Simon Granville

Evidence for Thermal Spin-Transfer Torque

Large heat currents are obtained in Co/Cu/Co spin valves positioned at the middle of Cu nanowires. The second harmonic voltage response to an applied current is used to investigate the effect of the heat current on the switching of the spin valves. Both the switching field and the magnitude of the voltage response are found to be dependent on the heat current. These effects are evidence for a thermal spin-transfer torque acting on the magnetization and are accounted for by a thermodynamic model in which heat, charge and spin currents are linked by Onsager reciprocity relations.

Low-temperature hopping and absence of spin-dependent transport in single crystals of cobalt-doped ZnO

Long needle-shaped single crystals of Zn1−xCoxO were grown at low temperatures using a molten salt solvent technique, up to x = 0.10. The conduction process at low temperatures is determined to be by Mott variable range hopping. Both pristine and cobalt doped crystals clearly exhibit a crossover from negative to positive magnetoresistance as the temperature is decreased. The positive magnetoresistance of the Zn1−xCoxO single crystals increases with increased Co concentration and reaches up to 20 % at low temperatures (2.5 K) and high fields (>1 T). SQUID magnetometry confirms that the Zn1−xCoxO crystals are predominantly paramagnetic in nature and the magnetic response is independent of Co concentration. The results indicate that cobalt doping of single crystalline ZnO introduces localized electronic states and isolated Co ions into the host matrix, but that the magnetotransport and magnetic properties are decoupled.

Current susceptibility of magnetization in spin valves

We observed the second harmonic voltage response of pseudo-spin valves subjected to currents oscillating at frequencies in the sub-kilohertz range. Peaks appear in its magnetic field dependence, with a signal-to-noise ratio equal to or greater than the magnetoresistance response of the same samples. This signal is interpreted as arising from the response of the magnetization to the spin torque induced by current when the magnetic layers are in non-collinear orientations. Thus, the method probes the current susceptibility of the magnetization which is shown to be sensitive to non-collinear states undetectable in the magnetoresistance.

Preparation and Properties of Cobalt Doped ZnO Nanowires

The template method was used for preparing Zn1-xCoxO nanowires with x ranging from 0.01 to 0.05. Thus, electrochemical deposition was employed for filling up the pores of polycarbonate ion track nanoporous membranes with the desired material. The method allows a good control over the morphology and composition of the deposited nanowires, as evidenced by scanning electron microscopy (SEM) and energy dispersive X ray analysis (EDX). Measurements of the magnetic properties showed a paramagnetic behavior of the nanowire arrays for the whole set of temperatures and Co concentrations.

Second Harmonic Detection of Spin-Dependent Transport in Magnetic Nanostructures

Detection of the second harmonic response of magnetic nanostructures to an ac current is shown to be a very sensitive probe of the magnetization reversal process. A temperature oscillation is obtained by Joule heating instead of using a laser as the heat source, as in thermo-galvanic voltage measurements (TGV). Joule heating is used to produce a large local temperature gradient in asymmetric Co/Cu/Co spin valves. Evidence is found for an effect of a heat current on magnetization.

Preparation and Properties of Transition Metal Doped ZnO Nanowires

We employed template replication by electrochemical deposition as the technique to prepare transition metals doped zinc oxide nanowires. Polycarbonate nanoporous membranes obtained by swift heavy ions irradiation and subsequent etching were used as templates. The pores were filled with the desired material by electrochemical deposition from an aqueous bath. The properties of the nanowires were investigated by scanning electron microscopy, energy dispersive X ray analysis and optical spectroscopy. We investigated the effect of preparation condition (i.e. deposition potential, deposition bath composition) on nanostructures properties

Magnetic properties of the magnetoelectric compound Cu 2 OSeO 3

We present magnetization and 77Se Nuclear Magnetic Resonance (NMR) measurements in single crystals of the magneteoelectric compound Cu2OSeO3. The temperature and field dependence of the magnetization suggest a ferrimagnetic ordering at Tc ? 60 K in a 3up-1down configuration. The easy axis of the magnetization is along the [100] crystallographic direction. The 77Se NMR line shape data collected at 14.09 T are consistent with the symmetries imposed by the cubic P213 space group in the temperature range 20?290 K and confirm that the magnetic transition is not accompanied by any lowering of the crystal symmetry as has recently been proposed by Bos et al. [Phys. Rev. B 78 094416 (2008)].

Magnetic properties of the magnetoelectric compound Cu2OSeO3: Magnetization and 77Se NMR study

We present magnetization and 77Se Nuclear Magnetic Resonance (NMR) measurements in single crystals of the magneteoelectric compound Cu2OSeO3. The temperature and field dependence of the magnetization suggest a ferrimagnetic ordering at Tc ? 60 K in a 3up-1down configuration. The easy axis of the magnetization is along the [100] crystallographic direction. The 77Se NMR line shape data collected at 14.09 T are consistent with the symmetries imposed by the cubic P213 space group in the temperature range 20?290 K and confirm that the magnetic transition is not accompanied by any lowering of the crystal symmetry as has recently been proposed by Bos et al. [Phys. Rev. B 78 094416 (2008)].

Magnetic properties of the magnetoelectric compound Cu2OSeO3: Magnetization and Se-77 NMR study

We present magnetization and 77Se Nuclear Magnetic Resonance (NMR) measurements in single crystals of the magneteoelectric compound Cu2OSeO3. The temperature and field dependence of the magnetization suggest a ferrimagnetic ordering at Tc ? 60 K in a 3up-1down configuration. The easy axis of the magnetization is along the [100] crystallographic direction. The 77Se NMR line shape data collected at 14.09 T are consistent with the symmetries imposed by the cubic P213 space group in the temperature range 20?290 K and confirm that the magnetic transition is not accompanied by any lowering of the crystal symmetry as has recently been proposed by Bos et al. [Phys. Rev. B 78 094416 (2008)].