Easy Direction Research Articles

Hot Deformation Behavior of AA-FGH720Li Superalloy

The hot deformation behavior of FGH720Li superalloy was investigated by hot compressive tests on Gleeble-1500D thermal simulation test machine in different temperatures and strain rates. The true stress-strain curves were obtained, and based on the deformation data, the constitutive equation of FGH720Li superalloy was built. The Deformation Active Energy of FGH720Li was determined to be Q=787.6KJ/mol. The main deformation modes were dislocation glide and twinning. At the beginning of the deformation, a large number of dislocations generated, glided and scrambled in the alloy, then entwisted to form dislocation cells, which were the recrystallization nucleus. At the later period of the deformation, the dislocation would rotate to easy glide direction through twinning, inducing that the deformation of the alloy ensued. At the same time, the deformation had significant effect on grain refinement and the crushed of the primary particle boundary.

Composition anisotropy compensation and magnetoelastic properties of Mn-doped TbxHo1−xFe2 Laves compounds (0.08 ≤ x ≤ 0.16)

The structural, magnetic and magnetoelastic properties of TbxHo1−xFe1.9Mn0.1 (0.08 ≤ x ≤ 0.16) alloys have been investigated by means of X-ray diffraction (XRD), Mössbauer spectra, a vibrating sample magnetometer and a standard strain technique. The easy magnetization direction (EMD) at room temperature rotates continuously from the 〈100〉 axis for x = 0.10 to 〈111〉 for x = 0.14 through an intermediate direction around x = 0.12, subjected to the anisotropy compensation between Tb3+ and Ho3+ ions. The magnetocrystalline-anisotropy compensation can be obtained by performing XRD on magnetic-field aligned powders and by evaluating the EMD, magnetization process and magnetostriction. The compensation point achieved is around x = 0.12, shifting to the Ho-rich side at room temperature compared with the Mn-free system. Mn causes opposite contributions to the resultant anisotropy of the alloys as compared to Ho. A minimum in anisotropy is obtained for the Tb0.12Ho0.88Fe1.9Mn0.1 compound, which has a high low-field magnetostriction (λa ∼ 340 ppm @ 2 kOe).

The influence of dipolar and quadrupolar interactions on the magnetoresistivity and magnetocaloric effect in TmZn investigated through a microscopic model

Interesting behaviors in the magnetocaloric effect and magnetoresistivity are predicted for cubic CsCl-type TmZn compound in which, recently, the giant magnetocaloric effect was reported. Our model includes the crystalline electrical field, exchange, Zeeman and elastic-quadrupolar interactions. The calculated giant magnetocaloric effect is in agreement with the experimental data upon magnetic field variation along the easy magnetic direction 〈001〉. For applied magnetic field direction 〈110〉an inverse magnetocaloric effect was predicted in the temperature range from 0.7 to 8.2K. For applied magnetic field along 〈111〉direction, a discontinuity in magnetic entropy change was predicted at 14.1K leading to a latent heat of 80J/mol and magnetic entropy change of 36Jmol−1K−1 in the field change from zero to 5T. Besides, strong correlation between the anisotropic magnetoresistivity and magnetocaloric effects was reported.

Anisotropic physical properties of single-crystal U2Rh2Sn in high magnetic fields

We report on the crystal and magnetic structures, magnetic, transport, and thermal properties of ${\mathrm{U}}_{2}{\mathrm{Rh}}_{2}\mathrm{Sn}$ single crystals studied in part in high magnetic fields up to 58 T. The material adopts a ${\mathrm{U}}_{3}{\mathrm{Si}}_{2}$-related tetragonal crystal structure and orders antiferromagnetically below ${T}_{N}=25$ K. The antiferromagnetic structure is characterized by a propagation vector $\mathit{k}=(00\frac{1}{2})$. The magnetism in ${\mathrm{U}}_{2}{\mathrm{Rh}}_{2}\mathrm{Sn}$ is found to be associated mainly with $5f$ states. However, both unpolarized and polarized neutron experiments reveal at low temperatures in zero field non-negligible magnetic moments also on Rh sites. U moments of 0.50(2) ${\ensuremath{\mu}}_{B}$ are directed along the tetragonal axis while Rh moments of 0.06(4) ${\ensuremath{\mu}}_{B}$ form a noncollinear arrangement confined to the basal plane. The response to applied magnetic field is highly anisotropic. Above $\ensuremath{\sim}15\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ the easy magnetization direction is along the tetragonal axis. At lower temperatures, however, a stronger response is found perpendicular to the $c$ axis. While for the $a$ axis no magnetic phase transition is observed up to 58 T, for the field applied at 1.8 K along the tetragonal axis we observe above 22.5 T a field-polarized state. A magnetic phase diagram for the field applied along the $c$ axis is presented.

