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Black phosphorus (BP) allotrope has an orthorhombic crystal structure with a narrow bandgap of 0.35 eV. This material is promising for 2D technology since it can be exfoliated down to one single layer: the well-known phosphorene. In this work, bulk BP was synthesized under high-pressure conditions at high temperatures. A detailed structural investigation using neutron and synchrotron X-ray diffraction revealed the occurrence of anisotropic strain effects on the BP lattice; the combination of both sets of diffraction data allowed visualization of the lone electron pair 3s2. Temperature-dependent neutron diffraction data collected at low temperature showed that the a axis (zigzag) exhibits a quasi-temperature-independent thermal expansion in the temperature interval from 20 up to 150 K. These results may be a key to address the anomalous behavior in electrical resistivity near 150 K. Thermoelectric properties were also provided; low thermal conductivity from 14 down to 6 Wm-1K-1 in the range 323-673 K was recorded in our polycrystalline BP, which is below the reported values for single-crystals in literature.

The reduction of the lattice thermal conductivity is one of the crucial steps in improving thermoelectric materials. In skutterudites, a well-known approach is to reduce the thermal conductivity by filling the structural cage with rare-earth atoms. In this work, we show that it is not just the amount of such filling itself but its nanoscale structuration that lowers the thermal conductivity. A straightforward synthesis procedure under high pressure yields Ce- and Yb-filled CoSb3 skutterudites, with and without an inhomogeneous distribution of the filler atoms. The composition of the phases is evaluated from synchrotron X-ray diffraction (SXRD) data; the highly nanostructured morphology is verified by high-resolution transmission electron microscopy (TEM). The filling fluctuation, i.e., the uneven distribution of filling atoms in the sample originating a phase segregation, brings about low lattice thermal conductivity, as a strong source of phonon scattering. This effect is prominent in the Ce-filled compo...

Thermoelectric mischmetal-filled MmxCo4Sb12 (Mm: natural cocktail of rare-earth elements, mostly Ce and La) skutterudites have been synthesized and sintered in one step under high-pressure conditions at 3.5 GPa in a piston–cylinder hydrostatic press. Synchrotron X-ray diffraction patterns display a splitting of the diffraction peaks ascribed to purely Ce-, and Mm-filled skutterudite phases, which have been analyzed and confirmed by high-resolution TEM and EELS. A total thermal conductivity (κ) of 1.51 W m−1 K−1 is measured at 773 K for Mm0.5Co4Sb12, below that of other filled skutterudites, which is promoted by the enhanced phonon scattering over a broad range of the phonon spectrum due to the inhomogeneous and nanoscale mischmetal inclusion. Compared to undoped CoSb3 skutterudite synthesized by conventional methods, κ is reduced by a factor of 3, while the power factor is also substantially enhanced., This work was supported by the Spanish Ministry of Science, Innovation and Universities through grants MAT2017-84496-R, MAT2017-87134-C2-2-R and MAT2015-66888-C3-3-R co financed by FEDER. JPG would also like to thank this Ministry for granting a “Juan de la Cierva” fellowship and to Community of Madrid for granting an “Atracción de Talento” fellowship (2017-T2/I ND-5597). Financial support from the ERC grant PoC2015-MAGTOOLS is also acknowledged. The authors wish to express their gratitude to ALBA technical staff for making the facilities available for the synchrotron X-ray diffraction experiment number 2017072260. Transmission electron microscopy studies were performed at the ICTS ELECMI node at Centro Nacional de Microscopía Electrónica (CNME) at the Universidad Complutense de Madrid (UCM)., We acknowledge support of the publication fee by the CSIC Open Access Support Initiative through its Unit of Information Resources for Research (URICI)

