Magnetic anisotropy saturation

The magnetic properties of iron oxides can be determined using Mossbauer spectroscopy, neutron powder diffraction and magnetometry (see Chap. 7). The characteristic parameters are the magnetic moment, the permeability, the saturation magnetization, the magnetic anisotropy constants and the Bhf (Tab. 6.2). 

Oxide Temperature K Magnetic structure Saturation Magnetization <7s at 300 K Ptrr kg" Anisotropy Constant Jm- Magneto- Restriction Constant Jl Magnetic hypeifine field Bhf 295 K 4 K ... 

The temperature dependence of the individual linewidth, eq. (21), is rather complicated. At very low temperatures the Langevin function in this equation becomes saturated for the majority of the nanoparticles, so that the main mechanism of this dependence is the thermal modulation of the magnetic anisotropy energy. Indeed, one can see from figure 8 (bottom) that the Ar temperature dependence provides a good estimate of the experimental low-temperature linewidth. As the damping factor linearly depends on the linewidth, it follows the same temperature dependence [11],... 

The concept of an anisotropy magnetic field HA, which is referred to simply as the anisotropy field , is also introduced to describe magnetic anisotropy. The anisotropy energy is considered to be that of the saturation magnetization moment Ms in an induction /r0//A, i.e. K= -/r0//AMs cos 9, where 9 is the angle between IIA and Ms. 

A difference of high field magnetization along various directions can be explained by both high axis MCA and anisotropy of saturation magnetization. At low temperature this effect hides by MCA, but the saturation magnetization anisotropy are observed near 300 K. This behaviour shows that occupation of 3d-band by 3d-collective electrons of Fe-ions differs for various crystallographic directions. 

The anisotropy of the magnetic susceptibility A% is regarded as a criterion for an aromatic ring current [11] and it was found that magnetic anisotropy for unsaturated NHC is only slightly lower than for imidazole, but much greater than for saturated NHC... 

Magnetic columns FeNi(P) concern to a class of nanostructured materials. Therefore, for interpretation of the data on the approach magnetization to saturation, the special advanced techniques should be used [1], A field of local magnetic anisotropy Ha, correlation radius of casual magnetic anisotropy Rc, a field of anisotropy, the size of the basic unit of a nanostructured magiwtic, the stochastic magnetic domain can be determined with this technique. These parameters can be associated with the GMR effect. 

Ferromagnetic saturation curves were used to estimate the local magnetic anisotropy field using A/(//)/A/j = l-(l/15)(// ///). ... 

The local magnetic anisotropy field extracted from the Akulov law is Ha = 1 OkOe. This value corresponds to the shape anisotropy = 27rM , where is the saturation magnetization of the cobalt fee phase. Therefore the cobalt particles are assumed to form the system of stochastically oriented chains. 

The media were assumed to consist of a monolayer of hexagonal dots with saturation magnetization of 300 emu/cc, a perpendicular magnetic anisotropy field... 

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