Enhanced magnetic anisotropy and high hole mobility in magnetic semiconductor Ga_(1-x-y)Fe_(x)Ni_(y)Sb

(Ga,Fe)Sb is a promising magnetic semiconductor(MS)for spintronic applications because its Curie temperature(T_(C))is above 300 K when the Fe concentration is higher than 20%.However,the anisotropy constant Ku of(Ga,Fe)Sb is below 7.6×10^(3)erg/cm^(3)when Fe concentration is lower than 30%,which is one order of magnitude lower than that of(Ga,Mn)As.To address this issue,we grew Ga_(1-x-y)Fe_(x)Ni_(y)Sb films with almost the same x(≈24%)and different y to characterize their magnetic and electrical transport properties.We found that the magnetic anisotropy of Ga_(0.76-y)Fe_(0.24)Ni_(y)Sb can be enhanced by increasing y,in which Ku is negligible at y=1.7%but increases to 3.8×10^(5)erg/cm^(3)at y=6.1%(T_(C)=354 K).In addition,the hole mobility(μ)of Ga_(1-x-y)Fe_(x)Ni_(y)Sb reaches 31.3 cm^(2)/(V∙s)at x=23.7%,y=1.7%(T_(C)=319 K),which is much higher than the mobility of Ga_(1-x)Fe_(x)Sb at x=25.2%(μ=6.2 cm^(2)/(V∙s)).Our results provide useful information for enhancing the magnetic anisotropy and hole mobility of(Ga,Fe)Sb by using Ni co-doping.

First-principles study of electronic and magnetic properties of Fe atoms on Cu_(2)N/Cu(100)

First-principles calculations were conducted to investigate the structural,electronic,and magnetic properties of single Fe atoms and Fe dimers on Cu_(2)N/Cu(100).Upon adsorption of an Fe atom onto Cu_(2)N/Cu(100),robust Fe-N bonds form,resulting in the incorporation of both single Fe atoms and Fe dimers within the surface Cu_(2)N layer.The partial occupancy of Fe-3d orbitals lead to large spin moments on the Fe atoms.Interestingly,both single Fe atoms and Fe dimers exhibit in-plane magnetic anisotropy,with the magnetic anisotropy energy(MAE)of an Fe dimer exceeding twice that of a single Fe atom.This magnetic anisotropy can be attributed to the predominant contribution of the component along the x direction of the spin-orbital coupling Hamiltonian.Additionally,the formation of Fe-Cu dimers may further boost the magnetic anisotropy,as the energy levels of the Fe-3d orbitals are remarkably influenced by the presence of Cu atoms.Our study manifests the significance of uncovering the origin of magnetic anisotropy in engineering the magnetic properties of magnetic nanostructures.

Creation and annihilation of artificial magnetic skyrmions with the electric field

Recent theory and experiments show that artificial magnetic skyrmions can be stabilized at room temperature without the need for the external magnetic field,casting strong potentials for the device applications.In this work,we study the electric field manipulation of artificial magnetic skyrmions imprinted by Co disks on CoPt multilayers utilizing the micromagnetic simulations.We find that the reversible annihilation and creation of skyrmions can be realized with the electric field via the strain mediated magnetoelastic coupling.In addition,we also demonstrate controllable manipulation of individual skyrmion,which opens a new platform for constructing magnetic field-free and low-energy dissipation skyrmion based media.

Features of Recombination Radiation of GaAs Type Semiconductors with the Participation of Fine Acceptor Levels in a Magnetic Field

Using the method of Picus and Beer invariants, general expressions are obtained for the total intensity I and the degree of circular polarization Рcirc.of the luminescence of GaAs-type semiconductors with the participation of shallow acceptor levels in a longitudinal magnetic field H. Special cases are analyzed depending on the value and direction of the magnetic field strength, as well as on the constants of the g-factor of the acceptor g1,g2and the conduction band electron ge. In the case of a strong magnetic field H// [100], [111], [110], a numerical calculation of the angular dependence of the quantities I and Рcirc.was performed for some critical values of g2/g1, at which Рcirc.exhibits a sharp anisotropy in the range from −100% to +100%, and the intensity of the crystal radiation along the magnetic field tends to a minimum value.

