Showing papers on "Magnetic anisotropy published in 2012"
TL;DR: How currents can generate torques that affect the magnetic orientation and the reciprocal effect in a wide variety of magnetic materials and structures is explained.
Abstract: The magnetization of a magnetic material can be reversed by using electric currents that transport spin angular momentum. In the reciprocal process a changing magnetization orientation produces currents that transport spin angular momentum. Understanding how these processes occur reveals the intricate connection between magnetization and spin transport, and can transform technologies that generate, store or process information via the magnetization direction. Here we explain how currents can generate torques that affect the magnetic orientation and the reciprocal effect in a wide variety of magnetic materials and structures. We also discuss recent state-of-the-art demonstrations of current-induced torque devices that show great promise for enhancing the functionality of semiconductor devices.
1,049 citations
499 citations
TL;DR: It is visualize that cube has higher magnetization value than sphere with highest coercivity at 60 nm, and its hybridization into core-shell (CS) structure brings about a 14-fold increase in the coercivity with an exceptional energy conversion of magnetic field into thermal energy, the largest reported to date.
Abstract: With the aim of controlling nanoscale magnetism, we demonstrate an approach encompassing concepts of surface and exchange anisotropy while reflecting size, shape, and structural hybridization of nanoparticles. We visualize that cube has higher magnetization value than sphere with highest coercivity at 60 nm. Its hybridization into core–shell (CS) structure brings about a 14-fold increase in the coercivity with an exceptional energy conversion of magnetic field into thermal energy of 10600 W/g, the largest reported to date. Such capability of the CS-cube is highly effective for drug resistant cancer cell treatment.
384 citations
TL;DR: In this paper, a sputtered CoFeB/MgO-based magnetic tunnel junction with a perpendicular magnetic easy axis in a static external magnetic field is realized for a ∼180° magnetization reversal, where the bias voltage pulse duration is adjusted to a half period of the precession.
Abstract: The electric field-induced ∼180° magnetization reversal is realized for a sputtered CoFeB/MgO-based magnetic tunnel junction with perpendicular magnetic easy axis in a static external magnetic field. Application of bias voltage with nanoseconds duration results in a temporal change of magnetic easy axis in the free layer CoFeB to in-plane, which induces precessional motion of magnetization in the free layer. The magnetization reversal takes place when the bias voltage pulse duration is adjusted to a half period of the precession. We show that the back and forth magnetization reversal can be observed by using successive application of half-period voltage pulses.
376 citations
TL;DR: In this 3-terminal device, the SHE torque and the MTJ bias provide independent controls of the oscillation amplitude and frequency, enabling new approaches for developing tunable spin torque nano-oscillators.
Abstract: We show that a direct current in a tantalum microstrip can induce steady-state magnetic oscillations in an adjacent nanomagnet through spin torque from the spin Hall effect (SHE) The oscillations are detected electrically via a magnetic tunnel junction (MTJ) contacting the nanomagnet The oscillation frequency can be controlled using the MTJ bias to tune the magnetic anisotropy In this 3-terminal device, the SHE torque and the MTJ bias therefore provide independent controls of the oscillation amplitude and frequency, enabling new approaches for developing tunable spin torque nano-oscillators
355 citations
TL;DR: A methodology in which the use of additional characterization techniques, like single crystal magnetic measurements or luminescence experiments, complemented by relativistic ab initio calculations and a suitable choice of spin Hamiltonian models can be of great help to overcome difficulties in the rational design of lanthanide based Single Molecule Magnets with enhanced physical properties is exposed.
Abstract: Due to their usual large magnetic moments and large magnetic anisotropy lanthanide ions are investigated for the search of Single Molecule Magnets with high blocking temperature. However, the low symmetry crystal environment, the complexity of the electronic states or the non-collinearity of the magnetic anisotropy easy-axes in polynuclear systems make the rationalization of the magnetic behaviour of lanthanide based molecular systems difficult. In this perspective article we expose a methodology in which the use of additional characterization techniques, like single crystal magnetic measurements or luminescence experiments, complemented by relativistic ab initio calculations and a suitable choice of spin Hamiltonian models, can be of great help in order to overcome such difficulties, representing an essential step for the rational design of lanthanide based Single Molecule Magnets with enhanced physical properties.
