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Antiferromagnetic insulators have recently been proved to support spin current efficiently. Here, we report the damping-like spin- orbit torque (SOT) in Pt / NiO / CoFeB has a strong temperature dependence and reverses the sign below certain temperatures, which is different from the slight variation with temperature in the Pt / CoFeB bilayer. The negative damping-like SOT at low temperatures is proposed to be mediated by the magnetic interactions that tie with the “exchange bias” in Pt / NiO / CoFeB, in contrast to the thermal-magnon-mediated scenario at high temperatures. Our results highlight the promise to control the SOT through tuning the magnetic structure in multilayers.

We report the temperature and magnetic field dependence of transport properties in epitaxial films of the manganite La$_{1-x}$Ca$_{x}$MnO$_{3}$ in the overdoped region of the phase diagram for $x > 0.5$, where a charge--ordered (CO) and an antiferromagnetic (AF) phase are present. Resistivity, magnetoresistance and angular dependence of magnetoresistance were measured in the temperature interval $4.2 ~\mathrm{K} < T < 300 ~\mathrm{K}$, for three concentrations $x = 0.52, 0.58$ and $0.75$ and in magnetic fields up to 5 T. The semiconductor/insulator--like behavior in zero field was observed in the entire temperature range for all three concentrations \textit{x} and the electric conduction, at lower temperatures, in the CO state obeys 3D Mott's variable--range hopping model. A huge negative magnetoresistance for $x = 0.52$ and $x = 0.58$, a metal--insulator transition for $B > 3 ~\mathrm{T}$ for $x = 0.52$ and the presence of anisotropy in magnetoresistance for $x = 0.52$ and $x = 0.58$ show the fingerprints of colossal magnetoresistance (CMR) behavior implying the existence of ferromagnetic (FM) clusters. The declining influence of the FM clusters in the CO/AF part of the phase diagram with increasing $x$ contributes to a possible explanation that a phase coexistence is the origin of the CMR phenomenon., 33 pages, 7 figures, 1 table, accepted in Thin Solid Films

We investigate the dc resistivity and Hall effect of the quasi-two-dimensional organic materials κ–(ET)2X, where X=Ag2(CN)3 and B(CN)4 and compare them with the results for X=Cu2(CN)3. All three compounds are considered to be quantum-spin-disordered Mott insulators. Despite high similarities in chemical composition and crystal structure, large differences in the dc resistivity and Hall coefficient are found. While around room temperature the dc transport properties are dominantly determined by the strength of the electron correlations, upon reducing the temperature, dc transport happens by hopping due to inherent disorder. The most disordered compound with X=Cu2(CN)3 turns out to have the lowest dc resistivity and the highest charge carrier density, i.e., in the phase diagram it is located closest to the metal-insulator transition. The least disordered compound with X=B(CN)4 shows the highest resistivity and the lowest carrier density, i.e., lies farthest from the metal-insulator transition. We explain such counterintuitive behavior within the theory of Mott-Anderson localization as a consequence of disorder-induced localized states within the correlation gap.

The cobalt-based Heusler alloys are promising for spintronic applications, thanks to their high spin polarization and half-metallic character. This work investigates the spin-dependent transport and thermoelectric effects in epitaxial Co${}_{2}$TiSn thin films, with and without V doping. The anomalous Nernst angle and anomalous Hall angle are both determined, and the relationship between these two important parameters is discussed. These experimental results are a step toward realizing spin-caloritronic devices for efficient on-chip energy harvesting of waste heat.

Novel forms of the low-temperature phases in the two-dimensional molecular solids with competing interactions between charges, spins and lattice, in particular those featuring anomalous dielectric relaxation, have been the focus of intense activity in recent years. Open issues concern the nature of collective charge excitations as well as their coupling to applied ac and dc electric fields. The charge response is reasonably well understood by now in the charge-ordered phase with the formation of ferroelectric-like domains below the metal-to-insulator phase transition. Conversely, the dielectric response observed in dimer Mott insulator phases with no complete evidence for charge ordering is rather intriguing. We overview our recent results of anisotropic complex conductivity (dc – MHz) in the magnetic phase of κ - ( BEDT - TTF ) 2 Cu [ N ( CN ) 2 ] Cl and in the spin-liquid phase of κ - ( BEDT - TTF ) 2 Cu 2 ( CN ) 3 . We discuss possible explanations for the observed dynamics within current theoretical models and compare them with the well-known fingerprints of the spin density wave response to ac electric fields.

