Superconducting and normal-state interlayer exchange coupling in La0.67Sr0.33MnO3-YBa2Cu3O7-La0.67Sr0.33MnO3 epitaxial trilayers -: art. no. 224507

The issue of interlayer exchange coupling in magnetic multilayers with a superconducting spacer is addressed in La0.67Sr0.33MnO3 (LSMO)-YBa2Cu3O7 (YBCO)-La0.67Sr0.33MnO3 (LSMO) epitaxial trilayers through resistivity, ac susceptibility, and magnetization measurements. The ferromagnetic LSMO layers possessing in-plane magnetization suppress the critical temperature (T-c) of the c-axis oriented YBCO thin film spacer. The superconducting order, however, survives even in very thin layers (thickness d(Y)similar to 50 angstrom, similar to four unit cells) at T < 25 K. A predominantly antiferromagnetic exchange coupling between the moments of the LSMO layers at fields < 200 Oe is seen in the normal as well as the superconducting states of the YBCO spacer. The exchange energy J(1) (similar to 0.08 erg/cm(2) at 150 K for d(Y)=75 angstrom) grows on cooling down to T-c, followed by truncation of this growth on entering the superconducting state. The coupling energy J(1) at a fixed temperature drops exponentially with the thickness of the YBCO layer. The temperature and d(Y) dependencies of this primarily nonoscillatory J(1) are consistent with the coupling theories for systems in which transport is controlled by tunneling. The truncation of the monotonic T dependence of J(1) below T-c suggests inhibition of single-electron tunneling across the CuO2 planes as the in-plane gap parameter acquires a nonzero value.