Showing papers on "Ferromagnetism published in 2014"
TL;DR: This work reports the switching of out-of-plane magnetized Ta/Co(20)Fe(60)B(20)/TaO(x) structures by spin-orbit torques driven by in-plane currents, without the need for any external magnetic fields.
Abstract: Magnetization switching by current-induced spin-orbit torques is of great interest due to its potential applications in ultralow-power memory and logic devices. The switching of ferromagnets with perpendicular magnetization is of particular technological relevance. However, in such materials, the presence of an in-plane external magnetic field is typically required to assist spin-orbit torque-driven switching and this is an obstacle for practical applications. Here, we report the switching of out-of-plane magnetized Ta/Co(20)Fe(60)B(20)/TaO(x) structures by spin-orbit torques driven by in-plane currents, without the need for any external magnetic fields. This is achieved by introducing a lateral structural asymmetry into our devices, which gives rise to a new field-like spin-orbit torque when in-plane current flows in these structures. The direction of the current-induced effective field corresponding to this field-like spin-orbit torque is out-of-plane, facilitating the switching of perpendicular magnets.
789 citations
TL;DR: In this article, a review compiles results of experimental and theoretical studies on thin films and quantum structures of semiconductors with randomly distributed Mn ions, which exhibit spintronic functionalities associated with collective ferromagnetic spin ordering.
Abstract: This review compiles results of experimental and theoretical studies on thin films and quantum structures of semiconductors with randomly distributed Mn ions, which exhibit spintronic functionalities associated with collective ferromagnetic spin ordering. Properties of p-type Mn-containing III-V as well as II-VI, IV-VI, V-2 -VI3, I-II-V, and elemental group IV semiconductors are described, paying particular attention to the most thoroughly investigated system (Ga, Mn)As that supports the hole-mediated ferromagnetic order up to 190 K for the net concentration of Mn spins below 10%. Multilayer structures showing efficient spin injection and spin-related magnetotransport properties as well as enabling magnetization manipulation by strain, light, electric fields, and spin currents are presented together with their impact on metal spintronics. The challenging interplay between magnetic and electronic properties in topologically trivial and nontrivial systems is described, emphasizing the entangled roles of disorder and correlation at the carrier localization boundary. Finally, the case of dilute magnetic insulators is considered, such as (Ga, Mn)N, where low-temperature spin ordering is driven by short-ranged superexchange that is ferromagnetic for certain charge states of magnetic impurities.
731 citations
TL;DR: It is found that the magnetic order on graphene edges of controlled zigzag orientation can be stable even at room temperature, raising hopes of graphene-based spintronic devices operating under ambient conditions.
Abstract: The possibility that non-magnetic materials such as carbon could exhibit a novel type of s-p electron magnetism has attracted much attention over the years, not least because such magnetic order is predicted to be stable at high temperatures. It has been demonstrated that atomic-scale structural defects of graphene can host unpaired spins, but it remains unclear under what conditions long-range magnetic order can emerge from such defect-bound magnetic moments. Here we propose that, in contrast to random defect distributions, atomic-scale engineering of graphene edges with specific crystallographic orientation--comprising edge atoms from only one sub-lattice of the bipartite graphene lattice--can give rise to a robust magnetic order. We use a nanofabrication technique based on scanning tunnelling microscopy to define graphene nanoribbons with nanometre precision and well-defined crystallographic edge orientations. Although so-called 'armchair' ribbons display quantum confinement gaps, ribbons with the 'zigzag' edge structure that are narrower than 7 nanometres exhibit an electronic bandgap of about 0.2-0.3 electronvolts, which can be identified as a signature of interaction-induced spin ordering along their edges. Moreover, upon increasing the ribbon width, a semiconductor-to-metal transition is revealed, indicating the switching of the magnetic coupling between opposite ribbon edges from the antiferromagnetic to the ferromagnetic configuration. We found that the magnetic order on graphene edges of controlled zigzag orientation can be stable even at room temperature, raising hopes of graphene-based spintronic devices operating under ambient conditions.
653 citations
TL;DR: The kinetics of the switching process is examined, something not considered previously in theoretical work, and a deterministic reversal of the DM vector and canted moment using an electric field at room temperature is shown.
