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The paper presents the results of complex investigations of the potassium-erbium double tungstate. The following properties have been measured: specific heat, specific heat in magnetic field, thermal expansion, thermal expansion in magnetic field, magnetization and X-ray structural data, reflectance and optical absorption spectra. The experiments were performed in the broad temperature range from 0.4 K to 300 K, spectral range from 4000 cm-1 to 40000 cm-1 and magnetic field up to 10T. The magnetic phase transition was found at temperature T=0.84K. In thermal expansion experiment the strong anomaly was found at T=7.6 K in magnetic field 10T. The KEr(WO4)2 belongs to the optical class of biaxial and pleochroic (trichroic) crystals. Using spectroscopy methods, the orientation of optical axes and refractive indices have been found. The main optical absorption spectra have been measured. The temperature dependence of optical absorption was determined.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Magnetic ordering of in low-dimensional magnet CsDy(W04)2, (CsDyW) has been first studied by means ofmeasurements ofthe low temperature specific heat over a temperature range ofO.5-23 K. The ordering temperature (IN) of the Dy sublattice was established to be 1.34 K. The experimental data indicate on the antiferromagnetic (AFM) characterofDy ions interactions. The magnetic behavior above and below TN is discussed in the framework ofdifferent theoreticalmodels.Keywords: rare-earth tungstate; specific heat; antiferromagnetic ordering; low-dimensional magnet. 1. INfRODUCTION Investigations of the alkaline (M) - rare-earth (Re) double tungstates MRe(W04)2 are of a special interest because of apossible realization ofboth magnetic and structural phase transitions in them. The existence ofrare-earth ions with closelyspaced energy levels in these low-symmetry compounds results in the occurrence of structural phase transitions connectedwith the manifestation of the cooperative Jahn-Teller effect. Indeed, such structural phase transitions (SPT) have beenrecorded in a monoclinic KDy(W04)2 (T= 6.38 K) and RbDy(W04)2 (T 4.9 and 9.0 K) single crystals. The doubletungstates are also considered to be a model system to check the conceptions of the low-dimensional magnetism. Thesestudies are-also strongly stimulated by possible applications ofthese materials as active component in solid state lasers. Itis shown [1] that there is possibility of application of rubidium-dysprosium double tungstate as a cooling agent in anadiabatic demagnetization method for obtaining very low temperatures.

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.