La_(1.85)Sr_(0.15)CuO₄/La₂CuO₄ (LSCO15/LCO) bilayers with a precisely controlled thickness of N unit cells (UCs) of the former and M UCs of the latter ([LSCO15_N/LCO_M]) were grown on (001)- oriented SrLaAlO₄ (SLAO) substrates with pulsed laser deposition (PLD). X-ray diffraction and reciprocal space map (RSM) studies confirmed the epitaxial growth of the bilayers and showed that a [LSCO15_2/LCO_2] bilayer is fully strained, whereas a [LSCO15_2/LCO_7] bilayer is already partially relaxed. The in situ monitoring of the growth with reflection high energy electron diffraction (RHEED) revealed that the gas environment during deposition has a surprisingly strong effect on the growth mode and thus on the amount of disorder in the first UC of LSCO15 (or the first two monolayers of LSCO15 containing one CuO₂ plane each). For samples grown in pure N₂O gas (growth type B), the first LSCO15 UC next to the SLAO substrate is strongly disordered. This disorder is strongly reduced if the growth is performed in a mixture of N₂O and O₂ gas (growth type A). Electric transport measurements confirmed that the first UC of LSCO15 next to the SLAO substrate is highly resistive and shows no sign of superconductivity for growth type B, whereas it is superconducting for growth type A. Furthermore, we found, rather surprisingly, that the conductivity of the LSCO15 UC next to the LCO capping layer strongly depends on the thickness of the latter. A LCO capping layer with 7 UCs leads to a strong localization of the charge carriers in the adjacent LSCO15 UC and suppresses superconductivity. The magnetotransport data suggest a similarity with the case of weakly hole doped LSCO single crystals that are in a so-called 'cluster-spin-glass state.' We discussed several mechanisms that could lead to such a localization of holes that are embedded in a short-range ordered antiferromagnetic background for the case of a thick LCO capping layer with M = 7 but not for a thin one with M = 2.

SnSe has been recently reported as an attractive thermoelectric material, with an extraordinarily high, positive, Seebeck coefficient. Here, we describe the synthesis, structural, microscopic, and thermoelectric characterization of Sn1–xSbxSe intermetallic alloys prepared by a straightforward arc-melting technique. Sb-doped tin selenide was synthesized as strongly nanostructured polycrystalline pellets. Neutron diffraction studies reveal that Sb is placed at the Sn sublattice in the crystal structure, showing concentrations as high as 30%, and generates a significant number of Sn vacancies, while the increase of the interlayer distances favors the nanostructuration. The material is nanostructured both out-of-plane in nanometer-scale layers and in-plane by ∼5 nm undulations of these layers. This nanostructuring, along with an increased amount of Sn vacancies, accounts for a reduction of the thermal conductivity, which is highly desirable for thermoelectric materials. The phonon mean free path is estimated to be on the order of 2 nm from low temperature, thermal conductivity, and specific heat, in accordance with the nanostructuration observed by high-resolution transmission electron microscopy. The thermal conductivity of SnSe is characterized by three independent techniques to assure a room temperature value of Sn0.8Sb0.2Se of κ ∼ 0.6 W/m K. The freshly prepared Sb-doped compounds exhibit an abrupt change in the type of charge carriers, leading to large, negative Seebeck coefficients, although the arc-melt synthesized pellets remain too resistive for thermoelectric applications. Cold-pressed pellets evolve to be p-type at room temperature, but reproducibly turn n-type around 500 K, with increased electrical conductivity and maximum observed figure of merit, ZT ∼ 0.3 at 908 K.

With x-ray absorption spectroscopy and polarized neutron reflectometry we studied how the magnetic proximity effect at the interface between the cuprate high-TC superconductor YBa_(2)Cu_(3)O_(7) (YBCO) and the ferromagnet La_(2/3)Ca_(1/3)MnO_(3) (LCMO) is related to the electronic and magnetic properties of the LCMO layers. In particular, we explored how the magnitude of the ferromagnetic Cu moment on the YBCO side depends on the strength of the antiferromagnetic (AF) exchange coupling with the Mn moment on the LCMO side. We found that the Cu moment remains sizable if the AF coupling with the Mn moments is strongly reduced or even entirely suppressed. The ferromagnetic order of the Cu moments thus seems to be intrinsic to the interfacial CuO_(2) planes and related to a weakly ferromagnetic intraplanar exchange interaction. The latter is discussed in terms of the partial occupation of the Cu 3d_(3z^(2)−r^(2)) orbitals, which occurs in the context of the so-called orbital reconstruction of the interfacial Cu ions.

