O. V. Koplak

Magnetic phase transition in ɛ-InxFe2 − xO3 nanowires

This paper reports on a study of magnetic properties of ordered arrays of ɛ-InxFe2 − xO3 (x = 0.24) nanowires possessing a high room-temperature coercive force of 6 kOe. Lowering the temperature below 190 K brings about a sharp decrease of the coercive force and magnetization of nanowires driven by the magnetic phase transition from the ferrimagnetic into antiferromagnetic phase. The transition is accompanied by a decrease of the magnetic anisotropy constant, which accounts for the anomalous frequency dependence of the position of the maximum in the temperature dependence of dynamic magnetic susceptibility. In the low-temperature phase, a spin-flop transition in the magnetic field of 28 kOe has been observed at T = 2 K. Lines related to the high-temperature hard-magnetic and low-temperature phases have been identified in electron spin resonance spectra of the nanowires. A line lying near zero magnetic field and evolving from the nonresonant signal related to the microwave magnetoresistance of the sample has also been detected.

Ferromagnetism and microwave magnetoresistance of GaMnSb films

The influence of the concentration of holes on the ferromagnetism of MnSb clusters in GaMnSb films has been revealed. It has been found that the high concentration of holes leads to their tunneling through the Schottky barrier at the cluster-crystal lattice interface and to a change in the magnetization of clusters. The microwave resistance of the films depends on the spin polarization of holes, which is controlled by the magnetization of clusters and the external magnetic field. The parameters of the crystalline anisotropy of ferromagnetic clusters and the dipole-dipole interaction between them have been determined.

Spin-reorientation transition in ɛ-In0.24Fe1.76O3 nanowires

The magnetic phase transition in ɛ-In0.24Fe1.76O3 nanowires at a temperature of 190 K, which is accompanied by a sharp decrease in the magnetization and coercive force, has been discussed. A mechanism of the observed transition associated with a change in the direction of the easy magnetization axis owing to the competition between single-ion and dipole-dipole magnetic anisotropies has been proposed.

First MnIII complexes with tetradentate (N2O2) Schiff bases and tricyanomethanide: synthesis, crystal structure, and magnetic properties

The first MnIII complexes with Schiff bases and tricyanomethanide-anion were synthesized: [Mn(salen)C(CN)3(H2O)] (1), [Mn(5-Brsalen)C(CN)3(H2O)] (2), [Mn(salpn)C(CN)3(H2O)] (3), [Mn(3-MeOsalen)C(CN)3(H2O)] (4), [Mn(5-Brsalen)(MeOH)(H2O)][C(CN)3] (5), and [Mn(3-MeOsalpn)(H2O)2][C(CN)3] (6), where SalenH2 is N,N′-bis(salicylidene)ethylenediamine, 5-BrsalenH2 is N,N′-bis(5-bromosalicylidene)ethylenediamine, SalpnH2 is N,N′-bis-(salicylidene)-1,3-diaminopropane, 3-MeOsalenH2 is N,N′-bis(3-methoxysalicylidene)-ethylenediamine, 3-MeOsalpnH2 — N,N′-bis(3-methoxysalicylidene)-1,3-diaminopropane. The tricyanomethanide anion in complexes 1–4 acts as a the terminal ligand, whereas in complexes 5 and 6 tricyanomethanide is not coordinated by MnIII and acts as an out-of-sphere counterion. The structures of complexes 1–4 are characterized by the formation of dimers due to hydrogen bonds between the water molecules and oxygen atoms of the Schiff bases. The Mn...Mn distances inside the dimers are 4.69–5.41 Å. Complex 6 has a zigzag chain structure consisting of the [Mn(3-MeOsalpn)(H2O)2]+ cations bound by double bridging aqua ligands. The study of the magnetic properties of complexes 1, 3, 4, and 6 showed the existence of antiferromagnetic interactions between the MnIII ions through the system of hydrogen bonds.

