We have investigated the physical properties of a pyrochlore hafnate ${\mathrm{Nd}}_2{\mathrm{Hf}}_2{\mathrm{O}}_7$ using ac magnetic susceptibility ${\chi }_{\mathrm{ac}}\left(T\right)$, dc magnetic susceptibility $\chi \left(T\right)$, isothermal magnetization $M\left(H\right)$, and heat capacity $C_{\mathrm{p}}\left(T\right)$ measurements, and determined the magnetic ground state by neutron powder diffraction. An upturn is observed below 6 K in $C_{\mathrm{p}}\left(T\right)/T$, however both $C_{\mathrm{p}}\left(T\right)$ and $\chi \left(T\right)$ do not show any clear anomaly down to 2 K. The ${\chi }_{\mathrm{ac}}\left(T\right)$ 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 $m=0.62\left(1\right){\mu }_{\mathrm{B}}$/Nd at 0.1 K. The ordered moment is strongly reduced, reflecting strong quantum fluctuations in ordered state.

• Received 15 June 2015
• Revised 12 October 2015

DOI:https://doi.org/10.1103/PhysRevB.92.184418