The mechanism of the formation of heterovalent-substitution-induced defects as well as their influence on the magnetic properties of BiFeO3-based multiferroics has been studied. It has been shown that heterovalent A2+ substitution results in the formation of oxygen vacancies in the host lattices of both antiferromagnetic and weak ferromagnetic Bi1−xAxFeO3 (A = Ca, Sr, Pb, Ba; x = 0.2, 0.3) compounds, thus indicating the intrinsic (i.e. not related to defects themselves) mechanism of doping-induced enhancement of magnetization. A correlation between the ionic radius of the substituting element and the value of the spontaneous magnetization of the corresponding solid solution has been found. The experimental results suggest that A-site substitution with the biggest ionic radius ions effectively suppresses the spiral spin configuration of antiferromagnetic BiFeO3.

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The first experimental evidence is reported of crystallization induced in an amorphous alloy by a high density of electronic excitation deposited along the path of swift heavy ions. The formation of nanocrystalline iron boride phases was observed in an amorphous Fe73.5Cu1Nb3Si13.5B9 alloy irradiated at low temperature with 5 GeV Pb ions up to fluences of 1 x 10(11) ions cm-2. No evidence for the formation of the Fe(Si) phase was found. This phenomenon was interpreted in terms of the relaxation of the high level of energy deposited in electronic excitations along the path of Pb ions in the target, which induces extensive stress and strain that could destabilize the amorphous structure.

The properties of Nd 2 CoMnO 6+δ (δ = 0, 0.12) samples were investigated by Mössbauer, μSR and magnetization measurements. Our experimental data were interpreted in the following model. The samples consist mainly of clusters of cobalt and manganese ions with different degrees of order. The valence state of these ions is predominantly Co 2+ /Mn 4+ . Increasing the oxygen content leads to an enhancement of the disordered fraction of the sample which contains mainly three-valent ions. The highly ordered stoichiometric (δ = 0) compound exhibits both pronounced ferromagnetic and weak spin-glass-like components. Ionic disordering leads to a partial destruction of the ferromagnetic component and to strong enhancement of the spin-glass-like one in non-stoichiometric (δ = 0.12) samples. The spin-glass-like component transforms into the ferromagnetic one as a first-order metamagnetic phase transition in an external magnetic field.