Superexchange Interactions and Magnetic Anisotropy in MnPSe_(3)Monolayer

Two-dimensional van der Waals magnetic materials are of great current interest for their promising applications in spintronics.Using density functional theory calculations in combination with the maximally localized Wannier functions method and the magnetic anisotropy analyses,we study the electronic and magnetic properties of MnPSe_(3)monolayer.Our results show that it is a charge transfer antiferromagnetic(AF)insulator.For this Mn^(2)+3d^(5)system,although it seems straightforward to explain the AF ground state using the direct exchange,we find that the nearly 90oMn-Se-Mn charge transfer type superexchange plays a dominant role in stabilizing the AF ground state.Moreover,our results indicate that,although the shape anisotropy favors an out-of-plane spin orientation,the spin-orbit coupling(SOC)leads to the experimentally observed in-plane spin orientation.We prove that the actual dominant contribution to the magnetic anisotropy comes from the second-order perturbation of the SOC,by analyzing its distribution over the reciprocal space.Using the AF exchange and anisotropy parameters obtained from our calculations,our Monte Carlo simulations give the Néel temperature T_(N)=47 K for MnPSe_(3)monolayer,which agrees with the experimental 40 K.Furthermore,our calculations show that under a uniaxial tensile(compressive)strain,Néel vector would be parallel(perpendicular)to the strain direction,which well reproduces the recent experiments.We also predict that T_(N)would be increased by a compressive strain.

Thickness-dependent magnetic properties in Pt/[Co/Ni]_(n) multilayers with perpendicular magnetic anisotropy

We systematically investigated the Ni and Co thickness-dependent perpendicular magnetic anisotropy(PMA)coefficient,magnetic domain structures,and magnetization dynamics of Pt(5 nm)/[Co(t_(Co))/Ni(t_(Ni))]_(5)/Pt(1 nm)multilayers by combining the four standard magnetic characterization techniques.The magnetic-related hysteresis loops obtained from the field-dependent magnetization M and anomalous Hall resistivity(AHR)ρxy showed that the two serial multilayers with t_(Co)=0.2 nm and 0.3 nm have the optimum PMA coefficient K_(U) as well as the highest coercivity H_(C) at the Ni thickness t_(Ni)=0.6 nm.Additionally,the magnetic domain structures obtained by magneto-optic Kerr effect(MOKE)microscopy also significantly depend on the thickness and K_(U) of the films.Furthermore,the thickness-dependent linewidth of ferromagnetic resonance is inversely proportional to K_(U) and H_(C),indicating that inhomogeneous magnetic properties dominate the linewidth.However,the intrinsic Gilbert damping constant determined by a linear fitting of the frequency-dependent linewidth does not depend on the Ni thickness and K_(U).Our results could help promote the PMA[Co/Ni]multilayer applications in various spintronic and spin-orbitronic devices.

Effect of seed layers on the static and dynamic magnetic properties of CoIr films with negative effective magnetocrystalline anisotropy

The c-axis oriented hcp-Co_(81)Ir_(19)magnetic films were prepared on different seed layers(Ni,Cu,Ir,Pt,Au,and No seed).We systematically investigated the impact that surface-free energy and strain energy have on the orientation and defects and/or internal stress of the grains by increasing the lattice mismatch ratio.Moreover,the initial permeability and the natural resonance frequency were discussed in great detail using a comparison between calculated values and experimental values.We found that the almost unchanged 4πM_(s) andμ_(i) are not affected,while the changed H_(c),intrinsic K_(grain),and f_(r) are strongly dependent on the seed layer and seed layer material.Moreover,the extracted damping constant is sensitive to the defects and/or internal stress and orientation of the grains.Therefore,the soft magnetic properties and microwave properties are adjusted and optimized by seed layers with different materials.

Hole density dependent magnetic structure and anisotropy in Fe-pnictide superconductor

The competition between different magnetic structures in hole-doped Fe-pnicitides is explored based on an extended five-orbital Hubbard model including long-range Coulomb interactions.Our results show that the stabilized magnetic structure evolves with increasing hole doping level.Namely,the stripe antiferromagnetic phase dominates at zero doping,while magnetic structures with more antiferromagnetic linking numbers such as the staggered tetramer,staggered trimer,and staggered dimer phases become energetically favorable as the hole density increases.At a certain doping level,energy degeneracy of different magnetic structures appears,indicating strong magnetic frustration and magnetic fluctuations in the system.We suggest that the magnetic competition induced by the hole doping may explain the fast decrease of the Neel temperature TNand the moderately suppressed magnetic moment in the hole doped Fe-pnicitides.Moreover,our results show a sign reversal of the kinetic energy anisotropy as the magnetic ground state evolves,which may be the mechanism behind the puzzling sign reversal of the in-plane resistivity anisotropy in hole-doped Fe-pnicitides.