Abstract: The technological appeal of multiferroics is the ability to control magnetism with electric field1, 2, 3. For devices to be useful, such control must be achieved at room temperature. The only single-phase multiferroic material exhibiting unambiguous magnetoelectric coupling at room temperature is BiFeO3 (refs 4 and 5). Its weak ferromagnetism arises from the canting of the antiferromagnetically aligned spins by the Dzyaloshinskii–Moriya (DM) interaction6, 7, 8, 9. Prior theory considered the symmetry of the thermodynamic ground state and concluded that direct 180-degree switching of the DM vector by the ferroelectric polarization was forbidden10, 11. Instead, we examined the kinetics of the switching process, something not considered previously in theoretical work10, 11, 12. Here we show a deterministic reversal of the DM vector and canted moment using an electric field at room temperature. First-principles calculations reveal that the switching kinetics favours a two-step switching process. In each step the DM vector and polarization are coupled and 180-degree deterministic switching of magnetization hence becomes possible, in agreement with experimental observation. We exploit this switching to demonstrate energy-efficient control of a spin-valve device at room temperature. The energy per unit area required is approximately an order of magnitude less than that needed for spin-transfer torque switching13, 14. Given that the DM interaction is fundamental to single-phase multiferroics and magnetoelectrics3, 9, our results suggest ways to engineer magnetoelectric switching and tailor technologically pertinent functionality for nanometre-scale, low-energy-consumption, non-volatile magnetoelectronics.
591 citations
TL;DR: In this article, the anomalous Hall effect was shown to arise due to a material's intrinsic ferromagnetic topological insulator, and it was shown that anomalous states can be mapped onto the normal states.
Abstract: Quantized resistivity values for 2D electron systems don’t necessarily result from an external magnetic field as in the ‘normal’ quantum Hall effect; they can arise due to a material's intrinsic ferromagnetism too—the quantum anomalous Hall effect. Experiments with a ferromagnetic topological insulator now establish how the anomalous states can be mapped onto the normal states.
580 citations
TL;DR: In this paper, a room-temperature bistable antiferromagnetic (AFM) memory that produces negligible stray fields and is insensitive to strong magnetic fields is presented. But it is not suitable for high-density memory integration.
Abstract: The bistability of ordered spin states in ferromagnets provides the basis for magnetic memory functionality. The latest generation of magnetic random access memories rely on an efficient approach in which magnetic fields are replaced by electrical means for writing and reading the information in ferromagnets. This concept may eventually reduce the sensitivity of ferromagnets to magnetic field perturbations to being a weakness for data retention and the ferromagnetic stray fields to an obstacle for high-density memory integration. Here we report a room-temperature bistable antiferromagnetic (AFM) memory that produces negligible stray fields and is insensitive to strong magnetic fields. We use a resistor made of a FeRh AFM, which orders ferromagnetically roughly 100 K above room temperature, and therefore allows us to set different collective directions for the Fe moments by applied magnetic field. On cooling to room temperature, AFM order sets in with the direction of the AFM moments predetermined by the field and moment direction in the high-temperature ferromagnetic state. For electrical reading, we use an AFM analogue of the anisotropic magnetoresistance. Our microscopic theory modelling confirms that this archetypical spintronic effect, discovered more than 150 years ago in ferromagnets, is also present in AFMs. Our work demonstrates the feasibility of fabricating room-temperature spintronic memories with AFMs, which in turn expands the base of available magnetic materials for devices with properties that cannot be achieved with ferromagnets.
553 citations
TL;DR: This work demonstrates optical control of ferromagnetic materials ranging from magnetic thin films to multilayers and even granular films being explored for ultra-high-density magnetic recording, and shows that Optical control of magnetic materials is a much more general phenomenon than previously assumed.
Abstract: The interplay of light and magnetism allowed light to be used as a probe of magnetic materials. Now the focus has shifted to use polarized light to alter or manipulate magnetism. Here, we demonstrate optical control of ferromagnetic materials ranging from magnetic thin films to multilayers and even granular films being explored for ultra-high-density magnetic recording. Our finding shows that optical control of magnetic materials is a much more general phenomenon than previously assumed and may have a major impact on data memory and storage industries through the integration of optical control of ferromagnetic bits.
549 citations
TL;DR: In this paper, the authors demonstrate deterministic magnetization reversal by current pulses ranging from 180 to ms in Pt/Co/AlOx dots with lateral dimensions of 90 nm, and characterize the switching probability and critical current Ic as a function of pulse length, amplitude, and external field.
