Easy Direction Research Articles

Magnetocrystalline anisotropy correlated negative anisotropic magnetoresistance in epitaxial Fe30Co70 thin films

We report on the magnetoresistance in different crystallographic directions of epitaxial ferromagnetic Fe30Co70 thin films with magnetization rotated in the film plane. A negative single crystal anisotropic magnetoresistance (SCAMR) is found when the current is along the easy magnetization axis [110], and the SCAMR can be tuned to the conventional positive one when the current flows along the hard magnetization axis [100]. This finding is explained comprehensively by a magnetocrystalline anisotropy (MCA) symmetry-adapted model expanded along the easy magnetization direction, with which the SCAMR can be represented as a MCA-independent conventional term cos 2φM and a series of MCA-dependent terms cos 2nφA (n≥1). The results show that the MCA-dependent twofold term contributes to the negative SCAMR, which cannot be used as a fingerprint of the half-metallicity. Our finding provides an approach to understand and design the magnetoresistance with ferromagnets by MCA.

Antiferromagnetic semiconductor in porous boron nitride ([formula omitted]) sheet: First-principles investigation

This paper reports a new B6N6 sheet using first-principles calculations based on density functional theory (DFT). The B6N6 sheet prefers antiferromagnetic ground state with a direct band gap of 1.41 eV. The magnetic moment is mainly derived from N atoms as a result of the added impurities in the B6N6 sheet. The B6N6 sheet is found to be dynamically and mechanically stable. The calculated cohesive (5.6 eV) and formation (0.325 eV) energies per atom indicate that B6N6 sheet holds promise for experimental synthesis. The B6N6 sheet exhibits sizable magnetic anisotropy energy (MAE) of 17 μeV per unit formula with an out-of-plane easy axis magnetization direction. Based on the mean-filed approximation, a Neel temperature (TN) of 97 K for B6N6 sheet has been predicted. These findings show that B6N6 sheet holds a promise for future spintronics device applications.

Observing the magnetization reversal processes and anisotropic effective damping of epitaxial FeSi/MgO (001)

Epitaxial FeSi film on MgO (001) substrate was fabricated via a radio frequency magnetron sputtering technology. The epitaxial relationship of FeSi(001)/[110]//MgO(001)/[100] was characterized by crystal structure measurements and confirmed by in-plane biaxial magnetic anisotropy through vibrating sample magnetometer (VSM). By measuring Kerr magnetic hysteresis loops and recording the real-time magnetic domain images through surface magneto-optic Kerr effect (MOKE), two successive 90° domain wall displacement along easy axis and two discontinuous 90° domain wall displacement along hard axis were directly observed. Meanwhile, the difference of magnetic hysteresis loops obtained by VSM and MOKE devices were discussed. Furthermore, from the results of magnetic field sweeping ferromagnetic resonance measurements, it was found that FeSi film possesses an anisotropic effective damping constant of 0.0042 for easy axis direction and 0.0053 for hard axis direction, which was ascribed to the crystallographic defects induced two magnon scattering contributions.

Orientation control of optical mode ferromagnetic resonance: From uniaxial to omni-directional

Both high ferromagnetic resonance frequency (fr) and homogeneous angular performance are important for soft magnetic films to be used in high-frequency integrated circuit devices. However, high fr are obtainable only along the easy axis direction of the magnetic anisotropic materials. In uniaxially anisotropic FeCoB/Ru/FeCoB films, we could obtain an ultrahigh optical mode ferromagnetic resonance frequency (frO) up to 19.16 GHz along the easy axis under a self-bias field due to the enhancement from strong interlayer exchange coupling. However, the uniaxial intensity distribution of optical mode resonance seriously hinders the practical application in microwave components. In order to obtain the desired homogeneous angular performance, soft magnetic films with widely distributed magnetic anisotropy directions in the films were prepared and a nearly omni-directional frO with uniform values around 13.5 GHz was achieved. This study demonstrates that controlling the magnetic anisotropy's angular distribution is an effective way to obtain isotropic, self-bias magnetic films with ultrahigh fr.

