Hard Direction Research Articles

The energy of 180° domain walls of uniaxial crystals with the different magnetocrystalline anisotropy type

The main aim of the present work is to analyze the magnetocrystalline anisotropy (MCA) energy function of uniaxial crystals and to derive analytical expressions for the domain wall (DW) energy taking into account two MCA constants. Thus, the article presents a detailed analysis of the magnetocrystalline anisotropy energy function of uniaxial crystals taking into account two MCA constants (K1, K2). The values of the MCA energy extremes and the position of the easy magnetization directions (EMD) and hard magnetization directions (HMD) were determined. The MCA diagram was plotted in “K1”-“K2” coordinates. Six types of MCA have been found for uniaxial crystals. Two of them are simple with one maximum and one minimum of the EA(θ) function, and four are complex with two absolute and one local extreme for each. It is shown that EA(K1, K2) function has the smallest difference between the maximum and minimum values equal to |K1|/4 and the smallest angle between EMD and HMD equal to π/4 when the K1 + K2 = 0 condition is met. Analytical expressions for the 180° Bloch domain wall energy surface density (γ) were derived for uniaxial crystals with each MCA type. It is found that the γ(K1, K2) function has a minimum, equal to γ=2A|K1| when the relation K1 + K2 = 0 between MCA constants is satisfied. The derived analytical expressions are useful for a detailed spin-reorientation transition analysis. To illustrate this, examples of the application of the obtained results to MCA analyses of real crystals and DW energy calculations are given.

Mechanochemical grinding with aluminium-coated nickel and diamond mixed abrasive vitrified bond wheel for reducing anisotropy in (100) surface single-crystal diamond processing

While single-crystal diamond is a promising wide-bandgap semiconductor material, it is also the hardest material in nature and exhibits remarkable anisotropy, presenting a challenge for high-quality and efficient processing. To address this issue, this article introduces a method that utilises aluminium-coated nickel and diamond mixed abrasive vitrified bond grinding wheels for a mechanicochemical grinding process to reduce the anisotropic removal of diamond. Different cutting depths, abrasive ratios, grinding directions, and linear velocities were employed in the processing, with the material-removal mechanism studied through morphological characterisation, elemental content, and other detection methods. The experiment revealed that the catalytic effect of nickel metal occurred along the (111) crystal plane of the diamond. This catalytic process involves a transition from sp3 diamond to amorphous carbon, followed by graphitisation. The spin-rotating mechanicochemical grinding process mainly involves plastic removal in the soft direction and coupled chemical and mechanical removal in the hard direction. Employing this method reduced the surface roughness of the 7 × 7 mm as-grown crystal to Ra 0.467 nm, with a material removal rate of 4.73 μm/h, achieving a nearly damage-free machining surface.

Intrinsic and extrinsic relaxation mechanisms for controlling spin current intensity in Fe 100−x Co x /Ta bilayers

Controlling the damping parameter in metallic ferromagnetic thin films is a key step for spintronic applications in which spin currents are generated by spin pumping. The coexistence of two states with low and high damping constant values would allow to obtain states of high and low spin current intensity, respectively. We have fabricated Fe 100−x Co x /Ta (with nominal x = 0, 15, 20, 25, 30 and 35) bilayers in which the Fe 100−x Co x layers grow epitaxially and the Ta layer is polycrystalline. We have found the coexistence of Gilbert damping and two magnon scattering mechanisms linked to a sign change in the magnetocrystalline anisotropy constant that allows the manipulation of low and high intensity states of the measured inverse spin Hall effect voltage. Bilayers with lower Co concentrations ( x⩽ 25%) present different relaxation mechanisms (isotropic Gilbert damping and two magnon scattering) and an extra ferromagnetic resonance linewidth broadening produced due to mosaicity. Bilayers with Co concentration x> 25% present a dominating Gilbert damping for all directions in the film plane. However, in this concentration range the damping constant is anisotropic and when the magnetic field is applied along the hard magnetization direction α increases ∼420% with respect to the value obtained for the easy magnetization direction. Coexistence of isotropic Gilbert damping and two magnon scattering generated spin currents 2.5 times larger when the field is applied along the hard magnetization axis compared to the value observed in the easy magnetization axis. Thesefindings make the Fe 100−x Co x /Ta system an excellent candidate for spintronic device applications.

