Anisotropy of magnetic properties of the layered Co-based perovskite single crystals 'RBaCo2O5+x' (R = Dy, Tb, Eu)

Valentina I. Gatalskaya 3,2Sergej Shiryaev 3,2Georgij Bychkov 3Sergej Barilo 3Leonard Kurochkin 3Marek Baran 2Ritta Szymczak 2Henryk Szymczak 2

1. The Institute of Solid State & Semiconductor Physics, National Academy of Science of Belarus, 17 P.Brovka, Minsk 220072, Belarus
2. Polish Academy of Sciences, Institute of Physics, al. Lotników 32/46, Warszawa 02-668, Poland
3. The Institute of Solid State & Semiconductor Physics, National Academy of Science of Belarus, 17 P.Brovka, Minsk 220072, Belarus

Abstract

We describe anisotropic magnetic behaviour of single crystals of RBaCo2O5+x with x ~ 0.5 [R = Dy (DBC), Tb (TBC), Eu (EBC)] grown first from overstoichiometric flux melt by spontaneous crystallization. The temperature and field dependences of magnetization have been obtained in region 2-350 K under magnetic fields up to 5 T at the different field configurations. With decreasing temperature the crystals revealed a similar behaviour: at HII(ab) they display the PM-WFM-AFM magnetic transitions. At 100 Oe the PM-WFM transition occurs at 295 K (DBC), 271 K (TBC) and 235 K (EBC). The AFM transition was observed at TN = 230 K (DBC), 240 K (TBC) and 210 K (EBC). The calculations show that for HII(ab) peff = 2.8 μ B/Co3+ (TBC) with extracting the contribution from R-ion. Note that value is close to the expected value for Co3+ ion full IS of 2.83 μ B. For H = 1 kOe peff = 1.8 μ B/Co3+ corresponding to LS/IS = 0.8 : 0.2. Ergo, magnetic field H = 5T induces the cobalt ions spin transition from LS to IS state. Similar picture is observed for DBC and EBC. The magnetic moments corresponding to WFM state are 0.07 (DBC), 0.15 (TBC) and 0.19 μ B (EBC) at Tmax = 245, 265 and 210 K, respectively. We assume that only IS Co3+ ions in octahedral site contribute to spontaneous moment (SM) while other Co ions in square pyramide site are PM. The AFM transition (H = 1 kOe) is a cause of SM reduction down to 0.05 (DBC), 0.002 (TBC) and 0.008 μ B (EBC) per Co ion. For HIIc all crystals are PM and SM does not appear at lowest temperatures. But for TBC we observed the AFM ordering of Tb-sublattice at 3.44 K, which was not registered for HII(ab) up to 2 K. The M(H) dependences for HII(ab) show the FM component to survive down to the lowest temperatures. For HIIc hysteresis of M was not found in the whole temperature interval in TBC.
The work is supported by INTAS grant # 01-0278, NATO linkage grant PST CLG 979 369 and Polish KBN grant 5P03B01620.

 

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Presentation: poster at E-MRS Fall Meeting 2003, Symposium D, by Valentina I. Gatalskaya
See On-line Journal of E-MRS Fall Meeting 2003

Submitted: 2003-05-02 15:39
Revised:   2009-06-08 12:55