High-resolution neutron scattering study ofTb2Mo2O7: A geometrically frustrated spin glass

Abstract

The low-temperature magnetic properties of Tb 2 Mo 2 O 7 have been studied with bulk susceptibility measurements and with elastic and high-resolution inelastic neutron scattering. This system is a spin glass with a freezing temperature T g ϳ 25 K. A reverse Monte Carlo simulation of the neutron diffraction data shows weak ferromagnetic near-neighbor spatial correlations that do not extend beyond Շ10 Å. Neutron measurements of the spin dynamics reveal a slowing down with decreasing temperature without an anomaly at the glass transition. A low-lying Q-independent mode is seen at ប 0 ϳ 0.28 meV. This dispersionless crystal electric field transition is measurable up to 60 K.

Order and disorder in the local and long-range structure of the spin-glass pyrochlore, Tb2Mo2O7

“…Attempts to fit the data to such a model are not satisfactory, leading us to the conclusion that the magnitude of ∆R may vary randomly throughout the solid. [3] show that competition between near-neighbor AFM and FM correlations exists, consistent with the small θ CW . Although the Mo-Mo correlations cannot be easily obtained due to the small Mo 4+ magnetic moment, they are likely AFM, but weaker compared with the Mo-Mo interaction in Y 2 Mo 2 O 7 considering the doping study by Sato et al [15].…”

“…Polycrystalline Tb 2 Mo 2 O 7 samples were prepared using previously reported methods [3]. The magnetic-susceptibility measurements were made with a commercially available DC superconducting interference device (SQUID) magnetometer in a small applied field, no more than 2 mT.…”

“…For example, as the ionic radius of the A-site ion decreases from Nd (∼ 1.11Å) to Lu (∼ 0.98Å), the ground state changes from a ferromagnetic metal to a non-ferromagnetic insulator at Tb (ionic radius ∼ 1.04Å) [3]. Tb 2 Mo 2 O 7 and Y 2 Mo 2 O 7 (Y, ionic radius ∼ 1.02Å) are particularly important, since they are the first two spin glasses found in the pyrochlore family (SG transition temperatures, T SG , ∼ 25 and 22 K, respectively).…”

“…To understand the origin of the SG behavior of Tb 2 Mo 2 O 7 , a number of neutron scattering measurements have been conducted [3,12,13]. Taking account of the same effective moment of Mo 4+ measured in Y 2 Mo 2 O 7 , these measurements indicate that the Tb ion has an effective moment of µ ef f ≈ 8.83 µ B (close to Tb 3+ , L = 3, J = 6), which is three times larger than that of Mo 4+ .…”

Structural and magnetic short-range order in fluorite Yb2TiO5

“…Spectral weight in traditional spin glasses is typically well separated from the elastic band from, for example, crystal-field excitations. [56][57][58] . The signal at zero field in the present study, however, is qualitatively similar to previous studies on Yb-based pyrochlores, Yb 2 Ti 2 O 7 , Yb 2 Sn 2 O 7 , and Yb 2 Ge 2 O 7 14,18,59,60 .…”