Theoretical investigation of the giant magnetocaloric effect in Er0.7Tm0.3Al2

This study presents a theoretical investigation of the giant magnetocaloric effect recently reported in the intermetallic compound Er0.7Tm0.3Al2. Our model Hamiltonian includes the crystalline electrical field, exchange, and Zeeman interactions in both Er3+ and Tm3+ sublattices. A remarkable agreement was achieved between the theoretical calculations and experimental data concerning heat capacity, ΔST and ΔTad (magnetocaloric quantities). Additionally, the analysis of magnetic anisotropy and simulations for the rotating magnetocaloric effect in Er0. 7Tm0.3Al2 were performed. The maximum value for the rotating magnetocaloric effect was predicted around the temperature of spin reorientation transition from the <111>-easy to the <001>-hard magnetization directions.

Peningkatan Kesadaran Gotong Royong di Kalangan Masyarakat sebagai Pembangunan Desa Siunggam Tonga

This educational program to develop community motivation is based on collaboration between students studying real work in Siunggam Tonga Village, Padang Bolak Tenggara District, Mandailing Natal Regency. In this program, the most hoped for goal is to provide motivation and a high level of awareness of cleanliness on the part of the community in Siunggam Tonga. KKN Stain Madina Group 29 still needs hard work and direction from village officials or government to build a spirit of mutual cooperation in the community, because the community still has low awareness of cleanliness and how to build a village that is good and independent, comfortable and peaceful. The village government and KKN STAIN Madina have tried to carry out or establish several activities such as mutual cooperation, cleaning cemeteries, cleaning prayer rooms, renovating mosques and village offices and providing a little explanation about the importance of cleanliness and togetherness between one individual and another. With the participation of the STAIN MADINA KKN in this program and actively participating in every activity that has been held during the KKN in Siunggam Tonga village, many changes have emerged, especially in the sense of kinship and togetherness that is well established.

Wide-field imaging of the magnetization process in soft magnetic-thin film using diamond quantum sensors

The magnetization process of a soft magnetic CoFeB-SiO2 thin film was imaged using diamond quantum sensors with perfectly aligned nitrogen-vacancy centers along the [111] direction formed by CVD. Around the film edge, the easy and hard axes directions exhibited different responses to the external magnetic field, consistent with ones observed by magneto-optical Kerr effect microscopy. Moreover, quantum diamond imaging could observe discontinuous magnetization along domain walls as non-uniform magnetic charges (MCs). Quantum diamond imaging would help in visualization through MCs, such as irregularity in the material and relative orientation of magnetizations in neighboring domains.

Large magnetostriction in γʹ-Fe4N single-crystal thin film

An Fe4N(110) single-crystal film of 50 nm thickness with γʹ phase is prepared through hetero-epitaxial growth on an MgO(110) single-crystal substrate at 400 °C by reactive sputtering. The out-of-plane and in-plane lattice constants agree with those of bulk within small differences less than 0.2% and the orientation dispersions are about 1.2°. The degree of N site ordering in Fe4N structure is estimated to be 0.995. The arithmetical mean surface roughness is as small as 0.3 nm. These data show that a high-quality Fe4N single-crystal film is successfully formed. The Fe4N film shows in-plane magnetic anisotropy with the easy magnetization direction parallel to [001] and with the hard direction parallel to [1_11], which is reflecting the positive magnetocrystalline anisotropy, K1. A large negative λ100 value of –40 × 10–6 and a fairly-large positive λ111 value of +150 × 10–6 are observed. The present study has shown that γʹ-Fe4N compound is one of the strong candidates for rare-metal-free magnetostrictive materials.