The anomalous Nernst effect in a perpendicularly magnetized Ir22Mn78/Co20Fe60B20/MgO thin film is measured using well-defined in-plane temperature gradients. The anomalous Nernst coefficient reaches 1.8 mu V/K at room temperature, which is almost 50 times larger than that of a Ta/Co20Fe60B20/MgO thin film with perpendicular magnetic anisotropy. The anomalous Nernst and anomalous Hall results in different sample structures revealing that the large Nernst coefficient of the Ir22Mn78/Co20Fe60B20/MgO thin film is related to the interface between CoFeB and IrMn. Published by AIP Publishing.

Spin-dependent thermoelectric transport properties have been experimentally studied on a micro-structured device based on epitaxially grown 75-nm-thick Co2Ti0.6V0.4Sn0.75 Heusler film with integrated heater and thermometers. The anomalous Nernst coefficient is found to be 0.5 μV/K at 50 K. Thermoelectric power in both longitudinal and transverse directions have been measured with magnetic field rotated in-plane. Asymmetric peaks and valleys are observed at particular in-plane field angle around 25 K. These anomalous peaks show novel magnetic hysteresis due to the interplay between the magnetization and the temperature gradient. These complex behaviors of thermoelectric effect during magnetization reversal still need to be understood.

We present Hall effect measurements of two-leg ladder Sr 14 - x Ca x Cu 24 O 41 ( 0 ⩽ x ⩽ 11.5 ). In these composite materials charge and spin ordering occur within chain and ladder subsystems. They have been investigated intensively during the last years because of their fascinating physical properties, especially after the discovery of superconductivity under pressure (for x > 10 ). They are the first superconducting copper oxides (superconductivity occurs under pressure for x > 10 ) without the CuO 2 planes, characteristic for high-temperature superconductors. The question of charge dynamics and hole distribution between the ladders and chains is still open. Our Hall effect results show typical semiconducting behavior for x 10 . The x = 11.5 compound shows metallic behavior and our Hall effect results match qualitatively the behavior found in high- T c cuprates. We have determined the effective number of carriers and its dependence on composition (x) and compared it to the number of holes in the ladders obtained by other experimental techniques at room temperature.

We present the measurements of the magnetotransport properties of the spin liquid candidate κ -(BEDT-TTF) 2 Cu 2 (CN) 3 . The temperature dependencies of dc resistivity and Hall coefficient R H as well as magnetoresistance at fixed temperatures in magnetic fields up to 5 T suggest that the charge transport takes place via 2D variable range hopping among localized states.

We report Hall effect measurements performed in the normal phase and at ambient pressure of (TMTSF) 2 ReO 4 and (more anisotropic) (TMTTF) 2 AsF 6 quasi-1D organic conductors. For T>200 K, the Hall coefficient of (TMTSF) 2 ReO 4 is smoothly temperature-dependent, and its value corresponds to a carrier concentration of one hole/unit cell. On the other hand, the Hall coefficient of (TMTTF) 2 AsF 6 is enhanced above 220 K, and the corresponding carrier concentration is almost 100 times lower than the expected one for one hole/unit cell. Our results give evidence for the existence of a high temperature regime above 200 K in (TMTTF)2X salts, where the 1D Luttinger liquid features appear in the transport properties.

We have in detail characterized the anisotropic charge response of the dimer Mott insulator $\ensuremath{\kappa}\text{\ensuremath{-}}(\text{BEDT-TTF}{)}_{2}{\mathrm{Cu}}_{2}(\text{CN}{)}_{3}$ by dc conductivity, Hall effect, and dielectric spectroscopy. At room temperature, the Hall coefficient is positive and close to the value expected from stoichiometry; the temperature behavior follows the dc resistivity $\ensuremath{\rho}(T)$. Within the planes the dc conductivity is well described by variable-range hopping in two dimensions; this model, however, fails for the out-of-plane direction. An unusually broad in-plane dielectric relaxation is detected below about 60 K; it slows down much faster than the dc conductivity following an Arrhenius law. At around 17 K, we can identify a pronounced dielectric anomaly concomitantly with anomalous features in the mean relaxation time and spectral broadening. The out-of-plane relaxation, on the other hand, shows a much weaker dielectric anomaly; it closely follows the temperature behavior of the respective dc resistivity. At lower temperatures, the dielectric constant becomes smaller both within and perpendicular to the planes; also, the relaxation levels off. The observed behavior bears features of relaxorlike ferroelectricity. Because heterogeneities impede its long-range development, only a weak-tunneling-like dynamics persists at low temperatures. We suggest that the random potential and domain structure gradually emerge due to the coupling to the anion network.

