Spin injection and detection in lanthanum- and niobium-doped SrTiO3 using the Hanle technique

Abstract

There has been much interest in the injection and detection of spin-polarized carriers in semiconductors for the purposes of developing novel spintronic devices. Here we report the electrical injection and detection of spin-polarized carriers into Nb-doped strontium titanate single crystals and La-doped strontium titanate epitaxial thin films using MgO tunnel barriers and the three-terminal Hanle technique. Spin lifetimes of up to B100 ps are measured at room temperature and vary little as the temperature is decreased to low temperatures. However, the mobility of the strontium titanate has a strong temperature dependence. This behaviour and the carrier doping dependence of the spin lifetime suggest that the spin lifetime is limited by spin-dependent scattering at the MgO/strontium titanate interfaces, perhaps related to the formation of doping induced Ti 3 þ . Our results reveal a severe limitation of the three-terminal Hanle technique for measuring spin lifetimes within the interior of the subject material.

Origin of the Magnetoresistance in Oxide Tunnel Junctions Determined through Electric Polarization Control of the Interface

“…2(a) (top panel, right axis) for the same bias window (V C ¼ 0.4 V). We note that no signal is observed without the presence of an oxide barrier, consistent with previous reports [3,4,9,25]; ΔV C turns on for t LAO > 0 but subsequently decreases when t LAO > 3 u:c: The corresponding linewidths, in the range of 50-120 mT, are shown in the bottom panel of Fig. 2(a).…”

“…Combining such dramatic effects with SrTiO 3 , a semiconductor with high mobilities [16,17] and potentially long spin lifetimes [18], could lead to novel spintronic devices. To date, the primary experimental evidence for spin injection into SrTiO 3 is through the 3T approach, interpreted in terms of spin accumulation in ILS [3,4] (or the SrTiO 3 itself [19]), similar to Si and GaAs [2,5,13]. The epitaxial LaAlO 3 =SrTiO 3 ð001Þ heterostructure is one system with tunable interface properties, arising from the stacking of AlO − 2 and LaO þ charged layers.…”

“…Three-terminal magnetoresistance (3T MR) in ferromagnet-nonmagnet (FM-NM) tunnel junctions has developed into an important phase-sensitive characterization tool for the rapid identification of materials that can transport spin information over long distances, a crucial feature for spintronic devices [1][2][3][4][5]. In principle, spin injection from a FM electrode and detection of the resulting spin accumulation in a NM semiconductor can be achieved using a single FM electrode in a FM-I-NM structure [1,5], as first demonstrated in n-GaAs [6].…”

Controlled formation of high-mobility shallow electron gases in SrTiO3single crystal

“…We demonstrate that the sheet carrier density of the conduction channel is directly controlled by the irradiation time while maintaining high electron mobility, which enables pronounced quantum oscillations below 10 K. Near the onset of conductivity, gate-tunable linear magnetoresistance (MR) is observed, the ratio of which reaches 700% at 9 T. Furthermore, sub-100 nm-thin samples near the conductivity onset exhibit metalinsulator transition when a small gate voltage V g is applied at low temperatures. Our work provides a simple and reliable way to form a very thin high-mobility conduction channel beneath the surface of STO, which is applicable to studies on low-dimensional quantum transport phenomena 14) combined with superconductivity 6,15) and ferromagnetism 16) in strongly correlated metal oxide systems.…”

Electric Control of Spin Injection into a Ferroelectric Semiconductor

“…An efficient spin injection into metals has been commercially employed in today's magnetic read heads and magnetic random access memories through the tunneling magnetoresistance effect in magnetic tunnel junctions [2]. Significant interest has been addressed to the spin injection into semiconductors [3][4][5][6][7][8], and recent developments in the field have demonstrated the possibility of efficient spin injection and spin detection in various electronic systems [9,10]. All the above results rely, however, on a "passive" spin injection where the degree of transport spin polarization is determined by the spin polarization of the injector and the detector and by the electronic properties of the interface.…”