A cubic ${\text{Er}}_2$${\text{Ge}}_2$${\text{O}}_7$ pyrochlore was prepared under high-pressure and high-temperature conditions and its magnetic ground state was investigated by measurements of specific heat, dc and ac magnetic susceptibility as functions of temperature, pressure, and magnetic field. We found that ${\text{Er}}_2$${\text{Ge}}_2$${\text{O}}_7$ undergoes a long-range antiferromagnetic transition at $T_N$ ≈ 1.4 K, which can be further enhanced by applying external physical pressure. On the other hand, application of external magnetic fields suppresses the antiferromagnetic order to zero temperature around $H_c$ ≈ 2.3 T, where a magnetic-field-induced spin-flop transition was observed. $H_c$ increases accordingly with increasing $T_N$ under external pressure. A comparison of the magnetic ground states and structural variations along the isostructural series ${\text{Er}}_2$$B_2$${\text{O}}_7$ ($B$ = Sn, Ti, Ge) together with the high-pressure study on ${\text{Er}}_2$${\text{Ge}}_2$${\text{O}}_7$ indicated that the magnetic properties of these highly frustrated XY pyrochlore antiferromagnets are very sensitive to the minute structural changes that determine the anisotropic exchange interactions and the local crystal-electric-field environments of Er${}^{3+}$ ions.

• Received 11 November 2013
• Revised 17 January 2014

DOI:https://doi.org/10.1103/PhysRevB.89.064409