Study of transport and magnetic properties of strongly correlated electron systems (transition metal oxides and multicomponent compounds with rare-earth elements)

● Study of the nature of the paramagnetic-ferromagnetic phase transition in manganites with colossal magnetoresistance [1]. It is shown that the paramagnetic–ferromagnetic phase transition in the bulk sample of La_0.75Ca_0.25MnO₃ is the transition of the first order, but under the influence of high enough magnetic field it may become a second one.

● Giant temperature and magnetic-field variations in the radio-frequency (RF) (at 2:525 MHz) absorption are found in the vicinity of T_c (about 374 K) ) in a manganite sample of La_0.67Sr_0.33 MnO₃ [2]. Relative change of the RF absorption in magnetic field (magnetoabsorption) is about 67% in field 2.1 kOe and about 55% in field 1 kOe. This giant magnetoabsorption effect can be used to develop RF devices controlled by temperature and low magnetic field [2].

● Transport, magnetic, magneto-optical (Kerr effect) and optical (light absorption) properties have been studied in an oriented polycrystalline La_0.67Ca_0.33MnO₃ film which shows colossal magnetoresistance [3]. The correlations between these properties are presented. A giant change in infrared light transmission (more than a thousand-fold decrease) is observed on crossing the Curie temperature (about 270 K) from high to low temperature. Large changes in transmittance in a magnetic field were observed as well. The giant changes in transmittance and the large magnetotransmittance can be used for development of IR optoelectronic devices controlled by thermal and magnetic fields.

● Study of angular phase diagram of metamagnetic transitions in single crystal borocarbides HoNi₂B₂C and ErNi₂B₂C и Tb2Ni2B2C [4-6]. New peculiarities of metamagnetic states in these compounds were found. Particularly, the possible influence of multi-domain structure of antiferromagnetic state and the “frustrated” behavior of magnetic systems for the magnetic field directions near the hard magnetization axis. For HoNi₂B₂C two new phase boundaries in angular region of non-collinear phase were discovered. For ErNi₂B₂C new metamagnetic states were found which were not disclosed in previous neutron-diffraction and magnetizations studies.

1. Belevtsev B.I., Zvyagina G.A., Zhekov K.R., Kolobov I.G., Beliayev E.Yu., Panfilov A.S., Galtsov N.N., Prokhvatilov A.I., and Fink-Finowicki J. Influence of magnetic field on the paramagnetic-ferromagnetic transition in La_1-xCa_x MnO₃ crystal: Ultrasonic and transport studies// Phys. Rev. B, 74 , No.5, 054427-05438 (2006).
2. Belevtsev B.I., Kirichenko A.Ya.,Cherpak N.T.,Golubnichaya G.V., Maximchuk I.G., Beliayev E.Yu., Panfilov A.S., Fink-Finowicki J. Giant magnetic-field changes in radio-frequency absorption in La_0.67Sr_0.33MnO₃ near the Curie temperature// J. Magn. Magn. Mater., 281, No. 1, 97-104 (2004).
3. Sukhorukov Yu.P., Gan’shina E.A., Belevtsev B.I., Loshkareva N.N., Vinogradov A.N., Rathnayaka K.D.D., Parasiris A., Naugle D.G. Giant change in infrared light transmission in La_0.67Ca _0.33MnO₃ film near the Curie temperature // J. Appl. Phys., 91, No.5, 4403-4408 (2002).
4. Rathnayaka K.D.D., Belevtsev B.I., Naugle D.G. Torque magnetometry study of metamagnetic transitions in single-crystal HoNi₂B₂C at T = 1.9 K // Phys. Rev. B, 76, No.22, 224526-224537 (2007).
5. Naugle D.G., Belevtsev B.I., Rathnayaka K.D.D., S.-I. Lee, S.M. Yeo. Torque magnetometry studies of new low temperature metamagnetic states in ErNi₂B₂C // J. Appl. Phys. 103, 07B718-07B721 (2008).

6. Rathnayaka K.D.D., Naugle D.G., Belevtsev B.I. , Canfield P.C., and Bud'ko S.L. Low-temperature meta-magnetic states in single crystal Tb2Ni2B2C studied by torque magnetometry // J. Appl. Phys. 105, 07E111-07E113 (2009).