Efforts have been ongoing to establish superconducting spintronics utilizing ferromagnet/superconductor heterostructures. Previously reported devices are based on spin-singlet superconductors (SSCs), where the spin degree of freedom is lost. Spin-polarized supercurrent induction in ferromagnetic metals (FMs) is achieved even with SSCs, but only with the aid of interfacial complex magnetic structures, which severely affect information imprinted to the electron spin. Use of spin-triplet superconductors (TSCs) with spin-polarizable Cooper pairs potentially overcomes this difficulty and further leads to novel functionalities. Here, we report spin-triplet superconductivity induction into a FM SrRuO3 from a leading TSC candidate Sr2RuO4, by fabricating microscopic devices using an epitaxial SrRuO3/Sr2RuO4 hybrid. The differential conductance, exhibiting Andreev-reflection features with multiple energy scales up to around half tesla, indicates the penetration of superconductivity over a considerable distance of 15 nm across the SrRuO3 layer without help of interfacial complex magnetism. This demonstrates potential utility of FM/TSC devices for superspintronics.

Ferromagnetic SrRuO3 thin films are deposited on the ab-surface of single crystals of the spin-triplet superconductor Sr2RuO4 as substrates using pulsed laser deposition. The films are under a severe in-plane compressive strain. Nevertheless, the films exhibit ferromagnetic order with the easy axis along the c-direction below the Curie temperature of 158 K. The electrical transport reveals that the SrRuO3/Sr2RuO4 interface is highly conducting, in contrast with the interface between other normal-metals and the ab-surface of Sr2RuO4. Our results will stimulate the investigations on proximity effects between a ferromagnet and a spin-triplet superconductor.Hybrid structures with ferromagnetic metals (FMs) and superconductors are fascinating systems exhibiting unconventional phenomena originating from competition and cooperation between the ferromagnetic order and superconductivity. In the past, two aspects of exotic behavior of the proximity effect between a FM and a spinsinglet superconductor (SSC) have been revealed. Firstly, the amplitude and phase of the spin-singlet order parameter spatially oscillates in the FM due to exchange interaction and even leads to a π-junction.1 The penetration length of this effect is intrinsically limited to the order of a few nanometers. Secondly, a spin-triplet pair amplitude emerges over a length of the order of a micrometer into the FM if suitable magnetic inhomogeneity is present at the FM/SSC interface.2-7 The resulting superconducting symmetry in the FM is spin-triplet s-wave and thus classified as odd-frequency pairing.8 To induce such a superconductivity into a ferromagnet, half metallic FM CrO 2 with multi-fold magnetic anisotropy, 3,6 or alternatively ferromagnetic multilayer X/Co/X, where X can be PdNi, CuNi, Ni, or Ho, with non-collinear magnetization, is used in the SSC/FM/SSC Josephson junctions. 4, 5, 7Another approach to realize novel superconducting junctions with FM is to use a spin-triplet superconductor (TSC) with multiple degrees of freedom of the order parameter.10-12 Indeed, it has been theoretically predicted that not only charge supercurrent but also spin supercurrent emerges at FM/TSC interface and both can be controlled by the magnetization direction in the FM relative to the direction of the spins of the spin triplet Cooper pairs.11 Thus, FM/TSC junctions, with both controllable charge and spin supercurrents, would initiate a new research area that can be termed as "Superspintronics".Most likely, Sr 2 RuO 4 (SRO214) exhibits the chiral pwave spin-triplet superconducting order parameter analogous to the superfluid 3 He-A phase. 13, 14 SRO214 has also been attracting much attention as one of the leading candidates for the topological superconductor. Recently, its topological nature has been investigated with superconducting junctions.15-17 The main challenge in realizing a FM/TSC junction is the availability of thin films of spin triplet superconductors. By overcoming the difficulty in growing high quality SRO214 films, superconductivity has finally been ...

