Saturation magnetic moments

Fig. 2. Predicted dependence of atomic saturation magnetic moment a a as f unction of number of atomic d electrons.

For alloys of iron, cobalt, nickel, and copper the calculated values of saturation magnetic moments agree closely with the observed values in particular, the maximum value of about 2.48 magnetons at electron number about 26.3 is reproduced by the theory. There is, however, only rough agreement between the observed and calculated values of the Curie temperature. 

Fig. 11-1.—Observed values of saturation magnetic moments per atom of transition elements of the iron group and their alloys. Values for some alloys, which deviate from the curve, are not shown these alloys probably involve ferrimagnetism.

Values of the low-temperature saturation magnetic moment of ferromagnetic substances represent the maximum component of the atomic magnetic moment in the field direction for example, for spin alone the value in Bohr magnetons is 2S, whereas the magnetic moment obtained from the paramagnetic susceptibility is 2 /S(S + 1). 

Figure 5. Compositional dependencies of the saturation magnetic moment Ms(0) and the effective magnetic moment peff of Nio+x-Mni tCa (0 < x < 0.19) alloys.

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. 

From the Slater-Pauling curve for the saturation magnetic moment of the first-row transition metal alloys (Figure 1), it was found empirically that the number of metallic orbitals per atom has the value 0.72, corresponding to 28% M+, 44% M°, and 28% M-. Based on the statistical treatment discussed in the preceding section, it is now possible to deduce this value on purely theoretical grounds [36]. 

Refinement of the data show that the structure of SrjCrNbO, 53 is made up of a partially ordered array of CrOg and NbO comer-sharing octahedra (Fig. 5). The Cr/Nb(l) and Cr/Nb(2) site occupancy values are 63/37 and 37/63 % respectively (Table 1). The large amount of disorder between the Cr and Nb ions leads to AFM type magnetic interactions between identical neighboring transition metal ions. The presence of AFM type interactions leads to a reduction in the observed saturation magnetization moment and contributes to the observed spin-glass type behavior. 

In the simplest case of uniaxial relaxation, a relaxation process where the magnetization flips around an angle of 180°, the relaxation rate of a single-domain particle with the saturation magnetic moment /I in a magnetic field B at a given temperature T is expressed as... 

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