MAGNETIC AND ACOUSTIC RELAXATIONS IN Mn-FERRITES

Magnetic and acoustic losses were measured in single-crystal manganese ferrites at temperatures 80 ÷ 630 K. Relaxation peaks at 230 and 540 K were observed with activation energies of 0.27 ÷ 0.42 and 0.64 ÷ 0.82 eV, respectively. Both peaks are influenced by heat-treatments resulting in different degrees of inversion and vacancy distributions

EFFECT OF Mn3+ ION ORBIT LATTICE COUPLING ON MAGNETIC ANISOTROPY OF MnxFe3-xO4 SYSTEM

L'anisotropie magnétique des cristaux MnxFe3-xO4 (x = 0,99,1,24, 1,6) a été mesurée jusqu'à 4,2 °K par mesure de couple. L'analyse de Fourier de ces courbes de couple dans les plans (100), (110) et (111) indique que, dans ces ferrites, il est impossible de décrire la partie anisotrope de l'énergie libre seulement par les deux premières constantes d'anisotropie cubique. L'explication de ce comportement anormal est donnée par les interactions fortes entre les électrons de l'ion Mn3+ et le réseau cristallin (effet Jahn-Teller fort).Magnetic anisotropy of the MnxFe3-xO4 (x = 0.99, 1.24, 1.6) single crystals was measured down to liquid helium temperatures using the torque method. Fourier analysis of the torque curves in the (100), (110) and (111) crystallographic planes showed that in these ferrites the anisotropic part of the free energy cannot be properly described by means of the first and the second cubic anisotropy constants only. The explanation of this anomalous behaviour is given taking into account that there is a strong coupling between the electrons of the Mn3+ ion and the crystal lattice (strong Jahn-Teller-effect)

SEARCH FOR Fe4+ IN YIG : Ca GARNET FILMS

Spectral and temperature dependences of the Faraday rotation and X-ray photoemission spectroscopy of YIG: Ca garnet films have shown features characteristic for the presence of tetravalent iron ions in tetrahedral positions. The charge compensation of Ca2+ by Fe4+ ions becomes saturated at 0.16 Ca per formula unit suggesting the existence of O- ions at higher calcium contents