Isotope-induced generation of paramagnetic defects under plastic deformation of 29Si crystals

It has been found that the number of paramagnetic clusters formed during plastic deformation of silicon crystals increases in crystals enriched with the 29Si isotope. It has been shown that there are antiferromagnetic spin-spin couplings with energies of ∼30–50 K in deformation-induced clusters of paramagnetic defects. The effect of the hyperfine interaction on spin-dependent reactions of silicon with oxygen or changes in elastic constants and lattice dilatation can cause the formation of deformation-induced defects in crystals enriched with 29Si.

Stochastic jumps of magnetization in [Mn{(R/S)-pn}]2[Mn{(R/S)-pn}2(H2O)][Cr(CN)6]2 molecular magnet

Series of stochastic jumps of the magnetic moment (up to five individual jumps) have been observed at the demagnetization of single crystals of [Mn{(R/S)-pn}]2[Mn{(R/S)-pn}2(H2O)][Cr(CN)6]2 molecular magnet in a narrow range of magnetic fields near the coercive force (Hc = 7.5 Oe). The magnetic field at which jumps of the magnetization arise decreases with an increase in the temperature.

Ferromagnetism of Nanoclusters of Chromium Alloys and Luminescence Quenching in ZnSe/ZnMgSSe/ZnSSe : Cr Heterostructures

The quenching of photoluminescence in a ZnSSe layer with an increase in the Cr concentration has been investigated in heterostructures with ZnSSe: Cr/ZnMgSSe quantum wells. It has been found that an increase in the Cr concentration in the quantum well to 2 × 1020 cm−3 leads to the formation of two types of magnetically ordered nanoclusters of chromium alloys in the ZnSSe: Cr layer with the magnetization blocking temperature of 170 K and above 300 K.

Magnetic properties of CoFeB alloys doped with Dy and Pr

Powders of the ferrimagnetic alloy CoFeBDyPr have been synthesized by the gas atomization method. Annealing of the samples at 900°C leads to the recrystallization of the amorphous phase into the crystalline phase (Pr,Dy)2Fe7Co7B, which changes the magnetic properties of the alloy (the coercive force decreases, the shape of the magnetic hysteresis loop changes, etc.). The temperature dependences of the remanent magnetization and Mössbauer spectra depend on the size of particles. This indicates the contribution from subsurface magnetic states of the phase of different chemical composition, which is identified by X-ray photoelectron spectroscopy in particles with sizes of less than 10 μm. A weakening of the dipole-dipole interaction between particles in the sample, where they are diluted in the solid organic matrix (eicosane), leads to a change in the shape of the hysteresis loop. The elimination of the mechanical mobility of particles in eicosane significantly increases (to 2.5 times) the coercive force.

Epsilon-phase iron(III) oxide nanowires for a magnetic-resonance spin-current source

Abstractε-In0.24Fe1.76O3 nanowire arrays are investigated using superconducting quantum-interference device (SQUID) magnetometry and electron-spin-resonance (ESR) spectrometry. It is established that the substitutional In impurity decreases the coercivity of the ε-phase iron(III) oxide nanowires. At temperatures below 190 K, the magnetization and coercivity of the nanowires sharply drops due to rotation of the easy-magnetization axis. The spin-reorientation transition significantly reconstructs the electron-spin-resonance spectrum of the nanowires.

Relation between the magnetization and the electrical properties of alloy GaSb-MnSb films

The influence of the charge carrier concentration on the magnetic properties of GaSb-MnSb alloys is studied. The ferromagnetism of GaSb-MnSb films is caused by the presence of MnSb granules and manifests itself in both magnetometric measurements and the presence of an anisotropic magnetoresistance and the anomalous Hall effect. Electric conduction is executed by charge carriers (holes) in a GaSb matrix. The magnetization of clusters depends on stoichiometry and the concentration of Mn2+ and Mn3+ ions, which is specified by the film growth conditions. At high film growth temperatures, ferromagnetic clusters containing Mn2+ ions mainly form. At low growth temperatures, an antiferromagnetic phase containing Mn3+ ions forms.