Bidirectional flow of two-dimensional dusty plasma under asymmetric periodic substrates driven by unbiased external excitations

Collective transport properties of a one-dimensional (1D) asymmetric periodic substrate modulated two-dimensional (2D) dusty plasma driven by an unbiased sinusoidal excitation force are investigated using Langevin dynamical simulations. It is discovered that by changing the amplitude and frequency of the unbiased sinusoidal external excitations, as well as the depth of the 1D asymmetric periodic substrate, both the direction and speed of the persistent particle flow can be adjusted, i.e., both the flow rectification and its reversal of the ratchet effect of the steady drift motion for particles are achieved using various excitations. For the studied 2D dusty plasma under the 1D asymmetric periodic substrate, when the amplitude of the excitation increases from zero, the magnitude of the overall drift velocity increases from zero to its first maximum in the easy direction of the 1D asymmetric periodic substrate, next decreases gradually back to zero, and then increases from zero to its second maximum in the hard direction of the 1D asymmetric periodic substrate before finally gradually decaying. It is found that, as the frequency of the excitation and the depth of the 1D asymmetric periodic substrate change, the maximum overall drift velocity also varies, exhibiting a similar variation trend as that for the change of the excitation amplitude. The observed ratchet effect in both the easy and hard directions of 1D asymmetric periodic substrate for 2D dusty plasma is attributed to the combination of the spatial symmetry breaking of the 1D asymmetric periodic substrate and the inertial effects of particles, which is further confirmed by the three different presented diagnostics.

High magnetic, transport, and optical uniaxial anisotropies generated by controlled directionally grown nano-sheets in Fe thin films

Fe films with thicknesses between 17 and 95 nm were grown with a nano-sheet morphology, which enabled their high uniaxial magnetic, transport, and optical in-plane anisotropies. The top edge of the nano-sheets was directly visualized as nano-string-like structures of approximately 12.5–14 nm width and 100–300 nm length. The hysteresis loops showed a clear easy direction of magnetization in the longitudinal direction of the nano-sheets, whereas the hard direction loops were anhysteretic, with no remanence and zero coercive field. The anisotropy field exhibited values between 70 and 111 kA/m depending on the thickness of the films, with the maximum value corresponding to a 34 nm thick sample. The resistance of the films was also found to be highly anisotropic. The ratio (R⊥–R||)/R|| was ≈86%, with R|| and R⊥ being the resistances in the parallel and perpendicular directions of the nano-sheets, respectively. Likewise, the reflectivity of the samples behaved anisotropically; the ratio (IReflmax–IReflmin)/IReflmax of the intensity of reflected light by the films reached up to 61% for 34 nm thick samples, achieving the maximum value, IReflmax, when the plane of the incident light coincided with the direction of the nano-sheets and the minimum, IReflmin, when this plane was perpendicular to the direction of the nano-sheets. The origin of these anisotropic behaviors was established. These anisotropic films with high magnetization and high uniaxial anisotropies at the nanoscale can be useful for microelectronics applications, for devices such as magnetic sensors and transducers, or for ultrahigh frequency inductors.

Controlling Magnetic Anisotropy in Amplitude Expansion of Phase Field Crystal Model

The amplitude expansion for a magnetic phase‐field‐crystal (magnetic APFC) model enables a convenient coarse‐grained description of crystalline structures under the influence of magnetic fields. Considering higher‐order magnetic coupling terms, the possibility of tuning the magnetic anisotropy in these models is demonstrated. This allows reproducing the easy and hard directions of magnetization. Such a result can be achieved without increasing the computational cost, enabling simulations of the manipulation of dislocation networks and microstructures in ferromagnetic materials. As a demonstration, the simulation of the shrinkage of a spherical grain with the magnetic anisotropy of Fe is reported.

