Showing papers on "Magnetization published in 2011"
TL;DR: To prove the potential of in-plane current switching for spintronic applications, this work constructs a reprogrammable magnetic switch that can be integrated into non-volatile memory and logic architectures.
Abstract: Modern computing technology is based on writing, storing and retrieving information encoded as magnetic bits. Although the giant magnetoresistance effect has improved the electrical read out of memory elements, magnetic writing remains the object of major research efforts. Despite several reports of methods to reverse the polarity of nanosized magnets by means of local electric fields and currents, the simple reversal of a high-coercivity, single-layer ferromagnet remains a challenge. Materials with large coercivity and perpendicular magnetic anisotropy represent the mainstay of data storage media, owing to their ability to retain a stable magnetization state over long periods of time and their amenability to miniaturization. However, the same anisotropy properties that make a material attractive for storage also make it hard to write to. Here we demonstrate switching of a perpendicularly magnetized cobalt dot driven by in-plane current injection at room temperature. Our device is composed of a thin cobalt layer with strong perpendicular anisotropy and Rashba interaction induced by asymmetric platinum and AlOx interface layers. The effective switching field is orthogonal to the direction of the magnetization and to the Rashba field. The symmetry of the switching field is consistent with the spin accumulation induced by the Rashba interaction and the spin-dependent mobility observed in non-magnetic semiconductors, as well as with the torque induced by the spin Hall effect in the platinum layer. Our measurements indicate that the switching efficiency increases with the magnetic anisotropy of the cobalt layer and the oxidation of the aluminium layer, which is uppermost, suggesting that the Rashba interaction has a key role in the reversal mechanism. To prove the potential of in-plane current switching for spintronic applications, we construct a reprogrammable magnetic switch that can be integrated into non-volatile memory and logic architectures. This device is simple, scalable and compatible with present-day magnetic recording technology.
2,099 citations
TL;DR: This tutorial review discusses some basic aspects concerning the magnetic properties of rare-earth ions, and focuses on Dy(III) derivatives of the relation of the crystal field parameters, which determine the anisotropy of these systems and consequently their interesting magnetic properties.
Abstract: In this tutorial review we discuss some basic aspects concerning the magnetic properties of rare-earth ions, which are currently the subject of a renovated interest in the field of molecular magnetism, after the discovery that slow relaxation of the magnetization at liquid nitrogen temperature can occur in mononuclear complexes of these ions. Focusing on Dy(III) derivatives a tutorial discussion is given of the relation of the crystal field parameters, which determine the anisotropy of these systems and consequently their interesting magnetic properties, with the geometry of the coordination sphere around the lanthanide centre and with the pattern of f orbitals. The problem of systems of low point symmetry is also addressed by showing how detailed single crystal investigation, coupled to more sophisticated calculation procedures, is an absolute necessity to obtain meaningful structure–property relationships in these systems.
944 citations
TL;DR: In this article, the phase transformation from dendritic α-Fe2O3 to Fe3O4, Fe by partial and full reduction, and Fe 2O3 by reduction−oxidation process.
Abstract: Iron-based microstructured or nanostructured materials, including Fe, γ-Fe2O3, and Fe3O4, are highly desirable for magnetic applications because of their high magnetization and a wide range of magnetic anisotropy. An important application of these materials is use as an electromagnetic wave absorber to absorb radar waves in the centimeter wave (2−18 GHz). Dendrite-like microstructures were achieved with the phase transformation from dendritic α-Fe2O3 to Fe3O4, Fe by partial and full reduction, and γ-Fe2O3 by a reduction−oxidation process, while still preserving the dendritic morphology. The investigation of the magnetic properties and microwave absorbability reveals that the three hierarchical microstructures are typical ferromagnets and exhibit excellent microwave absorbability. In addition, this also confirms that the microwave absorption properties are ascribed to the dielectric loss for Fe and the combination of dielectric loss and magnetic loss for Fe3O4 and γ-Fe2O3.
866 citations
TL;DR: It is found that the ultrafast spin reversal in GdFeCo, where spins are coupled antiferromagnetically, occurs by way of a transient ferromagnetic-like state, which provides a concept for the possibility of manipulating magnetic order on the timescale of the exchange interaction.