353 citations
TL;DR: Slow magnetic relaxation effects were observed for 1 in the presence of a dc magnetic field, constituting the first example of field-induced single-molecule magnet behavior in a mononuclear six-coordinate Co(II) complex with a transverse anisotropy energy barrier.
Abstract: The novel mononuclear Co(II) complex cis-[CoII(dmphen)2(NCS)2]·0.25EtOH (1) (dmphen = 2,9-dimethyl-1,10-phenanthroline) features a highly rhombically distorted octahedral environment that is responsible for the strong positive axial and rhombic magnetic anisotropy of the high-spin CoII ion (D = +98 cm–1 and E = +8.4 cm–1). Slow magnetic relaxation effects were observed for 1 in the presence of a dc magnetic field, constituting the first example of field-induced single-molecule magnet behavior in a mononuclear six-coordinate Co(II) complex with a transverse anisotropy energy barrier.
342 citations
TL;DR: The measurements reveal that GHz-frequency VCMA torque and ST in low-resistance MTJs have similar magnitudes, and thus that both torques are equally important for understanding high-frequency voltage-driven magnetization dynamics in MTJs.
Abstract: We demonstrate excitation of ferromagnetic resonance in CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) by the combined action of voltage-controlled magnetic anisotropy (VCMA) and spin transfer torque (ST). Our measurements reveal that GHz-frequency VCMA torque and ST in low-resistance MTJs have similar magnitudes, and thus that both torques are equally important for understanding high-frequency voltage-driven magnetization dynamics in MTJs. As an example, we show that VCMA can increase the sensitivity of an MTJ-based microwave signal detector to the sensitivity level of semiconductor Schottky diodes.
264 citations
TL;DR: In this paper, the authors investigated the magnetic properties of electron-doped La0.23Ca0.77MnO3 manganite nanoparticles, with average size of 12 and 60 nm, prepared by the glycine-nitrate method, in the temperature range 5-300k and magnetic fields up to 90kOe.
Abstract: Magnetic properties of electron-doped La0.23Ca0.77MnO3 manganite nanoparticles, with average size of 12 and 60 nm, prepared by the glycine–nitrate method, have been investigated in the temperature range 5–300 K and magnetic fields up to 90 kOe. It is suggested that weak ferromagnetic moment results from ferromagnetic shells of the basically antiferromagnetic nanoparticles and from domains of frustrated disordered phase in the core. Assumption of two distinct sources of ferromagnetism is supported by the appearance of two independent ferromagnetic contributions in the fit of the T
3/2 Bloch law to spontaneous magnetization. The ferromagnetic components, which are more pronounced in smaller particles, occupy only a small fraction of the nanoparticle volume and the antiferromagnetic ground state remains stable. It is found that the magnetic hysteresis loops following field cooled processes, display size-dependent horizontal and vertical shifts, namely, exhibiting exchange bias effect. Time-dependent magnetization dynamics demonstrating two relaxation rates were observed at constant magnetic fields upon cooling to T < 100 K.
244 citations
TL;DR: In this paper, the superparamagnetic properties of the doped cobalt ferrite nanocrystals have been demonstrated by making use of the Williamson-Hall extrapolation, and the contribution of the spin-orbit coupling generating from the Co2+ ions in the octahedral lattice towards higher magnetic anisotropy and hence the magnetic properties is investigated.
Abstract: The superparamagnetic properties of the doped cobalt ferrite nanocrystals have been demonstrated. The significance of the sol–gel autocombustion method in yielding the as obtained doped cobalt ferrite oxide powder in the nano-range has been very well complemented with structural, dimensional and morphological analytical techniques such as X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM), particle size analysis and Scanning Electron Microscopy (SEM). The lattice strain and lattice parameters have been calculated by making use of the Williamson–Hall extrapolation. The valence states of the metal ions and single phase formation of the polycrystalline oxides have been confirmed with the help of X-ray Photoelectron Spectroscopy (XPS) and Raman Spectroscopy. The magnetic measurements M–H and M–T have been carried out demonstrating a change in the magnetic moment and a superparamagnetic–ferrimagnetic transition in the ferrite system. The influence of the distribution of the metal ions in the crystal lattice and the dimensions of the ferrite oxides on the resultant magnetic properties has been demonstrated. The contribution of the spin–orbit coupling generating from the Co2+ ions in the octahedral lattice towards higher magnetic anisotropy and hence the magnetic properties is investigated. The results provide an insight into the inter-relationship of the particle dimension, the spin–orbit coupling and the resulting superparamagnetic property.
