Superconducting and magnetic properties ofY0.9R0.1Rh4B4

Abstract

The magnetization, susceptibility, heat capacity, and upper critical field (H/sub c/2) versus temperature (T) curves have been determined for the Y/sub 0.9/R/sub 0.1/Rh/sub 4/B/sub 4/ system with R = Gd, Dy, Ho, Er, and Tm. These materials allow the effects of the different magnetic rare earths on the superconducting properties of the host material to be studied at a dilute concentration, where no long-range magnetic order has been observed. The Ginzburg-Landau parameters xi/sub GL/ and lambda/sub GL/ have been obtained from the values of the heat-capacity coefficient ..gamma.., (dH/sub c/2/dT)= T/sub c/, and T/sub c/. These parameters, which are derived from the data near T/sub c/ and at low fields, are relatively insensitive to the particular rare-earth ion. At higher values of H/T (roughly-equal1 kOe/K) the H/sub c/2-vs-T curves show dramatic differences which can be correlated with the type of order (superconducting or ferromagnetic) that occurs in the RRh/sub 4/B/sub 4/ compounds. For R = Gd, Dy, and Ho, which order ferromagnetically in the concentrated compounds, the curves are seen to bend over sharply with increasing H/T, whereas for R = Er and Tm, which are superconducting in the concentrated compounds, the H/sub c/2-vs-T curves are very similar to thatmore » of nonmagnetic YRh/sub 4/B/sub 4/. In addition, the critical-field curves show that the crystal fields strongly affect the response of the rare-earth ions in a magnetic field, which in turn determines the magnetic transition temperatures of the RRh/sub 4/B/sub 4/ compounds.« less