Atomistic simulation of finite-temperature magnetism of nanoparticles: Application to cobalt clusters on Au(111)

We developed a technique to determine suitable spin models for small embedded clusters of arbitrary geometry by combining the spin-cluster expansion with the relativistic disordered local moment scheme. We present results for uncovered and covered hexagonal Co clusters on Au(111) surface, and use classical Monte Carlo simulations to study the temperature dependent properties of the systems. To test the new method we compare the calculated spin-model parameters of the uncovered clusters with those of a Co monolayer deposited on Au(111). In general, the isotropic and DM interactions are larger between atoms at the perimeter than at the center of the clusters. For Co clusters covered by Au, both the contribution to the magnetic anisotropy and the easy axis direction of the perimeter atoms differ from those of the inner atoms due to reduced symmetry. We investigate the spin reversals of the covered clusters with perpendicular magnetic anisotropy and by measuring the magnetization variance in the easy direction we suggest a technique to determine the blocking temperature of superparamagnetic particles. We also determine the N\'eel relaxation time from the Monte Carlo simulations and find that it satisfies the N\'eel--Arrhenius law with an energy barrier close to the magnetic anisotropy energy of the clusters.

Magnetoresistive sensitivity and uniaxial anisotropy of spin-valve microstrips with a synthetic antiferromagnet

Microobjects (strips) were formed by contact photolithography using Та/Ni80Fe20/Co90Fe10/Cu/Co90Fe10/Ru/Co90Fe10/Fe50Mn50/Ta spin-valves prepared by magnetron sputtering. A mutually perpendicular arrangement of uniaxial and unidirectional anisotropy axes in microobjects has been formed using two different thermomagnetic treatment regimes. The magnetoresistive sensitivity of spin valve and spin-valve-based microobject has been found to depend on the mutual arrangement of the easy magnetization axis and direction of magnetic field applied upon thermomagnetic treatment. The obtained data have been interpreted taking into account changes in the induced anisotropy and anisotropy due to the shape of the microobject.

Fabrication and magnetic properties of Sm-Co/Fe-Co and Sm-Co/Fe-Co-Dy magnetic nanowires

The Sm-Co/Fe-Co and Sm-Co/Fe-Co-Dy nanowire arrays with smaller diameter are prepared by electrochemical deposition on the anodic aluminum oxide (AAO) templates in this paper. The crystal structure and magnetic properties of nanowires are characterized and analyzed. It is found that the Sm-Co nanowires change from amorphous phase to nanocrystalline state with hard magnetic characterization through annealing at 660 °C for 3 h. In this experiment, rare earth element Dy is added to the Fe-Co solution, and the three alloy nanowires are prepared and researched for the first time. The addition of Dy element produces a new Fe23Dy6 phase in the nanowires. The magnetic hysteresis loops illustrate that the magnetic properties of as-deposited nanowires is improved dramatically after heat treatment and the direction parallel to the nanowire arrays is the easy direction of magnetization which leads to nanowires possessing obvious shape anisotropy. The effect of different Dy ion concentration on nanowires' magnetic properties is investigated in this paper.