On the electronic and magnetic properties of RVO3 (R = Er, Ho, Y, Lu) vanadates: first principles study

In this paper, we investigate the influence of the rare earth element (R) on the physical properties of RVO3 (R = Er, Ho, Y, Lu). For this purpose, a theoretical work is reported in this study using ab initio method with the intent of enhancing our knowledge of the electronic, and magnetic properties of RVO3 (R = Er, Ho, Y, Lu) compounds. The electronic properties of these materials show the presence of Jahn-Teller effect, with a band gap of approximately 0.58eV, 1.57eV, 1.12eV, 1.28eV, for ErVO3, HoVO3, YVO3, LuVO3, respectively. The magnetic contribution of Ho, Er, and V atoms in HoVO3, and ErVO3 compounds was disentangled using X-ray magnetic circular dichroism (XMCD). The magnetic anisotropies of RVO3 with (R = Er, Ho, Y, Lu) are studied and analyzed using spin orbit coupling. We noticed an easy axis of magnetization along the c-direction with strong magneto-crystalline anisotropy energies for the non-magnetic rare earth elements (R = Lu, Y)VO3. For the magnetic rare earth elements, the easy and hard magnetization direction were found to be along b-axis and c-axis, and a-axis and c-axis for HoVO3, and ErVO3, respectively. This means that instead of the standard magnetization demagnetization process, large thermal effects can be obtained by spinning their single crystals in constant magnetic fields. The exchange coupling between (Ho–V) is also found to be greater than the other exchange interactions in HoVO3. Accordingly, a large conventional magnetocaloric could be created in HoVO3, since the Ho Ising moments experience a metamagnetic transition. However, the magnetocaloric effect (MCE) is expected to be lower in ErVO3 due to the weak (Er–V) exchange coupling.

Oscillatory sliding in the presence of asymmetric friction

Asymmetric friction corresponds to the case when different magnitudes of friction resist sliding in opposing directions. Asymmetric friction can also emerge in anisotropic solids (e.g. rocks) in sliding over fractures with an anisotropic face whose axis of anisotropy is inclined to the direction of sliding and constrained in the normal direction. It can therefore be important in geotechnical applications. Asymmetric friction can also be engineered using anisotropic blocks with an inclined anisotropy axis and used for designing new hybrid or metamaterials. Oscillations of a mass with asymmetric friction can be categorised under one of the following three cases: (1) steady state oscillations in the low friction direction, (2) oscillations in the low friction direction, with decreasing amplitude until the mass becomes stationary, and (3) stick–slip-type movement only in the low friction direction until the mass becomes stationary. In the case of high degree of asymmetric friction such that sliding in the hard direction is impossible, the spectra show peaks at both even and odd multiples of driving frequency.

Negative Longitudinal Piezoelectricity Coexisting with both Negative and Positive Transverse Piezoelectricity in a Hybrid Formate Perovskite.

Negative longitudinal piezoelectric response is a rare property, which has been found mostly in inorganic materials. We use first-principles density functional theory simulations to predict such an unusual response in [NH2NH3]Co(HCOO)3 ─a representative of a large family of hybrid organic-inorganic formate perovskites. A feature that sets aside [NH2NH3]Co(HCOO)3 from inorganic compounds with a negative longitudinal piezoelectric response is that this rare property coexists with both negative and positive transverse piezoelectric responses, which is highly desirable for tunable applications. Atomistic analysis reveals that this unusual electromechanical coupling originates from the high anisotropy of materials response to uniaxial stress. Such a deformation produces oxygen octahedral tilts in the framework, whose magnitude depends strongly on the direction of the applied strain. For hard directions, the tilts make the dominant contribution to the deformation-induced change in polarization, while for the softer direction, it is the tilts of the NH2NH3+ cation that dominate the polarization response. The latter occur as the complex hydrogen bond network responds to the octahedral tilts. As high anisotropy of mechanical properties is a common feature across the formate perovskites, we expect our findings to stimulate more discoveries of unusual electromechanical couplings in this family.

