Neel anisotropy

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... 

Relaxation induced by super-paramagnetic crystals is moreover complicated by another feature the influence of the electron magnetic moment is modulated by Neel relaxation, which depends on the crystal anisotropy (see Fig. 4). 

Another effect of increasing the anisotropy is the lengthening of Neel relaxation time, which generally dominates xq. Since the zero-field relaxation rate is proportional to xq, this lengthening will increase the low field relax-ivity, a consequence opposed to the slackening due to the hidden transitions. 

Therefore, for the internal (Neel) relaxation the parameter, r m plays the same role as the fluid viscosity r in the mechanism of the external (Brownian) diffusion. Note that the density of the anisotropy energy K is not included in x. This means that xD can be considered as the internal relaxation time of the magnetic moment only for magnetically isotropic particles (where K = a = 0). The sum of the rotations—thus allowing for both the diffusion of the magnetic moment with respect to the particle and for the diffusion of the particle body relative to the liquid matrix—determines the angle ft of spontaneous rotation of the vector p at the time moment t ... 

To realize second-order anisotropy, the atomic environment of the transition-metal atoms must have a sufficiently low symmetry [49, 62-65]. Figure 6 illustrates that this is often, but not always, the case for surface atoms. Magnetic surface anisotropy, first analyzed by Neel [62], is important in complicated structures and morphologies such as ultrathin transition-metal films [66], multilayers [67], rough surfaces [65], small... 

Fluorides with a BaMnF4 Structure. Two fluorides belong to this family BaMnF4 and BaNiF4. BaMnF4114 has been studied by Holmes et al.122. They found an exchange constant of — 2.72 K and a spin-flop phenomenon for He = 10.4 kOe. The anisotropy is described by the law H2 = 2HAHE (E - where Xf/Xi 0.047. The Neel tempera-... 

Comptes-rendus des seances de I Academie des sciences 228 664-666 Neel L (1953) L anisotropie superficielle des substances ferromagnetiques. Comptes-rendus des seances de I Academie des sciences 237 1468-1470... 

Neel L (1954) Anisotropie magnetique superficielle et surstructures d orientation. Journal de physique et le radium 15 225-239... 

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