We have measured the magnetic susceptibility, resistivity, magnetoresistivity and Hall effect of nonstoichiometric cuprous selenide between 5 and 350 K. Our results show that below 170 K Cu 2− x Se is a mixture of diamagnetic Cu 1.995 Se and paramagnetic Cu 3 Se 2 . The phase diagram of the Cu–Se system, in which 170 K represents the eutectic isotherm, governs the relative content of the two phases. For the Cu 3 Se 2 phase a transition to an antiferromagnetic state is observed at about 50 K, with the corresponding Weiss temperature Θ =120 K. On heating above 170 K Cu 2− x Se becomes completely diamagnetic, but the transformation is slow and strongly time dependent. The complicated magnetic behaviour is ascribed to a broad temperature hysteresis of the process.

We have measured the magnetoresistance and the Hall effect in the spin-density-wave (SDW) state of (TMTSF)_2PF_6 down to 2K and in magnetic fields up to 9T in order to gain an additional insight into the nature of the possible subphases in the SDW state. We have found that the temperature dependent magnetoresistance anisotropy changes below 4K ; this change being maximal for the current in the lowest conductivity direction. The Hall resistivity has showed different magnetic field dependencies for T>4K and T

We report on the magnetotransport properties and spin polarization of Co-doped (La,Sr)TiO 3 (Co-LSTO) thin films in which the host oxide is a strongly correlated metal with a high density of carriers. In order to probe the spin polarization, we have performed tunneling magnetoresistance (TMR) measurements on magnetic tunnel junctions associating Co-LSTO and Co electrodes. A large spin polarization of around -80% has been determined at low temperatures, indicating that the carriers in this system are highly spin-polarized. We also report on the planar magnetotransport experiments on Co-LSTO films grown on SrTiO 3 substrates. The electrical properties of these samples are strongly dependent on the growth conditions and large electronic mobilities as high as 10 4 cm 2 /Vs at T< 10 K are observed for specimens grown at the lowest oxygen pressure. We show that this high-mobility state is three-dimensional and we relate it to the doping of the SrTiO 3 substrate with oxygen vacancies.

Co particles were obtained by patterning trilayers such as Co/Cu/Co and NiFe/Cu/Co grown by sputtering. Using electronic lithography, we can design on these layers a microsensor for transport measurements and a Co particle on the top layer. The Co particle and the sublayers form a spin-valve structure due to their different coercivity. We used GMR measurements to detect the magnetization reversal in Co particles with sizes between 100 × 50 μm 2 and 180 × 20 nm 2 . We present the size dependence of the GMR ratio and of the reversal magnetic field. For the smallest size, we do not find a Stoner- Wolfahrt-like rotation (i.e. uniform rotation) of the Co particle magnetization, but GMR displays staircase curves indicating discrete variation of this magnetization.

We report the transverse magnetoresistance measurements at ambient pressure in the organic conductor (TMTTF)2Br in the temperature range between 4.2 K and 40 K and in magnetic fields up to 8.5 T. We have found isotropic, negative and temperature dependent magnetoresistance which becomes negligible, close to 40 K. We interpret the observed behaviour within the picture of strongly correlated quasi-one dimensional systems.

Hall effect measurements of the organic conductor (TMTSF) 2 NO 3 at low temperatures (1.8 ≤ T ≤7 K) and high magnetic fields (H ≤ 8.5 T), are reported. The large Hall coefficient R H indicates the semimetallic nature of the spin density wave (SDW) ground state, whereas its positive sign shows the dominance of the hole carriers. Both R H and resistivity increase with decreasing temperature, which suggests the possibility that the carrier concentration is reduced as the temperature is lowered. The field variation of Hall resistance R xy deviates from the linear dependence for T ≤ 4 K and H ≥ 3 T. This could be interpreted not only by the temperature induced change in the number of carriers or anisotropy of their mobilities, but also by the possibility that the SDW state might change with the applied magnetic field.

