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Abstract: The magnetic structure and phase transition in xBiFeO3–(1 – x)SrTiO3solid solutions, where xis from 0.2 to 1.0 with a step of 0.1, are studied systematically with Mössbauer spectroscopy. The multiferroic BiFeO3was modified via incorporation of a perovskite SrTiO3, and xBiFeO3–(1 – x)SrTiO3solid solutions that possess both ferrimagnetic and ferroelectric properties at room temperature were prepared. X-ray diffraction data indicate that there are no any additional phases in the xBiFeO3–(1 – x)SrTiO3systems, whereas Mössbauer data show that there is a mullinite (Bi2Fe4O9), when amount xof SrTiO3in the solid solution is from 1.0 to 0.8. The Mössbauer spectra of the xBiFeO3–(1 – x)SrTiO3system at room temperature show that when amount of BiFeO3in the solid solution decreases, the magnetic hyperfine field values decrease as well and the widths of absorption line increase due to the weakening of the magnetic exchange interaction. The Mössbauer spectra of the systems with x< 0.5 indicate that the solid solution is paramagnetic. A relationship between the intensity of Zeeman lines and an amount of BiFeO3in BiFeO3–(1 – x)SrTiO3solid solution showed that the transition of this system to the paramagnetic state proceeded at room temperature, when xvalue was 0.4 (between x= 0.3 and 0.5).

Abstract: The composition and the magnetic structure of Fe3O4/γ-Fe2O3nanoparticles placed into external magnetic field with a strength of 1.8 kOe are studied with Mössbauer spectroscopy. We showed that the thickness of the maghemite (γ-Fe2O3) shell can be changed by the synthesis conditions. We found that there is a layer, in which the magnetic moments are not oriented collinearly to those located in the depth of the shell, on the surface of maghemite (γ-Fe2O3) shell in the Fe3O4/γ-Fe2O3nanocomposites; in other words, there is a canted spin structure. An intermediate layer in the spin-glass state is formed between the core and the shell. The data on structure of core/shell particles are important to understand the properties of nanocomposites, which are of great interest to apply in various fields, including biomedicine.

Abstract: The magnetic structure and the composition of Fe3O4/γ-Fe2O3nanoparticles are studied at 300 and 80 K with Mössbauer spectroscopy. We found that the Fe3O4/γ-Fe2O3particles are a core–shell nanocomposite (NC), in which magnetite Fe3O4is covered with a maghemite shell (γ-Fe2O3). We showed that the thickness of the maghemite shell (γ-Fe2O3) depends on synthesis technology. We found that a layer, whose magnetic structure differs from that of the inner part of the shell (γ-Fe2O3), is formed on the surface of the maghemite shell (γ-Fe2O3) in the Fe3O4/γ-Fe2O3NC. An intermediate layer is formed in the spin-glass state between the core and the shell. The data on structure of core–shell nanocomposites open up prospects to explain the properties of such particles, which are of great interest to use in various fields, including biomedicine.

Abstract: The nanocrystalline magnetically ordered materials based on bismuth orthoferrite doped with calcium are synthesized via glycine-nitrate combustion. X-ray diffractometry, helium pycnometry, BET, scanning electron microscopy, and elemental energy dispersive microanalysis data showed that they are isostructural to bismuth orthoferrite and have an average crystallite size of about 40 nm to form particles with an average size of 0.3 μm. Mössbauer spectroscopy and magnetometry data showed that their magnetic properties and those of pure bismuth orthoferrite are significantly differed. We found that the samples contain nanocrystals with other magnetic parameters and a low-dispersed phase fractions with a magnetic order.

The nonuniqueness of solutions of the inverse problem of localizing and determining the parameters of a magnetostatic dipole on the basis of measurements of the tensor of first spatial derivatives of the dipole magnetic field at two points is investigated. Criteria for choosing the true solution are obtained. Schemes of observation-point distribution ensuring the uniqueness of the solution are determined.

An ambiguity of Mössbauer spectra measured under total external reflection conditions due to the increase of the number of parameters which should be determined can be compensated by measuring a series of experimental spectra. The interpretation of all experimental data must be done by means of numerical modeling (or fitting). The method enables us to study phase transformations within a layer of about 10 nm thickness.

Perturbations of the known solutions of the inverse problem of parameters localization and determination for a point magnetostatic dipole are analyzed in the presence of errors in the initial data: the magnetic-induction vector and the tensor of first spatial derivatives of the magnetic field. On the basis of perturbation theory for the eigenvalues of real symmetric matrices, analytical estimates are obtained for the upper bounds of perturbation of the solutions. The results of analytical consideration are confirmed and complemented by digital modeling of solutions of the inverse problem in conditions of uniform and normal error distribution in the initial data.

The original paper &lquot;Scalar calibration of vector magnetometers&rquot; conceived the idea of an &lquot;intrinsic reference frame system&rquot; (IRFS), which is capable of playing a key role in varied calibration and correction procedures for three-axial magnetometers and coil facilities. However, the IRFS matrix derived in the original was open to question. The present comment analyses the IRFS concept and corrects the IRFS matrix.

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