초등 수학 교과서의 수학 용어 정의에 대한 독일어 ‘표현’의 의미에 따른 분석

In this study, the representations used in the definition of mathematical terms in elementary school math textbooks according to the 2015 revised curriculum were analyzed by type according to the meaning of German ‘representation'. The definition of 172 mathematical terms presented as learning elements in the curriculum was analyzed by classifying them into four types (darstellen, vorstellen, vertretten, and bedeuten) depending on the meaning of the German word ‘representation'. As a result, even mathematical terms with abstract meanings were often described in a specific direction or presented with examples. This is interpreted as an attempt to easily represent the concept in an easy and specific direction, taking into account the developmental stage of elementary school students. Therefore, it is necessary to understand the meaning of these representations and to help students understand them by accurately representing them in the appropriate direction according to the nature of each mathematical term.

Correlation between Ferromagnetic Layer Easy Axis and the Tilt Angle of Self Assembled Chiral Molecules

The spin–spin interactions between chiral molecules and ferromagnetic metals were found to be strongly affected by the chiral induced spin selectivity effect. Previous works unraveled two complementary phenomena: magnetization reorientation of ferromagnetic thin film upon adsorption of chiral molecules and different interaction rate of opposite enantiomers with a magnetic substrate. These phenomena were all observed when the easy axis of the ferromagnet was out of plane. In this work, the effects of the ferromagnetic easy axis direction, on both the chiral molecular monolayer tilt angle and the magnetization reorientation of the magnetic substrate, are studied using magnetic force microscopy. We have also studied the effect of an applied external magnetic field during the adsorption process. Our results show a clear correlation between the ferromagnetic layer easy axis direction and the tilt angle of the bonded molecules. This tilt angle was found to be larger for an in plane easy axis as compared to an out of plane easy axis. Adsorption under external magnetic field shows that magnetization reorientation occurs also after the adsorption event. These findings show that the interaction between chiral molecules and ferromagnetic layers stabilizes the magnetic reorientation, even after the adsorption, and strongly depends on the anisotropy of the magnetic substrate. This unique behavior is important for developing enantiomer separation techniques using magnetic substrates.

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.

Percolation and Reynolds Flow in Elastic Contacts of Isotropic and Anisotropic, Randomly Rough Surfaces

In this work, we numerically study the elastic contact between isotropic and anisotropic, rigid, randomly rough surfaces and linearly elastic counterfaces as well as the subsequent Reynolds flow through the gap between the two contacting solids. We find the percolation threshold to depend on the fluid flow direction when the Peklenik number indicates anisotropy unless the system size clearly exceeds the roll-off wave length parallel to the easy flow direction. A critical contact area near 0.415 is confirmed. Heuristically corrected effective-medium treatments satisfactorily provide Reynolds fluid flow conductances, e.g., for isotropic roughness, we identify accurate closed-form expressions, which only depend on the mean gap and the relative contact area.Graphic

Enhanced magnetoelastic performance in Pr/Mn-doped Laves phase (Tb,Ho)Fe2 compounds

Abstract Magnetostrictive TbxHo0:8−xPr0:2Fe1:8Mn0:1 (0 ⩽ x ⩽ 0.20) alloys are prepared by arc-melting and subsequent annealing. The dopant of Pr/Mn introduced into RFe2 compounds effectively stabilizes the forming of single C15 Laves phase at ambient pressure. The easy magnetization direction (EMD) varies when Tb content increases, which is accompanied by a crystalstructural transition. EMD lies along ‹1 0 0› axis for x ⩽ 0.05, rotating to ‹1 1 1› axis for x ⩽ 0.12, with a tetragonal symmetry changing to a rhombohedral one. Magnetocrystalline-anisotropy compensation is obtained with the optimized composition of x = 0.12, shifting to the Tb-poor side in comparison to Pr/Mn-free counterpart. An enhanced effect on magnetoelastic properties is achieved in Tb0:12Ho0:68Pr0:2Fe1:8Mn0:1, which simultaneously possesses a low anisotropy and high magnetostriction performance, i.e. λs ~ 420 ppm, λ111 ~ 970 ppm, and a large low-field λa ~ 390 ppm/2 kOe, being 30 % higher than that of Pr/Mn-free compound. Combining low-cost light rare earth Pr with the lower Tb content, Tb0:12Ho0:68Pr0:2Fe1:8Mn0:1 may make it promising solution in magnetostrictive applications.

