Robustness of the dipole-octupole ground state and fragmented excitations in Nd-based pyrochlores

Nd-based pyrochlore oxide compounds are of peculiar interest due to the dipole-octupole character of the magnetic moment of the Nd³⁺ ion. In particular, Nd₂Zr₂O₇ was shown to stabilize exotic phases in which the magnetic moment has both dipolar and octupolar characters, and which result from the competition between ferromagnetic and antiferromagnetic interactions. When decreasing temperature, Nd₂Zr₂O₇ enters into an unconventional Coulomb phase below about 1 K, and eventually stabilizes a so-called “all in - all out” ordering below about 300 mK, which encompasses fragmented excitations. A rich field induced phase diagram has also been highlighted.

In this talk I will discuss the magnetic properties of the known Nd-based pyrochlore compounds, and their robustness with respect to perturbations. This includes (i) the impact of introducing non-magnetic disorder on the Nd and/or metal site and (ii) the effect of introducing magnetic ions such as Ir⁴⁺ or Ru⁴⁺ on the metal site of the pyrochlore lattice. I will show that, even in the presence of strong disorder, the Nd magnetic state, and the associated excitations are pretty robust. Nevertheless, the octupolar character of the correlated state is weakened in the presence of perturbations, which results in larger ordering temperature and ordered dipolar moment.