We have measured the Hall effect on recently synthesized single crystals of quasi-one-dimensional organic conductor TTF-TCNQ, a well known charge transfer complex that has two kinds of conductive stacks: the donor (TTF) and the acceptor (TCNQ) chains. The measurements were performed in the temperature interval 30 K < T < 300 K and for several different magnetic field and current directions through the crystal. By applying the equivalent isotropic sample (EIS) approach, we have demonstrated the importance of the choice of optimal geometry for accurate Hall effect measurements. Our results show, contrary to past belief, that the Hall coefficient does not depend on the geometry of measurements and that the Hall coefficient value is around zero in high temperature region (T > 150 K), implying that there is no dominance of either TTF or TCNQ chain. At lower temperatures, our measurements clearly prove that all three phase transitions of TTF-TCNQ could be identified from Hall effect measurements., Revised version; 7 pages, 5 figures

We study the extrinsic spin Hall effect induced by Ir impurities in Cu by injecting a pure spin current into a CuIr wire from a lateral spin valve structure. While no spin Hall effect is observed without Ir impurity, the spin Hall resistivity of CuIr increases linearly with the impurity concentration. The spin Hall angle of CuIr, $(2.1 \pm 0.6)$% throughout the concentration range between 1% and 12%, is practically independent of temperature. These results represent a clear example of predominant skew scattering extrinsic contribution to the spin Hall effect in a nonmagnetic alloy., 5 pages, 4 figures

We have studied the influence of the magnetic field in the plane perpendicular to the highly conducting axis on the ohmic and non-ohmic electrical transport in the spin-density wave state of the organic conductor (TMTSF) 2 NO 3 . In particular, we report (1) the angular dependence of the magnetoresistance at different temperatures and in low electric fields and (2) magnetic field dependence of the threshold electric field for the non-ohmic conductivity. We discuss obtained results and compare them with the behaviour found in the spin-density wave state of the other (TMTSF) 2 X compounds.

We present experiments of magnetization reversal by spin injection performed on pillar-shaped Co/Cu/Co trilayers. The pillars (200×600 nm2) are fabricated by electron beam lithography and reactive ion etching. Our data for the magnetization reversal at a threshold current confirm previous results on similar pillars. In addition, we present another type of experiment that also clearly evidences the control of the magnetic configuration by the current intensity. Our interpretation is based on a version of the Slonczewski model in which the polarization of the current is calculated in the Valet&#8211 ; Fert model of the giant magnetoresistance with current applied perpendicular to plane.

Among perovskites, SrTiO_3 (STO) is one of the most widely studied oxides because of its potential in many applications in oxide electronics. Recently it has been shown that irradiated STO surfaces exhibit high-mobility conduction in contrast to the insulating behaviour of stoichiometric STO single crystals. The possibility of modifying the properties of solids just by etching their surfaces opens up new perspectives for engineering of the functional properties of materials. But for that purpose, a deeper knowledge of damage extension and its consequences on the physical properties is highly desired. Bearing this in mind, we have characterized the spatial distribution and the nature of vacancy defects in insulating as-received as well as in ion-irradiated STO substrates exhibiting high-mobility conduction. Because tiny amounts of oxygen vacancies can trigger substantial modifications of the physical properties of STO, positron annihilation spectroscopy techniques appear as an appropriate characterization tool. We show that Ti vacancies are native defects homogeneously distributed in as-received substrates. In contrast, the dominant vacancy defects consist of non-homogeneous distributions of cation-oxygen vacancy complexes in ion-etched substrates. Their spatial extension is tuned over a few microns in ionetched samples. Our results shed light on the transport mechanisms of conductive STO crystals and on strategies for defect-engineered oxide quantum wells, wires and dots.

Using a combination of advanced characterization tools (positron annihilation spectroscopy, conductive-tip atomic force microscopy, and high-field magnetotransport), we have studied the extension, origin and properties of the high mobility electron gas (HMEG) generated by etching the SrTiO(3) surfaces with Ar(+) ions. Contrary to previous assumptions, we show that this HMEG is not confined to nanometric thickness but extends to a few micrometer from the surface. We discuss this unanticipated large spatial extension in terms of the striking large diffusion of oxygen vacancy-related defects. (C) 2010 American Institute of Physics.

