<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>μ</mml:mi><mml:mi>SR</mml:mi></mml:mrow></mml:math> study of the dipole-octupole quantum spin ice candidate <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Ce</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi>Zr</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>7</mml:mn></mml:msub></mml:mrow></mml:math>
J. Beare, E. M. Smith, J. Dudemaine, Robin Schäfer, Megan Rutherford, S. Sharma, A. Fitterman, Casey Marjerrison, T. J. Williams, A. A. Aczel, S. R. Dunsiger, A. Bianchi, B. D. Gaulin, G. M. Luke
Abstract
The ${\mathrm{Ce}}^{3+}$ pseudospin-$1/2$ degrees of freedom in ${\mathrm{Ce}}_{2}{\mathrm{Zr}}_{2}{\mathrm{O}}_{7}$ possess both dipolar and octupolar character which enables the possibility of novel quantum spin liquid ground states in this material. Here we report muon spin relaxation and rotation ($\ensuremath{\mu}\mathrm{SR}$) measurements on single-crystal samples of ${\mathrm{Ce}}_{2}{\mathrm{Zr}}_{2}{\mathrm{O}}_{7}$ in zero magnetic field and in magnetic fields directed along the $[1,\overline{1},0]$ and $[1,1,1]$ crystallographic directions, and for magnetic fields directed both longitudinal and transverse to the direction of muon polarization. Our zero-field results show no signs of magnetic ordering or spin freezing, consistent with earlier zero-field $\ensuremath{\mu}\mathrm{SR}$ measurements on a powder sample of ${\mathrm{Ce}}_{2}{\mathrm{Zr}}_{2}{\mathrm{O}}_{7}$, and also with the expectations for a quantum spin ice. However, we measure a more gentle relaxation rate for ${\mathrm{Ce}}_{2}{\mathrm{Zr}}_{2}{\mathrm{O}}_{7}$ in zero field at low temperatures than was previously reported. This difference in relaxation rate is likely due to the low oxidation and, correspondingly, the high stoichiometry of our single-crystal samples. Longitudinal field measurements confirm that the magnetic dipole moments in ${\mathrm{Ce}}_{2}{\mathrm{Zr}}_{2}{\mathrm{O}}_{7}$ remain dynamic at $T=0.1$ K on the microsecond timescale. For both $[1,\overline{1},0]$ and $[1,1,1]$ magnetic fields, our $\ensuremath{\mu}\mathrm{SR}$ Knight shift measurements show a field-induced leveling off of the magnetic susceptibility at low temperature which is qualitatively consistent with corresponding calculations using the numerical-linked-cluster method in combination with recent estimates for the nearest-neighbor exchange parameters of ${\mathrm{Ce}}_{2}{\mathrm{Zr}}_{2}{\mathrm{O}}_{7}$.