Abstract: The dynamics of spin ordering in magnetic materials is of interest for both fundamental understanding and progress in information-processing and recording technology. Radu et al. study spin dynamics in a ferrimagnetic gadolinium–iron–cobalt (GdFeCo) alloy that is optically excited at a timescale shorter than the characteristic magnetic exchange interaction between the Gd and Fe spins. Using element-specific X-ray magnetic circular dichroism spectroscopy, they show that the Gd and Fe spins switch directions at very different timescales. As a consequence, an unexpected transient ferromagnetic state emerges. These surprising observations, supported by simulations, provide a possible new concept of manipulating magnetic order on a timescale of the exchange interaction. Ferromagnetic or antiferromagnetic spin ordering is governed by the exchange interaction, the strongest force in magnetism1,2,3,4. Understanding spin dynamics in magnetic materials is an issue of crucial importance for progress in information processing and recording technology. Usually the dynamics are studied by observing the collective response of exchange-coupled spins, that is, spin resonances, after an external perturbation by a pulse of magnetic field, current or light. The periods of the corresponding resonances range from one nanosecond for ferromagnets down to one picosecond for antiferromagnets. However, virtually nothing is known about the behaviour of spins in a magnetic material after being excited on a timescale faster than that corresponding to the exchange interaction (10–100 fs), that is, in a non-adiabatic way. Here we use the element-specific technique X-ray magnetic circular dichroism to study spin reversal in GdFeCo that is optically excited on a timescale pertinent to the characteristic time of the exchange interaction between Gd and Fe spins. We unexpectedly find that the ultrafast spin reversal in this material, where spins are coupled antiferromagnetically, occurs by way of a transient ferromagnetic-like state. Following the optical excitation, the net magnetizations of the Gd and Fe sublattices rapidly collapse, switch their direction and rebuild their net magnetic moments at substantially different timescales; the net magnetic moment of the Gd sublattice is found to reverse within 1.5 picoseconds, which is substantially slower than the Fe reversal time of 300 femtoseconds. Consequently, a transient state characterized by a temporary parallel alignment of the net Gd and Fe moments emerges, despite their ground-state antiferromagnetic coupling. These surprising observations, supported by atomistic simulations, provide a concept for the possibility of manipulating magnetic order on the timescale of the exchange interaction.
827 citations
TL;DR: In this paper, the authors used local imaging of the magnetization and magnetic susceptibility to directly observe a landscape of ferromagnetism, paramagnetic response, and superconductivity.
Abstract: LaAlO{sub 3} and SrTiO{sub 3} are insulating, nonmagnetic oxides, yet the interface between them exhibits a two-dimensional electron system with high electron mobility, superconductivity at low temperatures, and electric-field-tuned metal-insulator and superconductor-insulator phase transitions Bulk magnetization and magnetoresistance measurements also suggest some form of magnetism depending on preparation conditions and suggest a tendency towards nanoscale electronic phase separation Here we use local imaging of the magnetization and magnetic susceptibility to directly observe a landscape of ferromagnetism, paramagnetism, and superconductivity We find submicron patches of ferromagnetism in a uniform background of paramagnetism, with a nonuniform, weak diamagnetic superconducting susceptibility at low temperature These results demonstrate the existence of nanoscale phase separation as suggested by theoretical predictions based on nearly degenerate interface subbands associated with the Ti orbitals The magnitude and temperature dependence of the paramagnetic response suggests that the vast majority of the electrons at the interface are localized, and do not contribute to transport measurements In addition to the implications for magnetism, the existence of a 2D superconductor at an interface with highly broken inversion symmetry and a ferromagnetic landscape in the background suggests the potential for exotic superconducting phenomena
782 citations
TL;DR: In this paper, three types of theories suitable for describing hysteresis loops of magnetic nanoparticles are presented and compared to numerical simulations: equilibrium functions, Stoner-Wohlfarth model based theories (SWMBTs), and a linear response theory (LRT) using the Neel-Brown relaxation time.
