Magnetic structure and crystal-field states of the pyrochlore antiferromagnetNd2Zr2O7

Abstract

We present synchrotron x-ray diffraction, neutron powder diffraction, and time-of-flight inelastic neutron scattering measurements on the rare earth pyrochlore oxide ${\mathrm{Nd}}_{2}{\mathrm{Zr}}_{2}{\mathrm{O}}_{7}$ to study the ordered state magnetic structure and cystal-field states. The structural characterization by high-resolution synchrotron x-ray diffraction confirms that the pyrochlore structure has no detectable O vacancies or Nd/Zr site mixing. The neutron diffraction reveals long-range all-in/all-out antiferromagnetic order below ${T}_{\mathrm{N}}\ensuremath{\approx}0.4$ K with propagation vector k = (0 0 0) and an ordered moment of $1.26(2)\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$/Nd at 0.1 K. The ordered moment is much smaller than the estimated moment of $2.65\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$/Nd for the local $\ensuremath{\langle}111\ensuremath{\rangle}$ Ising ground state of ${\mathrm{Nd}}^{3+}$ $(J=9/2)$ suggesting that the ordering is partially suppressed by quantum fluctuations. The inelastic neutron scattering experiment further confirms the Ising anisotropic ground state of ${\mathrm{Nd}}^{3+}$ and also reveals its dipolar-octupolar character which possibly induces the quantum fluctuation. The crystal-field level scheme and ground state wave function have been determined.