Фазовый состав и структура пленки BiFeO-=SUB=-3-=/SUB=-, выращенной на подложке MgO(001) методом ВЧ-катодного распыления в атмосфере O-=SUB=-2-=/SUB=-

The crystal structure and Mossbauer spectroscopy studies results for BiFeO3 film growth on the MgO(001) single crystal substrate are present in the paper. It been shown that film have high crystal perfection and low defectiveness which results in appearing of narrow lines during the θ-2θ and φ scanning and the small (lower than 0.7°) disorientation of film and substrate crystal axes. It is been revealed that unit cell of BiFeO3/MgO(001) heterostructure possess monoclinic symmetry and deformation of unit cell is negligible. The Mossbauer study shows that magnetic subsystem of film has spatial spin-modulated structure with zero value of anharmonicity parameter (m). This indicate that at room temperature the magnetic anisotropy changes from the "easy axis" type to "easy plane" type.

Температурные изменения магнитной структуры мультиферроика BiFe-=SUB=-0.80-=/SUB=-Cr-=SUB=-0.20-=/SUB=-O-=SUB=-3-=/SUB=-

The results of a Mössbauer study of the magnetic structure of multiferroic BiFe_0.80Cr_0.20O_3 in the temperature range of 5–550 K are presented. It is found that a collinear antiferromagnetic structure of the G type is present in BiFe_0.80Cr_0.20O_3 at temperatures below 260 K. Above 260 K, an anharmonic spin wave with a magnetic anisotropy of the easy-axis type with a high value of the anharmonicity parameter m arises. With a further increase in the temperature, the m parameter decreases and tends to zero at T ~ 420 K, at which a harmonic spin wave comes into existence. Above a temperature of about 420 K, the m parameter increases again and the spin wave becomes anharmonic with an easy-plane magnetic anisotropy. At the Néel temperature, T _N = 505 ± 10 K, the sample undergoes a transition from the magnetically ordered to the paramagnetic state. The change in the type of magnetic anisotropy at T ~ 420 K is explained by competing contributions of different signs to the effective magnetic anisotropy constant and their different temperature dependence for the BiFe_0.80Cr_0.20O_3 multiferroic.

Anharmonic thermal vibrations in Mg2Si

The recent X-ray diffraction data front Mg2Si, obtained by Panke & Wölfel (Z. Kristallogr. (1969), 129, 9) show systematic differences in the structure factors from those predicted by a model which assumes harmonic thermal vibration of the atoms. These differences indicate an anharmonic component in the thermal vibration of the magnesium atoms, consistent with their tetrahedral site symmetry. An analysis of these data has therefore been carried out in terms of a model which includes anharmonic thermal vibration and a least-squares refinement gave a value of the anharmonicity parameter (β Mg = − 2.39 × 10−12 erg.Å−3) which is similar in magnitude to those found for other systems with the fluorite structure.