Laboratory of Rare Earth Intermetallics

 

Chair of General Physics and Magneto-Ordered Matter

Faculty of Physics

M.V. Lomonosov Moscow State University

Vorobjovy Gory, 119992 Moscow, Russia

 

Head of the Laboratory - Leading researcher, Professor Ashot Markosyan

 

Members of the Laboratory

1

Ashot Markosyan

Leading researcher, doctor of physical and mathematical science (habilitation degree), Professor for majors

2

Irina Gaidukova

Associate Professor, candidate of physical and mathematical science (Ph.D. degree)

3

Igor Dubenko

Senior researcher, candidate of physical and mathematical science (Ph.D. degree)

4

Serguei Granovsky

Research associate, candidate of physical and mathematical science (Ph.D. degree)

5

Vadim Rodimin

Physicist, candidate of physical and mathematical science (Ph.D. degree)

6

Vladimir Uryvaev

Undergraduate student, 5th year

 

 

Click to magnify

From left to right: Granovsky S.A., Rodimin V.E.,  Gaidukova I.Yu, Dubenko I.S., Markosyan A.S.

 

 

General information on the scientific activity

 

The scientific interests of the group include various magnetic phenomena in materials containing 4f and 3d elements. The primary research work is related to the study of magnetic phase transitions in rare earth (RE/R) intermetallic compounds with transition elements of the iron group, i.e. R-3d intermetallics. Among the large variety of R-3d intermetallics one can find materials important for technical applications and modern technology, such as permanent magnets, magnetostrictive devices, elements for memory recording systems, and model compounds of current interest for basic research [1].

In the contemporary physics of magnetic phenomena, magnetism of the R-3d intermetallics is one of the most popular and most developing directions that draws attention of many explorers. Two magnetic subsystems of different nature are incorporated and contribute to magnetism in these compounds. One of them, the 4f-subsystem, is made up of the localized 4f-electrons and can be described well by atomic characteristics of the RE ions. The latter one, the d-subsystem, is formed as a result of the hybridization of the itinerant 3d-electrons of the transition metal and 5d-electrons of RE. Magnetism of this itinerant subsystem is usually described by characteristics of the hybridized 3d-5d band (d-band). Thus, the R-3d intermetallics combine the properties specific for both, 4f-metals (large anisotropic magnetostriction, Dl/l > 10-3, and large energy of the magneto-crystalline anisotropy, Ha > 10 T) and 3d-metals (magnetovolume effect DV/V of the order of 10-3, high values of TC exceeding substantially the room temperature).

 

The laboratory has different equipment for synthesis of alloys and intermetallic compounds and their heat treatment under controlled atmosphere: arc and induction furnaces, several resistance furnaces. We have in our disposition an X-ray diffractometer and an optical microscope for metallographic analysis. The low-temperature and high-temperature cameras that can be mounted on the diffractometer allow to study the thermal expansion of solids in a wide temperature interval from 5 to 900 K. Using this facility, magnetic and structural phase transitions, magnetoelastic distortions of the crystal structure (anisotropic magnetostriction), Invar (magnetovolume) effect can be studied.

 

The members of the group carry out studies of the magnetic and transport properties of the R-3d intermetallic compounds, in which the magnetic state of the itinerant-electron subsystem can change abruptly, by a first-order type phase transition, when varying external forces (e.g., pressure, temperature or a magnetic field). It is usually said of a magnetic instability of the itinerant magnetic subsystem in such compounds. Itinerant-electron metamagnetism, a field-induced ferromagnetism in an itinerant-electron paramagnet by a first-order type phase transition, is a particular case of the magnetic instability.

 

While the number of binary R-3d intermetallics is over several hundred, there are thousands among the ternary R-3d-M systems. In the area of the ternary intermetallics with the chemical formula RmTnMp, the compounds in which the R and 3d sublattices order independently at different temperatures interest our research group. In particular, we study the magnetic properties of the RMn2Ge2 and RMn2Si2 series.

 

Among the scientific achievements of the team are:

- In RMn2 intermetallic compounds, the magnetic ordering of the Mn subsystem has been found to occur through a first-order type phase transition. It is accompanied by a giant volume effect DV/V ~ 10-2 [2, 3] (Fig. 1).

- First experimental observation of the phenomenon of field-induced itinerant-electron metamagnetism in the pseudobinary compounds Y(Co1‑xAlx)2 [4] (Fig. 2).

- Discovery of the phenomenon of temperature-induced itinerant-electron metamagnetism in RCo3 compounds with magnetic RE [5] (Fig. 3).

These works stimulated studies of different aspects of a magnetic instability of the itinerant-electron subsystem in RMn2, RCo2, and RCo3 compounds in many research institutions and universities.

