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The Stoner–Wohlfarth (SW) model is the simplest model that describes adequately the physics of fine magnetic grains, the magnetization of which can be used in digital magnetic storage (floppies, hard disks and tapes). Magnetic storage density is presently increasing steadily in almost the same way as electronic device size and circuitry are shrinking, and magnetism in general appears as a new contender for many novel computing applications that were considered traditionally beyond its range. Denser storage leads to finer magnetic grains and smaller size leads to magnetic grains so fine that they contain a single magnetic domain, i.e. a region in the material with a well-defined uniform magnetization best described with the mathematics of the SW model.

The coercivity of magnetic thin film having a two-dimensional easy-axis distribution is investigated within the framework of a simple micromagnetic model. It is found that the coercivity decreases from 0.14H(K) to a minimum of 0.07H(K) as thickness increases, where H(K) is the anisotropy field. It is substantially lower than that given by the Stoner-Wohlfarth model and is consistent with available experimental data. The calculated hysteresis loop and the initial magnetization curve are also in good agreement with experiments.

We study the angular dependence of the exchange field and the coercivity of an in-plane exchange biased system in hysteresis loop measurements with the field applied out of the film plane by a Stoner–Wohlfarth model where the coherent rotation of the magnetization is assumed. The model shows an overall 1/cosψ dependence of both the exchange field and the coercivity, where ψ is the angle the applied field makes with the film plane. However, when ψ is close to 90°, the exchange field and the coercivity deviate from the 1/cosψ function. The coercivity in particular goes to zero when ψ approaches 90°. The principle and methodology of the model can also apply to other magnetic systems where the coercivity displays similar angular behaviour.

Bicrystal magnetoresistance hysteresis is studied within the model of coherent rotation of magnetization. The magnetoresistance hysteresis is calculated numerically in the limit of fully spin polarized current for symmetric bicrystal junctions with biaxial magnetic anisotropy and of varying misorientation angles. The shape of the curves obtained from the model displays different characteristic features, depending on the angular relationships, which are consistent with experimental data from the literature. The results show a magnetoresistance increasing with increasing misorientation angle. The influence of biaxial magnetocrystalline anisotropy is reflected in a hump in the maximum magnetoresistance curve at around a misorientation angle of 25°. This structure is absent in the case of uniaxial anisotropy.

In this paper, temperature-induced magnetization reversal in FeCr2−xAlxS4 (x = 0.8, 1.0) is reported. Low-field magnetization measurements indicate that this system displays substantial irreversibility between zero-field-cooling (ZFC) and field-cooling (FC) sequences. Upon warming, the ZFC magnetization is found to change sign twice; however, the FC magnetization changes sign only once. Magnetic hysteresis loop measurements reveal that this system displays a large coercivity at lower temperatures; with increasing temperature, the coercivity decreases abruptly. By accounting for magnetic domain freezing induced by large magnetic anisotropy and domain wall pinning of non-magnetic ions, the multiple sign changes of the magnetization are explained qualitatively.

The approach to the saturation magnetization of a nanocrystalline Fe90Zr7B3 alloy has been studied by means of differential magnetic susceptometry. The influence of the microstructure of the alloy on the approach to saturation magnetization has been studied. It has been found that for the optimum heat-treated sample (heated at 923 K for 0.25 h), which had an average grain size of 12 nm and a coercivity, Hc = 6.4 A m-1, the approach to saturation magnetization can be expressed using the law of approach to saturation magnetization, χ = aMsH-2 + 2bMsH-3 + c/2(H-1/2) (where χ is the differential magnetic susceptibility, Ms is the saturation magnetization, H is the magnetic field, and a, b and c are constants), without the H-3 term, while for the sample heated at 923 K for 240 h, which had an average grain size of 82 nm and a coercivity, Hc = 950 A m-1, the approach to saturation magnetization cannot be expressed in the same form. For both samples, the magnetic-anisotropy-related H-3 term cannot be found. As a result, the magnetic anisotropy in this nanocrystalline alloy cannot be determined by using the law of approach to saturation magnetization. The measurement with the differential susceptometer has been compared with the measurement made on the SQUID magnetometer. The result has shown that the measurement of differential susceptibility using a long ribbon sample on the differential susceptometer is more reliable than that using a small sample on the SQUID.

The relation between microscopic properties (e.g., layer thickness, easy axis orientation) and the macroscopic magnetic properties such as remanent magnetization of the ferromagnetic multilayer system is investigated based on a simple micromagnet approach. We concentrate on a multilayer design with periodic boundary condition, where alternating soft/hard layers build a nanostructured multilayer. For any easy axis direction in the soft and hard layers a simple explicit expression of remanence of the system has been derived analytically. We find that the remanence clearly depends on the thickness of the soft magnetic layer and is nearly independent of the thickness of hard magnetic layer. On the other hand, the remanence increases upon reducing the angle enclosed by the saturation magnetization and the easy axis directions of soft magnetic layer. However, it is unsensitive to the easy axis direction of hard magnetic layer, but there exists a maximum remanence for a certain easy axis direction of hard magnetic layer.

The magnetization processes of small (350 A) and nearly spherical particles of -Fe2O3 were studied at room temperature using the initial, hysteresis and remanence magnetization curves. The effective interparticle interactions were estimated for a number of virgin and alternating current demagnetized samples of -Fe2O3-SiO2 mixtures with different magnetic phase concentrations. A non-monotonous dependence of the interactions on the magnetic phase concentration was observed. It was related to the changes in the domain state of some of the particles from the single-domain to the multi-domain.

