Characterization and Magnetic Properties of Heavy Rare-Earth A₂Ir₂O₇ Pyrochlore Iridates, the Case of Tm₂Ir₂O₇

The magnetic properties of newly prepared Tm 2 Ir 2 O 7 were investigated by means of magnetization and specific heat measurements and compared to the properties of other heavy rare-earth pyrochlore iridates. A bifurcation of zero-field-cooled and field-cooled magnetization coinciding with the onset of the specific heat anomaly indicated the magnetic ordering of the Ir sublattice, in agreement with studies on other pyrochlore iridates. The phase diagram depicting the ordering/metal-insulator-transition temperature dependent on the rare-earth ionic radius was updated and completed. Magnetic dc susceptibilities and magnetic contributions to the specific heat of Er, Tm, and Yb analogues were well described by crystal field parameters and eigenenergies, previously reported for Er 2 Ir 2 O 7 and Yb 2 Ir 2 O 7 . The crystal field parameters for, the so-far-unstudied, Tm 2 Ir 2 O 7 were calculated by scaling the Er 2 Ir 2 O 7 parameters employing appropriate Stevens factors for Er 3+ and Tm 3+ . Iridates with the Kramers’ Er 3+ and Yb 3+ ions revealed a splitting of the ground-state doublet, leading to a broad anomaly in specific heat at around 2 K and 3 K, respectively. The previously reported low value of magnetic moment in Yb 2 Ir 2 O 7 was confirmed by magnetization measurements. The nonmagnetic ground-state crystal-field singlet in Tm 2 Ir 2 O 7 dictated by Tm trigonal Wyckoff position was confirmed by both evolution of specific heat at low temperature and temperature dependence of the magnetic entropy.