We report on the room temperature strong (∼80%) electroresistance (ER) in the double perovskite with mixed Mn valence: Sr 2− x Gd x MnTiO 6 , 0 ≤ x ≤ 1. Both, continuous and pulsed current–voltage curves are almost identical which indicates that the observed electroresistance is not associated with heating. This is also supported by simultaneous temperature measurements. ER is negligible (absent) in the x = 0 compound and increases with the increase of Gd content ‘ x ’. The amplitude of ER has a maximum for x = 0.75, suggesting that ER is determined by both the double exchange and the Mn 3+ concentration. At the same time, magnetic interactions change from the antiferromagnetic ( x = 0) to ferromagnetic ones as x → 1, thus linking the ER with ferromagnetism.

The energetic stability of FePO4 polymorphs (berlinite, heterosite, monoclinic, and high-pressure forms) is investigated combining first-principles and experimental methods. Calculations at the den...

This is the accepted manuscript of the following article: Sánchez-Andújar, M., Yáñez-Vilar, S., Biskup, N., Castro-García, S., Mira, J., Rivas, J., & Señarís-Rodríguez, M. (2009). Magnetoelectric behavior in the complex CaMn7O12 perovskite. Journal Of Magnetism And Magnetic Materials, 321(11), 1739-1742. doi: 10.1016/j.jmmm.2009.02.018 We report a magnetoelectric effect in the double perovskite CaMn7O12, that shows a complex magnetic behavior below 90 K with two magnetic phases coexisting (one ferrimagnetic and the other modulated). A second magnetic transition, associated with changes in the magnetic modulation and magnetic ordering coherence lengths of the two magnetic phases occurs at 50 K (TN2). A detailed structural characterization of this compound, that we have carried out by means of high-resolution X-ray powder diffraction, reveals an anisotropic thermal expansion of its lattice parameters at 50 K (TN2). In addition, our study of the complex permittivity of this sample as a function of temperature, frequency and magnetic field shows very interesting results below 90 K and specially below 50 K: the dielectric constant ε′r that was decreasing continuously on cooling experiences an upturn, and even more, on application of a magnetic field it shows a moderate magnetoelectric response. We attribute such dielectric behavior to the formation of electric dipoles by magnetostriction in this charge and spin ordered system, that are sensible to the presence of an external magnetic field The authors are grateful from financial support for MEC (Spain) under project FEDER MAT 2007-66696 and Xunta de Galicia under project PGIDIT06PXB103298PR. S. Yáñez-Vilar want to thank to MEC of Spain for her FPI fellowship and M. Sánchez-Andújar acknowledges to Xunta de Galicia for support under program Parga Pondal SI

In this work we present a detailed investigation of the dielectric properties of the oxyborate Fe2OBO3 . This compound exhibits a high dielectric constant at room temperature (epsivr' > 103) for frequencies up to 104 Hz. An impedance spectroscopy analysis of the data reveals an important extrinsic contribution to these high epsivr' values. In order to eliminate the extrinsic contribution, we have sandwiched the sample in-between two mica layers, obtaining relatively high values of epsivr' at room temperature for this kind of oxides (epsivr' ~ 45). The temperature dependence of the remaining intrinsic contribution shows a jump, that at high frequencies occurs at the temperature at which a rearrangement of the charge-order pattern takes place and at low frequencies occurs at temperatures close to the onset of the antiferromagnetic long-range order. This suggests a certain coupling between the electronic, magnetic and dielectric properties in this compound.

It has previously been reported that under high-pressure V2O5 (α-V2O5) transforms into a layered polymorph, β-V2O5, consisting of V5+O6 octahedra instead of V5+O5-square pyramids. Both polymorphs have a good performance as positive electrode for lithium batteries. In this work, we investigate the pressure-induced α → β transformation combining first principles and experimental methods. Density functional theory (DFT) predicts that α-V2O5 transforms to β-V2O5 at 3.3 GPa with a 11% volume contraction; experiments corroborate that at a pressure of 4 GPa, V2O5 (d = 3.36 g/cm3) transformed into a well-crystallized β-V2O5, with a much denser structure (d = 3.76 g/cm3). β-V2O5 can be also prepared at 3 GPa, although with a substantial degree of amorphization. The calculated bulk modulus of α-V2O5 (18 GPa) indicates that this is a very compressible structure; this being linked to the contraction along its b-axis (interlayer space) and to a significant decrease of a long V−O distance (V−O ≈ 2.9 A). As a result, th...

