Magnetization Direction Changes Research Articles

Nonvolatile ferroelectric control of both magnetic anisotropy and half-metallicity in multiferroic heterostructures GdI2/Al2Te3

Nonvolatile all-electric spin manipulation is optimal for low-power and compact spintronic devices. Herein, using first-principles density functional theory, we propose a bilayer van der Waals (vdW) multiferroic heterostructure (HS) GdI2/Al2Te3 constructed of ferromagnetic electride GdI2 and ferroelectric (FE) semiconductor Al2Te3 to possess robust magnetoelectric coupling near room temperature. By reversing the electrical polarization states in Al2Te3, the magnetoelectric coupling not only allows the reversible switch of GdI2 from semiconductor to half-metal but also promotes the reversible transition of magnetocrystalline anisotropy from in-plane to out-of-plane. More importantly, the high Curie temperature (TC) of GdI2 and the unspoiled semiconducting nature of Al2Te3 in the HS predict the practical feasibility of this spin manipulation. Additionally, GdI2 exhibits substantial valley polarization when its magnetization direction changes to out-of-plane. These findings pave the way for achieving robust and efficient spin manipulation through all-electric control and also provide implications for multiferroic memory devices with highly efficient data reading and writing based on the HS.

Determination of the magnetization direction via correlation between reduced‐to‐the‐pole magnetic anomalies and total gradient of the magnetic potential with vertical magnetization

AbstractThe total magnetization of an underground magnetic source is the vector sum of the induced magnetization and the natural remanent magnetization. The direction of the total magnetization serves as important a priori information in the inversion and processing of magnetic data. We demonstrated that the total gradient of the magnetic potential with vertical magnetization constitutes the envelope of the vertical component of the magnetic field for all directions of the Earth's field and source magnetization. The total gradient of the magnetic potential with vertical magnetization and the reduction‐to‐the‐pole field simultaneously tend to achieve maximum symmetry near the correct total magnetization direction. As a result, the total magnetization direction can be estimated by computing the correlations between the reduction‐to‐the‐pole and the total gradient of the magnetic potential with vertical magnetization. The proposed method yields accurate magnetization directions in synthetic model examples. The total gradient of the magnetic potential with vertical magnetization is less susceptible to data noise than transforms which are derived from the high‐order magnetic field derivatives or tensors. The estimation results are slightly affected by changes in the source magnetization direction. In a field example in the Weilasito region (North China), the reduction‐to‐the‐pole fields calculated using the estimated magnetization directions are well centred over the source. The proposed method obtained a more focused magnetization direction than that of a three‐dimensional magnetization vector inversion. The total gradient of the magnetic potential with vertical magnetization therefore provides a novel and accurate approach to determine the total magnetization direction from the total field anomaly in a variety of situations.

NUMERICAL study of MAGNETO convective Buongiorno nanofluid flow in a rectangular enclosure under oblique magnetic field with heat generation/absorption and complex wall conditions

