共查询到20条相似文献,搜索用时 31 毫秒
1.
《Journal of magnetism and magnetic materials》1987,66(3):337-344
We present the electron spin resonance measurements in powdered samples of the intermetallic compound YCo3 in Q, K and X microwave bands. The grains of the powdered samples were magnetically aligned in a static magnetic field. The resonant spectra consist of the lines connected with localized and unlocalized magnetic moments. We were able to describe only the part of the spectrum associated with localized moments and to estimate the anisotropy field at the room temperature. Next we present the magnetization data by the pulse magnetometer. The anisotropy field which was determined from these data is much larger than that from ferromagnetic resonance. We suggested a possible reason for such discrepancy. 相似文献
2.
We solve rigorously the equilibrium equations for a system of two classical magnetic moments in a transverse field, coupled by Dzialoshinskii antisymmetric exchange, as well as isotropic and anisotropic exchange, in the presence of uniaxial second order anisotropy, whose easy axis is parallel to the Dzialoshinskii D vector. The system allows for planar, axial and conical phases (the latter were never reported before). In all the possible phases the equilibrium equations allow for an exact solution, without introducing any approximation steaming from the assumption of some definite hierarchy of the interaction strengths. We discuss the application of this model to the low field-low temperature transverse magnetization curves reported for some diamagnetically substituted hexagonal ferrites, paying special attention to the conical phases. 相似文献
3.
C. Ederer 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,71(3):349-354
In this paper we present an analysis of the magnetic toroidal moment
and its relation to the various structural modes in R3c-distorted
perovskites with magnetic cations on either the perovskite A or B
site. We evaluate the toroidal moment in the limit of localized
magnetic moments and show that the full magnetic symmetry can be taken
into account by considering small induced magnetic moments on the
oxygen sites. Our results give a transparent picture of the possible
coupling between magnetization, electric polarization, and toroidal
moment, thereby highlighting the different roles played by the various
structural distortions in multiferroic BiFeO3 and in the recently
discussed isostructural material FeTiO3, which has been predicted
to exhibit electric field-induced magnetization switching. 相似文献
4.
Fillipi Klos Rodrigues de Campos Fernando Zanella C. A. Dartora 《Brazilian Journal of Physics》2017,47(2):151-156
It is demonstrated that the coexistence of superconductivity and magnetic ordering, occurring, for instance, in iron-based pnictides and uranium compounds, is not forbidden by classical Maxwell’s equations and London-type equations. It predicts simply that internal magnetization is allowed but localized magnetic moments are screened at distances of the order of the London penetration depth. A microscopic theory is considered for the case of ferromagnetic ordering, described in simple terms by electron-magnon coupling. For the sake of simplicity, we assume that itinerant electrons are not responsible for the magnetic ordering, but interact with phonon and magnon excitations, leading to an alternative Cooper pair channel. The temperature dependence and the isotope effect of the superconducting gap is also analysed. 相似文献
5.
The equilibrium orientations of magnetic moments that correspond to various values and directions of the biasing field are
found in a set of magnetic films with cubic crystalline anisotropy and uniaxial induced anisotropy. The films are coupled
by exchange interaction of the antiferromagnetic type. Field intervals are established where noncollinear and bistability
states causing orientational phase transitions and hysteresis exist. Ninety degree magnetization switching (per switching
cycle) of the magnetic moments of the films, as well as an orientational phase transition of bifurcation character, is discovered.
Hysteresis loops for 180° in-plane magnetization switching are constructed. 相似文献
6.
Wilhelm F Poulopoulos P Ceballos G Wende H Baberschke K Srivastava P Benea D Ebert H Angelakeris M Flevaris NK Niarchos D Rogalev A Brookes NB 《Physical review letters》2000,85(2):413-416
The magnetic moments in Ni/Pt multilayers are thoroughly studied by combining experimental and ab initio theoretical techniques. SQUID magnetometry probes the samples' magnetizations. X-ray magnetic circular dichroism separates the contribution of Ni and Pt and provides a layer-resolved magnetic moment profile for the whole system. The results are compared to band-structure calculations. Induced Pt magnetic moments localized mostly at the interface are revealed. No magnetically "dead" Ni layers are found. The magnetization per Ni volume is slightly enhanced compared to bulk NiPt alloys. 相似文献
7.
