Anisotropic Magnetic Materials Research Articles

Magnetic force microscopy characterization of unusual magnetic coupling in an extraordinarily responsive magnetic material

Gd/sub 5/(Si/sub 2/Ge/sub 2/) and related compounds with similar (nearly equal Si-to-Ge ratio) composition exhibit large magnetoresponsive properties including a giant magnetocaloric effect, colossal magnetostriction, and giant magnetoresistance near a structural-magnetic phase transition that occurs close to ambient temperature. Magnetic force microscopy (MFM) and vibrating sample magnetometry (VSM) measurements on single-crystal samples of these materials indicate that the easy magnetization axis is the b-axis of the orthorhombic magnetic phase-perpendicular to the slabs. In fact, the MFM image of a surface perpendicular to the b-axis is quite similar to domain patterns perpendicular to the easy axis of Co and other highly anisotropic magnetic materials. Therefore, it appears that Gd/sub 5/(Si/sub x/Ge/sub 1-x/)/sub 4/ may require modeling similar to other multilayers and superlattices of rare-earth metals with one or more nonmagnetic constituents that exhibit long-range magnetic order across nonmagnetic layers. Many of the important phenomena of these Gd compounds could be explained by the interaction of localized Gd magnetic moments across the covalent bonding between atomic slabs, adapting models already suggested for other similar materials.

Anisotropic molecular magnetic materials based on liquid-crystalline lanthanide complexes

The alignment of liquid crystals in an external magnetic field is discussed. Special attention is paid to paramagnetic metallomesogens containing trivalent lanthanide ions. The huge magnetic anisotropy of rare-earth compounds is favourable to achieve easy magnetic alignment. The principle of orientation of liquid-crystalline lanthanide complexes is illustrated for Schiff base complexes of the type [Ln(LH) 3(NO 3) 3], where Ln is a trivalent lanthanide ion and LH is a salicylaldimine. The compounds exhibit a smectic A phase. By a proper choice of the lanthanide ion, it is possible to align the director either parallel or perpendicular to the magnetic field. When the aligned mesophase is cooled in the presence of a magnetic field, the mesophase order is frozen into the glass state and an anisotropic molecular magnetic material is obtained.

Synthesis, mesomorphism, and unusual magnetic behaviour of lanthanide complexes with perfluorinated counterions.

Lanthanide complexes of the Schiff base ligand 4-dodecyloxy-N-hexadecyl-2-hydroxybenzaldimine and with perfluorinated alkyl sulfate counterions were synthesised. All of the metal complexes show a smectic A mesophase. The viscosity of this mesophase is much lower than that of analogous compounds with nitrate or alkyl sulfate counterions. The behaviour of these new highly anisotropic molecular magnetic materials was studied using high-temperature X-ray measurements in an external magnetic field and temperature-dependent magnetic susceptibility measurements. The mu(eff)-versus-temperature curve is more comparable with those expected for nematic phases than for smectic phases. The luminescence spectrum of a EuIII compound shows that the values of the second rank crystal field parameters are very large. The huge magnetic anisotropy can be related to this strong crystal-field perturbation.

Iron loss and magnetic fields analysis of permanent magnet motors by improved finite element method with E&S model

In this paper iron loss analysis of the permanent magnet motor considering anisotropy of magnetic material is carried out. The magnetic material can be measured using vector quantity technique. Non-oriented silicon steel sheets for the iron core material have the anisotropy. Therefore, it is necessary to carry out the analysis considering the anisotropy of the magnetic material. A magnetic field analysis, which considers the anisotropy by combining finite element method with the E&S (Enokizono and Soda) model, is considered.

Anisotropic vector Preisach model and magnetic field solutions

The implementation of a vector Preisach model for the modelling of anisotropic hysteretic soft magnetic materials is outlined. Some comparisons with measurements on alternate and rotational magnetic field excitations are shown. The hysteresis model is inserted inside a two‐dimensional finite element solver formulated in terms of magnetic vector potential and nonlinear solution is handled by means of the fixed point method with H‐scheme. Results obtained on a two‐dimensional geometry are described and discussed.

X-band characterization of anisotropic magnetic materials: application to ferrofluids

A simple, fast method of characterization of anisotropic magnetic materials uses a nonreciprocal X-band rectangular cell. The material may be a solid, powder, or magnetic liquid. A network analyzer measures the scattering parameters, and an original numerical processing routine computes the permeability tensor components. Two anisotropic magnetic materials have been characterized: a ferrofluid made with magnetite particles suspended in a hydrocarbon and a barium iron oxide powder. The knowledge of permeability behavior of magnetic liquids is important in designing specific nonreciprocal microwave devices. Experimental results are in good agreement with the proposed theoretical simulated model.