 

 

Fig. 1. Temperature dependence of the lattice parameters of YMn2 in the paramagnetic (cubic crystal structure of the MgCu2‑type) and antiferromagnetic (tetragonal) phases [2]. Below TN ~ 90 K the paramagnetic and antiferromagnetic phases co-exist. The volume effect at TN reaches ~ 6 % (the highest value of the effect known for magnetic materials). (c-a)/a = -2.6ґ10-3 at 5 K.

 

 

Fig. 2. Magnetization curves of the Y(Co1‑xAlx)2 compounds at 4.2 K [4]. The compounds with x < 0.1 are itinerant-electron paramagnets, and the external magnetic field induces a metamagnetic transition from a paramagnetic to a ferromagnetic state. In the compounds with x > 0.1, the metamagnetic transition occurs from a weak-ferromagnetic to a strong-ferromagnetic state. This effect is a consequence of a field-induced increase of the density of d-electron states at the Fermi level.

 

 

Fig. 3. Temperature dependence of the relative volume change of ErCo3 and HoCo3 normalized to the room temperature [6]. Below TC, a positive magnetic contribution in the thermal expansion appears smoothly due to a magnetic ordering of the itinerant d-electron subsystem (weak-magnetic state). The extra volume expansion at low temperatures (65 K for ErCo3 and 180 K for HoCo3) is a consequence of temperature-induced itinerant-electron metamagnetism of the d-subsystem when the intersublattice molecular magnetic field HRCo reaches the critical value by decreasing temperature.

 

 

Scientific collaboration with Russian Institutions

 

1.      Faculty of Physics, Ural State University (Ekaterinburg)

2.      Saint-Petersburg Institute of Nuclear Physics (Gatchina)

3.      Moscow Institute of Radio- Engineering Electronics and Automation (MIREA)

 

International scientific relations and collaboration

 

1.      Laboratoire du Magnetisme L. Nйel (Grenoble, France)

2.      Laboratoire Leon Brillouin (Saclay, France)

3.      Van der Waals - Zeeman Institute, University of Amsterdam (Netherlands)

4.      Institute of Solid State Physics, Vienna University of Technology (Austria)

5.      Institute of General Physics, Dresden Technical University (Germany)

6.      Institute of Physics of the Czech Academy of Science, Prague (Czech Republic)

7.      Institute of Solid State Physics, Tokyo University (Japan)

8.      Institute for Molecular Science, Okazaki National Research Institutes (Japan)

9.      Physics Department, Southern Illinois University, Carbondale (USA)

10.  Centro Brasiliero de Pesquisas Fisicas, Rio de Janeiro (Brasil)

11.  Institute for Metal Research, Shenyang (People Republic of China)

 

 

References

1.      A.S. Markosyan, Magnetism of alloys of 4f (R) and 3d elements (T), Encyclopedia of Materials: Science and Technology, Elsevier Science Ltd. (2001) Vol. Magnetism, pp. 78-85.

2.      I.Yu. Gaidukova, A.S. Markosyan, A first-order structural phase transition in the paramagnetic compound YMn2, Fiz. Met. Metalloved. 54 (1982) 184-186 (in Russian) [Phys. Met. Metallogr. 54 (1982) 168-170].

3.      I.Yu. Gaidukova, S.B. Kruglyashov, A.S. Markosyan, R.Z. Levitin, Yu.G. Pastushenkov, V.V. Snegirev, Metamagnetism of the manganese subsystem in the RMn2 intermetallic compounds, Zh. Eksp. Teor. Fiz. 84 (1983) 1858-1867 (in Russian) [Sov. Phys. JETP 57 (1983) 1083-1088].

4.      V.V. Aleksandryan, A.S. Lagutin, R.Z. Levitin, A.S. Markosyan, V.V. Snegirev, Metamagnetism of the itinerant d-electrons in YCo2: investigation of the metamagnetic transitions in Y(Co1‑xAlx)2, Zh. Eksp. Teor. Fiz. 89 (1985) 271-276 (in Russian) [Sov. Phys. JETP 62 (1985) 153-155].

5.      N. Ali, I.S. Dubenko, I.Yu. Gaidukova, A.S. Markosyan, V.E. Rodimin, Temperature induced magnetic instability in the itinerant Co subsystem of the Er1‑xYxCo3 compounds, Physica B 281&282 (2000) 696-698.

6.      E. Gratz, A.S. Markosyan, I.Yu. Gaidukova, V.E. Rodimin, St. Berger, E. Bauer, H. Michor, Temperature induced itinerant electron metamagnetism in ErCo3 and HoCo3: influence of an external field and pressure, Solid State Commun. 120 (2001) 191-194.