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The newly synthesized Tm2Ir2O7 iridate is investigated using neutron scattering techniques. Powder neutron diffraction patterns confirm that Tm2Ir2O7 crystallizes in a cubic structure of pyrochlore type, consistent with the rest of the rare-earth A2Ir2O7 series, and the crystal structure is preserved down to 0.2 K. The thermal expansion of the crystal lattice is well described by a Debye model of lattice vibrations. A weak magnetic signal consistent with the so-called all-in-all-out magnetic order (AIAO) is traced at low temperature; however, it cannot serve as unambiguous evidence of the AIAO structure in the compound. Nondispersive magnetic excitations in energy-momentum space are observed in inelastic neutron scattering spectra of Tm2Ir2O7. The crystal-field scheme and parameters of the thulium iridate are refined and discussed with respect to the specific heat and magnetization data. The results are supported by mean-field calculations., This work was supported by the Czech Science Foundation under Grant No. 18-09375Y. The preparation, characterization, and measurement of bulk physical properties on A2Ir2O7 samples were performed inMGML[60], which was supported.

Magnetization and specific-heat measurements on a UIrSi3 single crystal reveal Ising-like antiferromagnetism below TN=41.7K with the easy magnetization direction along the c axis of the tetragonal structure. The antiferromagnetic ordering is suppressed by magnetic fields >Hc (μ0Hc=7.3T at 2 K) applied along the c axis. The first-order metamagnetic transition at Hc exhibits asymmetric hysteresis reflecting a slow reentry of the complex ground-state antiferromagnetic structure with decreasing field. The hysteresis narrows with increasing temperature and vanishes at 28 K. A second-order metamagnetic transition is observed at higher temperatures. The point of change of the order of transition in the established H-T magnetic phase diagram is considered as the tricritical point (at Ttc=28K and μ0Htc=5.8T). The modified-Curie-Weiss law fits of temperature dependence of the a- and c-axis susceptibility provide opposite signs of Weiss temperatures, Θpa∼−51K and Θpc∼+38K, respectively. This result and the small value of μ0Hc contrasting to the high TN indicate competing ferromagnetic and antiferromagnetic interactions responsible for the complex antiferromagnetic ground state. The simultaneous electronic-structure calculations focused on the total energy of ferromagnetic and various antiferromagnetic states, the U magnetic moment, and magnetocrystalline anisotropy provide results consistent with experimental findings and the suggested physical picture of the system.

Magnetism in SmPd2Al3 was investigated on a single crystal by magnetometry and neutron diffraction. SmPd2Al3 represents a distinctive example of a Sm magnetism exhibiting complex magnetic behavior at low temperatures with four consecutive magnetic phase transitions at 3.4, 3.9, 4.4, and 12.5 K. The rich magnetic phase diagram of this compound reflects the specific features of the Sm3+ ion, namely, the energy nearness of the ground-state multiplet J = 5/2 and the first excited multiplet J = 7/2 in conjunction with strong crystal field influence. Consequently, a significantly reduced Sm magnetic moment in comparison with the theoretical Sm3+ free-ion value is observed. Despite the strong neutron absorption by natural samarium and the small Sm magnetic moment (∼0.2 μB), we have successfully determined the magnetic k vector (1/3, 1/3, 0) of the phase existing in the temperature interval 12.5–4.4 K. This observation classifies the SmPd2Al3 compound as a magnetically frustrated system. The complex magnetic behavior of this material is further illustrated by kinetic effects of the magnetization, inducing a rather complicated magnetic structure with various metastable states.