V.V. Snegirev

Magnetic and spectral studies of Er2BaNiO5 and other rare earth nickelates

Abstract Optical absorption spectra, magnetic susceptibility and magnetization of nickelates R 2 BaNiO 5 (R=Nd-Gd, Dy-Tm) containing isolated Nue5f8Oue5f8Ni chains have been measured. Magnetic ordering temperatures were found to be considerably higher than the temperatures of the maxima in the magnetic susceptibility. Most of the compounds R 2 BaNiO 5 exhibit two metamagnetic transitions. By comparison with neutron diffraction data for Er 2 BaCuO 5 it was shown that the interaction R-Ni dominates and that the magnetic behavior of the rare earth subsystem can be satisfactorily described in a molecular-field framework.

Magnetostriction measurements under high magnetic fields by a piezoelectric transducer glued on the sample

Abstract A method of magnetostriction measurements in high pulsed magnetic fields by a thin single-crystalline piezoelectric quartz transducer glued on the sample, is described. The method can also be used to measure the differential magnetostriction in static magnetic fields.

Field-induced noncollinear magnetic structures in Al-stabilized RCo2 Laves phases: Study of the Lu1-yTmy(Co0.88Al0.12)2 system

Abstract The magnetization of Lu 1- y Tm y (Co 1- x Al x ) 2 cubic Laves-phase ferrimagnets, in which magnetism of the itinerant d-subsystem is stabilized by partial Al-substitution, has been measured in magnetic fields up to 38T. Field-induced noncollinear magnetic structures are observed for H c1 ⩽ H ⩽ H c2 in compounds with Tm concentrations y ⩽0.6. The intersublattice molecular-field coefficient, λ fd , is found to be equal to -(13.5±1) Tf.u./μ B , and to be independent of the Tm concentration. At 4.2 K, the experimentally determined μ 0 H-y phase diagram can be described well, if we take into account the field dependence of the Tm moment.

Magnetic ordering and metamagnetism in Dy2BaCuO5

Abstract Specific heat, ac magnetic susceptibility and magnetization of the “green phase” Dy 2 BaCuO 5 polycrystalline samples were measured. Two magnetic transitions have been found: antiferromagnetic ordering of Cu 2+ and Dy 3+ magnetic moments at 18 K and 10 K, respectively. The Dy 3+ magnetic ordering is the first order phase transition. The metamagnetic transition in dysprosium subsystem, induced by magnetic field, is observed at temperatures lower than 10 K.

Anomalous magnetocaloric effect in van vleck paramagnet HoVO4 near energy level crossing

The anomalous magnetocaloric effect in singlet rare-earth paramagnets near energy level crossing has been experimentally observed for the first time. The magnetization and differential magnetic susceptibility of Ho1 − xYxVO4 crystals (x = 0, 0.5) measured along the tetragonal axis in a pulsed magnetic field with various change rates near the crossover field, dH/dt, from 3 × 103 to 2.5 × 102 T/s are compared to the data in static magnetic fields down to 0.1 K. These data indicate the large negative magnetocaloric effect in the pulsed magnetic field, so that the crystal with the initial temperature T0 = 4.2 K is cooled much lower than 1 K. The experimental data are qualitatively described in the crystal field model with various interactions including hyperfine interactions and with the known interaction parameters.

Spectral and magnetic studies of nickelates Lu2BaNiO5 and Yb2BaNiO5

Abstract High resolution optical spectra, ac magnetic susceptibility and magnetization in pulse fields were measured for polycrystalline Yb2BaNiO5 and Lu2BaNiO5 isostructural to the “green phase” R2BaCuO5 of high-Tc superconducting ceramics. Lu2BaNiO5 orders magnetically at 4.5 K while in Yb2BaNiO5 three-dimensional magnetic order does not, evidently, establish down to 1.9 K. Low-dimensional magnetic correlations are present in both compounds.

Structural and Magnetic Properties of Ni50Mn35In15 Thin Films

We present the results of macroscopic measurements, X-ray diffraction and neutron reflectivity experiments on ≈ 25 nm thin films of Ni50Mn35In15 grown using Pulsed laser deposition technique on MgO single-crystalline substrate. Intrinsic magnetization of the film below Tc ≈ 290 K was confirmed. Structural measurements show the large temperature-dependent residual strain on the substrate with no indication of martensitic transition.

Peculiarities of Elastic Properties of RE Cobaltites RBaCo4O7 (R = Dy - Er, Y) at Magnetic Phase Transitions

It has been found that the temperature dependences of the Young’s modulus for rare-earth cobaltites RBaCo4O7 (R = Dy - Er, Y) exhibit significant hysteresis and irreversible effects over a wide range (80–280) K between the structural and magnetic phase transition temperatures. At the magnetic phase transition temperature, there are weak and smoothed anomalies of the Young’s modulus, which correlate with the low dimensionality and frustration of the exchange interactions in the Kagome lattice of the Co subsystem for the studied rare-earth cobaltites.

Rapid suppression of ferromagnetism in Y2Ni7 and YNi3 intermetallic compounds for small substitutions of Ni by Al and Co

The magnetic properties of Y(Ni 1− x Me x )3 and Y 2 (Ni 1− x Me x ) 7 systems, where Me = Al, Co, have been investigated. Rapid suppression of ferromagnetism is found for both systems when nickel is substituted by aluminum. The temperature induced ferromagnetism has not been observed in both Y 2 Ni 7 and all the compositions with cobalt and aluminum. The transformation of magnetic properties of Y 2 Ni 7 and YNi 3 during the substitutions is explained qualitatively in the rigid d-band approximation.

High-field rare-earth magnetostriction of high-Tc HoBa2Cu3O7−δ compounds

Abstract The magnetostriction (MS) of the high-temperature superconductors HoBa2Cu3O7−δ (HoBaCuO) and YBa2Cu3O7−δ (YBaCuO) is investigated in order to clarify a contribution of the Ho 3+ ions into the magnetoelastic (ME) properties and to describe the ME interactions in the framework of the crystal field theory.