Theoretical analysis of the anisotropy of the magnetization of the Ho^3＋ ion in holmium iron garnet single crystals

The spontaneous magnetization of the Ho^3＋ ion in holmium iron garnet （HoIG） single crystals in the temperature range of 4.2-294K along the directions [111], [110], and [100] are calculated, taking into account the effects of six magnetically inequivalent sites occupied by the Ho^3＋ ions based on the quantum theory. The calculated results show that the magnetization of the Ho^3＋ ion in HoIG is obviously anisotropic. The theoretical results ave in agreement with those of experiments. A primary interpretation of the anisotropy of magnetization of the Ho^3＋ ion in HoIG is put forward.     

Magnetic noise as the cause of the spontaneous magnetization reversal of RE–TM–B permanent magnets

The relation between the macroscopic spontaneous magnetization reversal (magnetic viscosity) of (NdDySm)(FeCo)B alloys and the spectral characteristics of magnetic noise, which is caused by the random microscopic processes of thermally activated domain wall motion in a potential landscape with uniformly distributed potential barrier heights, is found.     

Bohr–Weisskopf effect: influence of the distributed nuclear magnetization on hfs

Nuclear magnetic moments provide a sensitive test of nuclear wave functions, in particular those of neutrons, which are not readily obtainable from other nuclear data. These are taking added importance by recent proposals to study parity non-conservation (PNC) effects in alkali atoms in isotopic series. By taking ratios of the PNC effects in pairs of isotopes, uncertainties in the atomic wave functions are largely cancelled out at the cost of knowledge of the change in the neutron wave function. The Bohr–Weisskopf effect (B–W) in the hyperfine structure interaction of atoms measures the influence of the spatial distribution of the nuclear magnetization, and thereby provides an additional constraint on the determination of the neutron wave function. The added great importance of B–W in the determination of QED effects from the hfs in hydrogen-like ions of heavy elements, as measured recently at GSI, is noted. The B–W experiments require precision measurements of the hfs interactions and, independently, of the nuclear magnetic moments. A novel atomic beam magnetic resonance (ABMR) method, combining rf and laser excitation, has been developed for a systematic study and initially applied to stable isotopes. Difficulties in adapting the experiment to the ISOLDE radioactive ion beam, which have now been surmounted, are discussed. A first radioactive beam measurement for this study, the precision hfs of ¹²⁶Cs, has been obtained recently. The result is 3629.515(∼0.001) MHz. The ability of ABMR to determine with high precision nuclear magnetic moments in free atoms is a desideratum for the extraction of QED effects from the hfs of the hydrogen-like ions. We also point out manifestations of B–W in condensed matter and atomic physics. This revised version was published online in July 2006 with corrections to the Cover Date.     

Studying the effect of biaxial anisotropy on nonlinear magnetization oscillations accompanying the 90° pulsed magnetization process in ferrite–garnet films with easy-plane anisotropy

Time dependences of the azimuthal component of the torque T _φ(t) acting on magnetization are calculated to understand the nature of the delayed magnetization acceleration effect observed during the 90° pulsed magnetization of real ferrite–garnet films, in which biaxial anisotropy exists alongside with in-plane anisotropy. A calculation technique based on analyzing an operating point trajectory is used. Calculations show that if the effective anisotropy field H _K2 is comparable to the magnetizing pulse amplitude H _ma, abruptly ascending regions at characteristic times t* in curves T _φ(t) arise, in the limit of which nonlinear magnetization oscillations formed. The shape of these regions depends weakly on the magnetizing pulse front duration τ_f. This explains the reason of the weak dependence of the nonlinear magnetization oscillations on duration of the magnetizing pulse front. Calculations also show that the main features of the delayed acceleration effect are less clear upon an increase of the pulse amplitude: the behavior of curves T _φ(t) becomes smoother near times t*, and an increase in the pulse front duration is accompanied by a stronger drop in the intensity of magnetization oscillations.     

