Observation of long-range magnetic ordering in pyrohafnateNd2Hf2O7: A neutron diffraction study

Abstract

We have investigated the physical properties of a pyrochlore hafnate ${\mathrm{Nd}}_{2}{\mathrm{Hf}}_{2}{\mathrm{O}}_{7}$ using ac magnetic susceptibility ${\ensuremath{\chi}}_{\mathrm{ac}}(T)$, dc magnetic susceptibility $\ensuremath{\chi}(T)$, isothermal magnetization $M(H)$, and heat capacity ${C}_{\mathrm{p}}(T)$ measurements, and determined the magnetic ground state by neutron powder diffraction. An upturn is observed below 6 K in ${C}_{\mathrm{p}}(T)/T$, however both ${C}_{\mathrm{p}}(T)$ and $\ensuremath{\chi}(T)$ do not show any clear anomaly down to 2 K. The ${\ensuremath{\chi}}_{\mathrm{ac}}(T)$ shows a well-pronounced anomaly indicating an antiferromagnetic transition at ${T}_{\mathrm{N}}=0.55$ K. The long-range antiferromagnetic ordering is confirmed by neutron diffraction. The refinement of the neutron diffraction pattern reveals an all-in/all-out antiferromagnetic structure, where for successive tetrahedra the four ${\mathrm{Nd}}^{3+}$ magnetic moments point alternatively all-into or all-out-of the tetrahedron, with an ordering wave vector k = (0, 0, 0) and an ordered state magnetic moment of $m=0.62(1)\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$/Nd at 0.1 K. The ordered moment is strongly reduced, reflecting strong quantum fluctuations in ordered state.