The magnetic susceptibility and specific heat of single crystals of KTm(MoO4)2 in the temperature interval 0.1–300 K are investigated. It is shown that the ground state of the rare-earth magnetic system of the Tm3+ ions can be represented by two close-lying singlet levels (a non-Kramers quasidoublet with MJ = | +/- 6⟩) separated by a rather large energy interval from the excited levels. The effect of the ‘freezing’ of energy levels on magnetic susceptibility and the Schottky anomaly on magnetic specific heat have been observed in the low-temperature region T < 2.5 K. These results show that this magnetic system can be considered as a simple two-level quantum system over a wide temperature range.

A study is made of the angular, frequency–field, and temperature dependences of the magnetic resonance of the quasi-one-dimensional Ising magnet [(CH3)3NH]CoCl3⋅2H2O in the paramagnetic phase. The experimental results obtained are explained in a model of spin-cluster resonance in a strongly exchange-coupled spin chain. The frequency–field dependences of the ferromagnetic resonance spectrum measured below the Néel temperature are studied for magnetic-field directions along the crystallographic axes a, b, and c. It is shown that for H→0 the spin-wave spectrum of this quasiferromagnet has two gaps (ν1=70.1 GHz and ν2=52.5 GHz).

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