systems showing enhanced paramagnetism but no spontaneous magnetization in the absence of an external magnetic field. Here we show that nanometre-sized ferromagnetic platelets suspended in a nematic liquid crystal can order ferromagnetically on quenching from the isotropic phase. Cooling in the absence of a magnetic field produces a polydomain sample exhibiting the two opposing states of magnetization, oriented parallel to the direction of nematic ordering. Cooling in the presence of a magnetic field yields a monodomain sample; magnetization can be switched by domain wall movement on reversal of the applied magnetic field. The ferromagnetic properties of this dipolar fluid are due to the interplay of the nematic elastic interaction (which depends critically on the shape of the particles) and the magnetic dipolar interaction. This ferromagnetic phase responds to very small magnetic fields and may find use in magneto-optic devices. The idea that magnetic particles suspended in a liquid crystal might spontaneously orient into a ferromagnetic state has hitherto not been confirmed experimentally, but such a state has now been realized using nanometre-sized ferromagnetic platelets in a nematic liquid crystal. The idea that magnetic particles suspended in a liquid crystal might spontaneously orient into a ferromagnetic state has been around for decades but had not been confirmed experimentally. Alenka Mertelj and colleagues have now realized such a state using nanosized ferromagnetic platelets in a nematic liquid crystal. The shape of the thin platelets is key to the development of ferromagnetic ordering. The resulting 'liquid magnet' phase responds to very small magnetic fields and may lead to new magneto–optic devices.
TL;DR: In this article, the grain boundary diffusion process using an Nd70Cu30 eutectic alloy has been applied to hot-deformed anisotropic Nd-Fe-B magnets, resulting in a substantial enhancement of coercivity, at the expense of remanence.
TL;DR: The analysis interestingly shows that the calculated BMP concentration scales linearly with concentration of oxygen vacancies and provides a stronger footing for exploiting defect engineered ferromagnetism in undoped TiO2 nanostructures.
Abstract: We report on the oxygen vacancy induced ferromagnetism (FM) at and above room temperature in undoped TiO2 nanoporous nanoribbons synthesized by a solvothermal route. The origin of FM in as-synthesized and vacuum annealed undoped nanoribbons grown for different reaction durations followed by calcinations was investigated by several experimental tools. X-Ray diffraction pattern and micro-Raman studies reveal the TiO2(B), TiO2(B)-anatase, and anatase–rutile mixed phases of TiO2 structure. Field emission scanning electron microscopy and transmission electron microscopy observations reveal nanoribbons with uniform pore distribution and nanopits/nanobricks formed on the surface. These samples exhibit strong visible photoluminescence associated with oxygen vacancies and a clear ferromagnetic hysteresis loop, both of which dramatically enhanced after vacuum annealing. Direct evidence of oxygen vacancies and related Ti3+ in the as-prepared and vacuum annealed TiO2 samples are provided through X-ray photoelectron spectroscopy analysis. Micro-Raman, infrared absorption and optical absorption spectroscopic analyses further support our conclusion. The observed room temperature FM in undoped TiO2 nanoribbons is quantitatively analyzed and explained through a model involving bound magnetic polarons (BMP), which include an electron locally trapped by an oxygen vacancy with the trapped electron occupying an orbital overlapping with the unpaired electron (3d1) of Ti3+ ion. Our analysis interestingly shows that the calculated BMP concentration scales linearly with concentration of oxygen vacancies and provides a stronger footing for exploiting defect engineered ferromagnetism in undoped TiO2 nanostructures. The development of such highly porous TiO2 nanoribbons constitutes an important step towards realizing improved visible light photocatalytic and photovoltaic applications of this novel material.
TL;DR: It is found that a structural anomaly arises for the particles with size close to the 62 nm period of the spiral modulated spin structure, which induces an obviously increased ferromagnetism and a clue to the magnetic structure at nanoscale is provided.
Abstract: Size effect of multiferroics is important for its potential applications in new type miniaturized multifunctional devices and thus has been widely studied. However, is there special size effect in the materials with spiral modulated spin structure (such as BiFeO3)? It is still an issue to be investigated. In this report, structural, magnetic and magnetoelectric coupling properties are investigated for sol-gel prepared BiFeO3 nanoparticles with various sizes. It is found that a structural anomaly arises for the particles with size close to the 62 nm period of the spiral modulated spin structure, which induces an obviously increased ferromagnetism. In addition, large magnetoelectric coupling effect is observed in 62 nm BiFeO3 nanoparticles. Our result provides another insight into the size effect of BiFeO3, and also a clue to the magnetic structure at nanoscale.