Structure of Nd2Fel4B / Fe Resulting from Reaction of Nd2Fe17 and B

A novel method to prepare anisotropic composite magnetic material was described. A block of Nd2Fe17 compound was heated with the surrounding B (or B2O3) powder and the reaction accelerator Ca. In the reaction region, rod-shaped Fe precipitates were formed inside Nd2Fe14B matrix grains. The longitudinal directions of those are parallel to the B diffusion path, while perpendicular to the c-axis of Nd2Fe14B crystals. The Fe diameter depends on the heating temperature, below 100nm at 1123K. This structure is regarded as eutectic, and differ from that formed by peritectic solidification. The similar reaction product was formed in the powder form by using Nd2Fe17 powder instead of the bulk material. That product has larger magnetization than Nd2Fe14B, but has no coercivity and the small anisotropy field about 1.6MA/m.

Magnetic field and core loss evaluation of ALA-motor synchronous reluctance machines taking into account material anisotropy

Currently, much attention is paid to the behavior of thin laminations of anisotropic soft magnetic materials with respect to magnetization out of the easy axis. A method for analyzing flux distribution and loss calculation is proposed for electric machines exhibiting strong material and 'structural' anisotropy. The method takes into account the curvature in anisotropic and composite flux barrier regions by introducing equivalent reluctivities. The results of a case study on an axially laminated anisotropic (ALA) rotor of a synchronous reluctance motor (SynRM) are presented.

2D/3D models for a three phase fed single sheet tester

2D and 3D models of the electromagnetic field in a single hexagonal sheet tester of anisotropic magnetic material are evaluated. The feeding magnetic flux is a rotational symmetrical three-phase excitation of positive sequence. The nonlinear characteristics of the anisotropic magnetic material are represented by vector hysteresis, developed on measured data. The numerical analysis of the electromagnetic field, based on the global variational method for 2D and 3D models is evaluated to study the behaviour of the magnetic material under rotating magnetic field.

Element-Specific Magnetic Anisotropy Determined by Transverse Magnetic Circular X-ray Dichroism

Understanding of the magnetocrystalline anisotropy in magnetic materials (the influence of different elemental components on the direction of easy magnetization) can be greatly enhanced by measuring the orbital moment anisotropy of the elemental constituents. A circular x-ray dichroism technique is presented that allows the determination of the microscopic origin of the spin reorientation transition in ultrathin single-crystalline cobalt/nickel films. The stronger anisotropy contribution of a much thinner cobalt layer redirects the easy magnetization direction of the entire film.

Electromagnetic shock waves and their structure in anisotropic magnetic materials

The analogy between non-linear electromagnetic waves in magnetizable media and non-linear elastic waves in anisotropic media is justified and used. The analogy occurs when dispersion and dissipation are ignored. By using existing results [1] one can therefore immediately formulate all that relates to investigating relations in Riemann waves and electromagnetic shock waves. To describe the structure of electromagnetic shock waves in magnetic materials the Landau-Lifshits equation is employed, which differs considerably from the relations used to describe the structure of shock waves in elastic media. A consequence of this is that the set of permissible shock waves (i.e. possessing a structure) acquires a complex structure and differs considerably from the analogous set for elastic shock waves. It is shown below, in particular, that the set of permissible electromagnetic shock waves is not the same as the set of initially evolution discontinuities. The requirement that a structure should exist distinguishes, on certain parts of the shock adiabat, a set which is a dashed line with a very short dash length. In addition, there is a large number of individual points on the shock adiabat of the electromagnetic shock waves. Each point corresponds to a discontinuity with a separate velocity of motion, recalling the slow-combustion front in gas dynamics.

The procedure of optimization of magnetic structure

The variation principle is used to search for the shape and magnetic structure of material when the objective function is extremized. The algorithm is derived analytically. Numerical computing leads to optimal distribution of anisotropic magnetic material.

Finite element analysis of MMIC waveguide structures with anisotropic substrates

This paper presents an extended finite element formulation for a full-wave analysis of biaxial and transverse plane electric and magnetic anisotropic materials with application to monolithic microwave integrated circuits (MMIC's). A convenient formulation of the characteristic impedance based on a power-voltage definition is developed using vector-based finite elements. The resultant generalized eigenvalue problem is solved using a numerically efficient algorithm based on a forward iteration, taking full advantage of the sparsity of the involved matrices. Numerical results are compared and agree well with existing published data for various MMIC configurations. Two specific coplanar waveguide structures, one with a conventional and the other with a suspended substrate, are examined using four common anisotropic materials. Principal axis rotations of the anisotropic substrates are also considered to improve dominant mode dispersion characteristics and minimize higher order mode interactions.

