A closed cycle cryostat intended for optical and Mössbauer investigations in the temperature range 4.2–300 K is described. Samples are cooled owing to the operation of a two-stage closed-cycle cryogenic refrigerator (CR) based on the Gifford-MacMahon cycle (with a refrigerating capacity of 1 W at T = 4.2 K at the second stage). The minimum temperature reached at the second stage of the CR was 2.7 K. The methods for reducing vibrations transferred from the CR to a sample are described in detail. The design proposed makes it possible to reduce the vibrational broadening of the resonance Mössbauer lines to a level of 10–15% at 5 K, thus exceeding the level of the best cryostat prototypes in the world.

Fe_1-xCo_x nanowires are obtained by electrochemical deposition into the pores of track-etched membranes. The characteristics of the growth process that allow controlling the length and aspect ratio of the nanowires are established. The elemental composition and magnetic properties of the nanowires depend on the diameter of the track-etched pores, which varies from 30 to 200 nm, and the electrochemical potential U (650–850 mV), which determines the nanowire growth rate. According to the results of elemental analysis and the Mössbauer spectroscopy data, the Co content in Fe_1-xCo_x lies in the range of x=0.20−0.25. It is found that the orientation of the magnetic moment of Fe–Co nanoparticles in the wires depends both on the track pore size d and on the nanowire growth rate. Thus, the magnetic moments in nanowires grown in 50-nm-diameter pores are oriented within 0°–40° with respect to the nanowire axis. The magnetic properties of the nanowires are explained in the framework of a theoretical model describing the magnetic dynamics of nanocomposites, which was extended to include the relaxation of the magnetization vector and to take into account interaction between the particles. The key physical parameters important for the technological applications of the nanowires are determined, their dependence on the nanowire growth conditions is traced, and the possibility of controlling them is established.

Arrays of iron nanowires prepared by the method of galvanic filling of polymer track-etched membrane pores (matrix synthesis) under different electrolysis modes and electrolyte temperatures have been...

The multiferroic RFe₃(BO₃)₄ family is characterized by diverse magnetic, magnetoelectric, and magnetoelastic properties, the fundamental aspects of which are essential for modern electronics. The present research, using single-crystal X-ray diffraction (XRD) and Mössbauer spectroscopy (MS) in the temperature range of 25–500 K, aimed to analyze the influence of local atomic coordination on magnetoelectric properties and exchange and super-exchange interactions in RFe₃(BO₃)₄. Low-temperature, single-crystal XRD data of the magnetically ordered phase of RFe₃(BO₃)₄ at 25 K, which were obtained for the first time, were supplemented with data obtained at higher temperatures, making it possible to draw conclusions about the mechanism of the structural dynamics. It was shown that, in structures with R = Gd, Ho, and Y (low-temperature space group P3₁21), a shift in oxygen atoms (O2, second coordination sphere of R atoms) was accompanied by rotation of the B2O₃ triangle toward R atoms at low temperatures, and by different rearrangements in iron chains of two types, in contrast to Nd and Sm iron borates (space group R32). These rearrangements in the structures of space group P3₁21 affected the exchange and super-exchange paths at low temperatures. The MS results confirm the influence of the distant environment of atoms on the magnetoelectric properties of rare-earth iron borates at low temperatures.