Searching for heavy fermion materials in Ce intermetallic compounds

The low temperature heat capacity, magnetic susceptibility and electrical resistivity were studied for a series of Ce intermetallic compounds. No heavy fermion behavior was found in these compounds. CePtGa[subscript]3 has a rounded peak at ~1.7K in its heat capacity, which is shifted to higher temperatures in magnetic fields (~6K at 9.8T). The origin of this peak is believed to be due to a spin glass type transition. CeCd[subscript]11 has an unusual temperature dependence of its heat capacity which is due to a crystalline electric field (CEF) effect which occurs at an exceptionally low temperature. The CEF effect also plays an important role in CeGa[subscript]2. Antiferromagnetic phase transitions were found in CeHg[subscript]3, CeCd[subscript]2, CeCd[subscript]3 and CeNi[subscript]12B[subscript]6. Discussions on the low temperature behaviors of these and other Ce intermetallic compounds are given

Enhanced spin-dependent tunneling magnetoresistance in magnetite films coated by polystyrene

Hematite films were deposited by magnetron sputtering. A phase transformation from hematite to magnetite occurred when polystyrene (PS) coated hematite films were annealed above 200 °C in hydrogen flow. Giant negative magnetoresistance (MR) was observed with the best MR ratio of over 8% (at room temperature and in a field of 5.5 T) found in samples annealed at 230 °C. The temperature dependence of the resistivity is characteristic of intergranular tunneling. After the PS layer was removed and the films annealed again at 230 °C in hydrogen flow, the resistivity increased by about one order of magnitude and the MR ratio decreased to 4.3%. These data show that PS coating layer can protect magnetite films from oxidation and enhance interganular spin-dependent tunneling magnetoresistance

Giant negative magnetoresistance of spin polarons in magnetic semiconductors–chromium-doped Ti2O3 thin films

Epitaxial Cr-doped Ti2O3 films show giant negative magnetoresistance up to –365% at 2 K. The resistivity of the doped samples follows the behavior expected of spin (magnetic) polarons at low temperature. Namely, rho= rho0 exp(T0/T)p, where p = 0.5 in zero field. A large applied field quenches the spin polarons and p is reduced to 0.25 expected for lattice polarons. The formation of spin polarons is an indication of strong exchange coupling between the magnetic ions and holes in the system

Magneto-impedance of glass-coated Fe-Ni-Cu microwires

The magneto-impedance (MI) of glass-coated Fe-Ni-Cu microwires was investigated for longitudinal radio-frequency (RF) currents up to a frequency of 200 MHz using an RF lock-in amplifier method. The MI, defined as DZ/Z = [Z(H)-Z(H=0.3T)]/Z(H=0.3T), displays a peak structure (negative MI) at zero field for RF currents with frequencies less than 20MHz and this crosses over to a sharp dip (positive MI) at higher frequencies. This crossover behavior is ascribed to the skin-depth-limited response primarily governed by the field-dependence of the permeability. Large saturation fields (300 to 600 Oe) and other anomalies indicate the possible influence of giant magneto-resistance (GMR) on the MI.Comment: 3 pages, 2-column, 3 figures. To be published in J. Appl. Phys. 2000 (44th MMM conference proceedings