CALCULATION OF FLUX DISTRIBUTION IN TRANSFORMER CORE TAKING HYSTERESIS INTO ACCOUNT

Calculation of flux distribution in three‐phase three‐limb transformer core has been made using 2D finite element method. The calculation has been performed with and without taking into account lthe hysteresis of magnetic material. Anisotropy of magnetic material has been modelled through the so‐called elliptic permeability model. Comparison of results of calculation and results of measurement has been performed for a scale model of transformer core. An agreement better than 3 per cent has been obtained, for calculated and measured results of third harmonics and of flux distortion factors, when hysteresis has been taken into account. The CPU‐time was 6–10 times longer when hysteresis has been included into calculation.

An improved numerical analysis of flux distributions in anisotropic materials

The method for analyzing flux distributions in transformer cores made of grain-oriented silicon steel is improved in order to reduce error in calculation due to anisotropy in magnetic materials. A model to verify the improved method is proposed, and the calculated results are compared with measured ones. >

Finite element analysis of anisotropic magnetic materials taking rotation magnetization into account

Computer simulation of the magnetizing process has been carried out by applying a numerical model to the theory of the rotation magnetization for magnetic materials. This model has been made in order to adjust to the two-dimensional magnetic property. This numerical model is combined with the finite element method in which the magnetic scalar potential and the magnetization are regarded as unknown quantities It is possible to calculate that the magnetic materials with single domain structure are magnetized in the mode of rotation or of reverse of the magnetization vector. >

Surface and interface excitations for bilayer Ising-model systems in a transverse field (abstract)

We present some calculations for the surface and interface excitations (spin waves) in layered solid structures which may be represented by the Ising model in a transverse magnetic field. In particular, we consider a two-medium system consisting of a ferromagnetic thin film on a semi-infinite substrate of another ferromagnetic material. By generalizing previous results for a single semi-infinite medium,1,2 we show that there may be excitations localized near the surface and interface of the coupled magnetic system, depending on the parameters of the model. We deduce dispersion relations for these surface and interface spin waves, as well as for the quantized (or ‘‘standing’’) bulk spin waves in the thin film, including the effects of relaxational damping of the modes. For nonzero values of the transverse field, the formalism can be applied at temperatures above and below the critical temperatures in the two media. Although our theory provides a description of some real anisotropic magnetic materials when placed in a transverse magnetic field, it is also of wider applicability within a pseudo-spin formalism for certain order–disorder ferroelectrics and Jahn–Teller systems.

A new method to measure magnetization and coercivity using a torque magnetometer (abstract)

A vibrating sample magnetometer (VSM) is commonly used to measure magnetization and coercivity. In this paper, we present a new method to determine magnetization and coercivity of uniaxial magnetic anisotropic materials using a torque magnetometer. To measure magnetization, a sample is saturated along the uniaxial orientation by applying an external magnetic field and then it is rotated by 90°. Under this arrangement, the torque τ at a low applied field H can be approximately expressed by τ=HM, where M is the magnetization. An accuracy of this approximation depends on the strength of the anisotropy field Hk of a sample. A better result is expected for a higher Hk. For an instance, an inaccuracy of 0.5% is yielded from a linear approximation of this method for a case of H/Hk=0.1. To measure the coercivity, the sample is rotated by (180+δ) degrees after it is saturated along the uniaxial orientation. Under this configuration, the torque is measured with an applied field. Then, the value of the torque becomes from positive to negative with increasing an applied field. Here, the field where the torque is zero is the coercivity of the sample. Our new method was compared with a conventional VSM technique by measuring several Co/Pd multilayers having a uniaxial anisotropy along the growth orientation. A difference of within 2% between two techniques was found in measuring the magnetization and coercivity, except the sample having a low anisotropy field less than about 1 kOe.

Crystallographic alignment analysis of Nd2Fe14B materials using standard x-ray powder diffraction spectra

The crystallographic alignment quality of anisotropic magnetic materials made from die-upset Nd2Fe14B (MQ-III) materials was determined using a phenomenological analysis of θ-2θ x-ray diffraction spectra. This analysis consisted of fitting a calculated diffraction spectrum for aligned Nd2Fe14B to an observed spectrum collected on a bulk MQ-III slab oriented with the c-axis alignment parallel to the direction normal to the surface of the slab. The calculated spectrum was then used as a standard for intensity shifts of diffraction peaks corresponding to crystallographic reorientation from random to c-axis alignment. Intensity shifts for other samples for Nd2Fe14B materials having various degrees of c-axis alignment were determined and compared to the standard shifts giving an alignment factor representing the nature and extent of the crystallographic alignment in the sample.

Effect of Magnetic Field on Magnetic Anisotropy Sensor

Nondestructive methods for measurement of mechanical stress are important to studies of magnetic materials. Magnetic anisotropy sensors (MAS), which have been employed in stress and torque sensors, can also be utilized in the noncontact detection of magnetic anisotropy in materials to estimate stress or defects in them. However, because MAS is a probe type sensor, it is affected by external magnetic fields, a serious drawback to practical use. This paper discusses the effect of external magnetic fields on MAS's and proposes a method to reduce their influence.