The requirements of multifunctionality in thin-film systems have led to the discovery of unique physical properties and degrees of freedom, which exist only in film forms. With progress in growth techniques, one can decrease the film thickness to the scale of a few nanometers (∼nm), where its unique physical properties are still pronounced. Among advanced ultrathin film systems, ferroelectrics have generated tremendous interest. As a prototype ferroelectric, the electrical properties of BaTiO3 (BTO) films have been extensively studied, and it has been theoretically predicted that ferroelectricity sustains down to ∼nm thick films. However, efforts toward determining the minimum thickness for ferroelectric films have been hindered by practical issues surrounding large leakage currents. In this study, we used ∼nm thick BTO films, exhibiting semiconducting characteristics, grown on a LaAlO3/SrTiO3 (LAO/STO) heterostructure. In particular, we utilized two-dimensional electron gas at the LAO/STO heterointerface as the bottom electrode in these capacitor junctions. We demonstrate that the BTO film exhibits ferroelectricity at room temperature, even when it is only ∼2 unit-cells thick, and the total thickness of the capacitor junction can be reduced to less than ∼4 nm. Observation of ferroelectricity in ultrathin semiconducting films and the resulting shrunken capacitor thickness will expand the applicability of ferroelectrics in the next generation of functional devices.

At micro- and nanoscales, materials with high Young's moduli and low densities are of great interest for high-frequency micromechanical resonator devices. Incorporating carbon nanotubes (CNTs), with their unmatched properties, has added functionality to many man-made composites. We report on the fabrication of < or = 100-nm-thick laminates by sputter-deposition of aluminium onto a two-dimensional single-walled CNT network. These nanolaminates--composed of Al, its native oxide Al(2)O(3) and CNTs--are fashioned, in a scalable manner, into suspended doubly clamped micromechanical beams. Dynamic flexural measurements show marked increases in resonant frequencies for nanolaminates with Al-CNT laminae. Such increases, further supported by quasi-static flexural measurements, are partly attributable to enhancements in elastic properties arising from the addition of CNTs. As a consequence, these nanolaminate micromechanical resonators show significant suppression of mechanical nonlinearity and enhanced strength, both of which are advantageous for practical applications and analogous to biological nanocomposites, similarly composed of high-aspect-ratio, mechanically superior mineral platelets in a soft protein matrix.

We investigated the resistance switching (RS) phenomenon in epitaxial NiO (epi-NiO) films by employing different types of top electrodes (TEs). Epi-NiO showed successive bipolar RS when Pt and CaRuO3 (CRO) were used as the TEs, but not when Al and Ti were used. We studied the temperature dependence of the current–voltage (I–V) characteristics for various TEs and resistance states to understand the conduction properties of TE/epi-NiO. Pristine CRO/epi-NiO showed metallic behavior, while pristine Pt/epi-NiO and Al/epi-NiO showed insulating behavior. Pt/epi-NiO and Al/epi-NiO, however, switched to a metallic or non-insulating state after electroforming. Transmission electron microscopy (TEM) images revealed the presence of a distinct stable interfacial AlO x layer in pristine Al/epi-NiO. On the other hand, the interfacial metal oxide layer was indistinguishable in the case of pristine Pt/epi-NiO and CRO/epi-NiO. Our experimental results suggested that epi-NiO has an oxygen defect on its surface and therefore the various TE/epi-NiO interfaces characterized in this study adopt distinctive electrical states. Further, the bipolar RS phenomenon can be explained by the voltage-polarity-dependent movement of oxygen ions near the interface.

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We studied the electrical conduction in the LaAlO3/SrTiO3 (LAO/STO) interface electron system with a sub‐critical LAO layer thickness of ∼3.5 unit cells (uc). It was found that the true dividing point between metallic and insulating behaviour without gating lies near the LAO thickness of 3.5 uc. Our marginally metallic 3.5 uc sample showed a sharp transition to insulating state at temperatures which strongly depended on the applied negative back‐gate voltage. The superior gate‐controllability of the sample was attributed to its sheet carrier density which was an order of magnitude lower than those of conducting LAO/STO samples with 4 uc or more of LAO layers. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)