Abstract: To optimize the heating properties of magnetic nanoparticles (MNPs) in magnetic hyperthermia applications, it is necessary to calculate the area of their hysteresis loops in an alternating magnetic field. The separation between “relaxation losses” and “hysteresis losses” presented in several articles is artificial and criticized here. The three types of theories suitable for describing hysteresis loops of MNPs are presented and compared to numerical simulations: equilibrium functions, Stoner–Wohlfarth model based theories (SWMBTs), and a linear response theory (LRT) using the Neel–Brown relaxation time. The configuration where the easy axis of the MNPs is aligned with respect to the magnetic field and the configuration of a random orientation of the easy axis are both studied. Suitable formulas to calculate the hysteresis areas of major cycles are deduced from SWMBTs and from numerical simulations; the domain of validity of the analytical formula is explicitly studied. In the case of minor cycles, the hysteresis area calculations are based on the LRT. A perfect agreement between the LRT and numerical simulations of hysteresis loops is obtained. The domain of validity of the LRT is explicitly studied. Formulas are proposed to calculate the hysteresis area at low field that are valid for any anisotropy of the MNP. The magnetic field dependence of the area is studied using numerical simulations: it follows power laws with a large range of exponents. Then analytical expressions derived from the LRT and SWMBTs are used in their domains of validity for a theoretical study of magnetic hyperthermia. It is shown that LRT is only pertinent for MNPs with strong anisotropy and that SWMBTs should be used for weakly anisotropic MNPs. The optimum volume of MNPs for magnetic hyperthermia is derived as a function of material and experimental parameters. Formulas are proposed to allow to the calculation of the optimum volume for any anisotropy. The maximum achievable specific absorption rate (SAR) is calculated as a function of the MNP anisotropy. It is shown that an optimum anisotropy increases the SAR and reduces the detrimental effects of the size distribution of the MNPs. The optimum anisotropy is simple to calculate; it depends only on the magnetic field used in the hyperthermia experiments and the MNP magnetization. The theoretical optimum parameters are compared to those of several magnetic materials. A brief review of experimental results as well as a method to analyze them is proposed. This study helps in the determination of suitable and unsuitable materials for magnetic hyperthermia and provides accurate formulas to analyze experimental data. It is also aimed at providing a better understanding of magnetic hyperthermia to researchers working on this subject.
761 citations
TL;DR: The authors showed that Lanthanum aluminate and strontium titanate are insulators, but when they bring them together, the interface between them becomes a two-dimensional superconductor.
Abstract: Lanthanum aluminate and strontium titanate are insulators, but when you bring them together, the interface between them becomes a two-dimensional superconductor. Even more surprising, magnetometry and transport measurements show that this superconducting state coexists with magnetic order.
719 citations
TL;DR: The high axiality and Ising exchange interaction efficiently suppress quantum tunneling of magnetization of an asymmetric dinuclear Dy(III) complex, as revealed by combined experimental and theoretical investigations.
Abstract: The high axiality and Ising exchange interaction efficiently suppress quantum tunneling of magnetization of an asymmetric dinuclear Dy(III) complex, as revealed by combined experimental and theoretical investigations. Two distinct regimes of blockage of magnetization, one originating from the blockage at individual Dy sites and the other due to the exchange interaction between the sites, are separated for the first time. The latter contribution is found to be crucial, allowing an increase of the relaxation time by 3 orders of magnitude.
642 citations
Patent•
14 Feb 2011TL;DR: A magnetoresistive element according to an embodiment includes: a first ferromagnetic layer having an axis of easy magnetization in a direction perpendicular to a film plane; a second nonmagnetic layer placed between the first and the second magnetoresists; and a second interfacial magnetic layer between the second and the nonmagians as mentioned in this paper.
