Microfabrication and spin polarized transport properties of half-metallic oxide tunnel junctions

D.B. Yu^{1, 3}, J.F. Feng¹, Y. Wang¹, X.F. Han¹, T.-H. Kim², X.-G. Zhang², A.P. Li², H. Yan³, Z. Zhang³

^[1] Beijing National Laboratory for Condensed Matter Physics & Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China

^[2] Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, 37831, USA

^[3] Laboratory of Thin Film Materials, Beijing University of Technology, Beijing, China

Three key epitaxial layers of La0.7Sr0.3MnO3(001)(100 nm)/La0.96Sr0.04MnO3(001)(5 nm)/ La0.7Sr0.3MnO3 (001)(100 nm) and La0.7Sr0.3MnO3 (100 nm)/ SrTiO3(5 nm)/ La0.7Sr0.3MnO3(100 nm) of the magnetic tunnel junctions (MTJs) were deposited by reactive magnetron sputtering on the heating SrTiO3(001)-substrate at 700 ^oC, then annealed in situ at same temperature for half hour. The top conducting layers such as Pt(20 nm) were continuously deposited on the three epitaxial layers by non-reactive magnetron sputtering. Finally, the MTJs with the ellipse-like junction size of 3×6 πμm² were micro-fabricated by lithography combined with Ar-ion etching methods. The colossal TMR^(H) ratio of over than 9000% [TMR^(H)= (RH=0—RH)/RH] was observed at 4.2 K under the external magnetic field of 12 T. The resistance in such half metal La0.7Sr0.3MnO3 MTJ-devices can have 2 orders variations in magnitude.

A space-charge trap induced Pauli blockade effect has been observed in the magnetic tunnel junction consisting of La0.7Sr0.3MnO3 (LSMO) electrodes and a SrTiO3 barrier. The blockade voltage provides a direct measurement of the energy gap between the Fermi energy and the top of the minority spin valence band of LSMO. Outside the Pauli blockade regime, the low temperature conductance oscillates with the bias voltage as the trap centers are charged by electrons. The Pauli blockade can be lifted when a large magnetic field lowers the LSMO minority spin mobility edge to below the Fermi energy. A very large magnetoresistance up to 10000% is observed and is correlated to the blockade effect.

*Author to whom correspondence should be addressed to X.F. Han, xfhan@aphy.iphy.ac.cn

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