Influence Of Magnetic Anisotropy Research Articles

Giant and highly anisotropic magnetocaloric effects in single crystals of disordered-perovskite RCr0.5Fe0.5O3 (R = Gd, Er)

Magnetic anisotropy is crucial in examining suitable materials for magnetic functionalities because it affects their magnetic characteristics. In this study, disordered-perovskite RCr0.5Fe0.5O3 (R = Gd, Er) single crystals were synthesized and the influence of magnetic anisotropy and additional ordering of rare-earth moments on cryogenic magnetocaloric properties was investigated. Both GdCr0.5Fe0.5O3 (GCFO) and ErCr0.5Fe0.5O3 (ECFO) crystallize in an orthorhombic Pbnm structure with randomly distributed Cr3+ and Fe3+ ions. In GCFO, the long-range order of Gd3+ moments emerges at a temperature of TGd (the ordering temperature of Gd3+ moments) = 12 K. The relatively isotropic nature of large Gd3+ moment originating from zero orbital angular momentum exhibits giant and virtually isotropic magnetocaloric effect (MCE), with a maximum magnetic entropy change of Delta {S}_{M} ≈ 50.0 J/kg·K. In ECFO, the highly anisotropic magnetizations result in a large rotating MCE characterized by a rotating magnetic entropy change Delta {S}_{theta } = 20.8 J/kg·K. These results indicate that a detailed understanding of magnetically anisotropic characteristics is the key for exploring improved functional properties in disordered perovskite oxides.

The influence of magnetic anisotropy on the Zeeman spectra of lanthanide doped nanoparticles

High-resolution infra-red spectra of KY3F10 nanoparticles doped with Nd3+ and Er3+ are measured in magnetic fields of up to 4T. A simple model of the magnetic splittings of the ground and excited states is used to show that the presence or absence of observable splittings depends on the anisotropy of the response to the magnetic field. Detailed crystal-field calculations accurately model the spectra, including nonlinear effects.

Observability of Paramagnetic NMR Signals at over 10 000 ppm Chemical Shifts

AbstractWe report an experimental observation of 31P NMR resonances shifted by over 10 000 ppm (meaning percent range, and a new record for solutions), and similar 1H chemical shifts, in an intermediate‐spin square planar ferrous complex [tBu(PNP)Fe‐H], where PNP is a carbazole‐based pincer ligand. Using a combination of electronic structure theory, nuclear magnetic resonance, magnetometry, and terahertz electron paramagnetic resonance, the influence of magnetic anisotropy and zero‐field splitting on the paramagnetic shift and relaxation enhancement is investigated. Detailed spin dynamics simulations indicate that, even with relatively slow electron spin relaxation (T1 ≈10−11 s), it remains possible to observe NMR signals of directly metal‐bonded atoms because pronounced rhombicity in the electron zero‐field splitting reduces nuclear paramagnetic relaxation enhancement.

Observability of Paramagnetic NMR Signals at over 10 000 ppm Chemical Shifts.

We report an experimental observation of 31P NMR resonances shifted by over 10 000 ppm (meaning percent range, and a new record for solutions), and similar 1H chemical shifts, in an intermediate‐spin square planar ferrous complex [ tBu(PNP)Fe‐H], where PNP is a carbazole‐based pincer ligand. Using a combination of electronic structure theory, nuclear magnetic resonance, magnetometry, and terahertz electron paramagnetic resonance, the influence of magnetic anisotropy and zero‐field splitting on the paramagnetic shift and relaxation enhancement is investigated. Detailed spin dynamics simulations indicate that, even with relatively slow electron spin relaxation (T 1 ≈10−11 s), it remains possible to observe NMR signals of directly metal‐bonded atoms because pronounced rhombicity in the electron zero‐field splitting reduces nuclear paramagnetic relaxation enhancement.

Review of Domain Wall Dynamics Engineering in Magnetic Microwires.

