Search

Magnetic properties of KGd(WO4)2, KYb(WO4)2 and KTm(WO4)2 single crystals have been studied. Temperature and field dependences of the magnetization along the main magnetic axes and angular dependence of the magnetization in the planes settled on the magnetic axes were recorded in the temperature range from 2 up to 100 K and in magnetic field up to 9 T. Paramagnetic Curie temperatures, g-factors and exchange interaction parameters were determined. Different theoretical models were used to describe magnetic properties of KGd(WO4)2 and KYb(WO4)2 crystals.

Magnetic and electron paramagnetic resonance (EPR) properties of EuFe3(BO3)4 single crystals have been studied over the temperature range of 300–4.2 K and in a magnetic field up to 5 T. The temperature, field and orientation dependences of susceptibility, magnetization and EPR spectra are presented. An antiferromagnetic ordering of the Fe subsystem occurs at about 37 K. The easy direction of magnetization perpendicular to the c axis is determined by magnetic measurements. Below 10 K, we observe an increase of susceptibility connected with the polarization of the Eu sublattice by an effective exchange field of the ordered Fe magnetic subsystem. In a magnetic field perpendicular to the c axis, we have observed an increase of magnetization at T < 10 K in the applied magnetic field, which can be attributed to the appearance of the magnetic moment induced by the magnetic field applied in the basal plane. According to EPR measurements, the distance between the maximum and minimum of derivative of absorption line of the Lorentz type is equal to 319 Gs. The anisotropy of g-factor and linewidth is due to the influence of crystalline field of trigonal symmetry. The peculiarities of temperature dependence of both intensity and linewidth are caused by the influence of excited states of europium ion (Eu3+). It is supposed that the difference between the g-factors from EPR and the magnetic measurements is caused by exchange interaction between rare earth and Fe subsystems via anomalous Zeeman effect.

The magnetocaloric effect in La0.6Ca0.4MnO3 manganite has been investigated. The isothermal magnetization versus applied magnetic field at various temperatures in the vicinity of Curie temperature was measured, and the temperature dependence of magnetic entropy change was determined using Maxwell’s relation. This value is comparable to that in Gd. Nevertheless, the relative cooling power of La0.6Ca0.4MnO3 was shown to be considerably lower than that of Gd. The experimental results have been analyzed in frames of a phenomenological statistical model. This model considers explicitly Jahn-Teller interactions and allows prediction of the field dependences of the magnetic entropy change and the relative cooling power.

The influence of the kinematic interaction and the indirect exchange of electrons on the magnetic structure of a narrow-gap Hubbard magnet is investigated using the diagram technique of the perturbation theory. The summation of an infinite series of like diagrams makes it possible to separate the effective self-consistent filed. In contrast to the previous studies, the proposed theory contains only two self-consistent parameters, i.e., the chemical potential and the average spin. The obtained system of equations for these parameters admits the analytical solution at zero temperature. The competition of the simplest kinematic contribution and the indirect antiferromagnetic exchange is clearly demonstrated using the concentration dependences of the Neel temperature as an example. The boundaries of the existence of the homogeneous ferromagnetic, antiferromagnetic, and paramagnetic phases as a function of the electron concentration and the indirect exchange parameter are determined by numerically analyzing the internal energy.

Magnetic phase transition in the CsDyW2O8 magnet has been studied by means of low temperature specific heat C(T) measurements. The magnetic ordering temperature of the Dy3+ sublattice was established to be 1.34 K. The experimental results indicate on the antiferromagnetic character of interactions between Dy3+ ions. The behavior of the C(T) dependencies above and below TN is discussed in frames of different theoretical models. The measurements data on temperature and field dependencies of magnetization are used to calculate the exchange and dipole-dipole interactions energy and to determine the possible magnetic structure of the ground state.

The results of measuring the temperature and field dependences of the magnetization of a RbDy(WO4)2 single crystal in the temperature range from 4.2 to 50 K and in magnetic fields up to 1.6 T are presented. The energies of the exchange and dipole-dipole interactions are estimated. The magnetic structure of the ground state is determined.

X-ray diffraction and magnetic using dc and ac methods measurements of the polycrystalline and nanosize REMnO3 (RE = Pr, Nd) powdered samples have been performed. The nanosize manganites were synthesized with a sol-gel method at different (800, 850 and 900 °C) temperatures. The average size of synthesized nanoparticles (from 56 to 89 nm) and polycrystalline powders (above 200 nm) was estimated using the x-ray diffraction data. All the compounds studied crystallize in the orthorhombic crystal structure (space group Pnma) at room temperature with smaller values of the lattice parameters in the nanosamples. The temperature-dependent ac magnetic susceptibilities show a sharp high-temperature peak connected with Mn magnetic moments ordering. The low-temperature maximum of magnetic susceptibility is proposed to be due to the polarization of the rare-earth sublattice by an effective exchange field of the Mn ordered sublattice. The antiferromagnetic ordering of Mn sublattice and paramagnetic Curie temperatures as well as the magnetic moment values for the nanosize samples was found to be smaller than those for polycrystalline sample.

We report on the pressure, field and temperature dependencies of magnetization and resistance in manganites of (La1-xCax)1-yMn1+y O3 type. The M(T) dependencies is established to exhibit the following peculiarities: the first is connected with the paramagnet (PM)-ferromagnet (FM) transition at 267 K; the peak of M(T) dependence eat 263K is presumable due to an existence of AFM clusters; an anomaly in magnetization is connected with the FM-canted phase transition at 42K and the large irreversibility in the field-cooled and zero field- cooled magnetization. As field is increased above 200 Oe, the sign of the M(T) anomaly changes, namely, the M(T) magnetization increases with increasing field at 42K. The character of M(T) dependencies does not change under pressure. However, both the Curie temperature, Tc, and the resistance peak corresponding to metal-insulator transition shift in the direction of high temperatures with increasing pressure. A pressure stabilizes the ferromagnetic metallic phase. The temperature of the FM-canting phase transition does not change under pressure. The magneto resistance effect increase by 15 percent under pressure of 12.6 kbar.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We report on the temperature and pressure dependences of the magnetization in the KDy(W04)2 single crystal. The directions ofmagnetic axes in the ciystal under study were established. It has been shown that at the point ofthe structural phase transition theCurie-Weiss temperature changes considerably. Under pressure ofabout 0.8 GPa the temperature ofthe structural phase transitionincreases nearly by a factor oftwo. As a result ofthe pressure effect the low temperature phase area is expanded. Keywords: KDy(W04)2, double tungstates, phase transition, cooperative Jahn-TeIler effect, magnetization, magnetizationunder pressure, constants ofexchange interactions, Curie-Weiss temperature 1. INTRODUCTION Investigations ofmagnetic resonance and thermal properties ofthe KDy(W04)2 double tungstate ' have shown that this compound is ofinterest because of structural and magnetic phase transitions observed in this low-dimensional magnetic material. The Jahn-Teller type structural phase transition (SPT) at Tp1- 6.38 K and the antilerromagnetic (AFM) phase transition at

The magnetic investigations of potassium holmium double tungstate KHo(WO⁴)² have been performed. The results of measurements of magnetic susceptibility and magnetization as a function of temperature (T from 0.3 K up to 100 K) and magnetic field (up to 1.5 T) are presented. A strong anisotropy of magnetic properties was found. The magnetic measurements data were used to calculate the interaction energy. It was shown that the interactions between nearest neighbors Ho³⁺ ions have antiferromagnetic character.