Magnetic order in geometrically frustrated Gd_2(Ti_(1-x)Zr_x)_2O_7 (x = 0.02 and 0.15) single crystals

摘要

Single crystals of Gd_2(Ti_(1-x)Zr_x)_2O_7 with x = 0.02 and 0.15 have been used to investigate the effects of Zr doping on the properties of the geometrically frustrated antiferromagnet Gd_2Ti_2O_7. Powder and single-crystal x-ray data, along with optical birefringence measurements, reveal that the x = 0.02 sample retains the cubic Fd~(-)_3m structure of pure Gd_2Ti_2O_7, while the x = 0.15 composition adopts a tetragonal I4_1/amd structure. Low-temperature magnetization and specific heat measurements show that for Gd_2(Ti_(0.98)Zr_(0.02))_2O_7 there are two magnetic transitions at T_(N1) = 1.02 K and T_(N2) = 0.70 K, but for Gd_2(Ti_(0.85)Zr_(0.15))_2O_7 a single transition is observed at T_N = 1.02 K. Changes in the specific heat with a magnetic field applied along the [110] and the [111] directions are used to construct the H-T phase diagrams for both samples.