Heidi Seinige

Structural, optical, and electrical properties of strained La-doped SrTiO3 films

The structural, optical, and room-temperature electrical properties of strained La-doped SrTiO3 epitaxial thin films are investigated. Conductive La-doped SrTiO3 thin films with concentration varying from 5 to 25% are grown by molecular beam epitaxy on four different substrates: LaAlO3, (LaAlO3)0.3(Sr2AlTaO6)0.7, SrTiO3, and DyScO3, which result in lattice mismatch strain ranging from −2.9% to +1.1%. We compare the effect of La concentration and strain on the structural and optical properties, and measure their effect on the electrical resistivity and mobility at room temperature. Room temperature resistivities ranging from ∼10−2 to 10−5 Ω cm are obtained depending on strain and La concentration. The room temperature mobility decreases with increasing strain regardless of the sign of the strain. The observed Drude peak and Burstein-Moss shift from spectroscopic ellipsometry clearly confirm that the La addition creates a high density of free carriers in SrTiO3. First principles calculations were performed to help understand the effect of La-doping on the density of states effective mass as well as the conductivity and DC relaxation time.

Temperature dependence of anisotropic magnetoresistance in antiferromagnetic Sr2IrO4

Temperature-dependent magnetotransport properties of the antiferromagnetic semiconductor Sr2IrO4 are investigated with point-contact devices. The point-contact technique allows to probe very small volumes and, therefore, to look for electronic transport on a microscopic scale. Point-contact measurements with single crystals of Sr2IrO4 were intended to see whether the additional local resistance associated with a small contact area between a sharpened Cu tip and the antiferromagnet shows magnetoresistance (MR) such as that seen in bulk crystals. Point-contact measurements at liquid nitrogen temperature revealed large MRs (up to 28%) for modest magnetic fields (250 mT) applied within an IrO2 (ab) plane with angular dependence showing a crossover from four-fold to two-fold symmetry with an increasing magnetic field. Point contact measurement exhibits distinctive anisotropic magnetoresistance (AMR) in comparison to a bulk experiment, imposing intriguing questions about the mechanism of AMR in this material. T...

Spin-transfer-torque switching in spin valve structures with perpendicular, canted, and in-plane magnetic anisotropies

We exploit canted anisotropies as possible means to enhance spin-transfer-torque (STT) and reduce switching currents. The STTs in spin-valve structures with perpendicular, canted, and, as a reference, in-plane magnetic anisotropies were studied. For perpendicular magnetic anisotropy and canted spin valves the thicknesses and number of Co and Pt layers were varied to obtain different angles of the magnetic anisotropy with respect to the sample plane. Point contact measurements were used to measure the change in the switching-field of the magnetization with the change in the bias current applied to the point contact. A larger STT effect, as evidenced by a larger change in the switching magnetic field for the unit change in the dc bias current, was observed for the sample with 45∘ tilt in magnetization compared to a sample with 12∘ tilt. Tilted magnetization of the reference layer causes precessional switching, decreasing the switching energy and time. Micromagnetic simulations were performed to explain the ...

Electrically tunable transport in the antiferromagnetic Mott insulator Sr2IrO4

Electronic transport properties of the antiferromagnetic Mott insulator

Current-driven parametric resonance in magnetic multilayers

\mathrm{S}{\mathrm{r}}_{2}\mathrm{Ir}{\mathrm{O}}_{4}

Anisotropic Magnetoresistance in Antiferromagnetic Sr 2 IrO 4

have been investigated under extremely high electric biases. Using nanoscale contacts, we apply electric fields up to a few MV/m to a single crystal of

Current-driven non-linear magnetodynamics in exchange-biased spin valves

\mathrm{S}{\mathrm{r}}_{2}\mathrm{Ir}{\mathrm{O}}_{4}

Ferromagnetic resonance: Electrical detection vs conventional absorption measurements

and observe a continuous reduction in the materials resistivity with increasing bias, characterized by a reduction in the transport activation energy by as much as

Ferromagnetic resonance detection by a point-contact bolometer

16%

Electrically tunable transport and high-frequency dynamics in antiferromagnetic Sr3Ir2O7

. Temperature-dependent resistivity measurements provide a means to unambiguously retrieve the bias dependence of the activation energy from the Arrhenius plots at different biases. We further demonstrate the feasibility of reversible resistive switching induced by the electric bias, which is of interest for the emerging field of antiferromagnetic spintronics. Our findings demonstrate the potential of electrical means for tuning electronic properties in