Thickness dependent domain wall dynamics in Fe2CoSi thin films

We report on the effect of thickness on the magnetic properties and domain wall motion in as deposited Fe2CoSi thin films. Reflections present in selected area electron diffraction (SAED) micrograph infer that they are allowed reflections and are related to the Fe2CoSi. The coercivity is found to increase with the film thickness and the same is explained on the basis of Néel domain wall model. Longitudinal magneto-optical Kerr effect (L – MOKE) infers that the formation of ripple kind of domains that depend on the orientation of the field. L – MOKE data also infers nearly perfect 4-fold anisotropy for the film with thickness 5 nm and a weaker 4-fold anisotropy at higher thicknesses. Up on varying the angle between magnetic field and the film edge to 0° or 90°, indeed there is a transformation of the film magnetization from easy direction to hard direction. Fast Fourier transform of magnetic force microscopy (MFM) and polar plots infer a uniaxial anisotropy and a four-fold anisotropy in the films. Micromagnetic simulations infer that the coercivity value depends on the void size and enhances up to certain radius, above which it decreases. Present results would indeed be helpful for the future spintronic applications.

Magnetic order and competition with superconductivity in (Ho-Er)Ni2B2C

The rare earth magnetic order in pure and doped Ho(1−x)Er x Ni2B2C (x = 0, 0.25, 0.50, 0.75, 1) single crystal samples was investigated using magnetization and neutron diffraction measurements. Superconducting quaternary borocarbides, RNi2B2C where R = Ho, Er , are magnetic intermetallic superconductors with the transition temperatures ∼10 K in which long range magnetic order develops in the same temperature range and competes with superconductivity. Depending on the rare earth composition the coupling between superconductivity and magnetism creates several phases, ranging from a near reentrant superconductor with a mixture of commensurate and incommensurate antiferromagnetism to an incommensurate antiferromagnetic spin modulation with a weak ferromagnetic component. All of these phases coexist with superconductivity. RKKY magnetic interactions are used to describe the magnetic orders in the pure compounds. However, the doping of Er on Ho sites which have two strong magnetic moments with two different easy directions creates new and complicated magnetic modulations with possible local disorder effects. One fascinating effect is the development of an induced magnetic state resembling the pure and doped R 2CuO4 cuprate with R = Nd and Pr.

First-principles study on the electric field manipulation of the magnetic property and the electronic structures for monolayer Fe2C MXene

In this research, we investigate the magnetic properties, electronic structures, magnetic anisotropy and Curie temperature (TC) of monolayer Fe2C by first-principles calculation. The calculation results show that the ground state of Fe2C should be ferromagnetic (FM) state. Introducing a vertical electric field (E⊥) to monolayer Fe2C, we find that the Dirac points can be opened or formed in FM state. For A-AFM state, the transitions of electronic structures appear with the variation of the electric field. We also calculate the magnetic anisotropy energy (MAE) and find that z-axis is the magnetic hard axis, xy-plane is the magnetic easy plane. The electric field can tune the magnetic easy direction. TC of monolayer Fe2C is estimated to be 662 K by the mean-field approximation method. As the electric field increases, the exchange parameters decrease, which results in the reduction of TC. When E⊥ reaches 0.35 V/Å, T≈C300 K. Therefore, this study provides a good theoretical guide for reducing the magnetic materials with high TC to room temperature.

Epitaxial thin-film Pd1−xFex alloy: a tunable ferromagnet for superconducting spintronics

In the paper we present the results of extensive studies of palladium-rich Pd1-xFex alloy films epitaxially grown on MgO single-crystal substrate. In a composition range of x = 0.01-0.07 these materials are soft ferromagnets, the saturation magnetization and magnetic anisotropy of which can be tuned by its composition. Vibrating sample magnetometry was used to study temperature dependences of spontaneous magnetic moment and to establish the temperature of magnetic ordering (Curie temperature). Ferromagnetic resonance (FMR) measurements at low temperatures in the in-plane and out-of-plane geometries revealed the four-fold in-plane magnetic anisotropy with the easy directions along the <110> axes of the substrate. The modelling of the angular dependence of the field for resonance allowed to extract the cubic and tetragonal contributions to the magnetic anisotropy of the films and establish their dependence on the concentration of iron in the alloy. Experimental data are discussed in the framework of existing theories of dilute magnetic alloys. Using the anisotropy constants established from FMR, the magnetic hysteresis loops are reproduced utilizing the Stoner-Wohlfarth model thus indicating the predominant coherent magnetic moment rotation at low temperatures. The obtained results compile a database of magnetic properties of a palladium-iron alloy considered as a material for superconducting spintronics.