Bismuth doping enhanced tunability of strain-controlled magnetic anisotropy in epitaxial Y_(3)Fe_(5)O_(12)(111) films

Y_(3)Fe_(5)O_(12)(YIG) and Bi Y_(3)Fe_(5)O_(12)(Bi:YIG) films were epitaxially grown on a series of(111)-oriented garnet substrates using pulsed laser deposition. Structural and ferromagnetic resonance characterizations demonstrated the high epitaxial quality, extremely low magnetic loss and coherent strain state in these films. Using these epitaxial films as model systems, we systematically investigated the evolution of magnetic anisotropy(MA) with epitaxial strain and chemical doping. For both the YIG and Bi:YIG films, the compressive strain tends to align the magnetic moment in the film plane while the tensile strain can compete with the demagnetization effect and stabilize perpendicular MA. We found that the strain-induced lattice elongation/compression along the out-of-plane [111] axis is the key parameter that determines the MA. More importantly, the strain-induced tunability of MA can be enhanced significantly by Bi doping;meanwhile, the ultralow damping feature persists. We clarified that the cooperation between strain and chemical doping could realize an effective control of MA in garnet-type ferrites, which is essential for spintronic applications.

Electric-field control of perpendicular magnetic anisotropy by resistive switching via electrochemical metallization

Electric-field control of perpendicular magnetic anisotropy(PMA) is a feasible way to manipulate perpendicular magnetization,which is of great importance for realizing energy-efficient spintronics.Here,we propose a novel approach to accomplish this task at room temperature by resistive switching(RS) via electrochemical metallization(ECM) in a device with the stack of Si/SiO_(2)/Ta/Pt/Ag/Mn-doped ZnO(MZO)/Pt/Co/Pt/ITO.By applying certain voltages,the device could be set at high-resistance-state(HRS) and low-resistance-state(LRS),accompanied with a larger and a smaller coercivity(H_(C)),respectively,which demonstrates a nonvolatile E-field control of PMA.Based on our previous studies and the present control experiments,the electric modulation of PMA can be briefly explained as follows.At LRS,the Ag conductive filaments form and pass through the entire MZO layer and finally reach the Pt/Co/Pt sandwich,leading to weakening of PMA and reduction of H_(C).In contrast,at HRS,most of the Ag filaments dissolve and leave away from the Pt/Co/Pt sandwich,causing partial recovery of PMA and an increase of H_(C).This work provides a new clue to designing low-power spintronic devices based on PMA films.

Fabric characteristics of in situ sand with/without liquefaction verified by anisotropy of magnetic susceptibility

It is well known that fabric of sand may significantly affect mechanical behaviors and liquefaction resistance of sand.Various optical techniques are currently utilized to visualize the fabric,especially the distribution of the long axis of soil particles.However,none of these methods provides an ideal solution in laboratory tests and in situ observation.In this study,anisotropy of magnetic susceptibility(AMS)was first proposed as a convenient and efficient way to evaluate the liquefaction of clean sand.At first,investigations with scanning electron microscopy(SEM)and AMS were simultaneously conducted on two groups of soil specimens with different initial fabrics to verify the feasibility of the AMS technique.Then,80 in situ samples were collected to analyze the feature of liquefied and non-liquefied sand layers through AMS tests.It is clearly known from the test results that the natural sedimentary fabric was destroyed during liquefaction and the fabric anisotropy was greatly changed after liquefaction.The feasibility of evaluating soil fabric using the AMS survey was verified by the laboratory tests.Furthermore,the applicability of AMS in detecting liquefied layer in situ was confirmed for the first time.

Room temperature quantum anomalous Hall insulator in honeycomb lattice, RuCS_(3), with large magnetic anisotropy energy

The quantum anomalous Hall(QAH) effect has attracted enormous attention since it can induce topologically protected conducting edge states in an intrinsic insulating material. For practical quantum applications, the main obstacle is the non-existent room temperature QAH systems, especially with both large topological band gap and robust ferromagnetic order. Here, according to first-principles calculations, we predict the realization of the room temperature QAH effect in a two-dimensional(2D) honeycomb lattice, RuCS_(3) with a non-zero Chern number of C = 1. Especially, the nontrivial topology band gap reaches up to 336 me V for RuCS_(3). Moreover, we find that RuCS_(3) has a large magnetic anisotropy energy(2.065 me V) and high Curie temperature(696 K). We further find that the non-trivial topological properties are robust against the biaxial strain. The robust topological and magnetic properties make RuCS_(3) have great applications in room temperature spintronics and nanoelectronics.

