L.V. Panina

Coexistence of spontaneous polarization and magnetization in substituted M-type hexaferrites BaFe12–xAlxO19 (x ⩽ 1.2) at room temperature

Precision studies of the crystal and magnetic structures of substituted M-type barium hexaferrites BaFe12–xAlxO19 (x 1.2) in the temperature interval of 300–760 K have been performed by the power neutron diffraction method. The electric polarization and magnetization, as well as the magnetoelectric effect, of these compounds in electric (up to 110 kV/m) and magnetic (up to 14 T) fields at room temperature have been examined. The conservation of the collinear ferrimagnetic structure with substitution has been established. Spontaneous polarization and magnetization, as well as a strong coupling between the dielectric and magnetic subsystems at room temperature, have been revealed. The precision structural studies make it possible to determine the reason and mechanism of the appearance of spontaneous polarization in substituted M-type barium hexaferrites BaFe12–xAlxO19 (x 1.2) with the collinear ferrimagnetic structure.

Evolution of structure and physical properties in Al-substituted Ba-hexaferrites*

The investigations of the crystal and magnetic structures of the BaFe12−xAlxO19 (x = 0.1–1.2) solid solutions have been performed with powder neutron diffractometry. Magnetic properties of the BaFe12−xAlxO19 (x = 0.1–1.2) solid solutions have been measured by vibration sample magnetometry at different temperatures under different magnetic fields. The atomic coordinates and lattice parameters have been Rietveld refined. The invar effect is observed in low temperature range (from 4.2 K to 150 K). It is explained by the thermal oscillation anharmonicity of atoms. The increase of microstress with decreasing temperature is found from Rietveld refinement. The Curie temperature and the change of total magnetic moment per formula unit are found for all compositions of the BaFe12−xAlxO19 (x = 0.1–1.2) solid solutions. The magnetic structure model is proposed. The most likely reasons and the mechanism of magnetic structure formation are discussed.

Anomalies in growth of electrodeposited Ni–Fe nanogranular films

Thin Ni–Fe films were produced via electrodeposition onto silicon substrates using direct current and pulse current (with different pulse durations) regimes. The correlation between the technological regimes, chemical composition and microstructure of Ni–Fe nanogranular films was investigated. Analysis of the microstructure evolution revealed that the mechanism of film growth changes from Volmer–Weber (island film growth) to Stranski–Krastanov (layer by layer growth) with the shortening of the pulse duration below 10 μs. This anomalous behavior was explained by the increase of the binding energy between the initial film atoms and the substrate surface. The results showed that using electrodeposition regimes, which ensure growth with an average crystal size less than the critical value of 10 nm, provides less roughness and defectiveness and better film uniformity in thickness.