In this paper we present an atomic-resolution electron microscopy study of superlattices (SLs) where the colossal magnetoresistant manganite La_(0.67)Ca_(0.33)MnO_(3) (LCMO) and the high critical temperature superconducting cuprate La_(1.85)Sr_(0.15)CuO_(4 (LSCO) are combined. Although good quality epitaxial growth can be achieved, both the choice of substrate and the relatively large lattice mismatch between these materials (around 2%) have a significant impact on the system properties [Phys. C 468, 991 (2008); Nature (London) 394, 453 (1998)]. Our samples, grown by pulsed laser deposition, are epitaxial and exhibit high structural quality. By means of cutting-edge electron microscopy and spectroscopy techniques we still find that the epitaxial strain is accommodated by a combination of defects, such as interface steps and antiphase boundaries in the manganite. These defects result in inhomogeneous strain fields through the samples. Also, some chemical unhomogeneities are detected, up to the point that novel phases nucleate. For example, at the LCMO/LSCO interface the ABO3-type manganite adopts a tetragonal LSCO-like structure forming localized layers that locally resemble the composition of La_(2/3)Ca_(4/3)MnO_(4). Structural distortions are detected in the cuprate as well, which may extend over lateral distances of several unit cells. Finally, we also analyze the influence of the substrate-induced strain by examining superlattices grown on two different substrates: (LaAlO_(3))_(0.3)(Sr_(2)AlTaO_(6))_(0.7) (LSAT) and LaSrAlO_(4) (LSAO). We observe that SLs grown on LSAT, which are nonsuperconducting, present reduced values of the c axis compared to superlattices grown on LSAO (which are fully superconducting). This finding points to the fact that the proper distance between copper planes in LSCO is essential in obtaining superconductivity in cuprates.

We demonstrate that a combination of electronic structure modification and oxygen vacancy ordering can stabilize a long-range ferromagnetic ground state in epitaxial LaCoO_(3) thin films. Highest saturation magnetization values are found in the thin films in tension on SrTiO_(3) and (La,Sr)(Al,Ta)O_(3) substrates and the lowest values are found in thin films in compression on LaAlO_(3). Electron microscopy reveals oxygen vacancy ordering to varying degrees in all samples, although samples with the highest magnetization are the most defective. Element-specific x-ray absorption techniques reveal the presence of high spin Co^(2+) and Co^(3+) as well as low spin Co^(3+) in different proportions depending on the strain state. The interactions among the high spin Co ions and the oxygen vacancy superstructure are correlated with the stabilization of the long-range ferromagnetic order.

We report on magnetic resonances observed in the doped lanthanum manganite La0.8Li0.2MnO3 (LLMO) below the Curie temperature Tc ~ 235 K. Fields up to 30 T were employed. The data are compared with that from the archetypal colossal magnetoresistance perovskite La0 7Ca0 3MnO3 (LCMO) taken under similar conditions. In contrast to LCMO, LLMO exhibits two resonances, one above and one below the LCMO resonant field. These are attributed to a ferromagnetic interaction and a canted ferromagnetic interaction.

We studied the structural, magnetic and electronic properties of [Formula: see text] (SFO) thin films and [Formula: see text]/[Formula: see text] [Formula: see text]MnO3 (LCMO) superlattices that have been grown with pulsed laser deposition (PLD) on [Formula: see text] [Formula: see text] [Formula: see text] [Formula: see text] [Formula: see text] (LSAT) substrates. X-ray reflectometry and scanning transmission electron microscopy (STEM) confirm the high structural quality of the films and flat and atomically sharp interfaces of the superlattices. The STEM data also reveal a difference in the interfacial layer stacking with a SrO layer at the LCMO/SFO and a LaO layer at the SFO/LCMO interfaces along the PLD growth direction. The x-ray diffraction (XRD) data suggest that the as grown SFO films and SFO/LCMO superlattices have an oxygen-deficient [Formula: see text] structure with I4/ mmm space group symmetry ([Formula: see text]). Subsequent ozone annealed SFO films are consistent with an almost oxygen stoichiometric structure ([Formula: see text]). The electronic and magnetic properties of these SFO films are similar to the ones of corresponding single crystals. In particular, the as grown [Formula: see text] films are insulating whereas the ozone annealed films are metallic. The magneto-resistance effects of the as grown SFO films have a similar magnitude as in the single crystals, but extend over a much wider temperature range. Last but not least, for the SFO/LCMO superlattices we observe a rather large exchange bias effect that varies as a function of the cooling field.

