Easy-plane Magnetic Anisotropy Research Articles

Magnetic properties of the Ce 2Fe 17−xMn x helical magnets up to high magnetic fields

Magnetic properties of the Ce 2Fe 17− x Mn x , x=0–2, alloys in magnetic fields up to 40 T are reported. The compounds with x=0.5–1 are helical antiferromagnets and those with 1< x⩽2 are helical ferromagnets or helical antiferromagnets at low and high T, respectively. Mn ions in the system carry average magnetic moment of 3.0±0.2 μ B that couple antiparallelly to the Fe moments. Easy-plane magnetic anisotropy in the Ce 2Fe 17− x Mn x compounds weakens upon substitution of Mn for Fe. The absolute value of the first anisotropy constant in the Ce 2Fe 17− x Mn x helical ferromagnets decreases slower with increasing temperature than that calculated from the third power of the spontaneous magnetization. Noticeable magnetic hysteresis in the Ce 2Fe 17− x Mn x , x=0.5–2, helical magnets over the whole range of magnetic fields reflects mainly irreversible deformation of the helical magnetic structure during the magnetization of the compounds. A contribution from short-range order (SRO) magnetic clusters to the magnetic hysteresis of the helical magnets has been also estimated.

Evidence for magnetic state of uranium in U 2(Fe 1− xCo x) 13.6Si 3.4

Single crystals of solid solutions U 2(Fe 1− x Co x ) 13.6Si 3.4 (0 ≤ x ≤ 1) having the hexagonal Th 2Ni 17 crystal structure were grown by a Czochralski method. Magnetization measurements along the principal axes reveal the easy-plane magnetic anisotropy in compounds with x up to 0.95, whereas terminal compound U 2Co 13.6Si 3.4 has the uniaxial anisotropy. Magnitudes of the anisotropy constants K 1 and K 2 for x up to ∼0.8 are high enough to suggest a U contribution to the anisotropy, i.e., a magnetic state of U. The observed rapid weakening of the anisotropy and the change of its type at highest Co content are attributed to the 3d-metal sublattice, namely to the considerable change of c/ a ratio at the Fe Co substitution in the “dumbbells”.

Magnetic properties of U 2(Fe 1−xCo x) 13.6Si 3.4 single crystals

Magnetization was measured on single crystals U 2(Fe 1− x Co x ) 13.6Si 3.4 (0⩽ x⩽1) grown by Czochralski method. Compounds with x up to 0.95 exhibit the easy-plane magnetic anisotropy. The anisotropy constants K 1 and K 2 for x up to ∼0.8 are high enough to suggest a U contribution to the anisotropy, i.e., a magnetic state of U. Both K 1 and K 2 behave non-monotonously with increasing x, K 2 changes sign at x=0.3. We suppose that U becomes non-magnetic above x=0.9. The weakening of the anisotropy and the change of its type at high Co content are attributed to the 3d-metal sublattice.

A Single-Chain Magnet Formed by a Twisted Arrangement of Ions with Easy-Plane Magnetic Anisotropy

A unique "single-chain quantum magnet" was formed by an alternating arrangement of high-spin FeII/low-spin FeIII ions. Although the predominant spin-carrier components (high-spin FeII) possess easy-plane magnetic anisotropy (D > 0), twisted arrangement of easy-planes along the chain axis defines a novel class of one-dimensional Ising system.

Phase separation effects in charge-ordered Pr 0.5 Ca 0.5 MnO 3 thin film

Compressed Pr0.5Ca0.5MnO3 films (250nm) deposited on LaAlO3 have been studied by Electron Spin Resonance technique under high frequency and high magnetic field. We show evidences for the presence of a ferromagnetic phase (FM) embedded in the charge-order phase (CO), in form of thin layers which size depends on the strength and orientation of the magnetic field (parallel or perpendicular to the substrate plane). This FM phase presents an easy plane magnetic anisotropy with an anisotropy constant 100 times bigger than typical bulk values. When the magnetic field is applied perpendicular to the substrate plane, the FM phase is strongly coupled to the CO phase whereas for the parallel orientation it keeps an independent ferromagnetic resonance even when the CO phase becomes antiferromagnetic.

