R.Z. Levitin

Cascade of phase transitions in GdFe3(BO3)4

Cascade of phase transitions in GdFe3(BO3)4 at 156, 37, and 9 K has been detected by specific heat measurements and further studied by Raman scattering and Nd3+ spectroscopic probe method. A weakly first-order structural phase transition at 156 K is followed by a second-order antiferromagnetic ordering phase transition at 37 K and a first-order spin-reorientational phase transition at 9 K.

The magnetic phase transitions in R(Co, Al)2 compounds (R: Dy, Ho, Er)

Abstract The type of the magnetic phase transition in the R(Co1-xAlx)2 (R=Dy, Ho, Er) compounds is studied by means of magnetization, thermal-expansion and electrical-resistivity measurements. With increasing Al content, a change from a first-order to a second-order transition is observed, at x≃0.075, 0.075 and 0.025 for Er, Ho and Dy, respectively. An explanation is offered in terms of the Inoue-Shimizu model by introducing a concentration dependence of T3, the temperature at which a3(T) changes sign (a3 is the coefficient of the M4d-term in the expansion of the free energy of the d-subsystem). In fact, T3 is taken proportional to Tm, the temperature at which the susceptibility of the corresponding Y(Co, Al)2 shows a maximum.

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.

Magnetoelastic properties of rare-earth paramagnetic garnets: Magnetostriction and thermal expansion

Abstract The differential longitudinal magnetostriction (MS), in fields up to 50 KOe, for the [111], [110] and [001] crystal axes at 4.2 K and the crystal lattice parameter between 5 and 290 K for garnets R 3 Ga 5 O 12 and R 3 Al 5 O 12 (R = GdYb) are measured. The MS for all garnets except GdGG is very anisotropic and does not saturate; its value and sign change in an irregular way throughout the series of rare-earth (RE) ions. Within the terms of the crystal-field model the quadrupole approximation for the magnetoelastic energy is discussed. For the garnet structure with inequivalent sites of RE ions, the MS is expressed in terms of the field-induced changes of quadrupole moments which are numerically calculated for the known crystal fields. Semiquantitative analysis of experimental data allows one to account for the variation of the sign and value of MS from one garnet to another. Anomalies of the crystal lattice parameter observed at low temperatures for some RE garnets are described.

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.

Field-induced transitions of Y1−xGdx(Co0.93Al0.07)2 in ultrahigh magnetic fields up to 100T

Abstract The magnetization process of Y 1−x Gd x (Co 0.93 Al 0.72 ) 2 with 0 ≤ x ≤ 0.08 has been measured in ultrahigh magnetic fields up to 100 T. A metamagnetic transition to a ferrimagnetic state in a paramagnet with x ≤ 0.06 and a spin-flip transition to a noncollinear state in a ferrimagnet with x = 0.08 have been observed at low temperatures. From the transition fields the exchange constant between Co and Gd can be estimated to be J GdCo = ( −1.78±0.06) ×10 −22 J.

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.

Importance of higher order terms in CF Hamiltonian for interpretation of magnetization curves in Tb(Cu0.7Ni0.3)2

Abstract The crystal field (CF) contribution to the magnetic field dependence of the magnetization in the ferromagnetic compound Tb(Cu0.7N0.3)2 has been analysed theoretically. Contrary to the susceptibility data, the step-like appearance in the magnetization curves along the b axis cannot be explained in terms of second order in orthorhombic CF Hamiltonian only. It is shown, that to account for all features of the magnetization data in fields up to 24 T, the higher order terms should be included into the CF Hamiltonian.

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.