TL;DR: In this article, a quaternary Heusler half-metallic ferromagnets CoFeCrZ was designed and its first-principles calculations showed that, within a generalized gradient approximation for the electronic exchange correlation functional, both CoFeFeCrGa and CoFeGe are nearly halfmetals.
TL;DR: Here it is demonstrated a method for thermalizing artificial spin ices with square and kagome lattices by heating above the Curie temperature of the constituent material, which achieves unprecedented thermal ordering of the moments.
Abstract: Artificial spin-ice systems are lithographically fabricated arrays of interacting ferromagnetic nanometre-scale islands; a procedure to thermalize two types of artificial spin ice with different geometries has now been developed, resulting in unprecedentedly large ground-state domains in square lattices and crystallites of ordered magnetic charges in kagome lattices. Artificial spin-ice systems, first reported in 2006, are lithographically fabricated arrays of interacting ferromagnetic nanoislands. The magnetic moments of the islands, or 'spins', attempt to align with each other but not all succeed, creating a 'frustrated' system. Frustration prevents complete order and gives rise to interesting dynamic and magnetic properties. A limitation of artificial spin-ice systems has been that they are usually found in an 'athermal', frozen state, preventing the experimental investigation of novel phases that can emerge from thermal fluctuations of frustrated structures. Zhang et al. have now developed a procedure to thermalize two types of artificial spin ice with different geometries. They observe the formation of unprecedented large ground-state domains for square lattices, and the crystallization of magnetic (monopole-like) charges in kagome spin ice. The work opens the possibility of studying a new landscape of magnetic phases and behaviour. Artificial spin ice1 is a class of lithographically created arrays of interacting ferromagnetic nanometre-scale islands. It was introduced to investigate many-body phenomena related to frustration and disorder in a material that could be tailored to precise specifications and imaged directly. Because of the large magnetic energy scales of these nanoscale islands, it has so far been impossible to thermally anneal artificial spin ice into desired thermodynamic ensembles; nearly all studies of artificial spin ice have either treated it as a granular material activated by alternating fields2 or focused on the as-grown state of the arrays3. This limitation has prevented experimental investigation of novel phases that can emerge from the nominal ground states of frustrated lattices. For example, artificial kagome spin ice, in which the islands are arranged on the edges of a hexagonal net, is predicted to support states with monopolar charge order at entropies below that of the previously observed pseudo-ice manifold4. Here we demonstrate a method for thermalizing artificial spin ices with square and kagome lattices by heating above the Curie temperature of the constituent material. In this manner, artificial square spin ice achieves unprecedented thermal ordering of the moments. In artificial kagome spin ice, we observe incipient crystallization of the magnetic charges embedded in pseudo-ice, with crystallites of magnetic charges whose size can be controlled by tuning the lattice constant. We find excellent agreement between experimental data and Monte Carlo simulations of emergent charge–charge interactions.
TL;DR: In this paper, a lattice-shaking technique was used to induce a strong effective spin-interaction, leading to the formation of ferromagnetic domains in optical lattices.
Abstract: Ultracold atoms in optical lattices are used to study various phenomena in condensed-matter physics, such as magnetism A lattice-shaking technique can induce a strong effective spin-interaction, leading to the formation of ferromagnetic domains
TL;DR: In situ 90° electric field-induced uniform magnetization rotation in single domain submicron ferromagnetic islands grown on a ferroelectric single crystal using x-ray photoemission electron microscopy is demonstrated.
Abstract: We demonstrate in situ 90\ifmmode^\circ\else\textdegree\fi{} electric field-induced uniform magnetization rotation in single domain submicron ferromagnetic islands grown on a ferroelectric single crystal using x-ray photoemission electron microscopy. The experimental findings are well correlated with micromagnetic simulations, showing that the reorientation occurs by the strain-induced magnetoelectric interaction between the ferromagnetic nanostructures and the ferroelectric crystal. Specifically, the ferroelectric domain structure plays a key role in determining the response of the structure to the applied electric field, resulting in three strain-induced regimes of magnetization behavior for the single domain islands.
TL;DR: Combining the X-ray photoelectron spectroscopy, transmission electron microscopy, and electron spin resonance results, it is suggested that the observed magnetization is related to the presence of edge spins on the edges of the nanosheets.