Abstract: Spin-orbit torques induced by spin Hall and interfacial effects in heavy metal/ferromagnetic bilayers allow for a switching geometry based on in-plane current injection. Using this geometry, we demonstrate deterministic magnetization reversal by current pulses ranging from 180 ps to ms in Pt/Co/AlOx dots with lateral dimensions of 90 nm. We characterize the switching probability and critical current Ic as a function of pulse length, amplitude, and external field. Our data evidence two distinct regimes: a short-time intrinsic regime, where Ic scales linearly with the inverse of the pulse length, and a long-time thermally assisted regime, where Ic varies weakly. Both regimes are consistent with magnetization reversal proceeding by nucleation and fast propagation of domains. We find that Ic is a factor 3–4 smaller compared to a single domain model and that the incubation time is negligibly small, which is a hallmark feature of spin-orbit torques.
454 citations
TL;DR: In this article, a small electric field is used to switch a FeRh thin film from anti-to ferromagnetic above room temperature, by taking advantage of the strong magnetoelectric coupling with a BaTiO3 substrate.
Abstract: Electric-field-induced switching of material’s magnetization is a promising approach for achieving energy-efficient memory devices. By taking advantage of the strong magnetoelectric coupling with a BaTiO3 substrate, a small electric field is used to switch a FeRh thin film from anti- to ferromagnetic above room temperature.
443 citations
Journal Article•
TL;DR: Ferroelectricity in BaTiO3 crystals is used to tune the sharp metamagnetic transition temperature of epitaxially grown FeRh films and electrically drive a transition between antiferromagnetic and ferromagnetic order with only a few volts, just above room temperature, correspond to a magnetoelectric coupling larger than previous reports by at least one order of magnitude.
Abstract: Controlling magnetism by means of electric fields is a key issue for the future development of low-power spintronics1. Progress has been made in the electrical control of magnetic anisotropy2, domain structure3,4, spin polarization5,6 or critical temperatures7,8. However, the ability to turn on and o robust ferromagnetism at room temperature and above has remained elusive. Here we use ferroelectricity in BaTiO3 crystals to tune the sharp metamagnetic transition temperature of epitaxially grown FeRh films and electrically drive a transition between antiferromagnetic and ferromagnetic order with only a few volts, just above room temperature. The detailed analysis of the data in the light of first-principles calculations indicate that the phenomenon is mediated by both strain and field e ects from the BaTiO3. Our results correspond to a magnetoelectric coupling larger than previous reports by at least one order of magnitude and open new perspectives for the use of ferroelectrics in magnetic storage and spintronics.
371 citations
TL;DR: The evaluated low cleavage energy and high in-plane stiffness indicate that the free-standing MnPSe3 nanosheet can be exfoliated from its bulk structure in experiment, and render the 2D Mn PSe3 crystal with great potentials for application in electric-field controlled spintronic devices.
Abstract: Searching two-dimensional (2D) half-metallic crystals that are feasible in experiment is essential to develop next-generation nanospintronic devices. Here, a 2D exfoliated MnPSe3 nanosheet with novel magnetism is first proposed based on first-principles calculations. In particular, the evaluated low cleavage energy and high in-plane stiffness indicate that the free-standing MnPSe3 nanosheet can be exfoliated from its bulk structure in experiment. The MnPSe3 nanosheet is an antiferromagnetic semiconductor at its ground state, whereas both electron and hole doping induce its transition from antiferromagnetic semiconductor to ferromagnetic half-metal. Moreover, the spin-polarization directions of 2D half-metallic MnPSe3 are opposite for electron and hole doping, which can be controlled by applying an external voltage gate. The Monte Carlo simulation based on the Ising model suggests the Curie temperature of the doped 2D MnPSe3 crystal is up to 206 K. These advantages render the 2D MnPSe3 crystal with great potentials for application in electric-field controlled spintronic devices.
TL;DR: The control of magnetism by electric fields is an important goal for the future development of low-power spintronics as discussed by the authors, and various approaches have been proposed on the basis of either single-phase multiferroic materials or hybrid structures in which a ferromagnet is influenced by the electric field applied to an adjacent insulator.