Clogging, diode and collective effects of skyrmions in funnel geometries

Using a particle-based model, we examine the collective dynamics of skyrmions interacting with a funnel potential under dc driving as the skyrmion density and relative strength of the Magnus and damping terms are varied. For driving in the easy direction, we find that increasing the skyrmion density reduces the average skyrmion velocity due to jamming of skyrmions near the funnel opening, while the Magnus force causes skyrmions to accumulate on one side of the funnel array. For driving in the hard direction, there is a critical skyrmion density below which the skyrmions become trapped. Above this critical value, a clogging effect appears with multiple depinning and repinning states where the skyrmions can rearrange into different clogged configurations, while at higher drives, the velocity-force curves become continuous. When skyrmions pile up near the funnel opening, the effective size of the opening is reduced and the passage of other skyrmions is blocked by the repulsive skyrmion–skyrmion interactions. We observe a strong diode effect in which the critical depinning force is higher and the velocity response is smaller for hard direction driving. As the ratio of Magnus force to dissipative term is varied, the skyrmion velocity varies in a non-linear and non-monotonic way due to the pile up of skyrmions on one side of the funnels. At high Magnus forces, the clogging effect for hard direction driving is diminished.

UI3 – 5f-electron magnetic van der Waals material

We grew high-quality single crystals of the 5f electron van der Waals compound UI3 and investigated them by measurements of specific heat and magnetization as function of temperature and magnetic field. UI3 behaves as an antiferromagnet with a first-order magnetic phase transition at the Neél temperature TN ​= ​2.65 ​K. It is characterized by a sharp symmetric specific-heat peak which is gradually shifted to lower temperatures by increasing magnetic field applied along either the a- or b-axis. The behavior in magnetic field reveals orthorhombic magnetocrystalline anisotropy with the hard magnetization direction along the c-axis. The 2-K a- and b-axis magnetization curves exhibit a metamagnetic transition at the critical field μ0Hc ​≈ ​3 ​T and ≈ 1.8 ​T, respectively. In higher fields, when the long-range antiferromagnetism is suppressed by a metamagnetic transition, signs of short-range magnetic ordering of antiferromagnetic correlations in the paramagnetic state show up both in specific heat and magnetization. The anomalous S-shape field dependence of a-axis magnetization well above Hc can be understood as the crossover from the correlated paramagnetic regime to the high-field polarized paramagnet. The magnetic phase diagrams for the magnetic field applied along the a- and b-axis, respectively, designed using the mentioned experimental results are presented. We have also found that the UI3 crystals are easily cleavable which predisposes this material for direct investigation of 5f electron magnetism in the 2D limit on exfoliated atomically thin samples.

First principles calculations to investigate electronic, magnetic anisotropy energy and optical properties of MnCrP half-Heusler alloy

In this current research work, the electronic, magnetic and optical properties of half Heusler alloy MnCrP are calculated and discussed within DFT framework. These calculations are done by using Wien2k code with Perdew–Burke–Ernzerhof Generalized Gradient Approximation and Tran-Blaha modified Becke-Johnson (TB-mBJ) exchange and correlation potentials. Band gap study along with density of states analysis divulge the magnetic nature of MnCrP. The magnetic moments with PBE-GGA and TB-mBJ are 4.426μB and 4.4542μB respectively. It shows the suitability of this material in spintronic device fabrications. The magnetic anisotropy energy of this half Heusler is also determined by the difference of energies in easy and hard magnetization directions. Several optical parameters are calculated, including dielectric constants, absorption parameter, refractive indices, reflectivity, extinction coefficient, energy loss function and conductivity. The imaginary part of the dielectric constant also predicts that the compound MnCrP is optically metallic and suitable for sensor application and optoelectronic device.

Proof-of-Principle Design of a High-Field Overpass/Underpass Nb3Sn Dipole

A block coil geometry is appealing in the body of particle accelerator dipole or quadrupole magnets, but less so in the ends of conventional designs, because conductors near the midplane of the beam tube must be bent in the hard direction to cross over to the other side of the tube. To avoid damage to brittle conductors such as Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn or HTS, the bend must be very gradual, resulting in undesirably long magnet ends. An alternative design - “overpass/underpass” or “cloverleaf” - can ramp the conductor within a short length with bending only in the easy direction. Described here is a proof-of-principle design and analysis of an “overpass/underpass” coil geometry for a block coil dipole of 11 T or more.