A. M. Shutyĭ 《Physics of the Solid State》2008,50(12):2275-2284
Based on a numerical solution of the equations of motion found over a wide range of frequencies of an alternating magnetic field, the nonlinear precession dynamics of magnetization are studied in thin-film structures of the (100) type with a stripe domain structure in a perpendicular bias field. The conditions are determined under which high-amplitude regular and chaotic dynamic regimes occur. Bifurcational variations in the precession of coupled magnetic moments and dynamic-bistability states are detected. The specific features of the spectrum of Lyapunov exponents and of time analogs of Poincaré cross sections of trajectories in chaotic regimes are considered. 相似文献
8.
We investigate the stability of the collinear ferromagnetic state in kinetic exchange models for (III,Mn)V semiconductors with randomly distributed Mn ions. Our results suggest that noncollinear ferromagnetism is common to these semiconductor systems. The instability of the collinear state is due to long-range fluctuations involving a large fraction of the localized magnetic moments. We address conditions that favor the occurrence of noncollinear ground states and discuss unusual behavior that we predict for the temperature and field dependence of its saturation magnetization. 相似文献
9.
Spin-Fermion systems which obtain their magnetic properties
from a system of localized magnetic moments being coupled to
conducting electrons are considered. The dynamical degrees of freedom are spin-s
operators of localized spins and spin-1/2 Fermi operators of
itinerant electrons. Renormalized spin-wave theory, which accounts for the magnon-magnon interaction,
and its extension are developed to describe the two ferromagnetic phases in
the system: low temperature
phase 0 < T < T*, where all electrons contribute the ordered ferromagnetic
moment, and high temperature phase T* < T < T
C
, where only localized spins form
magnetic moment.
The magnetization as a function of temperature is calculated. The theoretical predictions are utilize
to interpret the experimentally measured magnetization-temperature curves of UGe2. 相似文献
10.
We present results of a Monte Carlo study over the ferromagnetism of Co-doped ZnO. The magnetic interaction has the form of the donor impurity band exchange model, where the Co magnetic moments are exchange coupled to band electrons. These are assumed to occupy large hydrogenic orbitals and originate from shallow intrinsic ZnO defects. A number of parameters of this model remain uncertain and here we investigate the dependence of the Curie temperature on the strength of the magnetic coupling. We find an unusual concave upward shape in the magnetization curves consistent with other Monte Carlo studies for dilute systems and we predict high temperature ferromagnetism for sufficiently strong coupling. 相似文献
11.
B.M. Letfulov 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(2):195-203
This paper gives a simplified model of the double exchange which is a kind of indirect exchange interaction between localized
magnetic moments. The presented model is solved exactly in the case of infinite - dimensional space. Equations for single-particle
Green's function and magnetization of the localized spins subsystem are obtained. It is shown that our simple double exchange
model reveals an instability to the ferromagnetic ordering of localized moments. Magnetic and electric properties of this
system on Bethe lattice with are investigated in detail.
Received: 24 January 1997 / Revised: 14 February 1997 / Received in final form: 18 August 1997 / Accepted: 25 August 1997 相似文献
12.
We report an additional reversal mechanism of magnetic vortex cores in nanodot elements driven by currents flowing perpendicular to the sample plane, occurring via dynamic transformations between two coupled edge solitons and bulk vortex solitons. This mechanism differs completely from the well-known switching process mediated by the creation and annihilation of vortex-antivortex pairs in terms of the associated topological solitons, energies, and spin-wave emissions. Strongly localized out-of-plane gyrotropic fields induced by the fast motion of the coupled edge solitons enable a magnetization dip that plays a crucial role in the formation of the reversed core magnetization. This work provides a deeper physical insight into the dynamic transformations of magnetic topological solitons in nanoelements. 相似文献
13.
The origin of localized magnetic moments formation in metals is investigated theoretically using a self-consistent local spin density molecular cluster approach. Clusters with up to 55 atoms are employed to describe isolated impurity local moment behavior in the cases of Fe and Fe. Densities of states and spin magnetic moments were determined and compared with results of spectroscopic (notably photoemission) and magnetization measurements, respectively. In the case of a noble metal host, the spin magnetization density is found to be highly localized around the Fe site; the iron moment is ≈ 3.9μB and the polarization of the host Ag atoms is small. In the case of a transition metal host, the iron moment is ≈ 3.2 μB but here the strong hybridization of the Fe-3d and Pd-4d states results in a large induced magnetic moment in the host PD metal — in essential agreement with experiment for this giant moment system. 相似文献
14.