The influence of magnetic anisotropy, post-processing conditions, and defects on the domain wall (DW) dynamics of amorphous and nanocrystalline Fe-, Ni-, and Co-rich microwires with spontaneous and annealing-induced magnetic bistability has been thoroughly analyzed, with an emphasis placed on the influence of magnetoelastic, induced and magnetocrystalline anisotropies. Minimizing magnetoelastic anisotropy, either by the selection of a chemical composition with a low magnetostriction coefficient or by heat treatment, is an appropriate route for DW dynamics optimization in magnetic microwires. Stress-annealing allows further improvement of DW velocity and hence is a promising method for optimization of DW dynamics in magnetic microwires. The origin of current-driven DW propagation in annealing-induced magnetic bistability is attributed to magnetostatic interaction of outer domain shell with transverse magnetization orientation and inner axially magnetized core. The beneficial influence of the stress-annealing on DW dynamics has been explained considering that it allows increasing of the volume of outer domain shell with transverse magnetization orientation at the expense of decreasing the radius of inner axially magnetized core. Such transverse magnetic anisotropy can similarly affect the DW dynamics as the applied transverse magnetic field and hence is beneficial for DW dynamics optimization. Stress-annealing allows designing the magnetic anisotropy distribution more favorable for the DW dynamics improvement. Results on DW dynamics in various families of nanocrystalline microwires are provided. The role of saturation magnetization on DW mobility improvement is discussed. The DW shape, its correlation with the magnetic anisotropy constant and the microwire diameter, as well as manipulation of the DW shape by induced magnetic anisotropy are discussed. The engineering of DW propagation through local stress-annealing and DW collision is demonstrated.

Magnetoactive elastomer based on superparamagnetic nanoparticles with Curie point close to room temperature

A magnetoactive elastomer (MAE) consisting of single-domain La0.6Ag0.2Mn1.2O3 nanoparticles with a Curie temperature close to room temperature (TC = 308 K) in a silicone matrix has been prepared and comprehensively studied. It has been found that MAE particles are magnetized superparamagnetically with a low coercivity below 10 Oe at room temperature and above. The influence of magnetic anisotropy on the appearance of torque is justified. A coupling between magnetization and magnetoelasticity has also been established. The mechanisms of the appearance of magnetoelasticity, including the effect of MAE rearrangement and MAE compression by magnetized particles, have been revealed. It has been found that the magnetoelastic properties of MAE have critical features near TC. The magnetoelastic properties of MAE disappear at T > TC and are restored at T < TC. This makes it possible to use MAE at room temperature as a smart material for devices with self-regulating magnetoelastic properties.

Simulation of Uniaxial Deformation of a Ferrogel Sample Exposed by the External Magnetic Field

Ferrogels are magnetoactive composite materials with very soft hydrogel matrix, filled by ferromagnetic particles. This work is devoted to a numerical investigation of magneto-mechanical behaviour of a small sample of ferrogel. Our model is based on a coarse grained molecular dynamics approach: polymeric matrix is emulated by lattice of bead-strings chains and magnetic single-domain particles are considered as rigid spheres and placed in a nodes of the lattice. This model was previously successfully used for a research of equilibrium magnetization of the material. Here we examine of the reaction of ferrogel sample on uniaxial tension in presence of an external magnetic field. Modelling proves that key role in a changes of mechanical response during the magnetization plays an internal structure of material, specifically, the existence of particles aggregates, induced by forces of dipolar magnetic interaction. Also the influence of magnetic anisotropy on a process is considered.

Influence of anisotropy on magnetoresistance in magnetic multilayer structures

Abstract The results of Monte Carlo study of influence of magnetic anisotropy on magnetoresistance in magnetic multilayer nanostructures are presented. Influence of anisotropy reorientation on magnetoresistance is considered on example of Co/Cu(100)/Co structure with anisotropy in plane of cobalt films, which is changed to anisotropy out plane in Pt/Co/Cu/Co/Pt structure with insertion of ultrathin films of platinum. It was shown that case of nanostructure with anisotropy out plane is characterized by important increase of magnetoresistance for structures with thicknesses of ferromagnetic films N ⩽ 11 monolayers.