A mathematical model is presented to analyze the magnetohydrodynamic (MHD) convective flow in a rectangular enclosure. Earlier studies on the Tiwai-Das volume fraction nanofluid model did not consider the Buongiorno nanofluid model. This is the focus of the present analysis which examines the laminar mixed convection magnetohydrodynamic flow of a nanofluid in a differentially heated rectangular enclosure with complex boundary conditions under an inclined magnetic field. Buongiorno's two-component nanofluid model is employed, which incorporates the effects of Brownian motion and thermophoretic diffusion of nanoparticles. Magnetic nanofluids have considerable potential for enhancing transport processes in energy systems such as hybrid fuel cells. The study is essential with heat generation/absorption effects. Additionally, the work is highlighted by the general case of an oblique (inclined) magnetic field. The conservation equations for mass, primary and secondary momentum, energy, and nanoparticle concentration with wall boundary conditions are dimensionless using appropriate scaling transformations. A finite-difference computational scheme known as the Harlow-Welch Marker and Cell (MAC) method is employed to solve the dimensionless nonlinear coupled boundary value problem. A mesh independence study is included. Graphical plots are presented for the impact of key control parameters on streamline contours, isotherm contours, iso-concentration (nanoparticle mass) contours, and local Nusselt number. With heat sink (absorption), the Nusselt number is enhanced in magnitude whereas it is suppressed with heat generation since there is a heat reduction transmitted to the boundary. The configurations of streamlines, isotherms, and iso-concentrations are mostly invariant to magnetic field direction changes. The obtained results show interesting behaviors of the flow and thermal fields, which mainly involve the effect of Brownian motion and thermophoresis parameters, as well as unsteady regimes, depending on specific values of the Schmidt number, Richardson number, and Prandtl numbers. Increasing the Schmidt number induces a contraction in the central cooler zone in the enclosure and also reduces the iso-concentration magnitudes in the central region across the enclosure. The core region of the enclosure heats up as the thermophoresis and Brownian motion parameters rise, pushing the previously cooler top and bottom wall zones further away from the center. There is also a decrease in iso-concentration magnitudes in particular at the upper and lower boundaries at higher values of Brownian motion and thermophoresis parameters. At decreasing buoyancy ratios, the left vortex cell first decelerates while the right vortex cell accelerates. However, when the buoyancy ratio increases, the left vortex cell streamlines magnitudes increase with a contraction in vortex size, while the right cell develops. A Very minor alteration is observed in the isotherm and iso-concentration contours with an increasing buoyancy ratio. When the Richardson number increases, the vortex cell structures shift from a strong circulation cell on the left to a weaker cell on the right, resulting in reverse distribution. With the rising Richardson number, significant cooling is also caused in the core zone, as well as a drop in iso-concentrations, with the original dual low-concentration upper and lower zones merging into a single center zone. The original symmetric left and right vortex cells are gradually twisted diagonally towards the right wall as the magnetic field increases, yet the stronger right cell and the weaker left cell are maintained.

Controlling the Magnetoimpedance Property of Thin-Film Elements Using Joule Heating

Optimizing the performance of magnetoimpedance (MI) requires controlling the anisotropy of material which is often done with field annealing. However, field annealing needs large-scale equipment with a vacuum environment and consumes a large amount of electricity for heating and generating a large magnetic field. Conversely, Joule heating has advantages of simple, compact, and possible-to-use small current. Thus, we attempted controlling the magnetic anisotropy on thin-film MI elements using Joule heating and the applied field by magnets. Before annealing, the element has an easy axis with a direction parallel to the longitudinal direction of the element owing to shape anisotropy. After Joule heating, the MI behavior showed a double peak profile, which is a typical impedance profile when large impedance changes are obtained. The peak height in the impedance and inductance increases with the heating current up to 100 mA and then becomes constant or slightly increases. The field at which the impedance and inductance have a peak increases monotonically with increasing heat current. We confirm that the magnetic anisotropy direction changes with Joule heating and with a field applied by magnets based on observing the magnetic domain structure using a Kerr effect microscope.

Enhancement of the magnetic anisotropy in single semiconductor nanowires via surface doping and adatom deposition

The magnetic anisotropy of single semiconductor (ZnO and GaN) nanowires incorporating both a transition metal (Co and Mn, respectively) as a substitutional surface dopant and a heavy metal (Au, Bi, or Pt) adatom is studied by performing density-functional supercell calculations with the Hubbard U correction. It is found that a substantial enhancement in the magnetic anisotropy energy is obtained through the deposition of Bi; the deposition of Au and Pt leads to significant variation in other magnetic properties, but not in the magnetic anisotropy energy. An analysis within a band description shows that the coexistence of Bi adatom and a surface dopant with large spin moment activates a mechanism involving reorientation and readjustment of the spin moments of electrons in occupied bands in response to the change of magnetization direction, which promotes giant magnetic anisotropy. Our results for adsorption energetics indicate that the accommodation of Bi in the neighborhood of the surface dopant is more likely in GaN nanowires, because the Bi adatom does (not) tend to be closer to the Mn (Co) dopant on the surface of GaN (ZnO) nanowire. The stability of GaN nanowire with giant magnetic anisotropy owing to the incorporation of both Mn and Bi is demonstrated by performing ab initio molecular dynamics simulations at temperatures considerably higher than room temperature. These results suggest that adatom deposition and surface doping can be used complementarily to develop single nanowire-based spintronic devices.