Magnetostratigraphy and Anisotropy of Magnetic Susceptibility of the Lulehe Formation in the Northeastern Qaidam Basin

The timing of onset of deposition of the Lulehe Formation is a significant factor in understanding the genesis of the Qaidam basin and the evolution of the Tibetan Plateau. Here, we describe a detailed magnetostratigraphic and magnetic fabric study of the middle and lower parts of the Lulehe Formation. A total of 234 samples were collected from 117 sites throughout a thickness of almost 460 m of fluvial and lacustrine deposits at the Xitieshan section in the northeastern Qaidam basin. Out of these sites, 94 sites yielded well-defined characteristic remanent magnetization components by stepwise thermal demagnetization and were used to establish the magnetostratigraphy of the studied section. Based on correlation with the geomagnetic polarity timescale, the studied section spans the period from 53.8 Ma to 50.7 Ma. Our results show a three-fold decrease in sedimentation rates as well as marked change in facies from braided river to delta and shore-shallow lake around 52.6 Ma, which suggests tectonic uplift of the northeastern Qaidam basin margin ridge was rapid at the onset of formation of the Qaidam basin and subsequently weakened after 52.6 Ma. The anisotropy of magnetic susceptibility results indicate that tectonic compression stress had reached the northeastern Tibetan Plateau by the early stages of Indo-Eurasian plate collision and that the direction of stress in the study area was NE-SW. Furthermore, a weakening of tectonic compression stress around 52.6 Ma is consistent with sedimentary records. The age of initial deposition of the Qaidam basin （around 53.8 Ma） was almost synchronous with that of the Qiangtang, Hoh Xil, Xining, and Lanzhou basins, which implies that stress was transferred rapidly through the Tibetan Plateau during or immediately after the onset of Indo-Eurasian collision.

Critical behaviours and magnetic properties of three-dimensional bond and anisotropy dilution Blume-Capel model in the presence of an applied field

This paper studies the critical behaviours and magnetic properties of three-dimensional bond and anisotropy dilution Blume-Capel model （BCM） in the presence of an applied field within the effective field theory. The trajectory of tricritical point, reentrant transitions and degenerate patterns of anisotropy are obtained both for the bond and the anisotropy dilutions. The global phase diagrams demonstrate unusually reentrant phenomena. The temperature dependences of magnetization curves undergo remarkable spin glass behaviour at low temperatures, and transform from ferromagnetism to paramagnetism at high temperature in applied fields. Temperature dependence of magnetic susceptibility curve is in qualitative agreement with experimental result.

Modeling Density and Anisotropy of Energetic Electrons Along Magnetic Field Lines

The electromagnetic wave growth or damping depends basically on the number density and anisotropy of energetic particles as the resonant interaction takes place between the particles and waves in the magnetosphere. The variance of both the number density and anisotropy along the magnetic field line is evaluated systematically by modeling four typically prescribed distribution functions. It is shown that in the case of ＂the positive anisotropy＂ （namely, the perpendicular temperature T⊥ exceeds the parallel temperature T｜｜）, the number density of energetic electrons always decreases with the magnetic latitude for a regular increasing magnetic field and the maximum wave growth is therefore generally confined to the equator where the resonant energy is minimum, and the number density is the largest. However, the ＂loss-cone＂ anisotropy of the electrons with a ＂pancake＂ distribution or kappa distribution keeps invariant or nearly invariant, whereas the ＂temperature＂ anisotropy with a pure bi-Maxwellian distribution or Ashour-Abdalla and Kennel＇s distributions decreases with the magnetic latitude. The results may provide a useful approach to evaluating the number density and anisotropy of the energetic electrons at latitudes where the observation information is not available.

THE ANISOTROPY OF LOESS MAGNETIC SUSCEPTIBILITY IN THE NORTHEASTERN FRINGE OF QINGHAI-XIZANG PLATEAU AS AN INDICATOR OF PALAEOWIND DIRECTION

Estimates of the palaeo subaerial wind direction were studied systematically for the first time by using the anisotropy of loess magnetic susceptibility (AMS) measurements in the northwestern China. One hundred and forty undisturbed oriented aeolian loess samples were collected from Lanzhou, Linxia and Wudu areas for AMS measurements, which indicated the subaerial wind directions were not the same while the loess deposited. From the Early Pleistocene to Middle Pleistocene till Late Pleistocene, the wind direction experienced an anticlockwise rotation in the studied area. We suggested this change was related to the uplift of the Qinghai Xizang Plateau and the adjustment of current and landform effects.