Magnetic properties of various martensitic phases in Ni-Mn-Ga alloy

Single crystalline Ni/sub 48.7/Mn/sub 29.1/Ga/sub 22.2/ sample was studied in the temperature range 110 K-425 K. Magnetic properties of four different structure phases were measured at different temperatures. The magnetic anisotropies of the different phases were determined from magnetization curves. At room temperature, the structure is five-layered modulated tetragonal martensite with c/a<1 and uniaxial anisotropy K/sub u1/=1.6/spl times/10/sup 5/ J.m/sup -3/. Below 251 K, the structure is orthorhombic c<b<a with c being the easy magnetization axis. The magnetic anisotropy energy is 2.1/spl times/10/sup 5/ J.m/sup -3/ between c and a. At 218 K, the orthorhombic phase transforms to the tetragonal phase with c/a>1. A single variant of low-temperature martensite was obtained by cooling in magnetic field 1.4 T. At 173 K, the sum of magnetic anisotropy constants is K/sub 1/+K/sub 2/=1.5/spl times/10/sup 5/ J.m/sup -3/ assuming an easy-plane magnetic anisotropy.

Amorphous CoFeCrSiB ribbons for strain sensing applications

Magnetoelastic properties of amorphous Co 71− x Fe x Cr 7Si 8B 14 ribbons, with 2⩽ x⩽12, were investigated. The magnetostriction constant λ s changes linearly from −0.8×10 −6 to +4.0×10 −6 with increasing x. Stress-annealing at 350°C induces an easy plane magnetic anisotropy perpendicular to the ribbon axis. Magnetization reversal takes place by the moment rotation and the magnetizing curves are linear up to the anisotropy field, which is proportional to the stress applied during annealing. Simple strain sensors based on these materials show practically constant sensitivity nearly up to the mechanical strength of the ribbon and acceptable reproducibility of measurements.

Nondestructive testing with the help of hysteresis-free magneto-optical films

Advantages of hysteresis-free ferrite-garnet magneto-optical films with the easy-plane magnetic anisotropy over uniaxial magnetic films in nondestructive testing of various magnetic materials and devices based on such materials are considered.

Temperature dependence of magnetic anisotropy of La0.8Ca0.2MnO3 epitaxial thin films

Magnetic anisotropy of epitaxial La0.8Ca0.2MnO3(LCMO) thin films grown by pulsed laser deposition has been studied as a function of temperature and lattice strain. Pseudomorphic growth on (001) SrTiO3 substrates imposes an in-plane tensile stress on the LCMO films, which produces an easy-plane magnetic anisotropy in the growth plane, accompanied by a weak biaxial anisotropy in the easy plane. In contrast growth on (001) LaAlO3 substrates produces an in-plane compressive stress, which leads to an out-of-plane uniaxial easy axis. The observed behavior indicates the presence of a positive magnetostriction, and that the anisotropy energy is dominated by the epitaxial strain induced effects. Uniaxial magnetic anisotropy constants of 250 and 500 Å LCMO films have been determined by fitting the magnetization curves for temperatures between 5 and 200 K, and magnetostriction constants have been estimated subsequently.

Instability of a one-dimensional quantum antiferromagnet under magnetic anisotropy

It is shown by using the exact quantum-mechanical solution that a one-dimensional antiferromagnetic Heisenberg spin chain is unstable to the emergence of an easy-plane magnetic anisotropy in a real three-dimensional crystal. It is shown that the magnetic anisotropy is due to a Jahn–Teller type effect, i.e., a strong spin–lattice coupling. A change in the equilibrium position of ligands induces magnetic anisotropy in the spin chain.