Abstract: The control of magnetism by electric fields is an important goal for the future development of low-power spintronics. Various approaches have been proposed on the basis of either single-phase multiferroic materials or hybrid structures in which a ferromagnet is influenced by the electric field applied to an adjacent insulator (usually having a ferroelectric, piezoelectric, or multiferroic character). The electric field effect on magnetism can be driven by purely electronic or electrostatic effects or can occur through strain coupling. Here we review progress in the electrical control of magnetic properties (anisotropy, spin order, ordering temperature, domain structure) and its application to prototype spintronic devices (spin valves, magnetic tunnel junctions). We tentatively identify the main outstanding difficulties and give perspectives for spintronics and other fields.
TL;DR: In this paper, the authors demonstrate the possibility of realizing 2D ferromagnetic semiconductors simply by exfoliating layered crystals of CrXTe3 (X = Si, Ge).
Abstract: Two-dimensional (2D) ferromagnetic semiconductors hold a great potential for nano-electronic and spintronic devices. Nevertheless, their experimental realization remains a big challenge. Through first-principles calculations, we here demonstrate the possibility of realizing 2D ferromagnetic semiconductors simply by exfoliating layered crystals of CrXTe3 (X = Si, Ge). The exfoliation of CrXTe3 is feasible due to its small cleavage energy, and CrXTe3 nanosheets can form free-standing membranes. Interestingly, upon exfoliation, the ferromagnetism and semiconducting character are well preserved from bulk to the nanosheet form. Long-range ferromagnetic order with a magnetization of 3 μB per Cr atom is confirmed in 2D CrXTe3 from classical Heisenberg model Monte Carlo simulations. Both bulk and 2D CrXTe3 are indirect-gap semiconductors with their valence and conduction bands fully spin-polarized in the same direction, which is promising for spin-polarized carrier injection and detection. We further demonstrate the tunability and enrichment of the properties of CrXTe3 nanosheets via external operations. Under moderate tensile strain, the 2D ferromagnetism can be largely enhanced. By pure electron doping or adsorbing nucleophilic molecules, CrXTe3 nanosheets become 2D half metals.
TL;DR: A thermally assisted magnetoresistive random access memory device (TAS-MRAM) with reduced power for reading and writing was proposed in this article, where the storage and sense ferromagnetic layers include a non-magnetic material to reduce the magnetization of the respective layers.
Abstract: A thermally assisted magnetoresistive random access memory device (TAS-MRAM) with reduced power for reading and writing; the memory device comprising a tunnel barrier 14 sandwiched between a ferromagnetic sense layer 16 and a ferromagnetic storage layer 12. An antiferromagnetic pinning layer 30 is disposed adjacent to the ferromagnetic storage layer 12. The pinning layer 30 pins a magnetic moment of the storage layer until heating is applied. Either or both of the storage and sense ferromagnetic layers includes a non-magnetic material to reduce the magnetization of the respective layers. The reduction in the storage layer magnetization and sense layer magnetization reduces the magnetostatic interaction between the storage layer and sense layer, resulting in less read/write power. The ferromagnetic materials in the sense and storage layers may include at least one of Co, Fe, Ni, and any alloy including Co, Fe, Ni, whilst the non-magnetic material includes at least one of Ta, Ti, Hf, Cr, Nb, Mo, Zr and any alloy containing Ta, Ti, Hf, Cr, Nb, Mo, Zr. The antiferromagnetic pinning layer may have a diameter less than 250nm based on the reduction in magnetization of at least one of the storage or sense layer. The ferromagnetic storage layer may be formed by sputtering ,chemical vapour (vapor) deposition CVD or physical vapour deposition PVD , and may involve co-sputtering the ferromagnetic and non magnetic material, or forming multi-layers of ferromagnetic and non magnetic material. The ferromagnetic sense layer may also be formed by co-sputtering of ferromagnetic and non magnetic material or forming multilayers of the two materials. An alternative embodiment (figures 7A/B) comprises a tunnel barrier layer 14 sandwiched between a ferromagnetic storage layer 16 and a synthetic antiferromagnetic storage layer 12, which includes a first ferromagnetic storage layer 11 adjacent to the tunnel barrier layer and a non magnetic coupling layer 15 sandwiched between the first ferromagnetic storage layer 11 and a second ferromagnetic storage layer 13. The alternative structure further allows for a relative increase in the thickness of the first ferromagnetic layer 11.
TL;DR: In this article, the Fermi polaron problem is applied to the study of itinerant ferromagnetism, a long-standing problem in quantum mechanics, and it is shown that the polaron problems can be used to model the phase diagram of strongly interacting population-imbalanced quantum mixtures.