The Hamilton equations of ferrohydrodynamics with the Landau–Lifshitz equation for magnetization

A system of Hamilton equations of motions for the ideal nonconducting magnetic fluid with the Landau–Lifshitz equation for the magnetization vector is constructed based on the functional of total energy derived in this work and the Poisson bracket method.     

Dependence of the irreversible magnetization in Cu1−xCdxFe2O4 on the magnetizing field

The mean potential difference of Barkhausen jumps (V_B) and the frequency of Barkhausen jumps (F_B) were studied for polycrystalline samples of Cu_1−xCd_xFe₂O₄, where X = 0, 0.1, 0.2, 0.3 and 0.5. Both V_B and F_B have been measured against the magnetizing field. CuFe₂O₄ shows the highest values of V_B and F_B. These values decrease with an increase of cadmium content. Also the effect of the magnetizing frequency on V_B has been studied. V_B vanishes at certain values of the magnetizing frequency. The magnetizing frequency at which V_B vanishes decreases with the increase of cadmium content. The behaviour of V_B and F_B is attributed to the change of the magnetic ordering of the sample and to the effect of eddy current on the domain wall motion.     

Analysis of nonlinearity of magnetization of YBa2Cu3O7 − x by the magnetic field modulation method

Temperature dependences of the magnetization harmonics of YBa₂Cu₃O_{7 ? x} monodomain samples are studied experimentally at temperatures of 77–120 K. It is found that nonlinearity of magnetization of YBa₂Cu₃O_{7 ? x} (higher harmonics generation) is observed up to temperatures T = 103–112 K, which are much higher than the superconducting transition temperature of this compound. At the same temperatures, the temperature dependence of resistivity begins to deviate from linearity. The observed singularity of the magnetization of YBa₂Cu₃O_{7 ? x} is associated with the emergence of a pseudogap state in this compound.     

Kinetics of the magnetization reversal in permalloy–niobium microstrips under the effect of a pulsed magnetic field and an electric current

The kinetics of magnetization reversal in bilayer permalloy–niobium microstrips under the effect of both a pulsed magnetic field and an electric current has been experimentally studied. These two cases turn out to be fundamentally different in the types of arising magnetic structures and in the dynamic characteristics of the processes. Such difference is especially striking at low temperatures. An anomalously high rate of the processes under study is observed. According to the suggested qualitative explanation, this effect is due to nonlinear excitations appearing in front of the moving domain wall if the applied electric current lowers the barriers for its motion. For achieving the final conclusions, more accurate quantitative analysis is needed.     

On the manifestation of effect of delayed acceleration of the transient process during 180° pulsed magnetization reversal of real ferrite–garnet films with planar anisotropy

The regime of 180° pulsed magnetization reversal of ferrite–garnet films with planar anisotropy in the region of external fields, in which the mechanism of uniform rotation of the magnetization operates, is investigated for the first time. An analysis of the numerical solutions of the Landau–Lifshitz equation and the calculated and experimentally obtained signals showed that the presence of biaxial anisotropy in real ferrite–garnet films leads to the fact that at finite duration of the remagnetizing pulse front the initial slow rotation at definite moment of time is sharply accelerated so that over an interval of ~0.7 ns the azimuthal angle changes from 45° to the equilibrium value (160°–170°). As a result, appearence of the nonlinear damped oscillations of magnetization with a fundamental harmonic period of ~1.5 ns become possible.     

Multi-step magnetization of the Ising model on a Shastry-Sutherland lattice: a Monte?Carlo simulation

The magnetization behaviors and spin configurations of the classical Ising model on a Shastry-Sutherland lattice are investigated using Monte Carlo simulations, in order to understand the fascinating magnetization plateaus observed in TmB(4) and other rare-earth tetraborides. The simulations reproduce the 1/2 magnetization plateau by taking into account the dipole-dipole interaction. In addition, a narrow 2/3 magnetization step at low temperature is predicted in our simulation. The multi-step magnetization can be understood as the consequence of the competitions among the spin-exchange interaction, the dipole-dipole interaction, and the static magnetic energy.     