Abstract: A magnetoresistive element according to an embodiment includes: a first ferromagnetic layer having an axis of easy magnetization in a direction perpendicular to a film plane; a second ferromagnetic layer having an axis of easy magnetization in a direction perpendicular to a film plane; a nonmagnetic layer placed between the first ferromagnetic layer and the second ferromagnetic layer; a first interfacial magnetic layer placed between the first ferromagnetic layer and the nonmagnetic layer; and a second interfacial magnetic layer placed between the second ferromagnetic layer and the nonmagnetic layer The first interfacial magnetic layer includes a first interfacial magnetic film, a second interfacial magnetic film placed between the first interfacial magnetic film and the nonmagnetic layer and having a different composition from that of the first interfacial magnetic film, and a first nonmagnetic film placed between the first interfacial magnetic film and the second interfacial magnetic film
600 citations
TL;DR: From the neutron diffraction study, it is anticipated that a relatively short-period (3-6 nm) noncoplanar spin structure is stabilized from the proper screw state in a magnetic field to produce the largest topological Hall response among the B20-type (FeSi-type) chiral magnets.
Abstract: We have observed an unconventional, likely topological, Hall effect over a wide temperature region in the magnetization process of a chiral-lattice helimagnet MnGe. The magnitude of the topological Hall resistivity is nearly temperature-independent below 70 K, which reflects the real-space fictitious magnetic field proportional to a geometric quantity (scalar spin chirality) of the underlying spin texture. From the neutron diffraction study, it is anticipated that a relatively short-period (3--6 nm) noncoplanar spin structure is stabilized from the proper screw state in a magnetic field to produce the largest topological Hall response among the B20-type (FeSi-type) chiral magnets.
484 citations
TL;DR: A molecular spin switch that is bistable at room temperature in homogeneous solution is presented and preliminary data show promise for applications in magnetic resonance imaging.
Abstract: Magnetic bistability, as manifested in the magnetization of ferromagnetic materials or spin crossover in transition metal complexes, has essentially been restricted to either bulk materials or to very low temperatures. We now present a molecular spin switch that is bistable at room temperature in homogeneous solution. Irradiation of a carefully designed nickel complex with blue-green light (500 nanometers) induces coordination of a tethered pyridine ligand and concomitant electronic rearrangement from a diamagnetic to a paramagnetic state in up to 75% of the ensemble. The process is fully reversible on irradiation with violet-blue light (435 nanometers). No fatigue or degradation is observed after several thousand cycles at room temperature under air. Preliminary data show promise for applications in magnetic resonance imaging.
TL;DR: The thermal energy barrier to relaxation of magnetization of this single-molecule magnet was found at a temperature of 530 K and is the largest yet observed for any d- or f-block cluster compound.
Abstract: Single-molecule magnets: A square-pyramidal pentametallic dysprosium cluster was synthesized and showed slow magnetic relaxation at temperatures as high as 40 K. The thermal energy barrier to relaxation of magnetization of this single-molecule magnet was found at a temperature of 530 K and is the largest yet observed for any d- or f-block cluster compound.
TL;DR: Electric field–induced ferromagnetism at room temperature in a magnetic oxide semiconductor, (Ti,Co)O2, is demonstrated by means of electric double-layer gating with high-density electron accumulation and revealing the considerable role of electron carriers in high-temperature ferromagnetic state and demonstrating a route to room-tem temperature semiconductor spintronics.
Abstract: The electric field effect in ferromagnetic semiconductors enables switching of the magnetization, which is a key technology for spintronic applications. We demonstrated electric field–induced ferromagnetism at room temperature in a magnetic oxide semiconductor, (Ti,Co)O2, by means of electric double-layer gating with high-density electron accumulation (>1014 per square centimeter). By applying a gate voltage of a few volts, a low-carrier paramagnetic state was transformed into a high-carrier ferromagnetic state, thereby revealing the considerable role of electron carriers in high-temperature ferromagnetism and demonstrating a route to room-temperature semiconductor spintronics.
TL;DR: A nonvolatile, room temperature magnetization reversal determined by an electric field in a ferromagnet-multiferroic system demonstrates an avenue for next-generation, low-energy consumption spintronics.
Abstract: A reversal of magnetization requiring only the application of an electric field can lead to low-power spintronic devices by eliminating conventional magnetic switching methods. Here we show a nonvolatile, room temperature magnetization reversal determined by an electric field in a ferromagnet-multiferroic system. The effect is reversible and mediated by an interfacial magnetic coupling dictated by the multiferroic. Such electric-field control of a magnetoelectric device demonstrates an avenue for next-generation, low-energy consumption spintronics.