190 citations
TL;DR: A tunable organometallic synthesis of monodisperse iron carbide and core/shell iron/iron carbide nanoparticles displaying a high magnetization and good air-stability results in unprecedented hyperthermia properties at moderate magnetic fields, in the range of medical treatments.
Abstract: We report a tunable organometallic synthesis of monodisperse iron carbide and core/shell iron/iron carbide nanoparticles displaying a high magnetization and good air-stability. This process based on the decomposition of Fe(CO)(5) on Fe(0) seeds allows the control of the amount of carbon diffused and therefore the tuning of nanoparticles magnetic anisotropy. This results in unprecedented hyperthermia properties at moderate magnetic fields, in the range of medical treatments.
TL;DR: In this paper, the magnetic properties of CoFe2O4 nanoparticles (⟨D⟩ ≅ 4-8 nm) coated with oleic acid have been investigated in order to clarify the role of the molecular coating on the interparticle interactions and surface anisotropy.
Abstract: Molecular coating of nanoparticles represents probably the most important and, at the same time, critical step to design new nanostructured magnetic materials. The interaction between molecules and surface atoms leads to a strong modification of surface magnetic properties, that are one of the key points in the physics of magnetic nanoparticles. In this paper the magnetic properties of CoFe2O4 nanoparticles (⟨D⟩ ≅ 4–8 nm) coated with oleic acid have been investigated in order to clarify the role of the molecular coating on the interparticle interactions and surface anisotropy. An increase of magnetic anisotropy (i.e., coercive field and anisotropy constant) with particle size is observed in coated nanoparticles, indicating that the magnetic anisotropy is governed mainly by its magneto-crystalline component. The removal of molecular coating induces a strong increase of anisotropy, because of the increase of its surface component, as indicated by the increase of exchange bias field.
TL;DR: These Nd-doped ZnO nanowire arrays which exhibit stable room temperature ferromagnetism with a large saturation magnetic moment as well as a high coercivity are synthesized, indicating giant magnetic anisotropy in these magnetic oxide nanowires.
Abstract: As an important class of spintronic material, ferromagnetic oxide semiconductors are characterized with both charge and spin degrees of freedom, but they often show weak magnetism and small coercivity, which limit their applications. In this work, we synthesized Nd-doped ZnO nanowire arrays which exhibit stable room temperature ferromagnetism with a large saturation magnetic moment of 4.1 μB/Nd as well as a high coercivity of 780 Oe, indicating giant magnetic anisotropy. First-principles calculations reveal that the remarkable magnetic properties in Nd-doped ZnO nanowires can be ascribed to the intricate interplay between the spin moments and the Nd-derived orbital moments. Our complementary experimental and theoretical results suggest that these magnetic oxide nanowires obtained by the bottom-up synthesis are promising as nanoscale building blocks in spintronic devices.
TL;DR: In this article, the composition dependence of saturation magnetization and uniaxial magnetic anisotropy in epitaxial films of Mn-Ga binary alloys was investigated.
Abstract: Mn-Ga binary alloys show strong magnetism and large uniaxial magnetic anisotropy even though these alloys do not contain any noble, rare-earth metals or magnetic elements. We investigate the composition dependence of saturation magnetization ${M}_{\mathrm{S}}$ and uniaxial magnetic anisotropy ${K}_{\mathrm{u}}$ in epitaxial films of Mn${}_{x}$Ga${}_{1\ensuremath{-}x}$ alloys ($x\ensuremath{\sim}0.5$--0.75) grown by magnetron sputtering. The ${M}_{\mathrm{S}}$ values decrease linearly from approximately 600 to 200 emu/cm${}^{3}$ with increasing $x$, whereas the ${K}_{\mathrm{u}}$ values decrease slightly from approximately 15 to 10 Merg/cm${}^{3}$ with increasing $x$. These trends are distinct from those for known tetragonal hard magnets obtained in a limited composition range in Mn-Al and Fe-Pt binary alloys. These data are analyzed using a localized magnetic moment model.