Enhanced toughness in ceramic-reinforced polymer composites with herringbone architectures

Crack deflection is often used as evidence of substantive fracture toughness in both natural and synthetic composites. The associated microstructures of these tough composites are often highly anisotropic, exhibiting both easy and hard directions for crack propagation. Cracks generally deflect away from hard directions to propagate instead in easy directions tying the overall fracture toughness to its weak axis. Instead, enhanced fracture toughness can be realized when cracks are forced to propagate along the hard directions. Recent advances in composite manufacturing including 3D magnetic printing have enabled the creation of detailed microstructures that can locally tune the fracture toughness anisotropy. In this work, we investigate a family of architectures reminiscent of a herringbone pattern, in which propagating cracks are effectively trapped along the spine between two regions. Along this spine, a crack can be inhibited from deflecting and forced to propagate along a relatively hard direction, resulting in a significant boost in initial and overall fracture toughness. We expand these realizations to generate beautiful herringbone mosaics that exhibit isotropic and enhanced fracture toughness. We have approached this problem with both numerical and experimental modalities to systematically test and characterize this new class of composite architectures.

Roles of cobalt and boron in FeCoBSi soft magnetic composite with in-plane uniaxial magnetic anisotropy

The roles of cobalt and boron in an FeCoBSi soft magnetic composite (SMC) containing magnetic flakes with in-plane uniaxial magnetic anisotropy were investigated. When cobalt was added to the magnetic flakes in the SMC, in-plane uniaxial magnetic anisotropy was effectively induced, and coercivity in the easy axis direction remarkably decreased after annealing under a magnetic field in comparison with the case without addition of cobalt. In particular, the addition of cobalt was essential to decrease coercivity in the SMC, in marked contrast to simple amorphous ribbons in which coercivity decreased even without addition of cobalt but in-plane uniaxial magnetic anisotropy was not induced. Boron prevented crystallization of the magnetic amorphous phase, with boron content of more than approximately 18 at% relative to FeCo necessary to produce an amorphous phase without crystallization, resulting in low coercivity and in-plane uniaxial magnetic anisotropy. High saturation magnetization of 1.12 T and low coercivity of 0.32 Oe with in-plane uniaxial magnetic anisotropy were obtained with a composition of Fe55.5Co23.7B14.2Si6.6 (Co/(Fe + Co) = 30 at% and B/(Fe + Co) = 18 at%) in the fabricated SMC.

Application of DFT for magnetic anisotropy energy calculations of vanadium ferrite VFe2O4

Structural, electronic and magnetic properties of vanadium ferrite are studied using density functional theory with Perdew Burke Ernzerhof Generalized Gradient Approximation (PBE-GGA) type exchange-correlation functional. The calculated lattice constant of VFe2O4 has 0.667% difference with experimental one. The optimized lattice constant is used in self-consistent field calculations to investigate the magnetic and electronic properties. The magnetic properties of VFe2O4 reveals it's half magnetic nature. Furthermore; the magnetic moments, spin-exchange splitting, exchange coefficients, spin-polarized crystal field splitting and edge spin splitting energy of the spinel are also calculated for both spin channels. The large value of magnetic moment (13.999 μB) for VFe2O4 shows it's suitability for fabrication of the spintronic devices. Magnetic anisotropy energy of this spinel is also estimated from the difference of easy and hard directions of magnetization.

Strong magnetic anisotropy and unusual magnetic field reinforced phase in URhSn with a quasi-kagome structure

The physical properties of URhSn with quasi-kagome structure are studied using single-crystalline samples via electrical resistivity, magnetic susceptibility, heat capacity, thermal expansion, and high-field magnetization measurements. Remarkable magnetic anisotropy is found in the ferromagnetic (FM) state below ${T}_{\mathrm{C}}=16\phantom{\rule{4pt}{0ex}}\mathrm{K}$ as well as in the ordered state between ${T}_{\mathrm{C}}$ and ${T}_{\mathrm{O}}=54\phantom{\rule{4pt}{0ex}}\mathrm{K}$, where the easy and hard magnetization directions are the hexagonal [0001] and $[10\overline{1}0]$ axes. In the paramagnetic state, the magnetic susceptibility shows a Curie-Weiss behavior; the Weiss temperatures are positive and negative for [0001] and $[10\overline{1}0]$, respectively, indicating the presence of both FM and antiferromagnetic (AFM) correlations. The entropy release for $5f$ electrons is approximately $R\phantom{\rule{0.16em}{0ex}}\mathrm{ln}3$ at ${T}_{\mathrm{O}}$. The thermal expansion coefficient is strongly anisotropic around ${T}_{\mathrm{O}}$ between the hexagonal basal plane and the [0001] axis, indicating its remarkable anisotropic magnetoelastic response and uniaxial stress dependences. Interestingly, the magnetic field response of the higher-temperature ordered state is unusual: ${T}_{\mathrm{O}}(H)$ increases and the heat-capacity jump is enhanced with the magnetic field for $H\phantom{\rule{0.16em}{0ex}}||\phantom{\rule{4pt}{0ex}}[0001]$. Based on the established thermodynamic evidence for the second-order transition at ${T}_{\mathrm{O}}(H)$, a plausible scenario is the occurrence of a canted AFM ordering or a conical state under magnetic fields, which is stabilized when coupled with field-induced magnetic moments along the [0001] axis. Another possibility is the occurrence of quadrupole ordering at ${T}_{\mathrm{O}}(H)$.