Study of the possibility of suppressing the influence of changes in an external magnetic field direction on the relative frequency fluctuations of two rubidium atomic clocks

Study of the possibility of suppressing the influence of changes in an external magnetic field direction on the relative frequency fluctuations of two rubidium atomic clocks

Investigation of the itinerant metamagnetic system Hf0.75Ta0.25Fe2 under extreme conditions of pressure or magnetic field

The magnetic and structural properties of Hf0.75Ta0.25Fe2 have been investigated under the duplicate conditions, i.e., high magnetic fields and high pressures, by combining magnetization measurements up to 26 T, neutron powder diffraction experiments up to 14.5 T, and angle dispersive synchrotron x-ray diffraction up to 10 GPa. The intermetallic compound Hf0.75Ta0.25Fe2 exhibits an antiferromagnetic (AFM) ground state below the Néel temperature TN = 342 K. In the AFM structure, the Fe-6h magnetic moments (1.02 μΒ at 2 K) align along the c axis while Fe atoms at 2a sites are not magnetically ordered. We further show that the AFM ground state gets transformed into a ferromagnetic (FM) state via a field-induced metamagnetic phase transition. Magnetic-field dependent neutron diffractograms demonstrate that FM phase sets in with a change of the easy magnetization direction from axial to basal-plane and an extremely anisotropic lattice expansion. The unit cell expands drastically in the basal plane upon increasing the applied magnetic field, while its dimension along c-axis shrinks slightly; resulting in a huge positive volume magnetostriction ΔV/V = 0.78%. The application of hydrostatic pressure leads to the continuous decrease of the cell parameters. The shrinkage of the hexagonal cell is anisotropic with a larger compression along the six-fold symmetry axis c. A bulk modulus of K0 = 247 GPa has been deduced from the pressure-volume relationship.

Effect of Gd3+ substitution on proton relaxation and magnetic hyperthermia efficiency of cobalt ferrite nanoparticles

In this study, Gadolinium substituted Cobalt Ferrite nanoparticles (CoFe2-xGdxO4, 0 ≤ x ≤ 0.4) were prepared via hydrothermal route using triethylamine as reducing agent at 180°C for 12 h. X-ray diffraction studies revealed the single phase cubic spinel structure for both Cobalt ferrite (CF) and Gadolinium substituted Cobalt Ferrite (CFG) nanoparticles (x ≤ 0.24). An increase in the Specific absorption rate (SAR) was observed with increase in Gd concentration. Further with increase in the molar concentration (x > 0.24), gadolinium hydroxide was observed as the secondary phase, which was also confirmed by the Gd–O stretching vibrations observed in Fourier transform Infrared spectroscopy. The evolution of Gadolinium hydroxide showed a strong influence in the relaxivity (r1) and hyperthermia potential. Field emission scanning electron microscopy revealed that CF and CFG (x ≤ 0.24) nanoparticles were spherical in nature with particle size ranging from 10 to 25 nm, whereas the particle size increases above 30 nm for CFG (0.3 ≤ x ≤ 0.4) nanoparticles along with the presence of columnar shaped particles. Magnetic measurements confirmed the pseudo single domain, ferri-magnetic nature of CF and CFG nanoparticles. The magnetization data revealed a change in direction of magnetization towards easy axis with increasing Gd concentration. The orientation of magnetization direction towards easy axis had induced change in the hyperthermia potential. Proton relaxation studies of CF and CFG nanoparticles revealed that there is a strong interaction between the relaxivities r1 and r2. The specific absorption rate of CF and CFG nanoparticles were observed to be in the range from 91.49 W g−1 to 232.17 W g−1 at applied Hf of 4.19 × 109 Am−1 s−1.