Abstract: In this review, we discuss the properties of a few impurity atoms immersed in a gas of ultracold fermions--the so-called Fermi polaron problem. On one hand, this many-body system is appealing because it can be described almost exactly with simple diagrammatic and/or variational theoretical approaches. On the other, it provides a quantitatively reliable insight into the phase diagram of strongly interacting population-imbalanced quantum mixtures. In particular, we show that the polaron problem can be applied to the study of itinerant ferromagnetism, a long-standing problem in quantum mechanics.
TL;DR: A study of the magnetic response of cobalt atoms adsorbed on oxide surfaces may lead to much denser storage of data, and the maximum magnetic anisotropy allowed for a transition metal atom is realized by coordinating a single Co atom to the O site of an MgO(100) surface.
Abstract: Designing systems with large magnetic anisotropy is critical to realize nanoscopic magnets. Thus far, the magnetic anisotropy energy per atom in single-molecule magnets and ferromagnetic films remains typically one to two orders of magnitude below the theoretical limit imposed by the atomic spin-orbit interaction. We realized the maximum magnetic anisotropy for a 3d transition metal atom by coordinating a single Co atom to the O site of an MgO(100) surface. Scanning tunneling spectroscopy reveals a record-high zero-field splitting of 58 millielectron volts as well as slow relaxation of the Co atom's magnetization. This striking behavior originates from the dominating axial ligand field at the O adsorption site, which leads to out-of-plane uniaxial anisotropy while preserving the gas-phase orbital moment of Co, as observed with x-ray magnetic circular dichroism.
Journal Article•
TL;DR: Highly efficient dynamic spin injection from Y3Fe5O12 (YIG) into NiO, an antiferromagnetic insulator, via strong coupling, and robust spin propagation in NiO up to 100-nm thickness mediated by its AF spin correlations are observed.
Abstract: We observe highly efficient dynamic spin injection from ${\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ (YIG) into NiO, an antiferromagnetic (AF) insulator, via strong coupling, and robust spin propagation in NiO up to 100-nm thickness mediated by its AF spin correlations. Strikingly, the insertion of a thin NiO layer between YIG and Pt significantly enhances the spin currents driven into Pt, suggesting exceptionally high spin transfer efficiency at both $\mathrm{YIG}/\mathrm{NiO}$ and $\mathrm{NiO}/\mathrm{Pt}$ interfaces. This offers a powerful platform for studying AF spin pumping and AF dynamics as well as for exploration of spin manipulation in tailored structures comprising metallic and insulating ferromagnets, antiferromagnets, and nonmagnetic materials.
TL;DR: The real-space observation of a biskyrmion is shown, as defined by a molecular form of two bound skyrmions with the total topological charge of 2, realized under magnetic field applied normal to a thin plate of a bilayered manganite with centrosymmetric structure.
Abstract: The magnetic skyrmion is a topologically stable spin texture in which the constituent spins point to all the directions wrapping a sphere. Generation and control of nanometric magnetic skyrmions have large potential, for example, reduced power consumption, in spintronics device applications. Here we show the real-space observation of a biskyrmion, as defined by a molecular form of two bound skyrmions with the total topological charge of 2, realized under magnetic field applied normal to a thin plate of a bilayered manganite with centrosymmetric structure. In terms of a Lorentz transmission electron microscopy (TEM), we have observed a distorted-triangle lattice of biskyrmion crystal, each composed of two bound skyrmions with oppositely swirling spins (magnetic helicities). Furthermore, we demonstrate that these biskyrmions can be electrically driven with orders of magnitude lower current density (<10(8) A m(-2)) than that for the conventional ferromagnetic domain walls.
TL;DR: In this article, the authors proposed a quantum anomalous Hall platform with a large energy gap of 0.34 and 0.06 eV on honeycomb lattices comprised of Sn and Ge.
Abstract: Recently, the long-sough quantum anomalous Hall effect was realized in a magnetic topological insulator. However, the requirement of an extremely low temperature (approximately 30 mK) hinders realistic applications. Based on ab initio band structure calculations, we propose a quantum anomalous Hall platform with a large energy gap of 0.34 and 0.06 eV on honeycomb lattices comprised of Sn and Ge, respectively. The ferromagnetic (FM) order forms in one sublattice of the honeycomb structure by controlling the surface functionalization rather than dilute magnetic doping, which is expected to be visualized by spin polarized STM in experiment. Strong coupling between the inherent quantum spin Hall state and ferromagnetism results in considerable exchange splitting and, consequently, an FM insulator with a large energy gap. The estimated mean-field Curie temperature is 243 and 509 K for Sn and Ge lattices, respectively. The large energy gap and high Curie temperature indicate the feasibility of the quantum anomalous Hall effect in the near-room-temperature and even room-temperature regions.