Easy-Plane Magnetic Anisotropy Induced by Stress-Annealing in Finemet-Type Materials

It is shown that annealing under stress of FINEMET-type metallic glass ribbon (FeCuNbSiB) induces magnetic anisotropy of an easy-plane type (cross-section of the ribbon). This conclusion has been drawn analyzing experimental results obtained by means of Kerr-effect (domain structure) and Mossbauer spectroscopy operating in the so-called magic angle configuration which allows us to calculate all three spatial components of magnetiza tion. Additionally, it is also shown that no crystallographic texture is created in the sample after stress-annealing, the feature which would have been an origin of the observed anisotropy. PACS numbers: 75.30.Gw, 75.50.Kj, 75.60.Ch

Pulsed laser deposition epitaxial growth and magnetic properties of TbCo 2 and TbFe 2 ultra-thin films

TbCo 2 and TbFe 2 single crystal thin films have been grown for the first time by pulsed laser deposition. Epitaxy parallel to the (111) plane was initiated on a W(110) buffer layer deposited on a Al 2O 3(112̄0) substrate. W or Cr capping layers were then grown to prevent from oxidation. RHEED and grazing incidence X-ray diffraction data give evidence for new epitaxial relationships relative to fcc(111)/bcc(110) interface: [11̄0]TbFe 2 ‖[11̄0]W and [112̄]TbFe 2 ‖[001]W. The morphology of the films has been analysed through AFM. A 3D growth mode was observed for a deposition temperature of 500°C. At low effective thickness (3–4 nm), widely scattered islands have a mean size of 200 nm. For 6–10 nm thick films, large islands (up to 1 μm diameter) are present. In this range, the films exhibit a 0.3% compressive distortion along the [111] axis perpendicular to the film plane. A large easy plane magnetic anisotropy is measured in the large island films which cannot be entirely attributed to dipolar or magneto-crystalline volume contributions. This suggests the existence of a magneto-elastic anisotropy contribution due to the out-of-plane strain. A model calculation for this term is in good agreement with the experimental anisotropy data.

Neutron scattering determination of the crystal field parameters in ErCu 4Al 8 and ErFe 4Al 8 intermetallics

An inelastic neutron scattering experiment has been performed in order to determine the crystal field potential acting at the rare earth site in the paramagnetic phase of ErCu 4Al 8 and ErFe 4Al 8 intermetallic compounds. The profile refinement of the spectra measured at different temperatures, and experimental information on the electric field gradient available in the literature, allow a reliable estimate of the parameters for the tetragonal crystal field. Positive values of the lowest order term B 2 0 suggest an easy plane magnetic anisotropy of the Er sublattice, but the higher order terms could play an important role in determining the magnetisation direction.

Perpendicular Magnetic Anisotropy in Ultrathin Fe (110) Films on Cr (110)

ABSTRACTIn contrast to Fe(110) -films on W(110), which are magnetized always in the plane as a result of easy-plane magnetic surface anisotropies (MSA), Fe(110) -films on Cr(110) show perpendicular magnetization up to a thickness of roughly 3 Monolayers, as a result of a perpendicular MSA of the Fe(110)/Cr/(110) interface. Acoordingly, Fe(110) -films on W(110), covered with Cr(110), show asymmetric MSA, the easy-plane mSA of the W(110)/Fe(110) -interface opposing the perpendicular one of the Fe(110)/Cr(110) -interface. It turns out that MSA is asymmetric too in Fe(110) films on W(110) covered by Cu, Ag, Au or UHV.

Dynamics of solitons in segnetomagnets with easy plane magnetic anisotropy

Nonlinear waves in systems with ferroelectric and ferromagnetic properties (segnetomagnets) are studied. The magnetic sub-system is assumed to have easy plane anisotropy. If the ferroelectric subsystem is homogeneous, then a magnetic soliton is described by the double sG equation. The interaction of ferroelectric and magnetic solitons is investigated. The parameters of coupled states of ferroelectric and magnetic solitons are calculated.

Rotation alignment for measuring easy-plane magnetic anisotropy

A new method for preparing aligned specimens of polycrystalline materials with easy-plane magnetization has been developed in which a powder sample mixed with epoxy is rotated in an applied field. X-ray diffraction and magnetization measurements show that a significant improvement has been achieved in aligning the specimens with this method. For a Y 2Co 14B specimen prepared by this method, a peak corresponding to the anisotropy field was observed in the second derivative of the room-temperature magnetization curve at a magnetic field of 2.8 T. Computer simulation of the magnetization process shows that there is a peak in the second derivative curve for a well-aligned easy-plane anisotropy sample.