TL;DR: In this paper, the authors systematically document the known magnetic properties of greigite (at high, ambient, and low temperatures and with alternating and direct fields) and illustrate how grain size variations affect magnetic properties.
Abstract: Greigite (Fe3S4) is an authigenic ferrimagnetic mineral that grows as a precursor to pyrite during early diagenetic sedimentary sulfate reduction. It can also grow at any time when dissolved iron and sulfide are available during diagenesis. Greigite is important in paleomagnetic, environmental, biological, biogeochemical, tectonic, and industrial processes. Much recent progress has been made in understanding its magnetic properties. Greigite is an inverse spinel and a collinear ferrimagnet with antiferromagnetic coupling between iron in octahedral and tetrahedral sites. The crystallographic c axis is the easy axis of magnetization, with magnetic properties dominated by magnetocrystalline anisotropy. Robust empirical estimates of the saturation magnetization, anisotropy constant, and exchange constant for greigite have been obtained recently for the first time, and the first robust estimate of the low-field magnetic susceptibility is reported here. The Curie temperature of greigite remains unknown but must exceed 350°C. Greigite lacks a low-temperature magnetic transition. On the basis of preliminary micromagnetic modeling, the size range for stable single domain behavior is 17–200 nm for cubic crystals and 17–500 nm for octahedral crystals. Gradual variation in magnetic properties is observed through the pseudo-single-domain size range. We systematically document the known magnetic properties of greigite (at high, ambient, and low temperatures and with alternating and direct fields) and illustrate how grain size variations affect magnetic properties. Recognition of this range of magnetic properties will aid identification and constrain interpretation of magnetic signals carried by greigite, which is increasingly proving to be environmentally important and responsible for complex paleomagnetic records, including widespread remagnetizations.
TL;DR: The magnetic dilution method was employed in order to elucidate the origin of the slow relaxation of the magnetization in a Dy(2) single-molecule magnet (SMM) and the dominant single-ion relaxation was found to be entangled with the neighboring Dy(III) ion relaxation within the molecule, greatly influencing the quantum tunneling in this complex.
Abstract: The magnetic dilution method was employed in order to elucidate the origin of the slow relaxation of the magnetization in a Dy(2) single-molecule magnet (SMM). The doping effect was studied using SQUID and micro-SQUID measurements on a Dy(2) SMM diluted in a diamagnetic Y(2) matrix. The quantum tunneling of the magnetization that can occur was suppressed by applying optimum dc fields. The dominant single-ion relaxation was found to be entangled with the neighboring Dy(III) ion relaxation within the molecule, greatly influencing the quantum tunneling of the magnetization in this complex.
TL;DR: Evidence is given that this intrinsic pinning determines the threshold, and thus that the adiabatic spin torque dominates the domain wall motion in a perpendicularly magnetized Co/Ni nanowire, to achieve robust operation and low energy consumption in spintronic devices.
Abstract: The spin transfer torque is essential for electrical magnetization switching. When a magnetic domain wall is driven by an electric current through an adiabatic spin torque, the theory predicts a threshold current even for a perfect wire without any extrinsic pinning. The experimental confirmation of this 'intrinsic pinning', however, has long been missing. Here, we give evidence that this intrinsic pinning determines the threshold, and thus that the adiabatic spin torque dominates the domain wall motion in a perpendicularly magnetized Co/Ni nanowire. The intrinsic nature manifests itself both in the field-independent threshold current and in the presence of its minimum on tuning the wire width. The demonstrated domain wall motion purely due to the adiabatic spin torque will serve to achieve robust operation and low energy consumption in spintronic devices.
TL;DR: In this paper, the average crystallite sizes of Fe3O4-MN, Fe3 o4-OA-MN and Fe3 O4-PEG-MN were found to be 12, 6 and 8 nm.
