Spin-ice behavior of mixed pyrochlore Dy2GaSbO7 exhibiting enhanced Pauling zero-point entropy

Abstract

Herein, the low-temperature magnetothermal properties and spin-ice physics of a mixed pyrochlore, Dy2GaSbO7 (DGS), are investigated through dc magnetization, ac susceptibility, and heat capacity experiments, and crystal-field computation. A Curie-Weiss (CW) fit to the dc susceptibility data yields effective magnetic moment, μeff = 10.0 μB/Dy3+ and CW temperature, θCW = +1.62 K. Magnetization attains a saturation value of Msat = 5.06μB/Dy above H ≈ 8 T and at T = 2 K, which is half of the μeff due to the effective Ising-type anisotropy along local 〈111〉 axes of the elementary Dy4O′ tetrahedron, illustrating DGS as an effective spinS∼ = 1/2 system. The dc susceptibility data are interpreted satisfactorily within the framework of a crystal-field theory and a mean-field approximation taking account of long-range dipolar interactions and anisotropic exchange interactions between the nearest-neighbor Dy3+-ions. AC susceptibility exhibits anomaly at a temperature Tice ≈ 3.13 K at frequency of f = 111 Hz, which is a signature of dynamical freezing of spins into a disordered state in compliance with the spin-ice rules. Heat capacity at zero field also shows a peak at 1.36 K and a low kink at 3.25 K which smears out on application of the magnetic field. The calculated magnetic entropy of DGS at zero field is 2.82 J K−1(mol-Dy)−1, which is much less than the Pauling spin-ice value of 4.1 J K−1mol−1. The spin-ice entropy is restored with a value of 4.50 J K−1(mol-Dy)−1 at a field of 1 T. The zero-point entropy of DGS becomes 2.94 J K−1(mol-Dy)−1 which is larger than Pauling zero-point entropy of 1.686 J K−1mol−1 for cannonical dipolar spin-ice materials, e.g., Dy2Ti2O7 and Ho2Ti2O7. The enhanced entropy of DGS may be induced due to random chemical disorder and varied chemical pressure of B-site (GaSb tetrahedra) ions. Thus, the present study creates a new pathway to extend the horizon of spin-ice physics.