The effect of holmium doping on the magnetic and transport properties of La_0.7-xHo_xSr_0.3MnO₃ (0≤ x≤ 0.4)

Abstract

We have studied the evolution of the transport and magnetic properties with holmium doping for La_0.7-xHo_xSr_0.3MnO₃ (0≤ x≤ 0.4). We observe a systematic decrease in the ferromagnetic transition temperature T_c, the metal - insulator transition temperature T_p and the rhombohedral cell volume with increasing holmium concentration. For the concentration with x = 0.4, we observe a metallic spin-glass phase with the spin-glass freezing temperature T_cusp∼ 50K, and a large magnetoresistance ratio at low temperature, which indicates that a proportion of the spins are in a frustrated state. The high-field magnetization of the holmium-doped samples is much less than the magnetization that would be expected if the Mn³⁺/ Mn⁺⁺ were in a ferromagnetic state, showing that there is substantial 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.