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We study the low-temperature heat transport, as well as the magnetization and the specific heat, of TmMnO3 single crystals to probe the transitions of magnetic structure induced by magnetic field. It is found that the low-T thermal conductivity (k) shows strong magnetic-field dependence and the overall behaviors can be understood in the scenario of magnetic scattering on phonons. In addition, a strong "diplike" feature shows up in k(H) isotherms at 3.5--4 T for H ||c, which is related to a known spin reorientation of Mn3+ moments. The absence of this phenomenon for H||a indicates that the magnetic-structure transition of TmMnO3 cannot be driven by the in-plane field. In comparison, the magnetothermal conductivity of TmMnO3 is much larger than that of YMnO3 but smaller than that of HoMn03, indicating that the magnetisms of rare-earth ions are playing the key role in the spin-phonon coupling of the hexagonal manganites. [ABSTRACT FROM AUTHOR]

The very-low-temperature thermal conductivity (κ) is studied for BaCo2V2O8, a quasi-one-dimensional Ising-like antiferromagnet exhibiting an unusual magnetic-field-induced order-to-disorder transition. The nearly isotropic transport in the longitudinal field indicates that the magnetic excitations scatter phonons rather than conduct heat. The field dependence of K shows a sudden drop at ∼4 T, where the system undergoes the transition from the Néel order to the incommensurate state. Another dip at lower field of ∼3 T indicates an unknown magnetic transition, which is likely due to the spin-flop transition. Moreover, the K{H) in the transverse field shows a very deep valleylike feature, which moves slightly to higher field and becomes sharper upon lowering the temperature. This indicates a magnetic transition induced by the transverse field, which however is not predicted by the present theories for this low-dimensional spin system. [ABSTRACT FROM AUTHOR]