Sublattice magnetization

It is possible to systematically alter the net magnetic moment of ferrites by chemical substitutions. A very important industrial appHcation is the increase of the magnetic moment in mixed MnZn-ferrites and NiZn-ferrites. When Zn ions are introduced in Mn-ferrite or Ni-ferrite, these ions prefer to occupy A-sites. Because is nonmagnetic, the A-sublattice magnetization is reduced and consequendy the total net magnetic moment is increased. 

For a ferromagnet the order parameter is the magnetization, while for antiferromagnets it is the sublattice magnetization. For spin glasses the magnetization is zero at all temperatures, and an appropriate order parameter was proposed by Edwards and Anderson [78] as the average value of the autocorrelation function... 

Figure 6.28 Reduced sublattice magnetization as a function of reduced temperature for K2C0F4,. The solid line is the theoretical fit to the two-dimensional Ising model. (After Tressaud Dance, 1982.)...

Minimizatation of (2) with respect to the variables mi and rn2, taking account of the limits of their variation, yields the following solutions for the sublattice magnetizations at different intensities of the magnetic field ... 

The molecular-field approximation suggests the following relation for the field and temperature dependence of the sublattice magnetization ... 

For one-sublattice magnets, such as Fe and Co, the Akulov or Callen and Callen theory [81] relates the temperature dependence of the anisotropy to the spontaneous magnetization and yields hi and Af° power laws for uniaxial and cubic magnets, respectively. This theory has become popular far beyond its range of applicability [82] but is unable to describe structures such as rare-earth transition-metal magnets [16, 60], actinide magnets [83], and L10 type compounds [44, 84]. 

The hyperfine field is directly proportional to the sublattice magnetization. Moreover, the appearance of the sextuplet(s) of 57Fe in the ordered regions provides the 3-D ordering temperature. In the case of low-dimensional systems, zero-point spin reduction is often observed. 

Fig. 15. Reduced sublattice magnetization as a function of the reduced temperature for K2CoF4. Full curve is the theoretical function of the 2-D Ising model...

Figure 1 displays the plots of the TCATC/G quantity as a function of ATC derived from our experimental results for the R2Fei4B compounds and their hydrides. The data for the lutetium compounds (TCo = 535 K for Lu2Fei4B and Tco = 620 K for Lu2Fe14BH2 5) have been adopted as a TCo- It is known that the 4f electron shell of the Lu3+ (4f14) - ion has no magnetic moment. Therefore, in our case, the Lu compound models the iron sublattice magnetization for the whole series of R-Fe compounds under consideration. 

A B20 crystal field parameter decreases as hydrogen atoms concentration increases (Fig. 6) and, therefore, the rare-earth sublattice magnetic anisotropy constant Kir (K1r -J2B20Bj2(x), where Bj2(x) is the 2nd order generalized Brillouin function) also decreases. Hydrogenation leads to a decrease of the... 

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