Coronal-jet-producing Minifilament Eruptions as a Possible Source of Parker Solar Probe Switchbacks

Abstract The Parker Solar Probe (PSP) has observed copious rapid magnetic field direction changes in the near-Sun solar wind. These features have been called “switchbacks,” and their origin is a mystery. But their widespread nature suggests that they may be generated by a frequently occurring process in the Sun’s atmosphere. We examine the possibility that the switchbacks originate from coronal jets. Recent work suggests that many coronal jets result when photospheric magnetic flux cancels, and forms a small-scale “minifilament” flux rope that erupts and reconnects with coronal field. We argue that the reconnected erupting-minifilament flux rope can manifest as an outward propagating Alfvénic fluctuation that steepens into an increasingly compact disturbance as it moves through the solar wind. Using previous observed properties of coronal jets that connect to coronagraph-observed white-light jets (a.k.a. “narrow CMEs”), along with typical solar wind speed values, we expect the coronal-jet-produced disturbances to traverse near-perihelion PSP in ≲25 minutes, with a velocity of ∼400 km s−1. To consider further the plausibility of this idea, we show that a previously studied series of equatorial latitude coronal jets, originating from the periphery of an active region, generate white-light jets in the outer corona (seen in STEREO/COR2 coronagraph images; 2.5–15 R ⊙), and into the inner heliosphere (seen in Solar-Terrestrial Relations Observatory (STEREO)/Hi1 heliospheric imager images; 15–84 R ⊙). Thus it is tenable that disturbances put onto open coronal magnetic field lines by coronal-jet-producing erupting-minifilament flux ropes can propagate out to PSP space and appear as switchbacks.

Dynamic field line draping at comet 67P/Churyumov-Gerasimenko during the Rosetta dayside excursion

Context. The Rosetta dayside excursion took place in September–October 2015 when comet 67P/Churyumov-Gerasimenko (67P/CG) was located at ~1.36 AU from the Sun after it had passed perihelion on 13 August 2015 at ~1.25 AU. At this time, the comet was near its most active period, and its interaction with the solar wind was expected to be at its most intense, with ion pickup and magnetic field line draping. The dayside excursion was planned to move through different regions that were expected upstream of the cometary nucleus, and to possibly detect the location of the bow shock. Aims. The goal of this study is to describe the dynamic field line draping that takes place around the comet and the plasma processes that are connected to this. Methods. The data from the full Rosetta Plasma Consortium (RPC) were used to investigate the interaction of solar wind and comet, starting from boxcar-averaged magnetic field data in order to suppress high-frequency noise in the data. Through calculating the cone and clock angle of the magnetic field, we determined the draping pattern of the magnetic field around the nucleus of the comet. Then we studied the particle data in relation to the variations that are observed in the magnetic field. Results. During the dayside excursion, the magnetic field cone angle changed several times, which means that the magnetic field direction changes from pointing sunward to anti-sunward. This is caused by the changing directions of the interplanetary magnetic field that is transported toward the comet. The cone-angle direction shows that mass-loading of the interplanetary magnetic field of the solar wind leads to dynamic draping. The ion velocity and the magnetic field strength are correlated because the unmagnetized ions are accelerated more (less) strongly by the increasing (decreasing) magnetic field strength. There is an indication of an anticorrelation between the electron density and the magnetic field strength, which might be caused by the magnetized electrons being mirrored out of the strong field regions. The Rosetta RPC has shown that (dynamic) draping also occurs as mildly active comets, as was found at highly active comets such as 1P/Halley and 21P/Giacobini-Zinner, but also that determining both dynamic and nested draping will require a combination of fast flybys and slow excursions for future missions.