Preparation and properties of pure crystalline perovskite CeFeO3 thin films with vanadium doping

AbstractCerium ferrite (CeFeO3) thin films doped with vanadium (V:CeFeO3) were grown on SiO2 quartz glass and <100>‐oriented SrTiO3 (STO) crystal substrates by the radio‐frequency magnetron sputtering method in this study. The effects of crystallization, substrate, and V‐doping on the quality, the magnetic property and the magneto‐optical property of as‐prepared films are investigated. V:CeFeO3 film grown on STO substrate has better crystallinity and has better lattice integrity due to the higher lattice matching between substrate and film. The magnetic hysteresis loop and the magnetic circular dichroism spectra show that the magnetization strength and the magneto‐optical properties of V:CeFeO3 films have the significant anisotropy. Moreover, V‐doping and the stress lead to the change in easy magnetization direction of film. It shows that the perovskite B‐site doping with transition‐metal ion has significant influence on the magnetic and the magneto‐optical properties of CeFeO3 thin films.

Fcc and bcc structured ferromagnetic films with five to twenty spin layers explained by second order perturbed Heisenberg Hamiltonian

Second order perturbed 2-D Heisenberg Hamiltonian model was employed to explain the magnetic properties of fcc and bcc structured ferromagnetic thin films with five to twenty spin layers. Magnetic energy versus azimuthal angle of spin was plotted to find the angle corresponding to maximum energy and minimum energy. Hence magnetic easy and hard directions were determined. The magnetic easy axis gradually rotates from out of plane (perpendicular) to in plane direction as the number of spin layers is increased. This implies that the films indicates a preferred in plane easy axis orientation at higher thicknesses. The energy required to rotate spin from hard to easy (or vice versa) directions gradually increases with number of spin layers. Our results agree with the experimental data obtained for ferromagnetic thin films.

Ultra-low magnetic damping of perovskite La0.7Sr0.3MnO3 thin films

The perovskite La0.7Sr0.3MnO3 (LSMO) films grown on different substrates were investigated by an angle resolved broadband ferromagnetic resonance technique. All films exhibited a four-fold magnetocrystalline anisotropy, which is in accord with the crystal structure. Moreover, a perpendicular uniaxial anisotropy changed from the (001)pc easy plane to the [001]pc easy direction when the strain of LSMO films varies from tensile to compressive. The ultra-low magnetic damping constant of 5.2 × 10−4 was obtained for a 44.6 nm LSMO film on an NdGaO3 (110) substrate. The breathing Fermi surface model in which the damping constant is proportional to the density of states at Fermi energy is the dominant mechanism for the intrinsic magnetic relaxation.

Crystal structure and magnetic properties of (Nd,Tb)2Fe14B nanoflakes prepared by surfactant-assisted ball milling

The microstructure, crystal structure, and magnetic properties were studied for (Nd,Tb)2Fe14B nanoflakes prepared by surfactant-assisted high-energy ball milling (HEBM). Effects of ball-milling time on the c-axis crystallographic alignment, morphology, and magnetic properties of (Nd,Tb)2Fe14B nanoflakes were systematically investigated. X-ray diffraction (XRD) results indicate that the average crystal grain size of the nanoflakes decreases from 60 nm of 1 hour milling to 33 nm of 7 hours milling. The nanoflakes milled for 3 hours bear an average thickness of 100 nm and an average diameter of 2 μm leading to a high aspect ratio of 20. In addition, the intensity ratio of I(006)/I(105) indicates that the degree of c-axis crystal texture increases first, peaks for 3 hours, then drops with increasing the milling time. Meanwhile, the coercivity (Hc) of the nanoflakes drops monotonically. The remanence (Mr) of nanoflakes milled for 3 hours in the easy axis direction is 11 kG, while the Mr in the hard axis direction is 1.8 kG, indicating a strong magnetic anisotropy. The optimal magnetic properties of Mr of 11 kG, and Hc of 7 kOe, (BH)max of 24.7 MGOe have been achieved.

Temperature-dependent Faraday rotation and magnetization reorientation in cerium-substituted yttrium iron garnet thin films

We report on the temperature dependence of the magnetic and magneto-optical properties in cerium-substituted yttrium iron garnet (Ce:YIG) thin films. Measurements of the Faraday rotation as a function of temperature show that the magnetic easy axis of thin Ce:YIG films reorients from in-plane to out-of-plane on cooling below −100 °C. We argue that the temperature-dependence of the magnetostriction and magnetocrystalline anisotropy of Ce:YIG is the dominant factor contributing to the change in easy axis direction, and we describe the changes in the magneto-optical spectra with temperature.