Yoshii S Yamamoto T Hagiwara M Michimura S Shigekawa A Iga F Takabatake T Kindo K 《Physical review letters》2008,101(8):087202
We report high-field magnetization and magnetostriction measurements on the rare-earth-metal tetraboride TbB4, in which the Tb moments form a Shastry-Sutherland lattice in the tetragonal basal plane. A number of magnetization plateaus appear when the magnetic field is perpendicular to the magnetic easy plane. We propose that the magnetization plateaus arise from the combined effect of magnetic frustration and quadrupole interaction in the unique two-dimensional network. 相似文献
15.
A. K. Zhuravlev Yu. N. Gornostyrev 《Journal of Experimental and Theoretical Physics》2014,119(3):503-513
Thermodynamic properties of systems with coupled magnetic and lattice degrees of freedom are analyzed by the numerical spin-lattice dynamics (SLD) method. A scheme of numerical integration is developed for SLD equations in a thermostat, that follows the earlier formulated approaches and is modified to describe systems with realistic interatomic interactions. The method proposed allows one to calculate the spectral density of oscillations, heat capacity, magnetization, and thermal expansion coefficient within a single scheme. It is established that, due to short-range magnetic order, the interplay between magnetic and lattice degrees of freedom contributes to the thermodynamic properties of the system even in the paramagnetic state. It is shown that there exist two mechanisms how the spin-lattice interaction influences the thermodynamic properties: static and dynamic mechanisms; the first is determined by its contribution to the thermal expansion of the lattice, and the second, by the dynamic interaction between magnetic moments and crystal lattice vibrations. 相似文献
16.
A. M. Lugovykh T. B. Charikova V. I. Okulov K. D. Moiseev Yu. A. Kudryavtsev 《Physics of the Solid State》2016,58(11):2240-2243
The temperature and field dependences of the specific magnetization and magnetoresistance in heterostructures with a GaAs/Ga0.84In0.16As/GaAs quantum well and a δ-layer of atomic Mn in the barrier layer near the quantum well filled with holes are studied. A change in the resistance and magnetization behavior upon ordering of localized magnetic moments in the cap layer due to a change in the manganese ion distribution topology is detected. 相似文献
17.
A model based on the idea of localized magnetic moments is presented which allows to calculate the local magnetic moment expectation values of FeNi alloys. The only parameters of the model are the exchange integralsJ FeFe,J FeNi,J NiNi. By assuming a “mixed” exchange interaction the concentration dependence of the exchange integralsJ FeFe andJ FeNi is calculated. The model allows the iron magnetic moments to orient parallel or antiparallel to the magnetization axis, depending on the local environment. It explains the magnetic abnormalies of FeNi Invar alloys as for example the concentration dependence of the mean magnetic moment and the Curie temperatures as well as the characteristic “flat” courves of the spontaneous magnetization. 相似文献
18.
Non-equilibrium properties of a model system comprised of a subsystem of magnetic moments strongly coupled to a selected Bose field mode and weakly coupled to a heat bath made of a plurality of Bose field modes was studied on the basis of non-equilibrium master equation approach combined with the approximating Hamiltonian method. A variational master equation derived within this approach is tractable numerically and can be readily used to derive a set of ordinary differential equations for various relevant physical variables belonging to the subsystem of magnetic moments. Upon further analysis of the thus obtained variational master equation, an influence of the macroscopic filling of the selected Bose field mode at low enough temperatures on the relaxation dynamics of magnetic moments was revealed. 相似文献
19.
Klatyk J Schnelle W Wagner FR Niewa R Novák P Kniep R Waldeck M Ksenofontov V Gütlich P 《Physical review letters》2002,88(20):207202
The iron nitridometalates Li2[(Li(1-x)Fe(I)(x))N] display ferromagnetic ordering and spin freezing. Large magnetic moments up to 5.0mu(B)/Fe are found in the magnetization. In M?ssbauer effect studies huge hyperfine magnetic fields up to 696 kOe are observed at specific Fe sites. These extraordinary fields and moments originate in an unusual ligand field splitting for those Fe species leading [within local spin density approximation (LSDA)] to a localized orbitally degenerate doublet. Including spin-orbit interaction and strong intra-atomic electron correlation (LDA+SO+U) gives rise to a large orbital momentum. 相似文献
20.
We address the role of correlations between spin and charge degrees of freedom on the dynamical properties of ferromagnetic systems governed by the magnetic exchange interaction between itinerant and localized spins. For this we introduce a general theory that treats quantum fluctuations beyond the random phase approximation based on a correlation expansion of the Green's function equations of motion. We calculate the spin susceptibility, spin-wave excitation spectrum, and magnetization precession damping. We find that correlations strongly affect the magnitude and carrier concentration dependence of the spin stiffness and magnetization Gilbert damping. 相似文献