We present an investigation of the low temperature properties of the ternary intermetallic alloy YbNiSn by X-ray and neutron diffraction, resistivity, magnetisation and 170Yb Mossbauer spectroscopy measurements. It is shown that YbNiSn is a ferromagnet (Tc = 5.65 K) with the Yb3+ magnetic moments lying along the orthorhombic c axis. At low temperatures a strong anisotropy of the interionic exchange coupling is evidenced (λc ≃ 100 kOe/μB, λa ≃ 15 kOe/μB) which competes with the Crystal Electric Field anisotropy (gc ≃ 1.67, ga ≃ 3.72), leading to the unusual situation where the ferromagnetic moments do not lie along the easy magnetisation axis a. Hybridisation of the 4f electrons with band electrons leads to a reduction of the spontaneous moment (saturated value 0.85μB) and is likely to be the origin of the large value of the molecular field constant λc, as well as of the anisotropy of the exchange interaction and of the resistivity.

In light of new experimental data on Fe(001)/Cr(001) superlattices, we discuss the role of the main parameters involved in the giant magnetoresistance: thicknesses, interface roughness and temperature.

We present Hall-effect measurements of two-leg ladder compounds ${\text{Sr}}_{14\ensuremath{-}x}{\text{Ca}}_{x}{\text{Cu}}_{24}{\text{O}}_{41}$ $(0\ensuremath{\le}x\ensuremath{\le}11.5)$ with the aim to determine the number of carriers participating in dc transport. Distribution of holes between the ladder and chain subsystems is one of the crucial questions important for understanding the physics of these compounds. Our Hall-effect and resistivity measurements show typical semiconducting behavior for $xl11.5$. However, for $x=11.5$, the results are completely different, and the Hall coefficient and resistivity behavior are qualitatively similar to that of high-temperature copper-oxide superconductors. We have determined the effective number of carriers at room temperature and compared it to the number of holes in the ladders obtained by other experimental techniques. We propose that going from $x=0$ to $x=11.5$ less than 1 hole per f.u. is added to the ladders and is responsible for a pronounced change in resistivity with Ca doping.

${\text{Ru}}_{1\ensuremath{-}x}{\text{Sn}}_{x}{\text{Sr}}_{2}{\text{EuCu}}_{2}{\text{O}}_{8}$ and ${\text{Ru}}_{1\ensuremath{-}x}{\text{Sn}}_{x}{\text{Sr}}_{2}{\text{GdCu}}_{2}{\text{O}}_{8}$ have been comprehensively studied by microwave and dc resistivity and magnetoresistivity and by the Hall measurements. The ruthenium magnetic ordering temperature ${T}_{m}$ is considerably reduced with increasing Sn content. However, doping with Sn leads to only slight reduction of the superconducting critical temperature ${T}_{c}$ accompanied with the increase in the upper critical field ${B}_{c2}$, indicating an increased disorder in the system and a reduced scattering length of the conducting holes in ${\text{CuO}}_{2}$ layers. In spite of the increased scattering rate, the normal state resistivity and the Hall resistivity are reduced with respect to the pure compound, due to the increased number of itinerant holes in ${\text{CuO}}_{2}$ layers, which represent the main conductivity channel. Most of the electrons in ${\text{RuO}}_{2}$ layers are presumably localized, but the observed negative magnetoresistance and the extraordinary Hall effect lead to the conclusion that there exists a small number of itinerant electrons in ${\text{RuO}}_{2}$ layers that exhibit colossal magnetoresistance.

Systematic study of electrical resistivity of Hf_{100-x}Fe_x (x=20,25), Hf_{100-x}Cu_x (x=30,40,50), and Ti_{65}Cu_{35} metallic glasses has been done in the temperature range 0.3 K - 290 K, and in magnetic fields B = 0.44 K, which is well above T_c of pure crystalline Hf (0.13 K). From the initial slopes of the upper critical fields, (dH_{c2}/dT)_{T_c}, and resistivities we determined the dressed electronic densities of states, N_{\gamma}(E_F), for all alloys. Both T_c and N_{\gamma}(E_F) decrease with increasing x (Fe and Cu content). The results are compared with those for corresponding Zr-base metallic glasses and ion-implanted Hf films., Comment: 9 pages, 4 figures, 1 table

