Half-metallic La0 Research Articles

Electrical bistability and spin valve effect in a ferromagnet/organic semiconductor/ferromagnet heterojunction

We report a study of the electrical bistability and bias-controlled spin valve effect in an organic device using rubrene (C42H28) as an organic semiconductor channel. The halfmetallic La0.7Sr0.3MnO3 (LSMO) and Fe are used as the two ferromagnetic electrodes. The device displays reproducible switching between a low-impedance (ON) state and a highimpedance (OFF) state by applying different polarities of high biases. In the ON state, the device shows a spin valve effect with magnetoresistance values up to 3.75%. The observed spin valve effect disappears when the device recovers to the initial OFF state.

Planar-type spin valves based on low-molecular-weight organic materials with La0.67Sr0.33MnO3 electrodes

The spin injection and transport properties of low-molecular-weight organic semiconductors such as pentacene and bis(l,2,5-thiadiazolo)-p-quinobis(l,3-dithiole) (BTQBT) were investigated utilizing planar-type spin-valve devices with half-metallic La0.67Sr0.33MnO3 electrodes. The devices showed clear spin-valve characteristics with a magnetoresistance (MR) ratio of up to 29% at 5K. The MR ratio was found to depend on the gap spacing of the electrodes, the applied bias voltage, temperature, and the crystallinity of the films. It was also affected by gas adsorption onto the films, indicating that the spins were scattered by carriers and/or radical ions in the films generated through charge transfer from gas molecules.

Ferrodistortive Instability at the (001) Surface of Half-Metallic Manganites

We present the structure of the fully relaxed (001) surface of the half-metallic manganite La0.7Sr0.3MnO3, calculated using density functional theory. Two relevant ferroelastic order parameters are identified and characterized. The known tilting of the oxygen octahedra, which is present in the bulk phase, decreases towards the surface. A ferrodistortive Mn off-centering, triggered by the surface and not reported before, decays monotonically into the bulk. This distortion affects neither the half-metallicity nor the zero-temperature magnetization, but does change the effective spin-spin interactions, and thus the temperature dependence of the magnetic properties.

Magnetoresistance and electrical hysteresis in stable half-metallic La0.7Sr0.3MnO3 and Fe3O4 nanoconstrictions

We have studied the transport properties of mechanically stable Fe3O4 and La0.7Sr0.3MnO3 nanoconstrictions patterned by focused ion-beam milling. The magnetoresistance decreases with the square of the applied voltage and scales with the resistance of the constriction, with values up to 8000% for magnetite and 100% for La0.7Sr0.3MnO3. These results are interpreted within a model for domain-wall magnetoresistance. Some samples exhibit electrical hysteresis with discrete changes of resistance that disappear in the presence of a magnetic field, indicating domain-wall displacement driven by a spin-polarized current.

Temperature and electric field response of a dielectric (Ba,Sr)TiO3 layer between perovskite‐type manganite electrodes

AbstractEpitaxial films of ferroelectric (00l)Ba0.25Sr0.75TiO3 (BSTO) and ferromagnetic half metal La0.67Sr0.33MnO3 were grown by laser ablation, forming a trilayer heterostructure with combined ferroelectric and magnetic properties, on (001)(LaAlO4)0.3 + (Sr2AlTaO6)0.7 substrates. Maxima TM in the dielectric permittivity of ϵ of the BSTO film were 30–50 K lower than in bulk and ϵ follows a Curie‐Weiss law above TM. The ϵ was suppressed up to 50% at ±2.5 V between the electrodes. Below 100 K, loss function tan δ was found to be 0.005–0.01 at 1 kHz and 100 kHz.

Ｌａ０．７Ｓｒ０．３ＭｎＯ３トンネル接合のＴＭＲ特性

Magnetic tunnel junctions using half-metallic La0.7Sr0.3MnO3 (LSMO) were investigated. Two types of junctions, Co/SrTiO3(STO)/LSMO (CSL junction) and LSMO/STO/LSMO (LSL junction) were prepared, where the Co layer on the STO layer of the CSL junction was grown at room temperature and the LSMO layer on the STO layer of the LSL junction was grown at 500°C or 700°C. The observed TMR ratios for CSL and LSL junctions were 50% and -4%, respectively. The junction resistance of CSL increased exponentially with increasing STO thickness (tSTO), whereas that of LSL was almost independent of tSTO. It was found that the low TMR ratio of LSL was due to the inferior quality of the STO layer, caused during the growth of LSMO on the STO layer in an Ar atmosphere at high temperature. The inferiority of the STO layer-that is, introduction of defects into the STO layer- causes a decrease in the junction resistance and affects the decrease in the spin polarization of the upper LSMO layer, and subsequently results the small TMR ratio.

Direct injection of spin-polarized carriers across YBa2Cu3O7-δ-La0.3Ca0.7MnO3 interface at 77 K

We report here injection of spin-polarized carriers from a half-metallic La0.3Ca0.7MnO3 (LCMO) colossal magnetoresistive (CMR) thin film into a high-temperature superconducting YBa2Cu3O7-δ (YBCO) thin film studied using a micro-bridge. The LCMO and YBCO films were grown on 〈100〉 LaAlO3 (LAO) substrate sequentially using pulsed laser deposition (PLD). I-V measurements carried out at 77 K show that while normal critical current, Icn, of the micro-bridge is 80 mA, the critical current, Icp, through the micro-bridge when injected from the CMR layer is 38 mA. This clearly shows that spin-polarized quasiparticles injected from the the CMR layer into the YBCO layer suppress the critical current of the superconductor via the pair-breaking phenomena.