THE EFFECT OF HOLMIUM DOPING ON THE MAGNETIC AND TRANSPORT-PROPERTIESOF LA0.7-XHOXSR0.3MNO3 LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-0.4)

We have studied the evolution of the transport and magnetic properties with holmium doping for La0.7-xHoxSr0.3MnO3 (0 less than or equal to x less than or equal to 0.4). We observe a systematic decrease in the ferromagnetic transition temperature (T-c), the metal-insulator transi tion temperature (T-p) and the rhombohedral cell volume with increasin g holmium concentration. For the concentration with x = 0.4, we observ e a metallic spin-glass phase with the spin-glass freezing temperature Tcusp similar to 50 K, and a large magnetoresistance ratio at low tem perature, which indicates that a proportion of the spins are in a frus trated state. The high-field magnetization of the holmium-doped sample s is much less than the magnetization that would be expected if the Mn 3+/Mn4+ were in a ferromagnetic state, showing that there is substanti al canting in the manganese lattice. We believe that the ferromagnetic component in the spin-glass phase for x = 0.4 crosses the percolation threshold, giving rise to metallicity in the sample.