The magnetic anisotropy measurements of metallic Y-Ba-Cu-O compounds in the normal phase reveal a temperature-dependent diamagnetic component of the susceptibility that increases with decreasing temperature. The temperature variation of the susceptibility anisotropy and its total change do not seem to be much affected by the presence of the superconductivity at some lower temperature and could not be accounted for by superconducting fluctuations. Rather, the data remind one of the behavior of some quasi-two-dimensional metals with anisotropic Fermi surfaces, reflecting the properties of the low-energy excitations in the normal phase. The anisotropy measurements above the bulk superconducting transition temperature ${\mathit{T}}_{\mathit{c}}$ reveal the nonlinear effects, which are due to the onset of superconductivity in disconnected grains. The existence of a two-step transition, typical for granular superconductors, should be taken into consideration if the normal-phase susceptibility data are compared with the theoretical predictions in the vicinity of ${\mathit{T}}_{\mathit{c}}$.

We have investigated the dimensionality and origin of the magnetotransport properties of LaAlO3 films epitaxially grown on TiO2-terminated SrTiO3(001) substrates. High-mobility conduction is observed at low deposition oxygen pressures (PO2

Strongly underdoped RuSr_1.9La_0.1GdCu_2O_8 has been comprehensively studied by dc magnetization, microwave measurements, magnetoresistivity and Hall resistivity in fields up to 9 T and temperatures down to 1.75 K. Electron doping by La reduces the hole concentration in the CuO2 planes and completely suppresses superconductivity. Microwave absorption, dc resistivity and ordinary Hall effect data indicate that the carrier concentration is reduced and a semiconductor-like temperature dependence is observed. Two magnetic ordering transitions are observed. The ruthenium sublattice orders antiferromagnetically at 155 K for low applied magnetic field and the gadolinium sublattice antiferromagnetically orders at 2.8 K. The magnetoresistivity exhibits a complicated temperature dependence due to the combination of the two magnetic orderings and spin fluctuations. It is shown that the ruthenium magnetism influences the conductivity in the RuO2 layers while the gadolinium magnetism influences the conductivity in the CuO2 layers. The magnetoresistivity is isotropic above 4 K, but it becomes anisotropic when gadolinium orders antiferromagnetically., 7 pages, 9 figures, submitted to European Physical Journal B

The study reports on the magnetic properties and spin polarization of (La,Sr)Ti1-xCoxO3 (Co-LSTO) thin films. Tunneling magnetoresistance (TMR) measurements on magnetic tunnel junctions were performed to probe the spin polarisation. A large spin of -80% has been determined at low temperature, indicating that the carriers are highly spin-polarized in this system. Structural analysis was done through use of combining high-resolution transmission electron microscopy, Auger electron spectroscopy and X-ray magnetic circular dichroism. As a result, the measured ferromagnetism and high spin polarization are intrinsic properties of this DMOS. Finally a report on planar magnetotransport experiments on Co-LSTO films grown on SrTiO3 (STO) substrates is presented.

We present the high-temperature $(70\phantom{\rule{0.3em}{0ex}}\mathrm{K}lTl300\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ resistivity anisotropy and Hall effect measurements of the quasi-one-dimensional (1D) organic conductor $(\mathrm{TMTTF}{)}_{2}{\mathrm{AsF}}_{6}$. The temperature variations of the resistivity are pronouncedly different for the three different directions, with metalliclike at high temperatures for the $\mathbf{a}$ axis only. Above $220\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ the Hall coefficient ${R}_{H}$ is constant, positive, and strongly enhanced over the expected value; and the corresponding carrier concentration is almost 100 times lower than calculated for one hole/unit cell. Our results give evidence for the existence of a high-temperature regime above $200\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ where the 1D Luttinger liquid features appear in the transport properties. Our measurements also give strong evidence of charge ordering in $(\mathrm{TMTTF}{)}_{2}{\mathrm{AsF}}_{6}$. At the charge-ordering transition ${T}_{\mathrm{CO}}\ensuremath{\approx}100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, ${R}_{H}(T)$ abruptly changes its behavior, switches sign, and rapidly increases with further temperature decrease.