TL;DR: These MBE-grown epitaxial films exhibit pronounced magnetic properties at room temperature, including ultrahigh perpendicular coercivity, giant perpendicular magnetic anisotropy and large magnetic energy products up to 2.60 MGOe, which allow various applications in ultrahigh density recording, spintronics, and permanent magnets.
Abstract: A new kind of multifunctional L1(0) -Mn(1.5)Ga film is demonstrated for the first time. These MBE-grown epitaxial films exhibit pronounced magnetic properties at room temperature, including ultrahigh perpendicular coercivity up to 42.8 kOe, giant perpendicular magnetic anisotropy with a maximum of 21.7 Merg/cm(3) and large magnetic energy products up to 2.60 MGOe, which allow various applications in ultrahigh density recording, spintronics, and permanent magnets.
TL;DR: In this paper, the experimental and theoretical study of local anisotropy alignment on DyIII metal centers and their orientation relative to other centers in rare, dinuclear quadruply-stranded helicate/mesocate complexes is presented.
Abstract: In order for molecular magnetic materials to become functional, they must retain their magnetization at reasonable temperatures implying high energy barriers for spin reversal. The field of single-molecule magnets (SMMs) has recently experienced an explosion of research targeting these high anisotropic barriers. Achieving such feats has involved increasing the spin of a complex and/or increasing the inherent magnetic anisotropy. Exerting control over the total spin of a complex has been possible contrary to controlling the global anisotropy. Herein, we report the experimental and theoretical study of local anisotropy alignment on DyIII metal centers and their orientation relative to other centers in rare, dinuclear quadruply-stranded helicate/mesocate complexes. A detailed study of these supramolecular architectures has advanced our knowledge of the origins of magnetic relaxation in SMMs which was shown to arise from minute changes in bond distances around the metal centers leading to changes in the local anisotropy and, in turn, the effective energy barriers.
TL;DR: The description of single-ion and inter-ion anisotropic magnetic interactions is achieved here for the first time fully ab initio, i.e., without use of phenomenological parameters.
Abstract: A toroidal magnetic moment in the absence of conventional total magnetic moment is observed in a {Dy6} ring. The reason for the net toroidal arrangement of the local magnetic moments is the high symmetry of the complex in combination with strong intra-molecular dipolar interactions between Dy ions. The description of single-ion and inter-ion anisotropic magnetic interactions is achieved here for the first time fully ab initio, i.e., without use of phenomenological parameters.
01 Sep 2012
TL;DR: In this article, the voltage-controlled magnetic anisotropy (VCMA) effect in thin magnetic films, and their device implications are discussed, as well as its modulation by voltage.
Abstract: Electric-field-control of magnetism can dramatically improve the energy efficiency of spintronic devices and enhance the performance of magnetic memories. More generally, it expands the range of applications of nonvolatile spintronic devices, by making them energetically competitive compared to conventional semiconductor solutions for logic and computation, thereby potentially enabling a new generation of ultralow-power nonvolatile spintronic systems. This paper reviews recent experiments on the voltage-controlled magnetic anisotropy (VCMA) effect in thin magnetic films, and their device implications. The interfacial perpendicular anisotropy in layered magnetic material stacks, as well as its modulation by voltage, are discussed. Ferromagnetic resonance experiments and VCMA-induced high-frequency magnetization dynamics are reviewed. Finally, we discuss recent progress on voltage-induced switching of magnetic tunnel junction devices and its potential applications to magnetic random access memory (MRAM).
TL;DR: In this paper, the authors demonstrate all-optical magnetization switching for different TbxCo1-x ferrimagnetic alloy composition and demonstrate alloptical switching for films with anisotropy fields reaching 6 T corresponding to anisotropic constants of 3x106 ergs/cm3.
Abstract: Magnetization reversal using circularly polarized light provides a new way to control magnetization without any external magnetic field and has the potential to revolutionize magnetic data storage. However, in order to reach ultra-high density data storage, high anisotropy media providing thermal stability are needed. Here, we evidence all-optical magnetization switching for different TbxCo1-x ferrimagnetic alloy composition and demonstrate all-optical switching for films with anisotropy fields reaching 6 T corresponding to anisotropy constants of 3x106 ergs/cm3. Optical magnetization switching is observed only for alloys which compensation temperature can be reached through sample heating.
