Magnetoelastic Coupling in the Stretched Diamond Lattice of TbTaO4

The magnetic structure of diamond-like lattice has been studied extensviely in terms of the magnetic frustration. Here we report the distortion of stretched diamond lattice of Tb3+ (4f8) in M-TbTaO4 on application of a magnetic field. We have investigated the structural and magnetic properties of M phase terbium tantalate M-TbTaO4 as a function of temperature and magnetic field using magnetometry and powder neutron diffraction. Sharp λ-shape transitions in d(χT)/dT, dM/dH and specific heat data confirm the previously reported three-dimensional (3D) antiferromagnetic ordering at TN∼2.25 K. On application of a magnetic field the Néel temperature is found to decrease and variable field neutron diffraction experiments below TN at 1.6 K show an increase in both the bond and angle distortion of the stretched diamond lattice with magnetic field, indicating a potential quantum magneto-elastic coupling effect. By combining our magnetometry, heat capacity and neutron diffraction results we generate a magnetic phase diagram for M-TbTaO4 as a function of temperature and field.