La3+ substitution effect on structural and magnetic properties of frustrated Ho2Ti2O7 pyrochlore

Abstract

A renowned quantum material Ho2Ti2O7 in which structural and magnetic properties are coupled, is identified by its unusual spin freeze state. In the current report, magnetic and structural behaviour of Ho2−xLaxTi2O7 (x = 0.0, 0.1, and 0.2) pyrochlore prepared through solid state standard method, were investigated by partial replacement of Ho3+ with nonmagnetic La3+. The XRD along with Raman spectroscopy studies confirmed single phasic cubic pyrochlore structure with red and blue shift of the phonon mode and increase in the structural ordering due to increase in the ionic radii ratio by incorporation of La in Ho2−xLaxTi2O7. Cell parameter is also increased linearly with increasing La content and follow Vegard’s rule. The crystalline size (71 ± 5 nm, 87 ± 6 nm and 107 ± 5 nm for x = 0.0, 0.1 and 0.2, respectively) calculated from W-H plot is increased with nonmagnetic La doping which is consistent with electron microscopy studies. No spin glassy pattern was traced in magnetic studies even letting down the temperature up to 2 K. It was found that Curie Weiss temperature (θCW) and effective magnetic moment (μeff) shrinking with rising chemical pressure that leads to weakening of ferromagnetic character of the compounds. Observed shift in the energy barrier is explained on the basis of change in dipolar and exchange interaction which is responsible for the magnetic behaviour of Ho2−xLaxTi2O7 pyrochlore. Furthermore, reduction in the value of θCW also depends upon the nature and location of the dopant. Large reduction in the θCW for Ho2Ti2O7 doped with La3+ suggested that doping at the A site can be used for the tuning the θCW.