TL;DR: In this paper, the role of magnetic anisotropy on the specific absorption rate of cobalt-ferrite nanoparticles with diameters ranging from 3 to 14 nm was discussed.
Abstract: Considerable effort has been made in recent years to optimize materials properties for magnetic hyperthermia applications. However, due to the complexity of the problem, several aspects pertaining to the combined influence of the different parameters involved still remain unclear. In this paper, we discuss in detail the role of the magnetic anisotropy on the specific absorption rate of cobalt-ferrite nanoparticles with diameters ranging from 3 to 14 nm. The structural characterization was carried out using x-ray diffraction and Rietveld analysis and all relevant magnetic parameters were extracted from vibrating sample magnetometry. Hyperthermia investigations were performed at 500 kHz with a sinusoidal magnetic field amplitude of up to 68 Oe. The specific absorption rate was investigated as a function of the coercive field, saturation magnetization, particle size, and magnetic anisotropy. The experimental results were also compared with theoretical predictions from the linear response theory and dynamic h...
TL;DR: In this article, all-optical magnetization switching for different TbxCo1−x ferrimagnetic alloy compositions using fs- and ps-laser pulses was demonstrated for films with anisotropy fields reaching 6'T corresponding to anisotropic constants of 3'×'106 ergs/cm3.
Abstract: Magnetization reversal using circularly polarized light provides a way to control magnetization without any external magnetic field and has the potential to revolutionize magnetic data storage. However, in order to reach ultra-high density data storage, high anisotropy media providing thermal stability are needed. Here, we evidence all-optical magnetization switching for different TbxCo1−x ferrimagnetic alloy compositions using fs- and ps-laser pulses and demonstrate all-optical switching for films with anisotropy fields reaching 6 T corresponding to anisotropy constants of 3 × 106 ergs/cm3. Optical magnetization switching is observed only for alloy compositions where the compensation temperature can be reached through sample heating.
TL;DR: It is shown that the precess dynamics can be controlled by matching the precession period with the round trip time of the acoustic echoes, and the calculation of the time-dependent precession torque τ=|M×H(eff)| allows understanding the underlying physics.
Abstract: We report about the magnetization dynamics of a ferromagnetic nickel film at room temperature excited by acoustic pulses generated with femtosecond laser pulses. The ultrafast change of magnetization is detected from both the front and back sides of the nickel film. The propagating strain associated with the acoustic pulses modifies the magnetic anisotropy and induces a precession of the magnetization. We model the time-dependent magnetoacoustic response of the metallic film by combining a three temperature model for the temperatures of the charges, the spins, and the lattice, the wave equation for the strain, and the Landau-Lifshitz-Gilbert equation for the magnetization. It is shown that the precession dynamics can be controlled by matching the precession period with the round trip time of the acoustic echoes. The calculation of the time-dependent precession torque $\ensuremath{\tau}=|M\ifmmode\times\else\texttimes\fi{}{H}_{\mathrm{eff}}|$ allows understanding the underlying physics.
TL;DR: The excellent tunable soft magnetic properties and magnetic bistability exhibited by low Co content Co-Ni nanowires indicate that they might become the material of choice for the development of nanostructured magnetic systems and devices as an alternative to Fe-Ni alloy based systems, being chemically more robust.
Abstract: CoxNi1 x alloy nanowires with varying Co content (0 x 0:95), having a diameter of 130 nm and length of around 20 m, are synthesized by template-assisted electrodeposition into the nanopores of SiO2 conformal coated hard-anodic aluminum oxide membranes. The magneto-structural properties of both single isolated nanowires and hexagonally ordered nanowire arrays of Co‐Ni alloys are systematically studied by means of magneto-optical Kerr effect magnetometry and vibrating sample magnetometry, respectively, allowing us to compare different alloy compositions and to distinguish between the magnetostatic and magnetocrystalline contributions to the effective magnetic anisotropy for each system. The excellent tunable soft magnetic properties and magnetic bistability exhibited by low Co content Co‐Ni nanowires indicate that they might become the material of choice for the development of nanostructured magnetic systems and devices as an alternative to Fe‐Ni alloy based systems, being chemically more robust. Furthermore, Co contents higher than 51 at.% allow us to modify the magnetic behavior of Co-rich nanowires by developing well controlled magnetocrystalline anisotropy, which is desirable for data storage applications. (Some figures may appear in colour only in the online journal)
TL;DR: In this article, the angular dependence of the coercivity of Co wires was investigated and it was confirmed that the crystal phase of nanowires with length 2.5 m and diameter 35 nm shifts from hcp to fcc as the Ni content increases.