Dysprosium Compounds with Hula-Hoop-like Geometries: The Influence of Magnetic Anisotropy and Magnetic Interactions on Magnetic Relaxation

Single-ion anisotropy is one of the crucial properties for mononuclear and even polynuclear single-molecule magnets (SMMs), which can be enhanced by the judicious choice of the coordination geometry around the metal centers. Meanwhile, magnetic interactions also play a significant role in high-performance polynuclear SMMs, especially the dinuclear SMMs. For exploring the influence of those two factors on the magnetic properties, we report a novel series of lanthanide complexes, [Dy(L)3(HL)(THF)2] (1), [Dy2(Py3CO)2(CF3SO3)4(H2O)2]·CH3CN (2), and [Dy2(Py3CO)2(PhCOO)4(MeOH)2]·MeOH (3), with hula-hoop-like geometries around the DyIII ions. All three complexes display slow relaxation of magnetization under a zero applied direct-current field with anisotropy barriers of 169 and 51 K for 1 and 3, respectively, while the slow relaxation of magnetization of complex 2 may mainly result from Raman relaxation. Besides, complex 1 demonstrates butterfly-type hysteresis below 4 K, and complex 2 shows no opening of the hysteresis loop with an inflection of around 0.25 T. Although complexes 2 and 3 have similar structures, the different coordinate anions induce distinct magnetic interaction states, antiferromagnetic and ferromagnetic for 2 and 3, respectively. Ab initio calculations reveal that the better SMM behavior of complex 1 should be ascribed to stronger single-ion anisotropy compared with complexes 2 and 3. The small value of the dipolar interaction results in an overall antiferromagnetic interaction for complex 2, while the large value of the dipolar interaction causes an overall ferromagnetic interaction for complex 3, where the dipolar interactions are ferromagnetic for both complexes.

Influence of Magnetic Anisotropy on Inverse Spin Hall Voltage

Spin pumping efficiency (SPE) in a ferromagnetic (FM)/Pt system relies on the effective magnetization damping of FM layer and the interface spin mixing conductance. However, there are very few studies on the influence of magnetic anisotropy of FM material on SPE. In this study, the spin pumping induced spin voltage [Formula: see text] in Fe3O4(58.9[Formula: see text]nm)/Pt(5.5[Formula: see text]nm) is investigated in two different orientations of the external magnetic field, one parallel and other perpendicular to the in-plane easy axis of Fe3O4. The value of [Formula: see text] with the magnetic field along the easy axis is 38% higher compared with that along the hard axis. The possible origin of this enhancement is investigated based on the model of ferromagnetic resonance induced spin pumping.

Influence of magnetic anisotropy on dynamic magnonic crystals created by surface acoustic waves in yttrium iron garnet films

Experimental results on the investigation of the influence of magnetic crystallographic anisotropy onto parameters of dynamic magnonic crystals arising at surface acoustic wave (SAW) propagation in yttrium iron garnet (YIG) films are presented. The main features of such an influence, as we have shown, are: 1) appearance of extra magnonic band gaps together with the normal magnonic band gap existing without anisotropy, 2) the absence of reflections of the incident surface magnetostatic wave at the frequency of these extra gaps, 3) the same depth for the extra gaps was achieved with a relatively small SAW power, almost by the order of magnitude less than in the case of normal magnonic gaps caused by SAW. A possible explanation of the features is given on the base of inelastic scattering of surface magnetostatic waves by SAW with the transformation of the reflected surface wave to the anisotropic direct volume magnetostatic wave existence of which is due to cubic crystallographic anisotropy in YIG. These results may be useful in designing new devices of information processing.