We report on the growth of heterostructures composed of layers of the high-Curie temperature ferromagnet Co-doped $(\mathrm{La},\mathrm{Sr}){\mathrm{TiO}}_{3}$ (Co-LSTO) with high-mobility ${\mathrm{SrTiO}}_{3}$ (STO) substrates processed at low oxygen pressure. While perpendicular spin-dependent transport measurements in STO//Co-LSTO/LAO/Co tunnel junctions demonstrate the existence of a large spin polarization in Co-LSTO, planar magnetotransport experiments on STO//Co-LSTO samples evidence electronic mobilities as high as $\ensuremath{\sim}{10}^{4}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{2}∕\mathrm{V}\phantom{\rule{0.2em}{0ex}}\mathrm{s}$ at $T=10\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. At high enough applied fields and low enough temperatures $(\ensuremath{\mu}\mathrm{H}\ensuremath{\geqslant}6\phantom{\rule{0.3em}{0ex}}\mathrm{T}$, $T\ensuremath{\leqslant}4\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ Shubnikov--de Haas oscillations are also observed. We present an extensive analysis of these quantum oscillations and relate them with the electronic properties of STO, for which we find large scattering rates up to $\ensuremath{\approx}{10}^{\ensuremath{-}11}\phantom{\rule{0.3em}{0ex}}\mathrm{s}$. Thus this work opens up the possibility to inject a spin-polarized current from a high-Curie temperature diluted oxide into an isostructural system with high mobility and a large spin diffusion length.

Reversing the magnetization of a ferromagnet by spin transfer from a current, rather than by applying a magnetic field, is the central idea of an extensive current research. After a review of our experiments of current-induced magnetization reversal in Co/Cu/Co trilayered pillars, we present the model we have worked out for the calculation of the current-induced torque and the interpretation of the experiments.

It is well documented that SDW in (TMTSF)2PF6 undergoes another phase transition at T*\approx 4K, though the nature of the new low temperature phase is controversial. We have shown recently that the new phase is well described in terms of unconventional SDW (USDW) which modifies the quasiparticle spectrum dramatically. In this paper we show that the same model describes consistently the Hall resistivity observed in (TMTSF)2PF6., 7 pages, 2 figures

We describe and analyze the effect of an applied field ${(H}_{\mathrm{appl}})$ on the current-driven magnetization reversal in pillar-shaped Co/Cu/Co trilayers. Depending on the magnitude of ${H}_{\mathrm{appl}},$ we observe two different types of transitions between the parallel (P) and antiparallel (AP) magnetic configurations of the the Co layers. If ${H}_{\mathrm{appl}}$ is smaller than some threshold value, the transitions between P and AP are relatively sharp and irreversible. For ${H}_{\mathrm{appl}}$ exceeding this threshold value, the transitions are progressive and reversible. We show that this behavior can be precisely accounted for by introducing the current-induced torque of the spin transfer models into a Landau-Lifshitz-Gilbert equation to determine the stability or instability of the P and AP states. This analysis also provides a good description for the field dependence of the critical currents.

We have studied the current-induced displacement of a domain wall (DW) in the permalloy (Py) layer of a Co/Cu/Py spin valve structure at zero and very small applied field. The displacement is in opposite direction for opposite dc currents, and the current density required to move DW is only of the order of 10^6 A/cm^2. For H = 3 Oe, a back and forth DW motion between two stable positions is observed. We also discuss the effect of an applied field on the DW motion., Comment: 4 pages, 3 figures

We investigated the transport properties of the quasi one-dimensional organic metal (TMTSF)2ReO4 above the anion-ordering metal-insulator transition (T_{AO} \approx 180K). The pronounced conductivity anisotropy, a small and smoothly temperature dependent Hall effect, and a small, positive and temperature dependent magnetoresistance are analyzed within the existing Fermi-liquid and non-Fermi liquid models. We propose that the transport properties of quasi one-dimensional Bechgaard salts at high temperatures can be described within the Fermi liquid description., Comment: RevTeX4, 8 pages, 5 figures, revised version

We present experimental results on the displacement of a domain wall by injection of a dc current through the wall. The samples are 1 micron wide long stripes of a CoO/Co/Cu/NiFe classical spin valve structure. The stripes have been patterned by electron beam lithography. A neck has been defined at 1/3 of the total length of the stripe and is a pinning center for the domain walls, as shown by the steps of the giant magnetoresistance curves at intermediate levels (1/3 or 2/3) between the resistances corresponding to the parallel and antiparallel configurations. We show by electric transport measurements that, once a wall is trapped, it can be moved by injecting a dc current higher than a threshold current of the order of magnitude of 10^7 A/cm^2. We discuss the different possible origins of this effect, i.e. local magnetic field created by the current and/or spin transfer from spin polarized current., Comment: 3 pages, 3 figures

