Intermetallics are alloys that form ordered solid-state compounds between two or more metallic elements. In the intermetallic compound, atoms of constituent elements are not randomly redistributed in the crystal lattice (as it is in solid-solutions), but they are fixed in well-defined crystallographic positions. A requirement for formation of intermetallic compounds in binary, ternary, quaternary etc. systems is a negative heat (enthalpy) of formation ΔH. The total number of intermetallic compounds is huge, and some of them are magnetically ordered at room temperature; in any case the variety of magnetic and magnetostructural transitions at low and high temperatures incl. high pressure induced transitions is enormous. Intermetallics with the most outstanding magnetic properties are enabling many functionalities in motors, generators, sensors, actuators, robotics, advanced prosthetics and energy conversion devices in general.

We grow single crystals of (I) binary RE-3d intermetallic systems, such as RCo5, R2(Fe1-xCox)17, R2Co7, LaCo13, etc; (II) Quasi-binary RE-3d systems, such as R2(Fe1-xCox)14B, RFe11Ti etc; (III) RE-free intermetallics such as Fe3Sn, Fe5Sn3, Fe3Sn2, (Fe1-xCox)B, MnBi, MnAlGe etc. The size of these single crystals is larger than 1x1x1 mm3, sufficient for precise measurements of their magnetic, magnetocaloric, elastic, thermal- and electro-transport properties. They are also suitable for precise X-ray and neutron diffractometry, X-ray absorption spectroscopy, high resolution transition electron microscopy and in-situ investigation of magnetic domain structure in a broad range of magnetic fields, pressures and temperatures.

[1] B. Fayyazi, K. P. Skokov, T. Faske, I. Opahle, M. Duerrschnabel, T. Helbig, I. Soldatov, U. Rohrmann, L. Molina-Luna, K. Güth, H. Zhang, W. Donner, R. Schäfer, O. Gutfleisch, Experimental and computational analysis of binary Fe-Sn ferromagnetic compounds, Acta Mater., 180, 126–140, (2019),
DOI: 10.1016/j.actamat.2019.08.054

[2] L. V. B. Diop, M. D. Kuz’min, K. P. Skokov, Y. Skourski, O. Gutfleisch, Origin of field-induced discontinuous phase transitions in Nd2Fe17, Phys. Rev. B, 97 (5), 054406, (2018),
DOI: 10.1103/PhysRevB.97.054406

[3] K. P. Skokov, Y. G. Pastushenkov, S. A. Nikitin, M. Fries, O. Gutfleisch, Rotational Magnetocaloric Effect in the Er2Fe14B Single Crystal, IEEE Trans. Magn., 52 (5), 2500304, (2016),
DOI: 10.1109/TMAG.2016.2530138

[4] G. Gomez Eslava, B. Fayyazi, K. Skokov, Y. Skourski, D. Gorbunov, O. Gutfleisch, N. M. Dempsey, D. Givord, A two-sublattice model for extracting rare-earth anisotropy constants from measurements on (Nd,Ce)2(Fe,Co)14B single crystals, J. Magn. Magn. Mater., 520 (October 2020), 167470, (2021),
DOI: 10.1016/j.jmmm.2020.167470

(a) SEM image of a (Nd0.85Ce0.15)2(Fe0.9Co0.1)14B single crystal used for magnetic measurements. (b) The uniaxial domain structure of the 2:14:1 phase observed by MOKE microscope along the c-axis. (c) Laue X-ray diffraction pattern with incident beam along [100] of the crystal. (d) Simulated pattern of the corresponding structure given by Clip software. [4]
(a) SEM image of a (Nd0.85Ce0.15)2(Fe0.9Co0.1)14B single crystal used for magnetic measurements. (b) The uniaxial domain structure of the 2:14:1 phase observed by MOKE microscope along the c-axis. (c) Laue X-ray diffraction pattern with incident beam along [100] of the crystal. (d) Simulated pattern of the corresponding structure given by Clip software. [4]

The crystal structures and the properties of formed intermetallic compounds differ markedly from those of their constituents, and there is no straightforward way to derive these properties basing of magnetic and structural features of components. Hence, a careful experimental study of the magnetic, structural, elastic, electric etc. properties is of most importance. Therefore, for many years, the study of magnetic intermetallic compounds is a hot research topic in our Functional Material group .

Magnetization curves of the Fe3Sn single crystal measured at T=300 K and 10 K along the a, b’ and c axes under a magnetic field of up to 3.5 T. [1]
Magnetization curves of the Fe3Sn single crystal measured at T=300 K and 10 K along the a, b’ and c axes under a magnetic field of up to 3.5 T. [1]

The class of compounds formed between Rare-Earths (RE) and 3d transition metals is of our particular interest. Moreover, magnetic RE-3d compounds with small amount of metalloids (e.g. Boron) or non-metals (e.g. Silicon) are also of high significance. Many of such materials are known to have extraordinary magnetic characteristics, but the most important for us are RE-3d compounds with four 3d metals, namely Mn, Fe, Co and Ni. They function as hard or soft magnetic materials, magnetocaloric materials, materials for magnetic recording, magnetostrictive materials, hydrogen absorbing alloys etc.

Magnetization curves of Nd2Fe17 single crystal, measured at T = 5K in pulsed magnetic fields applied along the principal axes [2]
Magnetization curves of Nd2Fe17 single crystal, measured at T = 5K in pulsed magnetic fields applied along the principal axes [2]

In particular, the most powerful permanent magnets are based on intermetallic compounds containing RE metals, such as Nd, Sm, Dy, Tb, and 3d metals, such as Fe and Co. The rare-earth elements possess a high single-electron spin-orbit coupling constant ζ, which are necessary to provide a high magnetocanisotropy and therefore ensure large magnetic hysteresis. On the other hand, the 3d metals are responsible for high spontaneous magnetization and a significant Curie temperature of permanent magnets.

A meaningful study of the ‘intrinsic’ physical properties of RE-3d intermetallic compounds can only be made on single phase materials. Moreover, unambiguous determination of anisotropy constants, spontaneous magnetization, elastic constants etc. requires single crystals of good quality. For this reason, in our group we use different experimental techniques for RE-3d single crystals growing: Bridgman technique, reactive flux method, chemical vapor transport and abnormal grain growth in solids.

Evolution of the magnetic domain structure near the spin-reorientation transition of Er2Fe14B, obtained by magnetic force microscopy (MFM) on the (100)-plane single crystal in zero magnetic field at different temperatures. [3]
Evolution of the magnetic domain structure near the spin-reorientation transition of Er2Fe14B, obtained by magnetic force microscopy (MFM) on the (100)-plane single crystal in zero magnetic field at different temperatures. [3]
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