Gate-voltage control of alternating-current-driven skyrmion propagation in ferromagnetic nanotrack devices

Magnetic skyrmions, with topologically protected particle-like magnetization configurations, are promising information carriers for future spintronics devices with ultralow energy consumption. Generally, during motion, skyrmions suffer from the skyrmion Hall effect(Sk HE) wherein the skyrmions deflect away from the intended path of the driving force.Numerous methods have been proposed to avoid this detrimental effect. In this study, we propose controllable alternating current(AC)-driven skyrmion propagation in a ferromagnetic nanowire based on combination of gate-voltage-controlled magnetic anisotropy(VCMA) and Sk HE. Micromagnetic simulations show that a skyrmion oscillatory closed-loop-like in situ motion driven by AC can be transformed into directional ratchet-like propagation along the nanotrack by creating a VCMA-gate barrier. Additionally, we show that the skyrmion propagation conditions depend on the gate barrier potential and driving AC parameters, and they can be used for the optimal design of nanotrack devices. Moreover, this mechanism could be used to control skyrmion macroscopic propagation directions by dynamically alternating the voltage of another series of gates. We further show the dynamic control of the long-distance propagation of skyrmions along with the pinning state. The study results provide a promising route for designing future skyrmion-based spintronics logical and memory devices.

High repetition granular Co/Pt multilayers with improved perpendicular remanent magnetization for high-density magnetic recording

Thanks to the strong perpendicular magnetic anisotropy(PMA), excellent processing compatibility as well as novel spintronic phenomenon, Co/Pt multilayers have been attracting massive attention and widely used in magnetic storage.However, reversed magnetic domains come into being with the increasing layer repetition ‘N’ to reduce magneto-static energy, resulting in the remarkable diminishment of the remanent magnetization(Mr). As a result, the product of Mrand thickness(i.e., the remanent moment-thickness product, Mrt), a key parameter in magnetic recording for reliable data storing and reading, also decreases dramatically. To overcome this issue, we deposit an ultra-thick granular [Co/Pt]80multilayer with a total thickness of 68 nm on granular SiNxbuffer layer. The Mrt value, Mrto saturation magnetization(Ms) ratio as well as out of plane(OOP) coercivity(Hcoop) are high up to 2.97 memu/cm^(2), 67%, and 1940 Oe(1 Oe = 79.5775 A·m^(-1)),respectively, which is remarkably improved compared with that of continuous [Co/Pt]80multilayers. That is because large amounts of grain boundaries in the granular multilayers can efficiently impede the propagation and expansion of reversed magnetic domains, which is verified by experimental investigations and micromagnetic simulation results. The simulation results also indicate that the value of Mrt, Mr/Msratio, and Hcoopcan be further improved through optimizing the granule size, which can be experimentally realized by manipulating the process parameter of SiNxbuffer layer. This work provides an alternative solution for achieving high Mrt value in ultra-thick Co/Pt multilayers, which is of unneglectable potential in applications of high-density magnetic recording.

Enhancing magnetic properties of anisotropic NdDyFeCoNbCuB powder by applying magnetic field at high temperature during hydrogen desorption

Anisotropic powder was prepared with precursor （NdDy）-（FeCoNbCu）-B sintered magnets by hydrogen decrepitation, desorption, and subsequent annealing treatment. The hydrogen desorption was performed in magnetic fields of 0, 1, 3, and 5 T. The orientation of tetragonal phase grains of the powder was evaluated from the hysteresis loops measured by extraction magnetometer. Residual hydrogen content of the powder was evaluated by thermal-magnetic analysis. The powder with Hcj, Br, and （BH）max of 1138 kA.m^-1, 1.029 T, and 172.5 kJ.m^-3, respectively, was achieved under the condition of the magnetic field of 3 T. Magnetic properties of the powder, especially, the remanence of the powder, are enhanced upon magnetic fields, which is due to better orientation of powder particles and less residual hydrogen in the powder resulted from the magnetic field during the hydrogen desorption process.

Research Progress of Stress-Induced Magnetic Anisotropy in Fe-Based Amorphous and Nanocrystalline Alloys

Since it was discovered that stress annealing induced larger anisotropies compared to other annealing methods in amorphous and nanocrystalline alloys, there has been a lot of research done to explain this phenomenon. This has led to many suggestions about the origin of this stress-induced magnetic anisotropy, but till now the origin is explained with two competing models: the magnetoelastic effect model and the diatomic pair ordering model. In spite of these theories, the origin of the stress-induced anisotropy is still under discussion because direct observation of structural anisotropy is still lacking. In this paper, we have reviewed some of the characterization techniques which have been used to discuss the origin of stress-induced magnetic anisotropy and the progress which has been made thus far in unifying all the contrasting views which has been suggested to be the origin of the stress-induced anisotropy in FINEMET alloys.