The influence of magnetic anisotropy on magnetostriction forces and vibration in three-phase three-limb transformers

The influence of magnetic anisotropy on magnetostriction forces and vibration in three-phase three-limb transformers

Relationship Between Magnetostriction and Magnetic Domain Structure in Fe-Based Alloy Single-Crystal Films With bcc(001) Orientation

Fe, Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">94</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> , Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">98</sub> C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , and Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">95</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> (at. %) single-crystal thin films of bcc(001) orientation are prepared on MgO(001) substrates using an ultrahigh-vacuum magnetron sputtering system. The influence of magnetic anisotropy on the magnetostriction under rotating magnetic field is investigated. Fe, Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">94</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> , and Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">98</sub> C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> films show four-fold symmetries in in-plane magnetic anisotropy, where easy and hard magnetization directions are, respectively, observed along bcc[100] and bcc[110]. Higher saturation fields measured along bcc[110] are recognized in the order of Fe (6 kOe) > Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">98</sub> C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (5 kOe) > Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">94</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> (4 kOe). Triangle output waveforms of magnetostriction appear when these films are measured under low-rotating fields. The behavior is related with the motion of 90° magnetic domain walls in magnetically unsaturated film. With increasing the rotating field, the films approach to magnetic saturations and the waveform gradually shifts to usual sinusoidal shape. Larger threshold rotating field is observed in the order of Fe > Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">98</sub> C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> > Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">94</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> , which is related to the saturation field. On the contrary, Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">95</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> film possesses an almost isotropic property in in-plane measurement and shows sinusoidal waveforms even when the film is magnetically unsaturated. The waveform is affected by the symmetry and the strength of magnetic anisotropy.

Influence of magnetic anisotropy thermoelectric effect on spin-dependent devices

While researching the thermoelectric effect of the nanocontact, we find that the thermoelectric voltage between both ends of the "Γ"-shaped Ni wire changes significantly by applying an external magnetic field, which we attribute to the influence of magnetic anisotropy of Ni wire. The effect of the external magnetic field always produces an extra force whose direction goes against the temperature gradient. And the extra force clearly corresponds to the magnetic field and temperature difference between both ends of the Ni wire. These results suggest that during studying spin-dependent devices, the testing methods and the configuration of magnetic material need to be noticed seriously in order to avoid interfusing additional electromagnetic signals which may bring about a miscarriage of justice to the experimental results.

Influence of magnetic anisotropy on the Kondo effect and spin-polarized transport through magnetic molecules, adatoms, and quantum dots

Transport properties in the Kondo regime of a nanosystem displaying uniaxial magnetic anisotropy (such as a magnetic molecule, magnetic adatom or quantum dot coupled to a localized magnetic moment) are analyzed theoretically. In particular, the influence of spin-polarized transport through a local orbital of the system and exchange coupling of conduction electrons to the system's magnetic core on the Kondo effect is discussed. The numerical renormalization group method is applied to calculate the spectral functions and linear conductance in the case of the parallel and antiparallel configurations of the electrodes' magnetic moments. It is shown that both the magnetic anisotropy as well as the exchange coupling between electrons tunneling through the conducting orbital and magnetic core play an important role in formation of the Kondo resonance, leading generally to its suppression. Specific transport properties of such a system appear also as a nontrivial behavior of tunnel magnetoresistance. It is also shown that the Kondo effect can be restored by an external magnetic field in both the parallel and antiparallel magnetic configurations.