Magnetic anisotropy and magnetization reversal of ultrathin iron films with in-plane magnetization on Si（111） substrates

The magnetic anisotropy and magnetization reversal of single crystal Fe films with thickness of 45 monolayer (ML) grown on Si(111) have been investigated by ferromagnetic resonance (FMR) and vibrating sample magnetometer (VSM). Owing to the significant modification of the energy surface in remanent state by slight misorientation from (111) plane and a uniaxial magnetic anisotropy, the azimuthal angular dependence of in-plane resonance field shows a six-fold symmetry with a weak uniaxial contribution, while the remanence of hysteresis loops displays a two-fold one. The competition between the first and second magnetocrystalline anisotropies may result in the switching of in-plane easy axis of the system. Combining the FMR and VSM measurements, the magnetization reversal mechanism has also been determined.     

Vanadium-induced decrease in the magnetization of a VxCo1−x alloy film on the W(110) surface

The magnetic and structural properties of a series of V_xCo_1?x alloy films prepared in a variety of compositions on a W(110) surface were investigated using spin-resolved photoemission spectroscopy (SRPES) and low-energy electron diffraction (LEED) measurements. The epitaxial structures of the films were preserved over all V concentrations, despite the observation of a structural phase transition (SPT: hcp/bcc at x = 0.38), which was apparent from the LEED images. A magnetic phase transition (MPT) from ferromagnetic to paramagnetic occurred in the Co-rich region at x = 0.38. The SPT (from hcp and bcc) and MPT (from ferromagnetic to paramagnetic) were clearly correlated at x = 0.38, possibly due to changes in the electronic and magnetic structures of the valence band, as monitored by SRPES and LEED. The magnetization in the V_xCo_1?x alloy films on a W(110) surface varied systematically with the V concentration, and correlations between the structural changes and magnetic properties were revealed using SRPES and LEED.     

Investigation of spontaneous magnetization of coupled 2×2 superconducting π ring array

We present the theoretical investigation of spontaneous magnetization of a coupled 2×2 πring array. It is indicated by free energy calculation that the system has the lowest energy when the four π rings have the full antiparallel configuration. Furthermore, the numerical evaluation results show that the system which favours full antiparallel spontaneous magnetization is a quantum effect deriving from the phase cohering of the superconducting quantum wavefunctions in the four superconducting rings through the shared Josephson junctions.     

Separation of the contributions to the magnetization of Tm1 − x Yb x B12 solid solutions in steady and pulsed magnetic fields

The magnetization of substitutional Tm_{1 ? x} Yb _x B₁₂ solid solutions is studied in the composition range 0 < x ≤ 0.81. The measurements are performed at low temperatures (1.9–300 K) in steady (up to 11 T) and pulsed (up to 50 T, pulse duration of 20–100 ms) magnetic fields. An analysis of the experimental data allowed the contributions to the magnetization of the paramagnetic phase of the Tm_{1 ? x} Yb _x B₁₂ compounds to be separated. These contributions include a Pauli component, which corresponds to the response of the heavy-fermion manybody states that appears in the energy gap in the vicinity of the Fermi level (density of states (3?4) × 10²¹ cm^?3 meV^?1), and a contribution with saturation in high magnetic fields attributed to the localized magnetic moments ((0.8–3.7)μ_B per unit cell) of the nanoclusters formed by rare-earth ions with an antiferromagnetic interaction.     

Mössbauer and magnetization studies of iron oxide nanocrystals

Monodisperse iron oxide nanocrystals have been produced following non-hydrolytic, thermal decomposition routes. Spherically shaped particles with diameter of 4 and 12 nm and cubic shaped particles with an edge length of 9 nm have been studied. The particles have been shown to consist of mainly maghemite. A reduction of the saturation magnetic hyperfine field is observed for the 4 nm particles as compared to the corresponding bulk value. The anisotropy energy determined from the temperature variation of the magnetic hyperfine field was strongly enhanced for the 4 nm particles.     