Comprehensive measurements of dc and ac susceptibility, dc resistance, magnetoresistance, Hall resistivity, and microwave absorption and dispersion in fields up to 8 T have been carried out on ${\mathrm{RuSr}}_{2}{\mathrm{GdCu}}_{2}{\mathrm{O}}_{8}$ with the aim to establish the properties of ${\mathrm{RuO}}_{2}$ and ${\mathrm{CuO}}_{2}$ planes. At $\ensuremath{\sim}130 \mathrm{K},$ where the magnetic order develops in the ${\mathrm{RuO}}_{2}$ planes, one observes a change in the slope of dc resistance, change in the sign of magnetoresistance, and the appearance of an extraordinary Hall effect. These features indicate that the ${\mathrm{RuO}}_{2}$ planes are conducting. A detailed analysis of the ac susceptibility and microwave data on both ceramic and powder samples show that the penetration depth remains frequency dependent and larger than the London penetration depth even at low temperatures. We conclude that the conductivity in the ${\mathrm{RuO}}_{2}$ planes remains normal even when superconducting order is developed in the ${\mathrm{CuO}}_{2}$ planes below $\ensuremath{\sim}45 \mathrm{K}.$ Thus, experimental evidence is provided in support of theoretical models which base the coexistence of superconductivity and magnetic order on decoupled ${\mathrm{CuO}}_{2}$ and ${\mathrm{RuO}}_{2}$ planes.

We review several topics in the field of spin electronics: (i) giant magnetoresistance observed in magnetic multilayers; (ii) magnetization reversal by spin injection and (iii) spin-polarized tunneling in magnetic tunnel junctions combining electrodes of ferromagnetic transition metal and half-metallic oxide.

We review recent results obtained at Orsay on two topics in the field of spin electronics: (i) Spin polarized tunneling in magnetic tunnel junctions combining electrodes of ferromagnetic transition metal and half-metallic oxide: we will describe the influence of the nature of the barrier on the sign of the spin polarization of electrons tunneling from the transition metal and we also discuss the temperature dependence of the TMR obtained with half metallic oxides. (ii) Magnetization reversal by spin injection: we will present and interpret experimental results obtained with pillar-shaped Co/Cu/Co trilayers.

We have studied the magnetoresistance anisotropy (at the ambient pressure) for different (TMTSF) 2 X crystals, with the current along the least conducting c direction, and the magnetic field rotated in the (a-b) plane. We compare and contrast the differences between the quenched (Q) and the relaxed (R) state for X=ClO 4 , and discuss the differences in the SDW state of X-PF 6 , X=ClO 4 (Q) and X=AsF 6 .

We report Hall effect (1.3–30 K) and magnetoresistivity (1.3–20 K) measurements on the YbNiSn compound. It has been found that it is a Kondo lattice system with a ferromagnetic ordering below Tc = 5.5 K. We observed that the Hall constant RH(T) increases as the temperature decreases and has a sharp peak at about Tc. Also, below Tc, the Hall resistivity ρxy versus H curves exhibit a highly non-linear magnetic field dependence with features suggesting a crossover to a new electronic state above 2 T. The magnetoresistivity ρ(H) is high with a magnetic field dependence similar to that of ρxy(H).

We present Hall effect measurements on disordered Ce(Cu x Ga 1- x ) 5 Kondo alloys ( x = 0.8 and 0.6) in the temperature interval 0.1 to 200 K and in magnetic fields up to 7 T. We observe a continuous increase of the Hall constant R H ( T ) at low temperatures, which is typical of incoherent Kondo systems. In CeCu 4 Ga, R H ( T ) exhibits also a weak maximum at ∼0.3 K. Above the Kondo temperature, R H ( T ) is well described by a single impurity skew scattering model. In addition, magnetoresistivity data for CeCu 4 Ga ( T > 0.2 K ) are presented, showing different behaviour for temperatures below and above 2 K.

We present the resistivity and transverse magnetoresistance results for three principal axes of (TMTSF) 2 PF 6 in the SDW ground state ( T ≥2.2 K and B ≤5 T). Our data show a clear change of the activation energy around 4 K and its magnetic field dependence above.