Abstract: Ordered arrays of Co${}_{x}$Ni${}_{1\ensuremath{-}x}$ nanowires ($0lxl1$) were fabricated by a template-assisted method using electrodeposition into anodic aluminum oxide membranes. Tuning of the Co-alloy composition by changing the Ni content enables control of the effective anisotropy axis, which is determined by the balance between the hcp and fcc magnetocrystalline and shape anisotropies. We report on the nanowires' structural and magnetic properties (e.g., hysteresis curves and their parameters as well as first-order reversal curve analysis), paying particular attention to their angular dependence. It is confirmed that the crystal phase of nanowires with length 2.5 $\ensuremath{\mu}$m and diameter 35 nm shifts from hcp to fcc as the Ni content increases. That results in a significant modification of the magnetization process and, accordingly, of the magnetic properties of the array. Analytical calculations of the angular dependence of the coercivity allow us to confirm that the magnetization reversal is mostly ascribed to the propagation of a transverse domain wall. Fitting of the experiment to these calculations indicates the presence of a transverse crystalline anisotropy (ascribed to the hcp phase) in Co wires, while this changes to an axial anisotropy (fcc phase) as the Ni content increases.
University of Tennessee1, Florida State University2, University of California, Santa Barbara3, University of Manitoba4, University of Winnipeg5, Tokyo Institute of Technology6, Oak Ridge National Laboratory7, University of Maryland, College Park8, National Institute of Standards and Technology9, Indiana University10, University of Florida11
TL;DR: Using magnetic, thermal, and neutron measurements on single-crystal samples, it is shown that Ba3CoSb2O9 is a spin-1/2 triangular-lattice antiferromagnet with the c axis as the magnetic easy axis and two magnetic phase transitions bracketing an intermediate up-up-down phase in magnetic field applied along the caxis.
Abstract: Using magnetic, thermal, and neutron measurements on single-crystal samples, we show that ${\mathrm{Ba}}_{3}{\mathrm{CoSb}}_{2}{\mathrm{O}}_{9}$ is a spin-$1/2$ triangular-lattice antiferromagnet with the $c$ axis as the magnetic easy axis and two magnetic phase transitions bracketing an intermediate up-up-down phase in magnetic field applied along the $c$ axis. A pronounced extensive neutron-scattering continuum above spin-wave excitations, observed below ${T}_{\mathrm{N}}$, implies that the system is in close proximity to one of two spin-liquid states that have been predicted for a 2D triangular lattice.
TL;DR: It is demonstrated that an in-plane easy axis arises from the combination of the crystal field and dynamic hybridization effects within the surface plane, contrary to what was assumed in recent investigations on the supposed opening of a gap.
Abstract: The robustness of the gapless topological surface state hosted by a 3D topological insulator against perturbations of magnetic origin has been the focus of recent investigations. We present a comprehensive study of the magnetic properties of Fe impurities on the prototypical 3D topological insulator Bi2Se3 using local low-temperature scanning tunneling spectroscopy and integral x-ray magnetic circular dichroism techniques. Single Fe adatoms on the Bi2Se3 surface, in the coverage range approximate to 1% of a monolayer, are heavily relaxed into the surface and exhibit a magnetic easy axis within the surface plane, contrary to what was assumed in recent investigations on the supposed opening of a gap. Using ab initio approaches, we demonstrate that an in-plane easy axis arises from the combination of the crystal field and dynamic hybridization effects.
TL;DR: These findings indicate that the onset of one-dimensional spin correlations within the chain compound 4 leads to a suppression of quantum tunneling of the magnetization within the easy plane, resulting in magnetic bistability and slow relaxation behavior.