Magnetic domains characterization of clusters of magnetite nanoparticles

In this paper, magnetite (Fe3O4) powders which were obtained by the emulsion method are analyzed to ascertain the structure and mechanism formation of domains in clusters of Fe3O4 nanoparticles. Magnetic force microscopy (MFM) occupies a special niche in the array of techniques which are currently available for imaging magnetic structures of magnetic nanomaterials, yielding high resolution under ambient conditions. The use of MFM in dynamic lift-mode to detect probe–sample interactions from Fe3O4 nanoparticles is reported here to detect and identify the magnetic domains characterization of nanoparticles. The experimental results showed orientation of magnetic domains in the clustering nanoparticles. Finally, an analysis of repulsion and attraction in magnetic field and direction changes of domains formed by magnetite nanoparticles were done. This approach for probing magnetic responses on nanoscale magnetic domains can be further extended to the analysis of local physical features.

Magnetic Field Surveys of Thin Sections

Scanning magnetic microscopy (SMM) maps the magnetic field generated by petrologic thin sections or polished rock surfaces at the sub-mm scale, creating the possibility to resolve the contribution of individual grains and mineral phases to bulk magnetic signal. The instrument developed at NTNU has the capability to measure both remanence properties and, uniquely, the magnetic response in a field of known magnitude and direction. A series of case studies are presented to examine the capabilities of the microscope and to describe applications to the study of crustal magnetism. The use of well-characterized samples allows signals in magnetic scans to be attributed to grains of known composition, including the discrimination of signal associated with discrete oxides and assemblages of exsolved oxides in silicates, which can be observed to have differing directions of magnetisation. The ability of this instrument to image in fields mimicking those experienced in the crust allows the observation of the induced magnetic response, both qualitatively in the form of changes in magnetization direction, and quantitatively by varying experimental conditions. This capability gives SMM the ability to map both remanent response and generate a map of susceptibility, and provides a powerful new tool for the examination of bulk magnetic response in the Earth’s crust.

Anomalous specific heat and magnetic properties of TmxDy1-xAl2 (0 ≤ x ≤ 1)

We study crystal structure, phase transitions and magnetism of pseudo-binary TmxDy1-xAl2 (0 ≤ x ≤ 1) compounds using temperature dependent X-ray powder diffraction, specific heat and magnetization measurements, first principles, and model calculations. In low external magnetic fields, Dy-rich compounds undergo continuous, second-order phase transitions at the respective Curie temperatures, TC. In contrast, the Tm-rich compounds exhibit discontinuous, first-order anomalies in the magnetically ordered states. These sharp transitions correlate with a substantial energy difference between the room temperature cubic and ground state rhombohedral structures of TmAl2. A clear anomaly in the lattice parameter is observed at ∼30 K for x = 0.5, which nearly coincides with TC = 31.2 K. The effective quadrupolar moment of the lanthanides changes sign around x = 0.5, which leads to a nearly zero anisotropy constant and approximately spherical effective 4f charge densities, providing an explanation for the lack of structural distortions below TC for x = 0.5. The calculations confirm [001] as the easy magnetization axis in the ground state tetragonal structure of DyAl2, and reveal collapse of the orbital magnetic moment when the easy magnetization direction changes to [111]. Within the rhombohedral ground state of TmAl2 [111] is the easy magnetization direction.

Pseudomorphic spinel ferrite films with perpendicular anisotropy and low damping

We report on epitaxial thin films of spinel ferrite Ni0.65Zn0.35Fe1.2Al0.8O4 with strain-induced perpendicular magnetic anisotropy (PMA) and low magnetic damping. Static magnetometry and broadband ferromagnetic resonance experiments show a distinct change in the preferred direction of magnetization from in-plane to out-of-plane when the coherent strain in films changes from ∼2% compressive on (001) MgAl2O4 to ∼0.5% tensile on (001) MgGa2O4 substrates. Significant deviations from the spin-only value (2.0) of the g-factor suggest spin-orbit effects and further support our conclusion of strain-driven magnetic anisotropy in these films. The low Gilbert damping parameter of α = 5 × 10−3 in these ferrite films, combined with their PMA, makes them promising for spintronic and frequency-agile microwave device applications.