Abstract: Freestanding MoS2 nanosheets with different sizes were prepared through a simple exfoliated method by tuning the ultrasonic time in the organic solvent. Magnetic measurement results reveal the clear room-temperature ferromagnetism for all the MoS2 nanosheets, in contrast to the pristine MoS2 in its bulk form which shows diamagnetism only. Furthermore, results indicate that the saturation magnetizations of the nanosheets increase as the size decreases. Combining the X-ray photoelectron spectroscopy, transmission electron microscopy, and electron spin resonance results, it is suggested that the observed magnetization is related to the presence of edge spins on the edges of the nanosheets. These MoS2 nanosheets may find applications in nanodevices and spintronics by controlling the edge structures.
TL;DR: It is shown for the first time that the MnO2 monolayer, synthetized 10 years ago, exhibits intrinsic ferromagnetism with a Curie temperature of 140 K, comparable to the highest TC value achieved experimentally for Mn-doped GaAs.
Abstract: The Mn atom, because of its special electronic configuration of 3d54s2, has been widely used as a dopant in various two-dimensional (2D) monolayers such as graphene, BN, silicene and transition metal dichalcogenides (TMDs). The distributions of doped Mn atoms in these systems are highly sensitive to the synthesis process and conditions, thus suffering from problems of low solubility and surface clustering. Here we show for the first time that the MnO2 monolayer, synthetized 10 years ago, where Mn ions are individually held at specific sites, exhibits intrinsic ferromagnetism with a Curie temperature of 140 K, comparable to the highest TC value achieved experimentally for Mn-doped GaAs. The well-defined atomic configuration and the intrinsic ferromagnetism of the MnO2 monolayer suggest that it is superior to other magnetic monolayer materials.
TL;DR: It is shown that a confined magnetism is realized at the interface between SrTiO3 and two insulating polar oxides, BiMnO 3 and LaAlO3, and in both cases the magnetism can be stabilized by a negative exchange interaction between the electrons transferred to the interface and local magnetic moments.
Abstract: Possible ferromagnetism induced in otherwise nonmagnetic materials has been motivating intense research in complex oxide heterostructures. Here we show that a confined magnetism is realized at the interface between SrTiO3 and two insulating polar oxides, BiMnO3 and LaAlO3. By using polarization dependent x-ray absorption spectroscopy, we find that in both cases the magnetism can be stabilized by a negative exchange interaction between the electrons transferred to the interface and local magnetic moments. These local magnetic moments are associated with magnetic Ti3+ ions at the interface itself for LaAlO3/SrTiO3 and to Mn3+ ions in the overlayer for BiMnO3/SrTiO3. In LaAlO3/SrTiO3 the induced magnetism is quenched by annealing in oxygen, suggesting a decisive role of oxygen vacancies in this phenomenon.
TL;DR: AlFe2B2 represents a rare case of a lightweight material prepared from earth-abundant, benign reactants which exhibits a substantial MCE while not containing any rare-earth elements.
Abstract: AlFe2B2 was prepared by two alternative synthetic routes, arc melting and synthesis from Ga flux. In the layered crystal structure, infinite chains of B atoms are connected by Fe atoms into two-dimensional [Fe2B2] slabs that alternate with layers of Al atoms. As expected from the theoretical analysis of electronic band structure, the compound exhibits itinerant ferromagnetism, with the ordering temperature of 307 K. The measurement of magnetocaloric effect (MCE) as a function of applied magnetic field reveals isothermal entropy changes of 4.1 J kg(-1) K(-1) at 2 T and 7.7 J kg(-1) K(-1) at 5 T. These are the largest values observed near room temperature for any metal boride and for any magnetic material of the vast 122 family of layered structures. Importantly, AlFe2B2 represents a rare case of a lightweight material prepared from earth-abundant, benign reactants which exhibits a substantial MCE while not containing any rare-earth elements.
TL;DR: In this paper, the structural, morphological and magnetic properties of nano-sized copper doped zinc ferrite powders were determined and characterized in detail by X-ray diffraction (XRD), high resolution scanning electron microscopy (HR-SEM), energy dispersive Xray spectroscopy (EDX) and vibrating sample magnetometer (VSM).
TL;DR: In this paper, a polymer precursor was used to synthesize barium hexaferrite (BaFe12O19) powders with hexagonal crystal structure using barium acetate and ferric acetylacetonate as precursors.
TL;DR: In this paper, the synthesis of undoped and Sc3+-doped BiFeO3 nanoparticles using the sonochemical technique was reported, where the substitution of Sc ions for Bi enhances the ferromagnetic as well as ferroelectric properties of this system.