This work has shown that isotropic single-phase materials can exhibit remanence enhancement due to exchange coupling between spins in grain boundary areas. Magnetic materials with remanence enhancement are required to have nanocrystalline structures with grain sizes comparable to the domain-wall thickness. The presence of non-magnetic phases may result in de-coupling of magnetic grains, therefore leading to an increase in coercivity but a decrease in remanence. The demagnetization processes of single-phase materials with enhanced remanence are different from those of nanocomposites consisting of hard and soft phases, in that no exchange-spring magnet behaviour was observed for single-phase ribbons of with a nanocrystalline structure. A negative deviation of the demagnetization remanence from the Wohlfarth model [15] was observed due to exchange coupling.

Rare-earth permanent magnet motors are being used increasingly in electrical machines and modern production methods frequently require in situ magnetization of the magnets. Magnetic measurements have been performed on magnetically anisotropic powder (Magnequench MQA-T), sintered and sintered and were compared in order to study the influence of the magnetizing field strength on the measured values of the remanence and intrinsic coercivity. For thermally de-magnetized material, the internal magnetic field necessary to obtain limiting values of the remanence and intrinsic coercivity varies with magnet type. For example, the and magnets studied have similar values of remanence and intrinsic coercivity , but the latter requires an internal magnetizing field three times larger than does the former in order for one to attain limiting values of the remanence and coercivity. Further insight into the magnetization processes in these three materials has been gained from the determination of the magnetic viscosity parameter, S, and the irreversible susceptibility, .

For pt.I see ibid., vol.5, p.2779-92 (1993). A comprehensive study of the remanence curve properties of an assembly of noninteracting single-domain particles with cubic magnetocrystalline anisotropy has been performed. The theoretical calculations presented represent an extension of the zero-temperature analysis of Joffe and Heuberger to include the effects of thermally activated magnetization reversal and particle size distribution. The numerical validity of these computations is completed through the analysis of interaction-sensitive Henkel plots, which confirm the non-interacting nature of the independently calculated remanence curves. The model system shows behaviour with intuition and analogous to similar models for the uniaxial case, with the exception of the expected increase in maximum remanence and decrease in energy barrier, i.e. remanence coercivity.

Nanocrystalline Sm2Fe14.5Cu0.5Ga2Cx (x = 1 and 2) and Sm2Fe15Ga(Si)2C ribbons prepared by melt spinning and subsequent annealing have been investigated by x-ray diffraction, thermomagnetic analysis, a superconducting quantum interference device magnetometer and an extracting sample magnetometer. The results show that the annealed ribbons consist of the Th2Zn17-type phase and a very small amount of α-Fe. The result, calculated from the high external field part of the demagnetization curve, shows that Heff (the effective field)-H (the external field) is linear with y (the ratio of the magnetization in the external magnetic field H and the saturation magnetization). This result is in agreement with the conclusion gained from a mean field Stoner-Wohlfarth model.

Magnetic properties of thin Co50Fe50 films on MgO(0 0 1) prepared with different annealing temperatures between room temperature and 300 °C are studied by vectorial magnetometry based on the magnetooptic Kerr effect. Independent from the annealing, the Co50Fe50 films reveal some similar magnetic properties, e.g. no quadratic magnetooptic Kerr effect and a magnetic reversal process which is completely in-plane with magnetic easy axes in Co50Fe50〈1 1 0〉 directions. If the alignment of the external magnetic field is close to the magnetic hard axes, incoherent rotation of magnetic moments between saturation and remanence occurs instead of coherent rotation as for the other directions. If the magnitude of the magnetization is polar plotted with respect to the azimuthal magnetization angle, sequential switching of magnetic moments from one magnetic easy axis to another can be proved by the course of the magnetization. Here, a two-domain switching process can be distinguished from a four-domain switching process generated by the incoherent rotation between saturation and remanence. Furthermore, both the uniaxial magnetic anisotropy constants and the domain wall pinning energies are determined from the magnetic switching fields using the Stoner–Wohlfarth model while the cubic magnetic anisotropy constants are obtained from fitting the magnetization curves. The domain wall pinning energies obtained from these analyses decrease with increasing annealing temperature due to fewer defects in the film. The cubic magnetic anisotropy also decreases slightly which can be attributed to relaxation of the crystal lattice for increasing annealing temperature due to a small change of spin–orbit coupling. Compared with the cubic magnetic anisotropy the uniaxial magnetic anisotropy is very small. This may be attributed to the reduction of strain in the film caused by a buffer stack Cr/Au/Cr between the Co50Fe50 film and MgO(0 0 1).

In this paper we present an application of the so called hyperbolic model of magnetization. The model was modified and it was applied for nine different soft magnetic alloys. The tested samples were electro-technical steels (FeSi alloys) and a permalloy (FeNi alloy) with strongly different magnetic properties. Among them there are top, medium and definitely poor quality soft magnetic materials as well. Their minor hysteresis loops and normal magnetization curves were measured by alternating current measurement. The hyperbolic model of magnetization was applied for the experimental normal magnetization curves. It was proved that the applied model is excellent for describing mathematically the experimental magnetization curves.

The galvanomagnetic effect in a polycrystal Co thin film was investigated by measuring magnetoresistance and Hall resistance. The observed magnetoresistance can be understood in term of the anisotropic magnetoresistance effect using the Stoner-Wohlfarth model. The observed Hall resistance cannot be explained syfficiently by the planar Hall effect using the Stoner-Wohlfarth model. In order to explain the observed Hall resistance, we took the exchange interaction from the current and voltage probes into consideration and numerically calculated the magnetoresistance and the Hall resistance. The calculated results obtained using this model are in reasonable agreement with the experimental results.

When the hard-direction remanence in a magnetic film is large, a model of domains and walls becomes inadequate. Asuming instead a sinusoidally varying magnetization distribution, a theoretical value is derived which closely approaches that observed.