Magnetization easy direction

This approximation is strictly valid only for systems of uniaxial symmetry, i.e, having two equivalent magnetic easy directions. For systems with more equivalent directions (magnetite for example... 

The fluctuations of the magnetization direction around an easy axis, known as collective magnetic excitations, can be considered fast compared to the time scale of Mossbauer spectroscopy because there are no energy barriers between magnetization directions close to an easy direction, and the magnetic splitting in the... 

Another process responsible for a fluctuation of the local magnetic field is Neel relaxation. It corresponds to the flip of the crystal magnetization vector from one easy direction of anisotropy to another. The correlation time of this... 

When the anisotropy energy is large enough it prevents any precession of the magnetic moment of super-paramagnetic crystals. The magnetic fluctuations then arise from the jumps of the moment between different easy directions. The precession prohibition is introduced into the Freed equations in order to meet that requirement every time the electron Larmor precession frequency appears in the equations, it is set to zero 12). 

The first type is the crystal anisotropy which is responsible for the dependence of the magnetization curves on the orientation of the crystal in the magnetic field. The energy E, which is necessary to deflect the magnetic moment in a single crystal from the easy direction into less easy ones is given for cubic crystals by ... 

We used in (9.17) the subtracted electron factor. However, it is easy to see that the one-loop anomalous magnetic moment term in the electron factor generates a correction of order a Za)Ep in the diagrams in Fig, and also should be taken into account. An easy direct calculation of the anomalous magnetic moment contribution leads to the correction... 

Fig. 9. Magnetic field dependence of the magnetization at selected temperatures for a 150-nm thick Ga xMn As film with a Mn composition x = 0.03S. The magnetic field is applied parallel to the sample surface (direction of magnetic easy axis) except for the closed circles at 5 K taken in perpendicular geometry. The solid line for S K shows the magnetization determined from transport measurements. The upper left inset shows a magnified view of the magnetization in the parallel field at 5 K. The lower right inset shows the temperature dependence of the remanent magnetization (Ohno et al. 1996a).

Magnetization of a material. Initially, magnetization increases by growth of favorably oriented domains. At high fields, the direction of magnetization rotates out of the easy direction. 

Magnetic anisotropy yields easy magnetization directions corresponding to local energy minima and energy barriers that separate the easy directions. On an atomic scale, the barriers are easily overcome by thermal fluctuations, but... 

In general a ferromagnetic material does not show isotropic magnetization behavior (Ch. 3). Experimentally certain directions can be found, which favor magnetization (easy axes) and others which do not (hard axes). This leads to a new energy term. 

Generally, isotropic permanent magnets with a remanence ration JJJS > 0.5 are referred as remanence enhanced materials. However, the theoretical limit for the remanence of noninteracting grains depends on the crystal symmetry, the crystallographic orientation of the easy directions, and the volume fraction and the saturation polarization of the phases. The remanence ratio a two-phase nanocomposite magnet is... 

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