Long-range antiferromagnetic order in the frustratedXYpyrochlore antiferromagnetEr2Ge2O7

Abstract

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 ${T}_{N}$ \ensuremath{\approx} 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 ${H}_{c}$ \ensuremath{\approx} 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.