Abstract: Fe3O4 magnetic nanoparticles (Fe3O4-MN) capped with either oleic acid (Fe3O4-OA-MN) or polyethylene glycol (Fe3O4-PEG-MN) were prepared by a co-precipitation method. From X-ray diffraction studies, the average crystallite sizes of Fe3O4-MN, Fe3O4-OA-MN and Fe3O4-PEG-MN were found to be 12, 6 and 8 nm, respectively. A reduction in the agglomeration of particles was observed when the magnetic nanoparticles (MN) were capped with oleic acid (OA) and polyethylene glycol (PEG), as confirmed by a transmission electron microscopy study. Magnetization of these MN was almost zero at room temperature in the absence of an applied magnetic field, indicating their superparamagnetic behavior. Magnetization was lower and the superparamagnetic fraction was higher for Fe3O4-OA-MN and Fe3O4-PEG-MN compared to Fe3O4-MN studied using a Mossbauer spectrometer. Compared to the control, an increased killing (35%) was observed in human breast cancer cells (MCF7) after Fe3O4-OA-MN treatment, which was further enhanced (65%) under induction heating conditions. However, MCF7 cells treated with Fe3O4-MN or Fe3O4-PEG-MN showed 5–10% killing after induction heating. These results showed the characterization of MN with different lipophilicity and suggests their suitability for hyperthermia applications in cancer therapy.
TL;DR: It is found that all the surface states are localized, while the transverse conductivity is quantized to be ±e2/2h as long as the Fermi energy is within the bulk gap, which greatly facilitates the realization of the topological magnetoelectric effect proposed by Qi et al.
Abstract: We study theoretically the role of quenched magnetic disorder at the surface of topological insulators by numerical simulation and scaling analysis based on the massive Dirac fermion model. This addresses the problem of Anderson localization on chiral anomaly. It is found that all the surface states are localized, while the transverse conductivity is quantized to be $\ifmmode\pm\else\textpm\fi{}\frac{{e}^{2}}{2h}$ as long as the Fermi energy is within the bulk gap. This greatly facilitates the realization of the topological magnetoelectric effect proposed by Qi et al. [Phys. Rev. B 78, 195424 (2008)] with the surface magnetization direction being controlled by the simultaneous application of magnetic and electric fields.
TL;DR: The authors' data are well described by a modified Landau-Lifshitz-Gilbert approach, in which a virtual, strain-induced tickle field drives the magnetization precession that causes a distinct magnetic field orientation dependence of elastically driven FMR.
Abstract: Surface acoustic waves (SAWs) in the GHz frequency range are exploited for the all-elastic excitation and detection of ferromagnetic resonance (FMR) in a ferromagnetic-ferroelectric (Ni/LiNbO(3)) hybrid device. We measure the SAW magnetotransmission at room temperature as a function of frequency, external magnetic field magnitude, and orientation. Our data are well described by a modified Landau-Lifshitz-Gilbert approach, in which a virtual, strain-induced tickle field drives the magnetization precession. This causes a distinct magnetic field orientation dependence of elastically driven FMR that we observe in both model and experiment.
TL;DR: Detailed magnetic measurements on the cubic helimagnet FeGe in external magnetic fields and temperatures near the onset of long-range magnetic order at T(C)=278.2(3) K are reported on.
Abstract: We report on detailed magnetic measurements on the cubic helimagnet FeGe in external magnetic fields and temperatures near the onset of long-range magnetic order at ${T}_{C}=278.2(3)\text{ }\text{ }\mathrm{K}$. Precursor phenomena display a complex succession of temperature-driven crossovers and phase transitions in the vicinity of ${T}_{C}$. The $A$-phase region, present below ${T}_{C}$ and fields $Hl0.5\text{ }\text{ }\mathrm{kOe}$, is split in several pockets. The complexity of the magnetic phase diagram is theoretically explained by the confinement of solitonic kinklike or Skyrmionic units that develop an attractive and oscillatory intersoliton coupling owing to the longitudinal inhomogeneity of the magnetization.
TL;DR: In this article, a large exchange bias was observed in Ni-Mn-In bulk alloys after zero-field cooling from an unmagnetized state, which is related to the newly formed interface between different magnetic phases during the initial magnetization process.