Perpendicular magnetic anisotropy of Co-Au multilayers induced by interface sharpening.

Co-Au multilayers with Co layer thicknesses between 22 and 5 \AA{}A, prepared by ion-beam sputtering, have an easy-plane magnetic anisotropy. Their saturation magnetization indicates the presence of diffuse interfaces, caused by ion-beam mixing. Annealing of the multilayers at 250-300\ifmmode^\circ\else\textdegree\fi{}C leads to a perpendicular anisotropy for Co thicknesses below about 14 \AA{}A. This effect is attributed to a stronlgy enhanced interface anisotropy, which is due to sharpening of the interfaces as revealed by x-ray diffraction.

Spatial structures of the intermediate state between superconductivity and ferromagnetism. II. Easy-plane magnetic anisotropy

For pt.I see ibid, vol.19, no.33, p.6505 (1986). The authors use a generalised Ginzburg-Landau mean-field model to examine possible structures of the intermediate state of ferromagnetic superconductors which combine magnetisation and superconductivity. A new alternating vortex lattice structure is proposed for materials with an easy-plane magnetic anisotropy. One component of the magnetisation is periodically divided into large oppositely polarised domains. Each domain contains one row of vortex (anti-vortex) lines. The magnetisation does not vanish in the Bloch walls, instead it is perpendicular to the magnetisation in the domains and has an oscillating structure because of the interaction with superconductivity. It is sinusoidally oscillating and not a spiral wave independent of any anisotropy in the easy plane. The fraction of the magnetisation which oscillates is substantial. This new structure agrees better with the properties of the intermediate state of ErRh4B4 than previous structures.

Spatial structures of the intermediate state between superconductivity and ferromagnetism. I. Easy-axis magnetic anisotropy

For pt.I see ibid, vol.19, no.33, p.6505 (1986). The authors use a generalised Ginzburg-Landau mean-field model to examine possible structures of the intermediate state of ferromagnetic superconductors which combine magnetisation and superconductivity. A new alternating vortex lattice structure is proposed for materials with an easy-plane magnetic anisotropy. One component of the magnetisation is periodically divided into large oppositely polarised domains. Each domain contains one row of vortex (anti-vortex) lines. The magnetisation does not vanish in the Bloch walls, instead it is perpendicular to the magnetisation in the domains and has an oscillating structure because of the interaction with superconductivity. It is sinusoidally oscillating and not a spiral wave independent of any anisotropy in the easy plane. The fraction of the magnetisation which oscillates is substantial. This new structure agrees better with the properties of the intermediate state of ErRh4B4 than previous structures.

A white brazing solder

Magnetization of a Ho2Fe14Si3 single crystal was measured in a steady magnetic field of up to 9 T and in pulsed fields of up to 60 T applied along the principal axes. Ho2Fe14Si3 is a ferrimagnet below TC = 480 K, has a spontaneous magnetic moment of about 8 μB/f.u. (at T = 4.2 K) and exhibits a large easy-plane magnetic anisotropy. There is also a certain anisotropy within the basal plane, the b axis [120] being the easy-magnetization direction. In fields applied along the a and b axes field-induced first-order phase transitions are observed at 29 T and at 22 T, respectively. Along the easy axis b we observe also an S-shaped anomaly at about 47 T, which does not correspond to a phase transition. A simple model predicts that the two observed first-order transitions are the only ones taking place in Ho2Fe14Si3; the magnetization should subsequently grow continuously and arrive at saturation at ∼100 T. This is in stark contrast to the behavior of the parent compound Ho2Fe17, where as many as three sequential first-order transitions are expected for H||b. The reason for the disparity is that the basal-plane anisotropy constant KHo is at least one order of magnitude smaller in Ho2Fe14Si3 than it is in Ho2Fe17.