Stochastic current-induced magnetization switching in a single semiconducting ferromagnetic layer.

We show experimental evidence of magnetization switching in a single (Ga,Mn)(As,P) semiconducting ferromagnetic layer, attributed to a strong reduction of the magnetization and the anisotropy due to current injection. The nucleation of magnetization reversal is found to occur even in the absence of a magnetic field and to be both anisotropic and stochastic. Our findings highlight a new mechanism of magnetization manipulation based on spin accumulation in a semiconductor material.

Unidirectional thermal effects in current-induced domain wall motion.

We report experimental evidence of thermal effects on the displacement of vortex walls in NiFe nanostrips. With the use of nanosecond current pulses, a unidirectional motion of the magnetic domain walls towards the hotter part of the nanostrips is observed, in addition to current-induced domain wall motion. By tuning the heat dissipation in the samples and modeling the heat diffusion, we conclude that this unidirectional motion can only be explained by the presence of a temperature profile along the nanostrip. A quantitative analysis of the experiments shows that, on top of the classical thermodynamic pressure on the domain wall, another force, probably the magnonic spin Seebeck effect, is displacing the domain walls.

Spin drift velocity, polarization, and current-driven domain-wall motion in (Ga,Mn)(As,P).

Current-driven domain-wall motion is studied in (Ga,Mn)(As,P) ferromagnetic semiconducting tracks with perpendicular anisotropy. A linear steady state flow regime is observed over a large temperature range of the ferromagnetic phase (0.1T(c)

Current induced domain wall motion in GaMnAs close to the Curie temperature.

Domain wall dynamics produced by spin transfer torques is investigated in (Ga, Mn)As ferromagnetic semiconducting tracks with perpendicular anisotropy, close to the Curie temperature. The domain wall velocities are found to follow a linear flow regime which only slightly varies with temperature. Using the Döring inequality, boundaries of the spin polarization of the current are deduced. A comparison with the predictions of the mean field k·p theory leads to an estimation of the carrier density whose value is compatible with results published in the literature. The spin polarization of the current and the magnetization of the magnetic atoms present similar temperature variations. This leads to a weak temperature dependence of the spin drift velocity and thus of the domain wall velocity. A combined study of field- and current-driven motion and deformation of magnetic domains reveals a motion of domain walls in the steady state regime without transition to the precessional regime. The ratio between the non-adiabatic torque ß and the Gilbert damping factor α is shown to remain close to unity.

Room-temperature I-V characteristics of a single hollow La2/3Ca1/3MnO3 microparticle.

In this work we present an electrical characterization of La2/3Ca1/3MnO3 particles obtained by spray pyrolysis. We optimized the synthesis conditions to obtain the desired compound with the expected structure and the ferromagnetic transition at the same temperature as the bulk material. We found that a post-deposition thermal treatment enhances the magnetic properties of the samples. The study of structural, morphological and magnetic properties shows that the walls of the hollow spheres are constituted by grains on the nanometer scale. The I-V characterization shows typical signatures of tunneling transport. This behavior can be associated with the grain boundaries within the microparticle's wall acting as tunnel barriers.

High-temperature behavior of Sr-doped layered cobaltites Y(Ba(1-x)Sr(x))Co2O5.5: phase stability and structural properties.

In this paper we present a neutron diffraction in situ study of the thermal evolution and high-temperature structure of layered cobaltites Y (Ba, Sr)Co(2)O(5 + δ). Neutron thermodiffractograms and magnetic susceptibility measurements are reported in the temperature range 20 K ≤ T ≤ 570 K, as well as high-resolution neutron diffraction experiments at selected temperatures. Starting from the as-synthesized samples with δ≈0.5, we show that the room temperature phases remain stable up to 550 K, where they start losing oxygen and transform to a vacancy-disordered structure with tetragonal symmetry. Our results also show how the so-called '122' structure can be stabilized at high temperature (around 450 K) in a sample in which the addition of Sr at the Ba site had suppressed its formation. In addition, we present the structural and magnetic properties of the resulting samples with a new oxygen content δ≈0.25 in the temperature range 20 K ≤ T ≤ 300 K.

Enhancing spin state phase separation by strontium addition in the Y (Ba(1-x)Sr(x))Co(2)O(5.5) layered cobaltite.

In this paper we present a neutron diffraction study of the effects of replacing Ba with smaller Sr cations in the layered cobaltite YBaCo(2)O(5+δ) for δ≈0.5. Neutron thermodiffractograms are reported in the temperature range 20 K≤T≤300 K, as well as high-resolution neutron diffraction experiments at selected temperatures. The systematic refinement of the series of samples with Sr substituting at the Ba site permits the understanding of the complex magnetic behaviour of this system, and reinforces a two-phase scenario for the parent compound. We have found that Sr addition destabilizes the ferrimagnetic spin state ordered phase, as well as the '122' order characteristic of cobaltites with δ = 0.5, favouring instead a tetragonal and less ordered structure.

Automated image analysis for monitoring oxidative burst in macrophages.

OBJECTIVE: To evaluate oxidative bursts induced by phorbol myristate acetate in phagocytes at the single-cell level by automated image analysis. STUDY DESIGN: The generation of reactive oxygen species was quantitatively expressed by means of histograms displaying the percentage of cells corresponding to each of the total optical densities measured. RESULTS: Macrophage subpopulations were quantitatively defined. This method allows detailed analysis of the amount of formazan per cell and the sites of deposition of blue precipitate in each cell. CONCLUSION: Image analysis is a reliable quantitative, single-cell assay for studying various cellular characteristics associated with macrophage functions.