90° pulsed magnetization of ferrite-garnet films with easy-plane anisotropy

The process of pulsed 90° magnetization of ferrite-garnet films was studied. These films, in addition to easy-plane anisotropy, have biaxial anisotropy in the film plane with an effective field H _K2 ? 40–55 Oe. the pulsed magnetization curve contains two portions separated by a kink observed at a field pulse amplitude H _p=H _p ^* ? 16–18 Oe. An analysis of the magnetization signals showed that the restoring torque, which is mainly caused by biaxial-anisotropy forces, is overcome in fields H _p ≥ H _p ^* and that magnetization rotation occurs. In fields H _p < H _p ^* , the magnetization vector rotates at the initial stage only and the angle of rotation ?_in is less than 25°–26°. The field H _p ^* and angle ?_in are calculated. The results of the calculations are confirmed by experimental data. In fields H _p > H _p ^* , the process of magnetization is accompanied by oscillations of the magnetization vector. In contrast to free magnetization oscillations, these oscillations are nonlinear and the frequency of the first harmonic (≈5 × 10⁸ Hz) is much lower than that for free oscillations, (7–12) × 10⁸ Hz. Oscillations are excited at a pulse rise time of ≈6 ns.     

Discontinuity of the magnetization in one-dimensional 1/¦x−y¦2 Ising and Potts models

Results from percolation theory are used to study phase transitions in one-dimensional Ising andq-state Potts models with couplings of the asymptotic formJ _x,y const/¦x–y¦². For translation-invariant systems with well-defined lim _x x ² J _x =J ⁺ (possibly 0 or ) we establish: (1) There is no long-range order at inverse temperatures withJ ⁺1. (2) IfJ ⁺>q, then by sufficiently increasingJ ₁ the spontaneous magnetizationM is made positive. (3) In models with 0<J ⁺< the magnetization is discontinuous at the transition point (as originally predicted by Thouless), and obeysM( _c )1/( _c J ⁺)^1/2. (4) For Ising (q=2) models withJ ⁺<, it is noted that the correlation function decays as xy()c()/|x–y|² whenever< _c . Points 1–3 are deduced from previous percolation results by utilizing the Fortuin-Kasteleyn representation, which also yields other results of independent interest relating Potts models with different values ofq.     

Analysis of 90° pulsed magnetization signals of ferrite-garnet films with easy plane-type anisotropy

The results from a numerical analysis of 90° pulsed magnetization signals of ferrite-garnet films with easy plane-type anisotropy are discussed. The possibility of nonlinear magnetization oscillations occurring at a magnetizing pulse front several times greater than the oscillation period is shown. The results from the calculations describe the actual shape of the longitudinal and transverse signals quite well. The calculated values of the oscillation frequency (∼500 MHz) are also in good agreement with the experimental data.     

Probing the magnetization switching with in-plane magnetic anisotropy through field-modified magnetoresistance measurement

Effective probing current-induced magnetization switching is highly required in the study of emerging spin-orbit torque(SOT)effect.However,the measurement of in-plane magnetization switching typically relies on the giant/tunneling magnetoresistance measurement in a spin valve structure calling for complicated fabrication process,or the non-electric approach of Kerr imaging technique.Here,we present a reliable and convenient method to electrically probe the SOT-induced in-plane magnetization switching in a simple Hall bar device through analyzing the MR signal modified by a magnetic field.In this case,the symmetry of MR is broken,resulting in a resistance difference for opposite magnetization orientations.Moreover,the feasibility of our method is widely evidenced in heavy metal/ferromagnet(Pt/Ni₂₀Fe₈₀ and W/Co₂₀Fe₆₀B₂₀)and the topological insulator/ferromagnet(Bi₂Se₃/Ni₂₀Fe₈₀).Our work simplifies the characterization process of the in-plane magnetization switching,which can promote the development of SOT-based devices.