TL;DR: Basic experiments on the LSSE in insulators provide a novel and versatile pathway to thermoelectric generation in combination of the inverse spin-Hall effects.
Abstract: The spin Seebeck effect refers to the generation of spin voltage as a result of a temperature gradient in ferromagnetic or ferrimagnetic materials. When a conductor is attached to a magnet under a temperature gradient, the thermally generated spin voltage in the magnet injects a spin current into the conductor, which in turn produces electric voltage owing to the spin-orbit interaction. The spin Seebeck effect is of increasing importance in spintronics, since it enables direct generation of a spin current from heat and appears in a variety of magnets ranging from metals and semiconductors to insulators. Recent studies on the spin Seebeck effect have been conducted mainly in paramagnetic metal/ferrimagnetic insulator junction systems in the longitudinal configuration in which a spin current flowing parallel to the temperature gradient is measured. This 'longitudinal spin Seebeck effect' (LSSE) has been observed in various sample systems and exclusively established by separating the spin-current contribution from extrinsic artefacts, such as conventional thermoelectric and magnetic proximity effects. The LSSE in insulators also provides a novel and versatile pathway to thermoelectric generation in combination of the inverse spin-Hall effects. In this paper, we review basic experiments on the LSSE and discuss its potential thermoelectric applications with several demonstrations.
TL;DR: In this paper, strong perpendicular magnetic anisotropy of the ferromagnetic layer in a W/CoFeB/MgO multilayer structure can be established by inserting a Hf layer as thin as 0.25 nm between the W and CoFeB layers.
Abstract: We report that strong perpendicular magnetic anisotropy of the ferromagnetic layer in a W/CoFeB/MgO multilayer structure can be established by inserting a Hf layer as thin as 0.25 nm between the W and CoFeB layers. The Hf spacer also allows transmission of spin currents generated by an in-plane charge current in the W layer to apply strong spin torque on the CoFeB, thereby enabling current-driven magnetic switching. The antidamping-like and field-like components of the spin torque exerted on a 1 nm CoFeB layer are of comparable magnitudes in this geometry. Both components originate from the spin Hall effect in the underlying W layer.
TL;DR: In this article, strong perpendicular magnetic anisotropy of the ferromagnetic layer in a W/CoFeB/MgO multilayer structure can be established by inserting a Hf layer as thin as 0.25 nm between the W and CoFeB layers.
Abstract: We report that strong perpendicular magnetic anisotropy of the ferromagnetic layer in a W/CoFeB/MgO multilayer structure can be established by inserting a Hf layer as thin as 0.25 nm between the W and CoFeB layers. The Hf spacer also allows transmission of spin currents generated by an in-plane charge current in the W layer to apply strong spin torque on the CoFeB, thereby enabling current-driven magnetic switching. The antidamping-like and field-like components of the spin torque exerted on a 1 nm CoFeB layer are of comparable magnitudes in this geometry. Both components originate from the spin Hall effect in the underlying W layer.
TL;DR: Using density functional theory combined with Monte Carlo simulations, it is shown that the two dimensional MnS2 and MnSe2 sheets are ideal magnetic semiconductors with long-range magnetic ordering and high magnetic moments.
Abstract: Using density functional theory combined with Monte Carlo (MC) simulations, we show that the two dimensional (2D) MnS2 and MnSe2 sheets are ideal magnetic semiconductors with long-range magnetic ordering and high magnetic moments (3 μB per unit cell), where all the Mn atoms are ferromagnetically coupled, and the Curie temperatures (TC) estimated for MnS2 and MnSe2 by the MC simulations are 225 and 250 K, respectively, which can be further increased to 330 K and 375 K by applying 5% biaxial tensile strains.
TL;DR: In this paper, the magnetic properties of the synthesized spinel ferrites were investigated using room temperature vibrating sample magnetometer (VSM) and their hysteresis loops were obtained.
