Anisotropy of magnetic properties of the layered Cobased perovskite single crystals 'RBaCo_{2}O_{5+x}' (R = Dy, Tb, Eu) 
Valentina I. Gatalskaya ^{3,2}, Sergej Shiryaev ^{3,2}, Georgij Bychkov ^{3}, Sergej Barilo ^{3}, Leonard Kurochkin ^{3}, Marek Baran ^{2}, Ritta Szymczak ^{2}, Henryk Szymczak ^{2} 
1. 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 RBaCo_{2}O_{5+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 2350 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 PMWFMAFM magnetic transitions. At 100 Oe the PMWFM transition occurs at 295 K (DBC), 271 K (TBC) and 235 K (EBC). The AFM transition was observed at T_{N} = 230 K (DBC), 240 K (TBC) and 210 K (EBC). The calculations show that for HII(ab) p_{eff} = 2.8 μ _{B}/Co^{3+} (TBC) with extracting the contribution from Rion. Note that value is close to the expected value for Co^{3+} ion full IS of 2.83 μ _{B}. For H = 1 kOe p_{eff} = 1.8 μ _{B}/Co^{3+} 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 T_{max} = 245, 265 and 210 K, respectively. We assume that only IS Co^{3+} 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 Tbsublattice 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.
