Field-induced transitions in Y2Cu2O5

VOLUME 38, NUMBER 10 PHYSICAL REVIEW B transitions Field-induced OCTOBER 1988 in Y2Cu205 J. D. Thompson, Z. Fisk, K. A. Kubat-Martin, and E. Garcia Los Alamos National Laboratory, Los Alamos, Ne~ Mexico 87545 S-W. Cheong, (Received 8 July 1988) measurements on single crystals of Magnetic susceptibility and isothermal magnetization Y2Cu205 show evidence for two field-induced phase transitions that develop out of an antiferro- magnetic ground state. The antiferromagnetic insulator La2Cu04 has received considerable attention since the discovery' that doping this material with a divalent atom such as Sr or Ba results near 40 K. Because of the possible in superconductivity in the doped ma- connection between superconductivity terial and magnetic order in the host, the nature of mag- netic correlations in La2Cu04 has been studied in some on Initial neutron scattering experiments2 detail. 2 sintered powder samples of La2Cu04 showed that antifer- romagnetic order at T~-250 K (the precise value of TN depending on oxygen stoichiometry) resulted from anti- ferromagnetic coupling of the Cu 3d9 spins in the ortho- rhombic Cu02 basal plane. However, magnetic suscepti- for T ~ TN indicated a positive bility measurements paramagnetic Curie temperature 8, suggesting the pres- More recent interactions. ence of ferromagnetic measure- and magnetoresistance magnetic-susceptibility ' on single crystals of La2Cu04 revealed a ments metamagnetic transition at T TN for fields applied per- pendicular to the Cu02 basal plane. The origin of this field-induced transition has been demonstrated by neu- tron scattering to arise from canting of the Cu spins out of the basal plane, a condition produced by the rotationally distorted octahedral coordination of oxygen atoms around the Cu. Given the interest in LazCu04, it is worthwhile to study other examples of Cu-0 systems that might show similar magnetic behavior. Y2Cu205, a common second phase found when producing the 90-K superconductor YBa2- CU307 is a potential candidate for undergoing a field- induced transition. The magnetic properties of powder samples of this compound have been measured by Troc, Bukowski, Horyn, and Klamut' who found antiferromag- netic order at T~ 13 K but also a positive 8 38. 5 K. Further, oxygen coordination about Cu forms an irregular hexahedron. To investigate the possibility of a field- induced transition we have determined the anisotropic susceptibility and isothermal magnetization of single crys- tals of Y2Cu205. Small parallelopiped crystals were prepared as a by- product of flux-grown YBa2Cu&0, crystals. Single- crystal x-ray diffraction showed an orthorhombic crystal structure (space group Pna2~) with lattice parameters a 10.782(2) A, b 3.4870(7) A, and c 12. 446(1) A. , results similar to those reported' for Ho2Cu205 in which there are two inequivalent Cu sites per cell. Suscepti- were performed with a quantum de- bility/magnetization sign superconducting-quantum-interference-device-based (SQUID-based) system. X of Figure 1 shows the magnetic susceptibility Y2Cu205 measured in a 0.5-T field applied parallel (XII) and perpendicular (X~) to the orthorhombic b axis. Clear Y2Gu ~ 05 ++I 0+ 1 Q I- V CL LU— O f 0 om 4 5 re~ e + c 3 0' QJ (I) U o ~C Q)E4 o 'o ~ C) CL E Y2Cu205 g)~6— Q E g) ~~3. co E Y2Cu UJ ~ TEMPERATURE (K) OJ M E e o Q 4o CU Z Z I 'o I A— c 03 em I I I I TEMPERATURE (K) TEMPERATURE (K) FIG. 1. Magnetic susceptibility of Y2Cu205 measured in a 0.5-T field applied parallel (l~~) and perpendicular (X~) to the orthorhomhic b axis. The inset shows 1/Xs vs temperature from which we obtain an effective moment of 2. 16pg per Cu and a paramagnetic Curie temperature of 37 K. FIG. 2. Magnetic susceptibility of Y2Cu205 in the vicinity of its Neel temperature. Left panel is for the field parallel'to the b axis and the right panel for the field perpendicular to the b axis. Symbols correspond to different fields: 0. 5 T (circles), 3 T (squares), 5 T (diamonds). The American Physical Society