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.

Magnetoelastic properties of epoxy resin based TbxHo0.9−xNd0.1 (Fe0.8Co0.2)1.93 particulate composites

Abstract TbxHo0.9−xNd0.1 (Fe0.8Co0.2)1.93 (0 ⩽ x ⩽ 0.40) particulate composites were prepared by embedding and aligning alloy particles in an epoxy matrix with and without a magnetic curing field. The magnetoelastic properties were investigated as functions of composition, particle volume fraction and macroscopic structure of the composite. The magnetic anisotropy compensation point was found to be around x = 0.25, where the easy magnetization direction (EMD) at room temperature was detected lying along ⟨ 1 1 1 ⟩ axis. The composite with ⟨ 1 1 1 ⟩ preferred orientation and pseudo-1-3 type structure was prepared under an applied magnetic field of 12 kOe. An enhanced magnetoelastic effect and large low-field magnetostriction λa, as high as 430 ppm at 3 kOe, were obtained for Tb0.25Ho0.65Nd0.1 (Fe0.8Co0.2)1.93 composite rod. The value of λa was of 72 % of its polycrystalline alloy (~595 ppm/3 kOe) although it only contained 30 vol.% of the alloy particles. This enhanced effect can be attributed to the larger λ111 (as compared to λ100), low magnetic anisotropy, easy magnetization direction (EMD) along the ⟨ 1 1 1 ⟩ axis and ⟨ 1 1 1 ⟩-textured orientation of the alloy particles as well as the chain-like structure of the composite. The good magnetoelastic properties of the composite, in spite of the fact that it contained only 30 vol.% of the alloy particles with light rare-earth Nd element in the insulating epoxy, would make it a potential material for magnetostriction application.

Magnetic anisotropy of polycrystalline high-temperature ferromagnetic MnxSi1-x ([formula omitted]) alloy films

A set of thin film MnxSi1-x alloy samples with different manganese concentration x≈0.44−0.63 grown by the pulsed laser deposition (PLD) method onto the Al2O3 (0001) substrate was investigated in the temperature range 4–300K using ferromagnetic resonance (FMR) measurements in the wide range of frequencies (f=7−60GHz) and magnetic fields (H=0−30kOe). For samples with x≈0.52−0.55, FMR data show clear evidence of ferromagnetism with high Curie temperatures TC∼300K. These samples demonstrate a complex magnetic anisotropy described phenomenologically as a combination of the essential second order easy plane anisotropy contribution and the additional fourth order uniaxial anisotropy contribution with easy direction normal to the film plane. The observed anisotropy is attributed to a polycrystalline (mosaic) structure of the films caused by the film-substrate lattice mismatch. The existence of extra strains at the crystallite boundaries initiates a random distribution of local in-plane anisotropy axes in the samples. As a result, the symmetry of the net magnetic anisotropy is axial with the symmetry axis normal to the film plane. The principal features of the observed anisotropy are explained qualitatively within the proposed microscopic model.

Calculated dependence of FePt damping on external field magnitude and direction

Near the Curie temperature (Tc), magnetic parameters including magnetization, anisotropy, and damping depend strongly on both temperature and length scale. This manifestation of renormalization theory is most readily seen in the case of magnetization where the magnitude of the atomic spin is largely unaffected by temperature, but the bulk magnetization vanishes at Tc. It has been previously argued that the Landau-Lifshitz-Gilbert damping parameter alpha exhibits a similar effect owing to its dependence on both atomic effects and magnon-magnon scattering, the latter having a strong length dependence. Here, we calculate, using an anisotropic exchange description of L10 FePt (Tc = 705 K), the damping (and other magnetic properties) dependence on temperature for FePt at length scales around 1.0 nm as appropriate for high temperature micromagnetic simulation. While the damping reduces as the applied field along the easy direction increases, it tends to increase as the field direction is changed to in-plane. The renormalized parameters are also calculated for higher and lower Tc (770K and 630K) by invoking the linear relationship between the exchange stiffness parameter and Curie temperature. This corresponds to doped and/or non-stoichiometric FePt and allows better understanding of the effects of varying anisotropy to exchange ratio.