Abstract: Exchange bias (EB) is usually observed in systems with an interface between different magnetic phases after field cooling. Here we report an unusual phenomenon in which a large EB can be observed in Ni-Mn-In bulk alloys after zero-field cooling from an unmagnetized state. We propose that this is related to the newly formed interface between different magnetic phases during the initial magnetization process. The magnetic unidirectional anisotropy, which is the origin of the EB effect, can be created isothermally below the blocking temperature.
Book•
23 Jun 2011
TL;DR: In this article, the authors present a survey of Magnetic Measurements and Diagnostics and their application in the field of Magnetic Diagnostics, including a discussion of magnetic sensors and their applications.
Abstract: Introduction to Magnetic Measurements Fundamentals of Magnetic Measurements Historical Background Main Terms The Magnetization Process of Ferromagnetic Materials Anisotropy and Texture Electromagnetic Loss Influence of the Magnetic Field on Physical Properties of a Material Magnetic Resonance Superconductivity Used in Magnetic Measurements Main Rules of Magnetics The Physical Principles of Magnetism The Magnetic Hysteresis Sources of a Magnetic Field The Samples and Circuits of the Material under Test Magnetic Shielding Magnetic Materials Soft Magnetic Materials: General Information Silicon Iron Electrical Steel Nickel- and Cobalt-Based Alloys Amorphous and Nanocrystalline Alloys Soft Ferrites Hard Magnetic Materials Special Magnetic Materials Magnetic Sensors General Remarks Induction Sensors Fluxgate Sensors Magnetoresistive and Magnetoimpedance Sensors Hall-Effect Sensors Resonance Sensors SQUID Sensors Resonance Sensors and Magnetometers Other Magnetic Sensors Testing of Magnetic Materials AC Testing of Soft Magnetic Materials DC Testing of Soft Magnetic Materials Testing of Hard Magnetic Materials Special Methods of Testing of Magnetic Materials Magnetic Field Measurements and Their Applications Environment Magnetic Fields Applications of Magnetic Field Measurements Magnetic Diagnostics Index References appear at the end of each chapter.
TL;DR: It is demonstrated that arene-bridged polyuranium clusters can exhibit SMM behaviour without relying on the superexchange coupling of spins, which may lead to increased blocking temperatures.
Abstract: Single-molecule magnets (SMMs) are compounds that, below a blocking temperature, exhibit stable magnetization purely of molecular origin, and not caused by long-range ordering of magnetic moments in the bulk. They thus show promise for applications such as data storage of ultra-high density. The stability of the magnetization increases with increasing ground-state spin and magnetic anisotropy. Transition-metal SMMs typically possess high-spin ground states, but insufficient magnetic anisotropies. Lanthanide SMMs exhibit large magnetic anisotropies, but building high-spin ground states is difficult because they tend to form ionic bonds that limit magnetic exchange coupling. In contrast, the significant covalent bonding and large spin–orbit contributions associated with uranium are particularly attractive for the development of improved SMMs. Here we report a delocalized arene-bridged diuranium SMM. This study demonstrates that arene-bridged polyuranium clusters can exhibit SMM behaviour without relying on the superexchange coupling of spins. This approach may lead to increased blocking temperatures. Single-molecule magnets (SMMs) are multinuclear clusters whose behaviour typically relies on intramolecular spin-coupling interactions between neighbouring metal ions. A diuranium–arene complex has now been prepared that shows behaviour characteristic of an SMM without relying on this type of superexchange mechanism. This may enable the construction of SMMs that maintain their magnetism at higher temperatures.
TL;DR: The synthesis of large single crystals of a new FeSe layer superconductor Cs( 0.8)(FeSe(0.98))(2) is reported on, which shows a slightly lower superconducting transition temperature and the T(c) dependence on the anion height was found to be analogous to those reported for As-containing Fe superconductors and Fe(Se(1 - x)Ch(x)), where Ch = Te, S.
