Magnetic properties of Yb2Mo2O7 and Gd2Mo2O7 from rare earth Mossbauer measurements

TL;DR

This study uses Mossbauer spectroscopy and other techniques to investigate the magnetic properties and lattice disorder in Yb2Mo2O7 and Gd2Mo2O7 pyrochlores, revealing different magnetic interactions and low-temperature spin dynamics.

Contribution

It provides new microscopic insights into the magnetic interactions, lattice disorder, and spin fluctuations in Yb2Mo2O7 and Gd2Mo2O7 pyrochlores using Mossbauer and complementary measurements.

Findings

Yb2Mo2O7 exhibits antiferromagnetic Mo interactions and lattice disorder.

Gd2Mo2O7 shows ferromagnetic Mo interactions and persistent low-temperature spin fluctuations.

Magnetic irreversibilities occur at 17K in Yb2Mo2O7 and 75K in Gd2Mo2O7.

Abstract

Using 170-Yb and 155-Gd Mossbauer measurements down to 0.03K, we have examined the semiconducting pyrochlore Yb2Mo2O7 where the Mo intra-sublattice interaction is anti-ferromagnetic and the metallic pyrochlore Gd2Mo2O7 where this interaction is ferromagnetic. Additional information was obtained from susceptibility, magnetisation and 172-Yb perturbed angular correlation measurements. The microscopic measurements evidence lattice disorder which is important in Yb2Mo2O7 and modest in Gd2Mo2O7. Magnetic irreversibilities occur at 17K in Yb2Mo2O7 and at 75K in Gd2Mo2O7 and below these temperatures the rare earths carry magnetic moments which are induced through couplings with the Mo sublattice. In Gd2Mo2O7, we observe the steady state Gd hyperfine populations at 0.027K are out of thermal equilibrium, indicating that Gd and Mo spin fluctuations persist at very low temperatures. Frustration is thus operative in this essentially isotropic pyrochlore where the dominant Mo intra-sublattice interaction is ferromagnetic.