Ratio Of Exchange Interactions Research Articles

The exchange interaction effect on magnetism for itinerant electron system

The magnetism of itinerant electron system i.e. the Extended Hubbard Model system with exchange interaction is investigated at any arbitrary electron density by making use of the perturbational expansion in terms of the transfer integral upto second order. It turns out that the ferromagnetic coupling exists as well as the antiferromagnetic coupling, and the competition between ferro- and antiferromagnetism depends not only on the transfer integral and electron density, but also on the ratio of exchange interaction to the transfer parts. It showes out that the exchange interaction can not be neglected, especially in the study of its magnetism even though is small in value.

Canted ferrimagnetism in Ca2+Sc3+ substituted yttrium-iron-garnet

The temperature dependence of the magnetization of Y3−y−zCayLuzFe5−xScxO12 (0.6≤x≤1.2, 0≤y≤0.3, 0≤z≤0.9) epitaxial garnet films was measured from 4.2 K up to the Curie temperature. For x=0.7 and T≥50 K, 4πMs is enhanced by about 10% compared to the magnetization of Sc0.7 YIG. At T<50 K, a reduction of the magnetization, increasing with increasing substitution, was observed for all the measured samples. Agreement between the experimental results and molecular field models was obtained by taking into account the canting of the unsubstituted sublattice, the presence of charge compensating Fe4+ ions, a low-temperature ordering of Fe3+ ions with less than two magnetic nearest neighbors, and assuming a lattice parameter-dependent exchange interaction ratio with d(Jdd/Jad)/da =28 nm.−1 For x=1.2 and T<10 K the magnetization can be influenced by cooling through the Curie point in a magnetic field.

A tricritical model with an experimentally accessible ordering field

The Blume-Capel (1966) model in a transverse field is studied in the mean field approximation. It is found that a tricritical point exists in the transverse field-temperature plane for a range of values of anisotropy to exchange interaction ratio. This is in contrast with the original Blume-Capel model which shows the tricritical phenomena only at a single value of this ratio. The most interesting feature, however, is that the ordering field, which is the externally applied field along the longitudinal direction, is experimentally accessible and can be set at one's will. This allows an experimentalist to investigate all aspects of a system describable by this model. Equations of the lines of critical points including the wing boundaries are derived. Phase diagrams for the whole range of values of anisotropy are described, and the experimental situation is discussed.