TL;DR: The far-from-equilibrium dynamics in ferromagnetic Heisenberg quantum magnets realized with ultracold atoms in an optical lattice is studied and a profound dependence of the decay rate on the wave vector is found.
Abstract: We study experimentally the far-from-equilibrium dynamics in ferromagnetic Heisenberg quantum magnets realized with ultracold atoms in an optical lattice. After controlled imprinting of a spin spiral pattern with an adjustable wave vector, we measure the decay of the initial spin correlations through single-site resolved detection. On the experimentally accessible time scale of several exchange times, we find a profound dependence of the decay rate on the wave vector. In one-dimensional systems, we observe diffusionlike spin transport with a dimensionless diffusion coefficient of 0.22(1). We show how this behavior emerges from the microscopic properties of the closed quantum system. In contrast to the one-dimensional case, our transport measurements for two-dimensional Heisenberg systems indicate anomalous superdiffusion.
TL;DR: It is demonstrated that magnetization self-oscillations can be excited in a one-dimensional magnetic system and that dimensions of the active region of spin torque oscillators can be extended beyond the nanometre length scale.
Abstract: Spin torque from spin current applied to a nanoscale region of a ferromagnet can act as negative magnetic damping and thereby excite self-oscillations of its magnetization. In contrast, spin torque uniformly applied to the magnetization of an extended ferromagnetic film does not generate self-oscillatory magnetic dynamics but leads to reduction of the saturation magnetization. Here we report studies of the effect of spin torque on a system of intermediate dimensionality--a ferromagnetic nanowire. We observe coherent self-oscillations of magnetization in a ferromagnetic nanowire serving as the active region of a spin torque oscillator driven by spin orbit torques. Our work demonstrates that magnetization self-oscillations can be excited in a one-dimensional magnetic system and that dimensions of the active region of spin torque oscillators can be extended beyond the nanometre length scale.
TL;DR: In this article, the Hofstadter butterfly is suppressed by suppression of quantum Hall antiferromagnetism at particular commensurate magnetic fluxes by means of capacitance spectroscopy.
Abstract: Graphene on boron nitride gives rise to a moire superlattice displaying the Hofstadter butterfly: a fractal dependence of energy bands on external magnetic fields. Now, by means of capacitance spectroscopy, further aspects of this system are revealed—most notably, suppression of quantum Hall antiferromagnetism at particular commensurate magnetic fluxes.
TL;DR: In this paper, the existence of the simplest magnetization texture holding a Bloch point at rest in cylindrical magnetic nanowires was confirmed by combining surface and transmission x-ray magnetic circular dichroism photoemission electron microscopy.
Abstract: Topological protection is an efficient way of warranting the integrity of quantum and nanosized systems. In magnetism, one example is the Bloch point, a peculiar three-dimensional object implying the local vanishing of magnetization within a ferromagnet. By combining surface and transmission x-ray magnetic circular dichroism photoemission electron microscopy, we experimentally confirm the existence of the simplest magnetization texture holding a Bloch point at rest: the Bloch-point domain wall in cylindrical magnetic nanowires. This opens the way to the experimental search for peculiar phenomena predicted during the motion of these protected Bloch-point-based domain walls.
TL;DR: In this article, structural and magnetic properties of NdMn2−xCuxSi2 compounds were investigated by high intensity x-ray and resolution neutron diffraction (3-450 K), specific heat, dc magnetization, and differential scanning calorimetry measurements.
Abstract: Structural and magnetic properties of NdMn2−xCuxSi2 compounds (x = 0–1.0) have been investigated by high intensity x-ray and resolution neutron diffraction (3–450 K), specific heat, dc magnetization, and differential scanning calorimetry measurements. Substitution of Cu for Mn leads to an increase in the lattice parameter a but a decrease in c at room temperature. Two magnetic phase transitions have been found for NdMn2−xCuxSi2 compounds with TN for the antiferromagnetic ordering of Mn-sublatttice and TC for the Nd-sublattice ferromagnetic ordering, respectively. TC increases significantly with increasing Cu content from 36 K at x = 0 to 100 K at x = 1.0. Moreover, it is found that the order of magnetic phase transition around TC also changes from first order at x < 0.6 to second order transition for x ≥ 0.6. The spontaneous magnetization found to decrease with the increase in Cu concentration which can be understood in the term of the dilution effect of Cu for Mn. The values of −ΔSM around TC decrease wi...