Magnetic energy flow imaging of magnetic recording head with enhanced resolution and sensitivity by A-MFM using high magnetic moment superparamagnetic tip

In this report, the magnetic energy flow of AC magnetic field is imaged from a perpendicular magnetic recording head by alternating magnetic force microscopy (A-MFM) with high magnetic moment Co0.43(GdOx)0.57 superparamagnetic (SP) tip. The present magnetic energy flow imaging phenomenon is able to detect the flow direction of AC magnetic field energy from the recording head. A simple model for the flow direction of the AC magnetic energy is given and revealed that when the AC magnetic field energy from the surface of main pole increases, the energy from the side cross section decreases due to the periodical change of magnetization direction at the main pole area. The A-MFM magnetic energy imaging performance by 100 nm Co0.43(GdOx)0.57 SP tip is compared with the magnetic field imaging with the 25 nm Co0.80Zr0.05Nb0.15 soft magnetic (SM) tip. The spatial resolution measured by Fourier analysis for Co0.43(GdOx)0.57 SP tip is enhanced dramatically to ∼10 nm with low thermal noise, as compared to ∼13 nm by Co0.80Zr0.05Nb0.15 SM tip as well as the previously reported MFM tip. Moreover, the sensitivity and resolution are investigated for a range of head current to confirm the suitability of the magnetic energy flow imaging by Co0.43(GdOx)0.57 SP tip to low as well as high magnetic field source. Further, the A-MFM measurements are performed with the 100 nm Au coated conducting tip to investigate the possibility of electrostatic contribution in magnetic energy imaging by Co0.43(GdOx)0.57 SP tip and revealed that the present A-MFM measurement is free from any electrostatic artifacts. The present magnetic energy flow imaging phenomena with the high magnetic moment Co0.43(GdOx)0.57 SP tip provides an avenue for the analysis of the magnetic field energy component from the head field profile.

Spin Direction-Controlled Electronic Band Structure in Two-Dimensional Ferromagnetic CrI3.

Manipulating physical properties using the spin degree of freedom constitutes a major part of modern condensed matter physics and is a key aspect for spintronics devices. Using the newly discovered two-dimensional van der Waals ferromagnetic CrI3 as a prototype material, we theoretically demonstrated a giant magneto band-structure (GMB) effect whereby a change of magnetization direction significantly modifies the electronic band structure. Our density functional theory calculations and model analysis reveal that rotating the magnetic moment of CrI3 from out-of-plane to in-plane causes a direct-to-indirect bandgap transition, inducing a magnetic field controlled photoluminescence. Moreover, our results show a significant change of Fermi surface with different magnetization directions, giving rise to giant anisotropic magnetoresistance. Additionally, the spin reorientation is found to modify the topological states. Given that a variety of properties are determined by band structures, our predicted GMB effect in CrI3 opens a new paradigm for spintronics applications.

Observational Aspects of Magnetic Reconnection at the Earth’s Magnetosphere

Magnetic field reconnection has shown to be the dominant process in the solar wind-Earth’s magnetosphere interaction. It enables mass, momentum, and energy exchange between different plasma regimes, and it is regarded as an efficient plasma acceleration and heating mechanism. Reconnection has been observed to occur in laboratory plasmas, at planetary magnetospheres in our Solar System, and the Sun. In this work, we focus on analyzing the characteristics of magnetic reconnection at the Earth’s magnetosphere according to spaceborne observations in the vicinity of our planet. Firstly, the locations where magnetic field reconnection are expected to occur within the vast magnetospheric region are addressed, and is shown how they are influenced by changes in the interplanetary magnetic field direction. The main magnetic field and plasma signatures of magnetic reconnection are discussed from both theoretical and observational points of view. Spacecraft observations of ion inertial length scale reconnection are also presented.