An investigation on primary Si refinement by Sr and Sb additions in a hypereutectic Al-Si alloy

The effect of Sr and Sb additions as potential primary Si refiners for A390 hypereutectic Al alloy was analyzed. Despite the impurity induced twining (IIT), the experimental results indicate that only twin formation is not responsible for primary Si refinement. Stacking fault, by enforcing the atoms to adjust the sequence, and kinks, by deviating the Si growth from its easy growth direction, cooperate in growth discontinuity. An enhanced IIT theory has been proposed for primary Si evolution where twining, stacking faults and kinks are contributing to control the Si growth. Type of alloying element determines the major contributing mechanism in primary Si evolution. To the best of Authors’ knowledge, the kink formation and its effect on primary Si refinement has yet been reported elsewhere.

Anisotropic quantum critical point in the Ce3Al system with a large magnetic anisotropy

A magnetic field driven quantum critical point (QCP) is studied experimentally in the Ce3Al magnetically anisotropic intermetallic compound, which shows both antiferromagnetic (AFM) ordering and heavy–fermion behavior. Measurements of the magnetic susceptibility, the magnetoresistance and the specific heat on a Ce3Al monocrystalline sample performed down to 0.35 K in magnetic fields up to 9 T demonstrate that the QCP is anisotropic regarding the orientation of the magnetic field relative to the magnetically easy direction. External magnetic field drives the AFM transition continuously toward zero temperature when applied in the (a, b) easy plane, reaching the QCP at the critical field 4.6 ± 0.4 T, where a quantum phase transition from the AFM to the paramagnetic state takes place. The magnetoresistance experiments below 1 K indicate that intermediate magnetic states may have formed near the QCP. For the field applied along the c hard direction, the QCP has not been observed within our experimental range of the magnetic field. The anisotropic, magnetic field driven QCP in the Ce3Al results from competition of the exchange interaction with the Zeeman interaction in the presence of a large magnetocrystalline anisotropy. The anisotropy of the QCP is a consequence of the fact that the magnetic anisotropy locks the magnetization into the easy plane and cannot be pulled out of the plane by the available laboratory field. Consequently, only the component of the magnetic field vector that lies in the easy plane participates in the QCP formation. In AFM systems with a large magnetic anisotropy, the magnetic field driven QCP is a continuous variable of the magnetic field vector orientation relative to the easy direction.

Manipulation of upconversion property and enhancement of sensitivity by tailoring the local structure

AbstractTailoring the local crystal environment around the activators is one of an important way to enhance the upconversion (UC) luminescence intensity. Herein, we substitute the Y3+ lattice with La3+ ion gradually in Y2Ti2O7:Yb3+, Er3+ phosphor and investigate the effect of La3+ concentration on the UC luminescent properties as well as the temperature sensing behaviors. During the phase transformation process from cubic Y2Ti2O7 to monoclinic La2Ti2O7, the La3+ ions also play an important role on the adjustment of size and morphology of particles. Furthermore, the cooperation of La3+ ion is in favor of the crystal growth toward the easy growth directions. The UC luminescence intensities can be enhanced efficiently with the increasing of La3+ concentration. The sensitivity for temperature sensing can be improved by the increasing of La3+ concentration in the Y2Ti2O7 and La2Ti2O7 two‐phase coexistence system and the maximum SA is 45.3 × 10−4 K−1 at 410K when the La3+ concentration is 80%. The maximum SA and corresponding temperature can be adjusted by controlling the La3+ concentration, which means that (Y0.94‐xLax)2Ti2O7: Er3+/Yb3+ phosphors may be applicable to different working environment.