Low temperature magnetism of the disordered fluorite Ho2Zr2O7

The arrangement of magnetic ions into the pyrochlore structure of corner-sharing tetrahedra gives rise to the frustration of their magnetic interactions, and thus to strongly correlated phases such as spin liquids and spin ices. Recently, there is an increasing interest on the understanding of how these magnetic states develop their correlations when a significant amount of disorder is at play. Fluorites with its intrinsic disorder lattice and same A2B2O7 composition are modelled to be excellent probes of dynamics in pyrochlores. In our work we compare the magnetic and thermal properties of the disordered fluorite Ho2Zr2O7 and spin-ice pyrochlore Ho2Ti2O7. Through dynamic measurements, nonzero values of ac magnetic susceptibility at the minimum of measured temperature evidence a significant spin dynamics on our compound. The recovered electronic magnetic entropy down to 70 mK is slightly higher than Rln(2), indicating the possible doublet ground state of Ho3+ and thus an absence of residual entropy; contrary to what it is observed in spin ice Ho2Ti2O7 [1]. This behavior resemblances to that exhibited one in the fluorite Dy2Zr2O7, which was reported as having no long-ranged order and developing very short-ranged antiferromagnetic spin correlations [2]. In field specific heat measurements confirm the presence of an electronic maximum around 2 K that moves to higher temperatures as the field is increased, revealing that below 10 K there is a nonnegligible contribution of excited crystal electric field levels.

[1] A. L. Cornelius and J. S. Gardner, Phys. Rev. B 64, 060406(R) (2001).
[2] J. G. A. Ramon, C. W. Wang, L. Ishida, P. L. Bernardo, M. M. Leite, F. M. Vichi, J. S. Gardner, and R. S. Freitas, Phys. Rev. B 99, 214442 (2019).