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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

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.

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.

Magnetoresistance in the spin-density wave (SDW) state of (TMTSF)2PF6 is known to exhibit a rich variety of the angular dependencies when a magnetic field B is rotated in the b'-c*, a-b' and a-c* planes. In the presence of a magnetic field the quasiparticle spectrum in the SDW with imperfect nesting is quantized. In such a case the minimum quasiparticle energy depends both on the magnetic field strength |B| and the angle \theta between the field and the crystal direction a, b' or c*. This approach describes rather satisfactory the magnetoresistance above T*~4K.

It is well documented that SDW in (TMTSF)2PF6 undergoes another phase transition at T* ≈ 4 K , though the nature of the new phase has not been identified. In particular the angular dependence of the magnetoresistance for B ‖( a, b ′) plane below 4.2 K is dramatically different from the one above 4.2 K. We propose that below T* the new phase unconventional SDW (USDW) appears which modifies drastically the quasiparticle spectrum. The present model describes the observed angular dependence of the magnetoresistance reasonably well, which cannot be interpreted in terms of the conventional SDW.

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.

We present the b'-axis transverse magnetoresistance study of the spin-density-wave (SDW) ground state in the quasi–one-dimensional conductor (TMTSF)2PF6 for temperatures down to 2.2 K and magnetic fields up to 5 T. The magnetoresistance is very large and highly anisotropic. We present the clear change in the activation energy for T > 4.2 K and T < 4.2 K, which depends on magnetic field. The results can be well described by the quasi-particles with the energy gap given in the model with imperfect nesting.

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.

${\text{Ru}}_{1\ensuremath{-}x}{\text{Sn}}_{x}{\text{Sr}}_{2}{\text{EuCu}}_{2}{\text{O}}_{8}$ 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.

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.

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

The low temperature phase (LTP) of alpha-(BEDT-TTF)2KHg(SCN)(4) salt is known for its surprising angular dependent magnetoresistance (ADMR), which has been studied intensively in the last decade. However, the nature of the LTP has not been understood until now. Here we analyze theoretically ADMR in unconventional (or nodal) charge-density wave (UCDW). In magnetic field the quasiparticle spectrum in UCDW is quantized, which gives rise to spectacular ADMR. The present model accounts for many striking features of ADMR data in alpha-(BEDT-TTF)2KHg(SCN)(4).

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

The presence of subphases in spin-density wave (SDW) phase of (TMTSF)_2PF_6 below T* \approx 4 K has been suggested by several experiments but the nature of the new phase is still controversial. We have investigated the temperature dependence of the angular dependence of the magnetoresistance in the SDW phase which shows different features for temperatures above and below T* \approx 4 K. For T > 4 K the magnetoresistance can be understood in terms of the Landau quantization of the quasiparticle spectrum in a magnetic field, where the imperfect nesting plays the crucial role. We propose that below T* \approx 4 K the new unconventional SDW (USDW) appears modifying dramatically the quasiparticle spectrum. Unlike conventional SDW the order parameter of USDW depends on the quasiparticle momentum $\Delta_1(\mvk)\propto \cos 2bk_y$. The present model describes many features of the angular dependence of magnetoresistance reasonably well. Therefore, we may conclude that the subphase in (TMTSF)2PF6 below T \approx 4 K is described as SDW plus USDW.

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.

Recently many people discuss unconventional density wave (i.e. UCDW and USDW). Unlike in conventional density waves, the quasiparticle excitations in these systems are gapless. The appearence of these systems suggests paradigm shift from quasi ID system to quasi 2D and 3D systems. Here we limit ourselves to the angular dependent magnetoresistance (ADMR) observed in the low temperature phase (LTP) of α-(BEDT-TTF)2KHg(SCN)4. Here we show that UCDW describes successfully many features of ADMR as manifestation of the Landau quantization of the quasiparticle spectrum in magnetic field. Indeed ADMR will provide a unique window to access UDW like the AF phase in URu2Si2, the pseudogap phase in high Tc cuprates and the glassy phase in organic superconductor κ-(ET)2 salts.

In spite of extensive experimental studies of the angular dependent magnetoresistance (ADMR) of the low temperature phase (LTP) of alpha-(BEDT-TTF)_2KHg(SCN)_4 about a decade ago, the nature of LTP remains elusive. Here we present a new study of ADMR of LTP in alpha-(ET)_2 salts assuming that LTP is unconventional charge density wave (UCDW). In the presence of magnetic field the quasiparticle spectrum in UCDW is quantized, which gives rise to striking ADMR in UCDW. The present model appears to account for many existing ADMR data of alpha-(BEDT-TTF)_2KHg(SCN)_4 remarkably well., 6 pages, 4 figures

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 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.

We present the results for the magnetic field dependence of the electrical resistivity in hydrogen-doped Zr 68 Fe 32 metallic glasses. The undoped sample is paramagnetic down to very low temperatures ( < 1 K) because of pronounced spin fluctuations. The observed magnetoresistance is positive and increases with hydrogen concentration. The results have been analyzed using a renormalized expression for the magnetoresistivity which takes into account the exchange enhancement of the spin-splitting contributions (through the Stoner factor) to the usual weak localization and electron-electron interaction terms. The magnetoresistivity enhancement of hydrogen-doped Zr 68 Fe 32 has been attributed to the increase of the Stoner factor (1 - I) -1 , and of the spin-scattering rate τ s -1 . That increase indicates enhancement of spin fluctuations with hydrogen.

We present the influence of a transverse magnetic field on the spin-density wave (SDW) ground state of the organic conductor (TMTSF) 2 NO 3 . Magnetic field increases the single-particle activation energy. A finite magnetic field (H C ) induces discontinuities in the magnetoresistance behaviour and its value is temperature dependent. The threshold electric field (E T ) for the SDW sliding increases in a magnetic field. All observed effects are strongly angle-dependent indicating that they are determined by the magnetic field component along the least-conduction (c * ) direction. We discuss these results in the framework of a theoretical model for the SDW with large imperfect nesting

We report a study of the transverse-magnetoresistance anisotropy in the spin-density wave phase of the organic conductor (TMTSF)2NO3 at temperatures down to 1.8 K and in fields up to 6 tesla. The transverse magnetoresistance is highly anisotropic and obeys a temperature- and angular-dependent power law behaviour: DELTArho/rho congruent-to H(n) (1 less- than-or-equal-to n < 2). The indication of a possible field-induced SDW phase is discussed. We suggest that the SDW with large imperfect nesting together with a periodic anion potential might be responsible for the observed magnetic-field effects.

We report the observation of the large Hall effect in the incommensurate spin-density wave (SDW) phase of (TMTSF)2NO3 and negative magnetoresistances in the semiconducting state above and below commensurate SDW phase transition of (TMTTF)2Br.