Characterization and Magnetic Properties of Heavy Rare-Earth A2Ir2O7 Pyrochlore Iridates, the Case of Tm2Ir2O7
Abstrakt
The magnetic properties of newly prepared Tm2Ir2O7 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 Er2Ir2O7 and Yb2Ir2O7.
The crystal field parameters for, the so-far-unstudied, Tm2Ir2O7 were calculated by scaling the Er2Ir2O7 parameters employing appropriate Stevens factors for Er3+ and Tm3+. Iridates with the Kramers' Er3+ and Yb3+ 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 Yb2Ir2O7 was confirmed by magnetization measurements. The nonmagnetic ground-state crystal-field singlet in Tm2Ir2O7 dictated by Tm trigonal Wyckoff position was confirmed by both evolution of specific heat at low temperature and temperature dependence of the magnetic entropy