Influence of magnetic anisotropy and dipolar interactions on magnetocaloric effect in nanostructured materials

AbstractWe outline the magnetic and magnetocaloric behaviour of magnetic nanoparticles distributed into columnar‐like arrangements with their easy axes collinear aligned along the chain direction, and comparing to that of ferromagnetic nanowires arrays. An extended Monte Carlo model taking into account the influence of both, the magnetic anisotropy and magnetostatic interactions of dipolar origin between ferromagnetic nanoparticles chains, has been developed. The existence of a maximum in thermomagnetic curves for applied magnetic fields up to 2.5 times the anisotropy field value of the system, and the coexistence of positive and negative magnetocaloric effect have been predicted confirming the experimental results found in highly ordered arrays of ferromagnetic nanowires.Positive and negative MCE regimes in an array of single magnetic domain ferromagnetic nanowires and its dependence on the applied field value. The inset shows the MFM image of the magnetic monodomain dipole structure for an isolated Ni‐rich nanowire.magnified image

Influence of magnetic anisotropy and its distribution on the hysteresis loops upon patterning thin films

We compare the hysteresis loops of ferromagnetic films and dots down to 0.2 μm. Samples are made of Co–Pt multilayers with different Co thicknesses so as to vary the perpendicular magnetic anisotropy. We determined the first- and second-order anisotropies of the films, as well as the first-order anisotropy distribution, and show that from these quantities the switching field distribution of dots can be predicted. We also explain through a simple criterion—the relation between the anisotropy distribution and the minimum nucleation field—why in some cases the hysteresis loops recorded along the easy axis on the films undergo a dramatic change after patterning.

Magnetic properties of the self-doped lanthanum manganitesLa1−xMnO3

The magnetic properties of different compositions in the self-doped lanthanum manganites, ${\mathrm{La}}_{1\ensuremath{-}x}\mathrm{Mn}{\mathrm{O}}_{3}$, have been studied by ac susceptibility and dc magnetization measurements in the temperature range $10--300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. All compositions with $xl0.125$ show an anomalous decrease in the ac susceptibility and zero field cooled (ZFC) dc magnetization at low temperatures, below the ferromagnetic ordering temperature. The temperature below which this anomalous behavior is observed, ${T}_{a}$, varies with the degree of La vacancy in the series where the ${\mathrm{Mn}}^{4+}$ concentration decreases with increasing $x$. Moreover, ${T}_{a}$ varies with the ${\mathrm{Mn}}^{4+}$ content for a given composition. However, in both cases, this temperature levels off when the concentration of ${\mathrm{Mn}}^{4+}$ is above 23%. The magnetic-transition-like feature broadens and shifts to further lower temperatures with increasing magnetic fields and vanishes when measured above a certain field. A small but drastic increase in the coercivity is observed below ${T}_{a}$. There is a direct correlation between the shapes of the curves of the inverse of the coercivity as a function of temperature and ac susceptibility, indicating the influence of magnetic anisotropy on the characteristics of the ac susceptibility and zero field cooled magnetization curves of the self-doped compounds. The direct correlation between the changes in the coercivity and ac susceptibility as well as ZFC magnetization when measured at low magnetic fields give evidence to the role of domain wall pinning effects, which varies with the degree of self-doping or ${\mathrm{Mn}}^{4+}$ concentration.

Interplay between magnetic anisotropy and interlayer coupling in nanosecond magnetization reversal of spin-valve trilayers

The influence of magnetic anisotropy on nanosecond magnetization reversal in coupled $\mathrm{FeNi}∕\mathrm{Cu}∕\mathrm{Co}$ trilayers was studied using a photoelectron emission microscope combined with x-ray magnetic circular dicroism. In quasi-isotropic samples the reversal of the soft FeNi layer is determined by domain-wall pinning that leads to the formation of small and irregular domains. In samples with uniaxial magnetic anisotropy, the domains are larger and the influence of local interlayer coupling dominates the domain structure and the reversal of the FeNi layer.

High-field investigation of the intersublattice interaction in GdCo5

An upturn of a magnetization curve of a GdCo5 single crystal was observed in a magnetic field of about 46T. The upturn is associated with a transition from collinear to canted magnetic structure. The sample was free to rotate, thus influence of magnetic anisotropy on the spin-reorientation process was eliminated. A threshold field of the transition yields the value of 233T for Co–Gd exchange field.