J. A. Cowen

Anomalous magnetoresistance near the metamagnetic transition in

, a layered intermetallic compound, displays two magnetic phase transitions below room temperature, the lower one being a metamagnetic transition occurring near 100 K. We have completed measurements of both zero-field resistivity for and the magnetoresistance in fields of up to 8 T for temperatures between 1.5 and 120 K; in addition the magnetization has been studied in fields up to 5.5 T in the temperature range . As the spin configuration in the ordered phases remains uncertain, these measurements concentrate on the behaviour near the `ferromagnetic-to-antiferromagnetic transition, and as such they can be compared and contrasted with those reported recently for Ru-doped in which the spin configurations are better known. Plots of the metamagnetic field as a function of temperature yield metamagnetic transition temperatures of between 94 and 96 K (in zero field), in good agreement with earlier estimates. Additional features are observed below 100 K in this system, suggesting differences between and the doped system, originating possibly from fundamental differences in spin structure.

Non-linear susceptibility of Gd2In near the low-temperature phase transition

Abstract We have investigated the variation of the AC susceptibility and the DC magnetisation in the intermetallic compound Gd 2 In over the applied field range 0 ⩽ H a ⩽ 40 Oe in the temperature interval 85 ⩽ T ⩽ 105 K which encompasses the low-temperature transition to a metamagnetic antiferromagnetic state. Using these data, the temperature dependence of the coefficient a 2 ( T ) of the leading field-dependent contribution to the susceptibility: χ ( H i , T ) = χ 0 ( T ) + a 2 ( T ) H 2 i has been estimated and shown to exhibit an anomaly near 96 K.

Superconducting properties of chill-cast YNi2B2C

Abstract Chill-cast samples of YNi2B2C show a significant depression in the critical temperature, Tc, from that observed for arc-melted buttons, presumably due to the introduction of strains and defects during the chill-casting process. Here we present a summary of measurements of the AC susceptibility and the field- and temperature-dependent resistivity and magnetisation (in fields up to 10xa0T) on samples in the as-cast state. A comparison of these data with those on subsequently annealed specimens indicates that annealing causes an increase in Tc, Hc1 and Hc2 as well as an (expected) decrease in the normal state resistivity. The critical current density, Jc, however, displays an anomalous increase after annealing, suggesting that the annealing process might result in the formation of a defect structure, a behaviour similar to that seen in high-Tc oxide superconductors.

Transport and magnetic properties of GdNiBC

Abstract The borocarbide series (RC) m (NiB) n (R=rare earth, Y; m , n =1 or 2) has attracted much interest since the R=Lu, m =1, n =2 compound was found to display superconductivity near 16.5xa0K. While the m =1, n =2 systems display not only superconductivity, but also heavy electron behaviour (Yb) and various forms of magnetic order, the series with m = n =1 has not been investigated as extensively. Here we summarise the results of transport and magnetic measurements on GdNiBC from which we infer the presence of two transitions (as in GdNi 2 B 2 C) rather than a single anomaly found in earlier studies. However, susceptibility data on a powdered specimen display a single peaked structure reminiscent of that reported previously, suggesting that the present arc-melted materials may develop orientational texture. Furthermore, magnetoresistance measurements on the latter reveal an enhanced response with ( ρ (0)− ρ ( H ))/ ρ (0) exceeding 33% near 10xa0K in fields of 8xa0T.