Abstract
Obtaining high efficiency spin filtering at room temperature using spinel ferromagnetic tunnel barriers has been hampered by the formation of antiphase boundaries due to their difference in lattice parameters between barrier and electrodes. In this work we demonstrate the use of LiTi2O4 thin films as electrodes in an all-spinel oxide CoFe2O4-based spin filter devices. These structures show nearly perfect epitaxy maintained throughout the structure and so minimise the potential for APBs formation. The LiTi2O4 in these devices is superconducting and so measurements at low temperature have been used to explore details of the tunnelling and Josephson junction behaviour.
Highlights
The broad spectrum of electronic and optical properties exhibited by functional oxides offers many opportunities for microelectronic devices
Of particular relevance to this paper, ultrathin films of ferromagnetic insulators (FIs) oxides can form tunnel barriers that generate nearly 100% spin-polarised currents by selectively filtering electrons according to their spins [2]
We demonstrated the successful superconducting tunnel process in an all-spinel SIS tunnel junctions with CoFe2O4 as FI barrier and LiTi2O4 as electrodes grown on MgAl2O4 substrates
Summary
The broad spectrum of electronic and optical properties exhibited by functional oxides offers many opportunities for microelectronic devices. The ion milling procedure was performed using a self-aligned process for junction fabrication [31] in a Nordiko 3600 ion beam deposition system [32] with an Ar+ beam (current density ~340 μA cm−2), first at an angle with respect to the substrate of 70° down to the CoFe2O4 barrier and subsequently at 40° until it penetrated the bottom LiTi2O4 electrode. This ensured a barrier with steep profile and well controlled nominal size, while avoiding pressure PO2 in the chamber [23, 25,26,27]. The measured current–voltage characteristics show conclusive evidence of the tunnel nature of these junctions, proving that LiTi2O4 can be used as bottom electrode in an almost APBs free tunnel junction
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