Interface-selective probing of magnetism is a key issue for the design and realization of spin-electronic junction devices. Here, magnetization-induced second-harmonic generation was used to probe the local magnetic properties at the interface of the perovskite ferromagnet La(0.6)Sr(0.4)MnO3 with nonmagnetic insulating layers, as used in spin-tunnel junctions. We show that by grading the doping profile on an atomic scale at the interface, robust ferromagnetism can be realized around room temperature. The results should lead to improvements in the performance of spin-tunnel junctions.

Transport properties have been studied for a perovskite heterojunction consisting of SrRuO3 (SRO) film epitaxially grown on SrTi0.99Nb0.01O3 (Nb:STO) substrate. The SRO/Nb:STO interface exhibits rectifying current-voltage (I-V ) characteristics agreeing with those of a Schottky junction composed of a deep work-function metal (SRO) and an n-type semiconductor (Nb:STO). A hysteresis appears in the I-V characteristics, where high resistance and low resistance states are induced by reverse and forward bias stresses, respectively. The resistance switching is also triggered by applying short voltage pulses of 1 µs -10 ms duration. 73.40.-c, 73.30.+y, 77.90.+k Recently, reversible resistance switching between two or multilevel resistance states has been found to take place by short voltage pulses at room temperature in capacitor-like devices composed of a wide variety of insulating perovskite oxides such as manganites, 1,2,3 titanates, 4 and zirconates 5 sandwiched between two metallic electrodes. This resistance switching attracts considerable attention due to the potential for device application such as resistance random access memories (RRAM). 6 The origin of resistance switching, however, is still an open question. One of the possibilities is the bulk effect 1,4,5,6 that a phase transition of perovskite takes place between insulating and conducting states, similar to the breakdown of charge-ordered insulating state in manganites induced by electric-field at low temperature. 7,8,9 The other is the interface effect, where voltage pulses reversibly alter the nature of potential barrier formed in the insulating (or semiconducting) perovskite in contact with metallic electrodes. 2,3 We have recently shown that the resistance switching occurs at a Ti/Pr 0.7 Ca 0.3 MnO 3 (PCMO) interface, 3 which exhibits Schottky-like currentvoltage (I-V ) characteristics, where Ti and PCMO can be regarded as a shallow work-function metal and a p-type semiconductor, respectively. A possible origin for the resistance switching is attributed to the change in Schottky barrier height (or width) by trapped charge carriers at the interface states. However, non-epitaxial structure and chemically incompatible materials combination make it difficult to characterize the transport properties and interface electronic structure in detail.In the present study, we have investigated the transport properties of a heteroepitaxial perovskite oxide interface consisting of SrRuO 3 (SRO) deposited on (001) SrTi 0.99 Nb 0.01 O 3 (Nb:STO) single crystal substrate. The SRO/Nb:STO interface exhibits rectifying Schottky-like I-V characteristics with large hysteresis and the resistance can be changed by applying pulsed-voltage stress.Epitaxial SRO thin films (100 nm) were grown on (001) Nb:STO single crystal substrates by a pulse laser deposition technique. Typical growth conditions were a substrate temperature of 700 • C and an oxygen pressure of 100 mTorr. After the deposition, the films were in-site annealed at 400 • C for 30 minutes under an oxygen pressure ...