Abstract: We report on the synthesis of large single crystals of a new FeSe layer superconductor Cs0.8(FeSe0.98)2. X-ray powder diffraction, neutron powder diffraction and magnetization measurements have been used to compare the crystal structure and the magnetic properties of Cs0.8(FeSe0.98)2 with those of the recently discovered potassium intercalated system KxFe2Se2. The new compound, Cs0.8(FeSe0.98)2, shows a slightly lower superconducting transition temperature (Tc = 27.4 K) in comparison to 29.5 in (K0.8(FeSe0.98)2). The volume of the crystal unit cell increases by replacing K by Cs—the c parameter grows from 14.1353(13) to 15.2846(11) A. For the alkali metal intercalated layered compounds known so far, (K0.8Fe2Se2 and Cs0.8(FeSe0.98)2), the Tc dependence on the anion height (distance between Fe layers and Se layers) was found to be analogous to those reported for As-containing Fe superconductors and Fe(Se1 − xChx), where Ch = Te, S.
TL;DR: In this paper, a magnetoelectric polycrystalline Ni thin film and (011)-oriented [Pb(Mg1/3Nb2/3)O3](1−x)−[PbTiO3]x]x heterostructure was reported to exhibit a 300 Oe anisotropy field and a 50% change in magnetic remanence.
Abstract: We report giant reversible and permanent magnetic anisotropy reorientation in a magnetoelectric polycrystalline Ni thin film and (011)-oriented [Pb(Mg1/3Nb2/3)O3](1−x)–[PbTiO3]x heterostructure. The electric-field-induced magnetic anisotropy exhibits a 300 Oe anisotropy field and a 50% change in magnetic remanence. The important feature is that these changes in magnetization states are stable without the application of an electric field and can be reversibly switched by an electric field near a critical value (±Ecr). This giant reversible and permanent magnetization change is due to remanent strain originating from a non-180° ferroelectric polarization reorientation when operating the ferroelectric substrate in a specific non-linear regime below the electric coercive field.
TL;DR: The measurements identified that subtle and microscopically reversible distortion of the polarization structure at the domain wall is at the origin of the dynamic conductivity, likely to be a universal property of topological defects in ferroelectric semiconductors.
Abstract: Topological walls separating domains of continuous polarization, magnetization, and strain in ferroic materials hold promise of novel electronic properties, that are intrinsically localized on the nanoscale and that can be patterned on demand without change of material volume or elemental composition. We have revealed that ferroelectric domain walls in multiferroic BiFeO3 are inherently dynamic electronic conductors, closely mimicking memristive behavior and contrary to the usual assumption of rigid conductivity. Applied electric field can cause a localized transition between insulating and conducting domain walls, tune domain wall conductance by over an order of magnitude, and create a quasicontinuous spectrum of metastable conductance states. Our measurements identified that subtle and microscopically reversible distortion of the polarization structure at the domain wall is at the origin of the dynamic conductivity. The latter is therefore likely to be a universal property of topological defects in ferr...
TL;DR: The quaternary intermetallic Heusler compounds CoFeMn$Z$ ($Z=\text{Al}$, Ga, Si, or Ge) with $1:1: 1:1$ stoichiometry were predicted to exhibit half-metallic ferromagnetism by ab initio electronic structure calculations as discussed by the authors.
Abstract: The quaternary intermetallic Heusler compounds CoFeMn$Z$ ($Z=\text{Al}$, Ga, Si, or Ge) with $1:1:1:1$ stoichiometry were predicted to exhibit half-metallic ferromagnetism by ab initio electronic structure calculations. The compounds were synthesized using an arc-melting technique and the crystal structures were analyzed using x-ray powder diffraction. The electronic properties were investigated using hard x-ray photoelectron spectroscopy. The low-temperature magnetic moments, as determined from magnetization measurements, follow the Slater-Pauling rule, confirming the proposed high spin polarizations. All compounds have high Curie temperatures, allowing for applications at room temperature and above.
TL;DR: The magnetic properties of high-entropy alloys based on equimolar FeCoCrNi were investigated using vibrating sample magnetometry to determine their usefulness in high-temperature magnetic applications.
Abstract: The magnetic properties of high-entropy alloys based on equimolar FeCoCrNi were investigated using vibrating sample magnetometry to determine their usefulness in high-temperature magnetic applications. Nuclear resonant inelastic x-ray scattering measurements were performed to evaluate the vibrational entropy of the 57Fe atoms and to infer chemical order. The configurational and vibrational entropy of alloying are discussed as they apply to these high-entropy alloys.