Driven superconducting vortex dynamics in systems with twofold anisotropy in the presence of pinning

We examine the dynamics of superconducting vortices with twofold anisotropic interaction potentials driven over random pinning, and compare the behavior under drives applied along the hard and the soft anisotropy directions. As the driving force increases, the number of topological defects reaches a maximum near the depinning threshold, and then decreases as the vortices form one-dimensional (1D) chains. This coincides with a transition from a pinned nematic to a moving smectic aligned with the soft anisotropy direction. The system is generally more ordered when the drive is applied along the soft direction of the anisotropy. For driving along the hard direction, there is a critical value of the twofold anisotropy above which the system remains aligned with the soft direction. Hysteretic behavior appears upon cycling the driving force, with 1D vortex chains persisting during the decreasing leg below the threshold for chain formation for increasing drive. More anisotropic systems have a greater amount of structural disorder in the moving state. For lower anisotropy, the system forms a moving smectic-A state, while at higher anisotropy, a moving nematic state appears instead.

Strain-engineering of magnetic anisotropy in CoxNi1−x−SrTiO3/SrTiO3 (001) vertically assembled nanocomposites

Ultrathin ${\mathrm{Co}}_{x}{\mathrm{Ni}}_{1\ensuremath{-}x}$ alloy nanowires vertically embedded in ${\mathrm{SrTiO}}_{3}/{\mathrm{SrTiO}}_{3}\phantom{\rule{0.16em}{0ex}}(001)$ thin films were grown using a self-assembly approach based on sequential pulsed laser deposition. Due to vertical epitaxial coupling of the metallic and oxide phases, a large average tensile strain of up to 4% arises within the nanowires, which is evidenced using a combination of x-ray diffraction and transmission electron microscopy. Macroscopic magnetometry experiments are used to demonstrate that this huge deformation allows us to enhance the uniaxial anisotropy of the nanowires, leading to saturation field in excess of 1 T in the hard direction, large coercive field at low temperature along the easy axis, and to a blocking temperature exceeding 600 K in the case of nanowires with a diameter of 5 nm and 78% Co content. These data are complemented with angular dependent x-ray magnetic circular dichroism measurements at the Co and Ni ${L}_{2,3}$ edges. The value of the magnetic moment was extracted from these measurements by applying sum rules and the anisotropy of the orbital moment was investigated.

Magnetic reshuffling and feedback on superconductivity in UTe2 under pressure

The discovery of superconductivity in the heavy-fermion paramagnet ${\mathrm{UTe}}_{2}$ has attracted a lot of attention, particularly due to the reinforcement of superconductivity near pressure- and magnetic-field-induced magnetic quantum phase transitions. A challenge is now to characterize the effects of combined pressure and magnetic fields applied along variable directions in this strongly anisotropic paramagnet. Here, we present an investigation of the electrical resistivity of ${\mathrm{UTe}}_{2}$ under pressure up to 3 GPa and pulsed magnetic fields up to 58 T along the hard magnetic crystallographic directions $\mathbf{b}$ and $\mathbf{c}$. We construct three-dimensional phase diagrams and show that, near the critical pressure, a field-enhancement of superconductivity coincides with a boost of the effective mass related to the collapse of metamagnetic and critical fields at the boundaries of the correlated paramagnetic regime and magnetically-ordered phase, respectively. Beyond the critical pressure, field-induced transitions precede the destruction of the magnetically-ordered phase, suggesting an antiferromagnetic nature. By bringing new elements about the interplay between magnetism and superconductivity, our paper appeals for microscopic theories describing the anisotropic properties of ${\mathrm{UTe}}_{2}$ under pressure and magnetic field.