Ferromagnetic clusters

When analyzing the experiments, one normally assumes that ferromagnetic clusters are monodomain particles that is, all magnetic moments of the... 

The Curie constant C = g2p xNoS(S + )/3koT. determined from 11%-T curve shown in fig. 1 lb gives a spin of S = 3, when the nominal value of the Mn concentration, x — 0.053, is used. Here No is the cation density, g (= 2.0) the Lande factor of the Mn ions, /tb is the Bohr magneton, k is the Boltzmann constant. Judging from this value of 5, some ferromagnetic clusters exist already above 7c. 

Due to the second effect the system may reach a percolation threshold and consequently a metal-insulator phase transition may be induced by the magnetic field. It has to be stressed that the contributions to the effective magnetostriction of cobaltites mentioned above have a different dependence on temperature. An increase of temperature induces low-spin to intermediate-spin transitions. At the same time the volume of ferromagnetic clusters decreases with increasing temperature. The competition of these mechanisms leads to the unusual dependence of the effective magnetostriction of cobaltites on temperature. 

The magnitude of GMR itself increases with an increase in the peak resistivity (at T M). In other words, one needs a bad metal to observe good GMR. Furthermore, even formally antiferromagnetic compositions (jc > 0.5) show GMR because of the presence of ferromagnetic clusters. 

The temperature dependence of the spontaneous magnetization of the ferromagnetic clusters is shown in Table II. Figure 5 shows the present data fitted to a... 

Figure 6.1 Two no-pair ferromagnetic clusters, Aug and Li,Q. The superscripts correspond to the 2S-I-1 spin multiplicity value. The spins illustrate the nature of the ferromagnetic electronic structure.

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