Uranium ferromagnet with negligible magnetocrystalline anisotropy:U4Ru7Ge6

Strong magnetocrystalline anisotropy is a well-known property of uranium compounds. The almost isotropic ferromagnetism in $\mathrm{U_{4}Ru_{7}Ge_{6}}$ reported in this paper represents a striking exception. We present results of magnetization, AC susceptibility, thermal expansion, specific heat and electrical resistivity measurements performed on a $\mathrm{U_{4}Ru_{7}Ge_{6}}$ single crystal at various temperatures and magnetic fields and discuss them in conjunction with results of first-principles electronic-structure calculations. $\mathrm{U_{4}Ru_{7}Ge_{6}}$ behaves as an itinerant 5$f$-electron ferromagnet ($T_{\mathrm{C}}= 10.7 K$, $\mu_{\mathrm{S}}= 0.85 \mu_{\mathrm{B}}/f.u.$ at 1.9 K. The ground-state easy-magnetization direction is along the [111] axis of the cubic lattice. The anisotropy field $\mu_{0}H_{\mathrm{a}}$ along the [001] direction is only of $\sim0.3 T$, which is at least 3 orders of magnitude smaller value than in other U ferromagnets. At $T_{r}=5.9 K$ the easy magnetization direction changes for [001] which holds at temperatures up to $T_{\mathrm{C}}$. The magnetoelastic interaction induces a rhombohedral (tetragonal) distortion of the paramagnetic cubic crystal lattice in case of the [111]([001]) easy-magnetization direction. The rhombohedral distortion is connected with two crystallographically inequivalent U sites. The ab initio calculated ground-state magnetic moment of $1.01 \mu_{\mathrm{B}}/f.u.$ is oriented along [111]. The two crystallographically inequivalent U sites are a consequence of spin-orbit coupling of the U 5$f$-electrons. In the excited state which is only 0.9 meV above the ground state the moment points to the [001] direction in agreement with experiment.

Dy substitution effect on the temperature dependences of magnetostriction in Pr1–xDyxFe1.9 alloys**Project supported by the National Natural Science Foundation of China (Grant No. U1232210), the Science Foundation of Guangxi Zhuang Autonomous Region, China (Grant No. 2015GXNSFBA139020), and the Enhancement of the Basic Ability of Teachers of Guangxi Zhuang Autonomous Region, China (Grant No. KY2016YB068).

The temperature dependences of magnetostriction in Pr1−xDyxFe1.9 (0 ≤ x ≤ 1.0) alloys between 5 K and 300 K were investigated. An unusual decrease of magnetostriction with temperature decreasing was found in Pr-rich alloys (0 ≤ x ≤ 0.2), due to the change of the easy magnetization direction (EMD). Dy substitution reduces the magnetostriction in high-magnetic field (10 kOe ≤ H ≤ 90 kOe) at 5 K, while a small amount of Dy substitution (x = 0.05) is beneficial to increasing the magnetostriction in low-magnetic field between 10 K and 50 K. This makes the alloys a potential candidate for low temperature applications.

Tunneling anisotropic magnetoresistance in a magnetic tunnel junction with half-metallic electrodes

Tunneling anisotropic magnetoresistance (TAMR) is the difference in resistance of a magnetic tunnel junction due to a change in magnetization direction of one or both magnetic electrodes with respect to the flow of current. We present the results of first-principles density functional calculations of the TAMR effect in magnetic tunnel junctions with $\mathrm{L}{\mathrm{a}}_{0.7}\mathrm{S}{\mathrm{r}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}$ (LSMO) electrodes and a $\mathrm{SrTi}{\mathrm{O}}_{3}$ (STO) tunneling barrier. We find an $\ensuremath{\sim}500%$ difference in resistance between magnetization in the plane and out of the plane. This large TAMR effect originates from the half-metallic nature of LSMO: When magnetization is out of plane spin-orbit coupling (SOC) contributions to the transmission come only from spin-flip scattering, which is intrinsically small due to the half-metallicity. For in-plane magnetization, however, there is a large non-spin-flip SOC contribution to the conductance. The large magnitude of the effect stems from the additional fact that there is an inherent polar discontinuity between LSMO and STO which leads to quasilocalized states at the interface whose influence on tunneling is strongly dependent on the magnetization orientation.