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The magnetic, structural, and vibrational properties of YMn 2 O 5 multiferroic have been studied by means of neutron, x-ray powder diffraction, and Raman spectroscopy at pressures up to 6 and 30 GPa, respectively. Application of high pressure, P > 1 GPa, leads to a gradual suppression of the commensurate and incommensurate antiferromagnetic (AFM) phases with a propagation vector q = (1/2,0,q z ∼1/4) and appearance of the commensurate AFM phase with q = (1/2,0,1/2). This observation is sharply contrasting to general trend towards stabilization of commensurate AFM phase with q = (1/2,0,1/4) found in other RMn 2 O 5 compounds upon lattice compression. At P ∼ 16 GPa a structural phase transformation accompanied by anomalies in lattice compression and pressure behavior of vibrational modes was observed. The comparative analysis of high-pressure and R-cation radius variation effects clarified a role of particular magnetic interactions in the formation of the magnetic states of RMn 2 O 5 compounds.

The crystal and magnetic structures of TlFeS 2 and TlFeSe 2 chalcogenides are studied by neutron diffraction in the temperature range 10-300 K. The investigated compounds feature monoclinic crystal sym metry with the C2/m space group. Antiferromagnetic ordering occurs in TlFeS 2 and TlFeSe 2 at the Néel tem perature T N = 210(5) and 295(5) K, respectively. The temperature dependences of magnetic moments, Fe-Fe bond lengths, and unit cell volume are established. The coefficients of thermal expansion for the paramag netic and antiferromagnetic phases are calculated.

The crystal structure of the semiconductors TlFeSe 2 and TlFeS 2 has been studied by mean of neutron diffraction at room temperature and high pressure up to 4.2 GPa and 5.2 GPa, respectively. The chain-like monoclinic crystal structure with space group C2/m remains unchanged in both compounds in the entire pressure range. The anisotropic lattice compression and the large difference in the bulk modulus and the compressibility coefficients of the structural parameters of the two compounds have been observed. The mechanism of the observed phenomena was discussed. The enhancement of the onedimensional antiferromagnetic and metallic character was predicted.