Abstract: We report the synthesis of undoped and Sc3+-doped BiFeO3 nanoparticles using the sonochemical technique. X-ray diffraction reveals that all samples are single phase with no impurities detected. EDX analysis was done to confirm the extent of Sc3+ doping in the samples. The size and morphology of the nanoparticles have been analyzed using transmission electron microscopy (TEM). XPS studies were done to check the presence of Fe2+ ions in the samples. The BiFeO3 nanoparticles show a weak ferromagnetic behavior at room temperature, which is quite different from the linear M–H relationship reported for bulk BiFeO3. The substitution of Sc ions for Bi enhances the ferromagnetic as well as ferroelectric properties of this system, which is mainly attributed to the antiferromagnetic core and ferromagnetic surface of the nanoparticles, together with the mild structural distortion. Temperature and field dependence of magnetization curves reveal the frustrated magnetic behavior of this system. The leakage current is co...
TL;DR: The orthoferrite YFeO3 with orthorhombic perovskite structure (Pnma) has been synthesized by mild hydrothermal method as discussed by the authors.
Abstract: The orthoferrite YFeO3 with orthorhombic perovskite structure (Pnma) has been synthesized by mild hydrothermal method. The temperature-dependent magnetization and hysteresis loops indicate that, due to the superexchange and Dzyaloshinskii-Moriya interactions in the crystals, the Fe spins order antiferromagnetically at the Neel temperature 655 K with a weak ferromagnetic moment. The observation of saturation polarization loops at room temperature and 77 K provide evidence for the ferroelectric character of the polycrystalline samples. Its Curie temperature has been obtained from the temperature dependence of the relative permittivities and thermal analysis. As a result, the structure exhibits simultaneously weak ferromagnetic and ferroelectric behavior.
TL;DR: These results merge two fields, femtosecond magnetism in metals and band insulators, and non-equilibrium phase transitions of strongly correlated electrons, in which local interactions exceeding the kinetic energy produce a complex balance of competing orders.
Abstract: Magnetic order in a manganite can be switched during femtosecond photo-excitation via coherent superpositions of quantum states; this is analogous to processes in femtosecond chemistry where photoproducts of chemical and biochemical reactions can be influenced by creating suitable superpositions of molecular states. Today's magnetic memory and logic devices operate at gigahertz switching speeds. To achieve the even faster terahertz regime will require new technologies, and ultrafast all-optical magnetic switching using coherent spin manipulation is a leading contender. Ilias Perakis and colleagues demonstrate a development of this technique that achieves femtosecond all-optical switching of the magnetic state through the establishment of a 'colossal' magnetization component from an antiferromagnetic ground state. The switch to ferromagnetic ordering in Pr0.7Ca0.3MnO3 occurs within a mere 120 femtoseconds, a remarkably short time interval for a non-equilibrium magnetic phase transition. This is a new principle in magnetic switching, analogous to processes in femtochemistryin which photoproducts of chemical and biochemical reactions can be influenced by creating suitable superpositions of molecular states. This work is also of relevance to the fields of spin-chemistry, quantum biology and spin-electronics. The technological demand to push the gigahertz (109 hertz) switching speed limit of today’s magnetic memory and logic devices into the terahertz (1012 hertz) regime underlies the entire field of spin-electronics and integrated multi-functional devices. This challenge is met by all-optical magnetic switching based on coherent spin manipulation1. By analogy to femtosecond chemistry and photosynthetic dynamics2—in which photoproducts of chemical and biochemical reactions can be influenced by creating suitable superpositions of molecular states—femtosecond-laser-excited coherence between electronic states can switch magnetic order by ‘suddenly’ breaking the delicate balance between competing phases of correlated materials: for example, manganites exhibiting colossal magneto-resistance suitable for applications3,4. Here we show femtosecond (10−15 seconds) photo-induced switching from antiferromagnetic to ferromagnetic ordering in Pr0.7Ca0.3MnO3, by observing the establishment (within about 120 femtoseconds) of a huge temperature-dependent magnetization with photo-excitation threshold behaviour absent in the optical reflectivity. The development of ferromagnetic correlations during the femtosecond laser pulse reveals an initial quantum coherent regime of magnetism, distinguished from the picosecond (10−12 seconds) lattice-heating regime characterized by phase separation without threshold behaviour5,6. Our simulations reproduce the nonlinear femtosecond spin generation and underpin fast quantum spin-flip fluctuations correlated with coherent superpositions of electronic states to initiate local ferromagnetic correlations. These results merge two fields, femtosecond magnetism in metals and band insulators1,7,8,9, and non-equilibrium phase transitions of strongly correlated electrons10,11,12,13,14,15,16,17, in which local interactions exceeding the kinetic energy produce a complex balance of competing orders.