Magnetic properties of a quasi-one-dimensional NaFeGe<Subscript>2</Subscript>O<Subscript>6</Subscript> polycrystal

The magnetic properties of a synthesized dielectric NaFeGe₂O₆. polycrystal have been studied. The antiferromagnetic ordering of this compound below 15 K has been established. The Mössbauer spectrum at 300 K is a quadrupole doublet; it is characterized by an isomeric shift typical of the high-spin Fe³⁺ ion in the octahedral coordination and quadrupole splitting, which indicates distortion of the oxygen octahedron around the iron cation. Quasi-one-dimensionality of the sample magnetic structure is proved.     

Magnetic properties, magnetoresistance, and Raman spectra of CuV x Cr1 − x S2

The results of investigations of the magnetic and Raman spectra, magnetic properties, and magnetoresistance of vanadium-substituted chromium copper disulfides CuV _x Cr_{1 ? x} S₂ (x = 0.1) are presented.     

Magnetic properties of single crystals of ludwigites Cu<Subscript>2</Subscript><Emphasis Type="Italic">M</Emphasis>BO<Subscript>5</Subscript> (<Emphasis Type="Italic">M</Emphasis> = Fe<Superscript>3+</Superscript>, Ga<Superscript>3+</Superscript>)

High-quality single crystals of ludwigites Cu₂ MBO₅ (M = Fe³⁺, Ga³⁺) have been grown, and the magnetic, resonance, and Mössbauer studies have been performed. It is established that the Cu₂FeBO₅ and Cu₂GaBO₅ compounds are antiferromagnets with Néel temperatures of 32 and 3.4 K, respectively. A model of the magnetic structure of the compounds is proposed. It is shown that the magnetic properties of the ludwigites are substantially dependent on the degree of ion distribution over crystallographic positions.     

Structural and Magnetic Characteristics of Nanogranular Co–Al2O3 Single- and Multilayer Films Formed by the Solid-State Synthesis

The results of structural and magnetic investigations of nanogranular Co–Al₂O₃ films formed from Co₃O₄/Al thin-film layered structures upon vacuum annealing are reported. The Co₃O₄/Al films have been obtained by sequential reactive magnetron sputtering of a metallic cobalt target in a medium consisting of the Ar + O₂ gas mixture and magnetron sputtering of an aluminum target in the pure argon atmosphere. It is shown that such a technique makes it possible to obtain nanogranular Co–Al₂O₃ single- and multilayer thin films with a well-controlled size of magnetic grains and their distribution over the film thickness.

     

New magnetic materials Cu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>S with a metal-insulator transition

This paper reports on first results of the synthesis and study of the thermal, structural, electrical, resonance, and magnetic properties of new sulfide materials Me _x Mn_{1 − x} S (Me = Cu, 0 < x < 0.2) synthesized based on manganese monosulfide. The materials have a NaCl cubic structure at 300 K and undergo a concentration metal-insulator transition with increasing degree of substitution and with varying temperature. The magnetic transition occurs in the region of the heat capacity anomaly. The Néel temperature is slightly dependent on the copper concentration. The samples with a high copper content exhibit metallic conduction at T < 260 K and semiconductor conduction at T > 260 K.     

Magnetic state of the GdFeTi2O7 compound

The X-ray diffraction, M?ssbauer, calorimetric, and magnetic characteristics of zirconolite GdFeTi₂O₇ have been measured to determine the ground magnetic state. A kink dependent on the magnetic prehistory of the sample has been revealed in the temperature dependence of the magnetic moment at T = 3 K. M?ssbauer spectroscopy has confirmed the nonequivalence of the iron ion positions in GdFeTi₂O₇. The experimental data obtained allow the conclusion on the formation of a spin glass state with the freezing temperature T _f = 3 K in the GdFeTi₂O₇ compound.     

Synthesis, crystal structure, and magnetic properties of the Li8FeSm22O38 single crystal

New single crystals of Li₈FeSm₂₂O₃₈ have been grown by spontaneous crystallization from a solution in melt. The structure of these crystals has been determined: it corresponds to the space group Im $\bar 3$ m. Investigations of the magnetic susceptibility in the ranges of temperatures 2?C24 K and fields up to 50 kOe have revealed a magnetic transition near 3 K. The temperature behavior of the magnetic susceptibility of the two-level system has been simulated. The results of the simulation agree with the experimental data. The resonance properties of Li₈FeSm₂₂O₃₈ have been studied in the temperature range 100?C300 K.     

New magnetically ordered CoBO3 crystal

Crystals of a new CoBO₃ compound were synthesized from a solution in melt. According to the X-ray diffraction data, CoBO₃ crystallizes in the calcite structure with lattice parameters a _H =4.631±0.005, c _H =14.51±0.01 Å. Measurements on SQUID and vibrating-coil magnetometers suggested that CoBO₃ is a magnetically ordered crystal with a saturation magnetization of 50 emu/g in the basal plane at 4.2 K and a Néel temperature of 53 K.     

Synthesis and magnetic properties of copper metaborate single crystals, CuB2O4

Large high-quality single crystals of copper metaborate are grown on the basis of the phase diagram of the ternary Li₂O-CuO-B₂O₃ system. Bright blue crystals with a volume of about 1 cm³ were grown by the method of spontaneous crystallization while slowly cooling the melt. The magnetic susceptibility and electron spin resonance were measured. It is shown that the effective magnetic moment of a Cu²⁺ ion is equal to 1.6 μ_B and the g-factor, to 2.170 and 2.133 for the magnetic field oriented parallel and perpendicular to the fourfold axis, respectively. At 21 and 10 K, sharp anomalies of magnetic susceptibility are observed.     

Weak ferromagnetism in copper metaborate CuB2O4

CuB₂O₄ single crystals have been grown and their magnetic and resonance properties have been investigated for the first time. The temperature dependence of the susceptibility was found to contain features at T=21 and 10 K. The CuB₂O₄ single crystal transformed at T=21 K to a weakly ferromagnetic state. The sharp drop in susceptibility at T<10 K is caused by a transition of the magnetic system of CuB₂O₄ to an antiferromagnetic state. The effective magnetic moment of the Cu₂₊ ion, determined from the high-temperature part of the magnetic susceptibility, is 1.77 μ _B. The room-temperature g factors are, respectively, 2.170 and 2.133 for magnetic field parallel and perpendicular to the c axis of the crystal. The antiferromagnetic resonance parameters in the weakly ferromagnetic and antiferromagnetic phases were measured. Fiz. Tverd. Tela (St. Petersburg) 41, 1267–1271 (July 1999)