XMCD study of the local magnetic and structural properties of microcrystalline NdFeB-based alloys

X-ray Magnetic Circular Dichroism (XMCD) technique was used to investigate local magnetic properties of microcrystalline Nd10.4Zr4.0Fe79.2B6.4 samples, oriented along either easy or hard magnetization direction. The Nd L 2,3 and Fe K edge XMCD spectra were measured at room temperature under a magnetic field of T. A very strong dependence of XMCD spectra on the sample orientation has been observed at the NdL 2,3-edges, whereas the Fe K-edge XMCD spectra are found to be practically isotropic. This result indicates that magnetic anisotropy of NdFeB-based alloys originates from the Nd sublattice. In addition, element selective magnetization curves have been recorded by measuring the intensity of XMCD signals as a function of an applied magnetic field up to T. To find a correlation between local and macroscopic magnetic properties of studied samples we compared these data with magnetization curves, measured by vibrating sample magnetometer up to T. Results are important for understanding the origin of high-coercivity state in NdFeB-based intermetallic compounds.

Magnetic Domain Structure and Magnetostriction of Fe-Ga Single Crystal Grown by the Czochralski Method

The magnetic domain structure on the (0 0 1) plane of an Fe 16.1 Ga 83.9 single crystal grown by the Czochralski method was observed by magneto-optic Kerr effect microscopy. In zero magnetic field, four different domain phases appeared, with magnetization in four kinds of '1 0 0 magnetic easy directions on the (0 0 1) plane. That is, the magnetic domain structure in zero field was composed of straight 90° domain walls and stair-like 180° domain walls. When a magnetic field was applied in the [0 1 0] direction, primarily 180° domain walls moved, whereas 90° domain walls did not. A striped domain structure composed of 90° domain walls was formed at a field of about 560 Oe, 180° domain walls having almost disappeared. A single domain structure was obtained by applying a field of about 1980 Oe. Magnetostriction in the [0 1 0] direction on the (0 0 1) plane was only about 10 ppm in a field of about 560 Oe and reached a saturation value of about 153 ppm at a field of about 1980 Oe. This magnetostrictive behavior contributes to the evolution of the magnetic domain structure.

Transport of underdamped active particles in ratchet potentials

We study the rectified transport of underdamped active noninteracting particles in an asymmetric periodic potential. It is found that the ratchet effect of active noninteracting particles occurs in a single direction (along the easy direction of the substrate asymmetry) in the overdamped limit. However, when the inertia is considered, it is possible to observe reversals of the ratchet effect, where the motion is along the hard direction of the substrate asymmetry. By changing the friction coefficient or the self-propulsion force, the average velocity can change its direction several times. Therefore, by suitably tailoring the parameters, underdamped active particles with different self-propulsion forces can move in different directions and can be separated.

Effect of Cu substitution on structural and hard magnetic properties of rapidly solidified Zr18Co82-xCux melt spun ribbons

The necessity to have rare earth free permanent magnets has driven the research efforts world over to explore the rare earth free compositions to make permanent magnets. The composition of Zr18Co82-xCux (x = 0–3) was chosen, melt spun followed by a detailed investigation on structural and magnetic properties. The melt spun ribbons obtained from these nominal compositions contained rhombohedral (R) Zr2Co11, orthorhombic (O) Zr2Co11 and fcc Co phases. The substitution of near atomic radius Cu for Co results in increase of O-Zr2Co11 phase. As a result, for an increase of Cu content from x = 0 to 3, the saturation magnetization (Ms) increases from 56 to 101emu/g, while the coercivity (Hc) decreases monotonously from 2.2 to 1.5 kOe. The easy magnetization direction lies along the plane of the ribbon. There is a significant change in the solidification morphology of the ribbons as a function of Cu content. It changes from dendritic to equiaxed and again to dendritic with increase in Cu addition.