Magnetic fragmentation in pyrochlores

Pyrochlore iridates of formula R₂Ir₂O₇ with two interpenetrating pyrochlore lattices (corner-sharing tetrahedra) filled with a rare-earth R³⁺ and a magnetic metal Ir⁴⁺ are interesting materials in the field of frustrated magnetism. The iridium sublattice indeed orders at rather high temperature (~100 K) in an antiferromagnetic configuration called all-in all-out and imposes in turn an all-in all-out staggered effective magnetic field on the rare-earth pyrochlore lattice. This leads to the stabilization of new phases. For example, an exotic fragmented state of monopole crystal [1], where order and disorder coexist, is evidenced in Ho₂Ir₂O₇ [2] and Dy₂Ir₂O₇ [3]. In this new state of matter, the magnetic moment fragments into an antiferromagnetic ordered part and a persistently fluctuating Coulomb phase. This state has been studied through experimental and theoretical approach and I will detail the results obtained on both Ho and Dy compounds. I will also address the changes of the ground state observed when Ru⁴⁺, another magnetic metal ion, is substituted to the iridium in the Ho based pyrochlore. We propose a novel kind of fragmentation in this Ru based system.

[1] M. E. Brooks-Bartlett, S. T. Banks, L. D. C. Jaubert, A. Harman-Clarke, P. C. W. Holdsworth, Magnetic-moment fragmentation and monopole crystallization. Phys. Rev. X 4, 011007 (2014).

[2] E. Lefrançois, V. Cathelin, E. Lhotel, J. Robert, P. Lejay, C.V. Colin, B. Canals, F. Damay, J. Ollivier, B. Fa°k, L.C. Chapon, R. Ballou, V. Simonet, Magnetic charge injection in spin ice: a new way to fragmentation", Nature Communications 8, 209 (2017).

[3] V. Cathelin, E. Lefrançois, J. Robert, P. C. Guruciaga, C. Paulsen, D. Prabhakaran, P. Lejay, F. Damay, J. Ollivier, B. Fa°k, L. C. Chapon, R. Ballou, V. Simonet, P. C. W. Holdsworth, and E. Lhotel, Magnetic fragmentation in Dy pyrochlore iridate, Phys. Rev. Research Rapid Com. 2, 032073(R) (2020).