Abstract: The model compounds (NBu4)2[ReCl4(CN)2] (1), (DMF)4ZnReCl4(CN)2 (2), and [(PY5Me2)2Mn2ReCl4(CN)2](PF6)2 (3) have been synthesized to probe the origin of the magnetic anisotropy barrier in the one-dimensional coordination solid (DMF)4MnReCl4(CN)2 (4). High-field electron paramagnetic resonance spectroscopy reveals the presence of an easy-plane anisotropy (D > 0) with a significant transverse component, E, in compounds 1–3. These findings indicate that the onset of one-dimensional spin correlations within the chain compound 4 leads to a suppression of quantum tunneling of the magnetization within the easy plane, resulting in magnetic bistability and slow relaxation behavior. Within this picture, it is the transverse E term associated with the ReIV centers that determines the easy axis and the anisotropy energy scale associated with the relaxation barrier. The results demonstrate for the first time that slow magnetic relaxation can be achieved through optimization of the transverse anisotropy associated with...
TL;DR: In this article, the authors calculate the number density, energy density, transverse pressure, longitudinal pressure, and magnetization of an ensemble of spin one-half particles in the presence of a homogenous background magnetic field.
Abstract: We calculate the number density, energy density, transverse pressure, longitudinal pressure, and magnetization of an ensemble of spin one-half particles in the presence of a homogenous background magnetic field. The magnetic field direction breaks spherical symmetry causing the pressure transverse to the magnetic field direction to be different than the pressure parallel to it. We present explicit formulas appropriate at zero and finite temperature for both charged and uncharged particles including the effect of the anomalous magnetic moment. We demonstrate that the resulting expressions satisfy the canonical relations $\ensuremath{\Omega}=\ensuremath{-}{P}_{\ensuremath{\parallel}}$ and ${P}_{\ensuremath{\perp}}={P}_{\ensuremath{\parallel}}\ensuremath{-}MB$, with $M=\ensuremath{-}\ensuremath{\partial}\ensuremath{\Omega}/\ensuremath{\partial}B$ being the magnetization of the system. We numerically calculate the resulting pressure anisotropy for a gas of protons and a gas of neutrons and demonstrate that the inclusion of the anomalous magnetic increases the level of pressure anisotropy in both cases.
TL;DR: In this article, the authors experimentally study the tunability of the Ruderman-Kittel-Kasuya-Yosida (RKKY) interlayer exchange coupling (IEC) in Pt/CoFeB/Pt/Ru/Pit/CoEb/Co Eb stacks with perpendicular magnetic anisotropy (PMA) and show that the IEC versus Pt thickness exhibits a simple exponential decay with a decay length of 0.16
Abstract: We experimentally study the tunability of the Ruderman-Kittel-Kasuya-Yosida (RKKY) interlayer exchange coupling (IEC) in Pt/CoFeB/Pt/Ru/Pt/CoFeB/Pt stacks with perpendicular magnetic anisotropy (PMA). The perpendicular magnetization of a single Pt/Co60Fe20B20/Pt (at. %) shows full remanence and square hysteresis loops for a CoFeB thickness range of 0.60–1.0 nm. By inserting a Pt layer between the Ru and CoFeB, the PMA of the ultrathin CoFeB layers is stabilized and the IEC can be tuned. In particular, we show that the IEC versus Pt thickness exhibits a simple exponential decay with a decay length of 0.16 nm.
TL;DR: In this article, the heating properties of cobalt ferrite and maghemite nanoparticles were investigated under the influence of a 500 kHz sinusoidal magnetic field with varying amplitude, up to 134 Oe.
Abstract: Further advances in magnetic hyperthermia might be limited by biological constraints, such as using sufficiently low frequencies and low field amplitudes to inhibit harmful eddy currents inside the patient's body. These incite the need to optimize the heating efficiency of the nanoparticles, referred to as the specific absorption rate (SAR). Among the several properties currently under research, one of particular importance is the transition from the linear to the non-linear regime that takes place as the field amplitude is increased, an aspect where the magnetic anisotropy is expected to play a fundamental role. In this paper we investigate the heating properties of cobalt ferrite and maghemite nanoparticles under the influence of a 500 kHz sinusoidal magnetic field with varying amplitude, up to 134 Oe. The particles were characterized by TEM, XRD, FMR and VSM, from which most relevant morphological, structural and magnetic properties were inferred. Both materials have similar size distributions and satu...