Fyzikální ústav Akademie věd ČR

We study magnetism and magneto-elasticity of rare-earth and uranium intermetallic compounds with high content of 3d-metal (Fe and Co). They combine the localized magnetism of the f-electron sublattice with the itinerant magnetism of the 3d-sublattice and belong to an important class of modern magnetic materials. The work is usually performed on high-quality single crystals grown in our lab. Some particular results are:
1. A systematic study of the R₂Fe₁₄Si₃ compounds, where the Fe sublattice is partly diluted by Si and R stands for either magnetic (Dy, Er, Nd) and non-magnetic (Y, Ce, Lu) rare-earth, allowed us to distinguish the individual sublattice contributions to magnetic anisotropy and other properties. Observation of field-induced transitions of different nature (spin reorientation and metamagnetism) in very high fields (30-45 T) and their adequate theoretical description contributed to understanding of formation of magnetism in these complicated systems with competitive exchange and anisotropic interactions [1.1;1.2].
2. A comparative study of R₂Co_17-xSi_x and R₂Fe_17-xSi_x compounds with R = Lu and U allowed us to identify the U sublattice contribution to magnetic anisotropy and thus to unambiguously confirm the magnetic state of U in these compounds, up to room temperature, which is rather unexpected effect in the compounds with a high content of 3d metals [2.1].
3. Different aspects of magnetoelasticity of the high-3d-metal-content intermetallics based mainly on Lu₂Fe₁₇ were investigated by magnetostriction, thermal expansion, application of external pressure and interstitial introduction of hydrogen (“negative chemical pressure”)[3.1].

Main publications.
1.1. M.I. Ilyn, A.V. Andreev, The magnetocaloric effect and spin reorientation transition in single-crystal Er₂Fe₁₄Si₃, J. Phys.: Condens. Matter 20 (2008) Art. No. 285206 (4 pp.).
1.2. A.V. Andreev, S. Yoshii, M.D. Kuz'min, F.R. de Boer, K. Kindo, M. Hagiwara, A high-field magnetization study of a Nd₂Fe₁₄Si₃ single crystal, J. Phys.: Condens. Matter 21 (2009) 146005 (8pp).
2.1. A.V. Andreev, E.A. Tereshina, E. Šantavá, K. Koyama, Y. Homma, I. Satoh, T. Yamamura, Y. Shiokawa, K. Watanabe, Magnetic properties of U₂Co_17-xSi_x single crystals, J. Alloys Comp. 450 (2008) 51-57.
3.1. E.A. Tereshina, A.V. Andreev, J. Kamarád, O. Isnard, Antiferromagnetic order in (Lu_0.8Ce_0.2)₂Fe₁₇ and Lu₂Fe_16.5Ru_0.5: High pressure study, J. Appl. Phys. 105 (2009) Art. No. 07A747 (1-3).