Epitaxial ${\mathrm{La}}_{1.85}{\mathrm{Sr}}_{0.15}{\mathrm{CuO}}_{4}/{\mathrm{La}}_{2/3}{\mathrm{Ca}}_{1/3}{\mathrm{MnO}}_{3}$ (LSCO/LCMO) superlattices on $(001)$-oriented ${\mathrm{LaSrAlO}}_{4}$ substrates have been grown with pulsed laser deposition technique. Their structural, magnetic, and superconducting properties have been determined with in situ reflection high-energy electron diffraction, x-ray diffraction, specular neutron reflectometry, scanning transmission electron microscopy, electric transport, and magnetization measurements. We find that despite the large mismatch between the in-plane lattice parameters of LSCO ($a=0.3779$ nm) and LCMO ($a=0.387$ nm) these superlattices can be grown epitaxially and with a high crystalline quality. While the first LSCO layer remains clamped to the ${\mathrm{LaSrAlO}}_{4}$ substrate, a sizable strain relaxation occurs already in the first LCMO layer. The following LSCO and LCMO layers adopt a nearly balanced state in which the tensile and compressive strain effects yield alternating in-plane lattice parameters with an almost constant average value. No major defects are observed in the LSCO layers, while a significant number of vertical antiphase boundaries are found in the LCMO layers. The LSCO layers remain superconducting with a relatively high superconducting onset temperature of ${T}_{c}^{\text{onset}}\ensuremath{\approx}36$ K. The macroscopic superconducting response is also evident in the magnetization data due to a weak diamagnetic signal below 10 K for $H$ $\ensuremath{\parallel}$ $ab$ and a sizable paramagnetic shift for $H$ $\ensuremath{\parallel}$ $c$ that can be explained in terms of a vortex-pinning-induced flux compression. The LCMO layers maintain a strongly ferromagnetic state with a Curie temperature of ${T}^{\text{Curie}}\ensuremath{\approx}190$ K and a large low-temperature saturation moment of about 3.5(1) ${\ensuremath{\mu}}_{B}$ per Mn ion. These results suggest that the LSCO/LCMO superlattices can be used to study the interaction between the antagonistic ferromagnetic and superconducting orders and, in combination with previous studies on ${\text{YBa}}_{2}{\text{Cu}}_{3}{\text{O}}_{7\ensuremath{-}x}/{\text{La}}_{2/3}{\text{Ca}}_{1/3}{\text{MnO}}_{3}$ superlattices, may allow one to identify the relevant mechanisms.

Precise resonant experiments on ${\mathrm{Fe}}_{8}$ magnetic clusters have been conducted down to 1.2 K at various tranverse magnetic fields, using a cylindrical resonator cavity with 40 different frequencies between 37 and 110 GHz. All the observed resonances for both single crystal and oriented powder have been fitted by the eigenstates of the Hamiltonian $\mathcal{H}=\ensuremath{-}{\mathrm{DS}}_{z}^{2}{+ES}_{x}^{2}\ensuremath{-}g{\ensuremath{\mu}}_{B}\mathbf{H}\ensuremath{\cdot}\mathbf{S}{+C(S}_{+}^{4}{+S}_{\ensuremath{-}}^{4}).$ We have identified the resonances corresponding to the coherent quantum oscillations for different orientations of spin $S=10.$

We report on low-temperature dielectric response of Pr 0.6 Ca 0.4 MnO 3 (PCMO), member of manganite family showing colossal magnetoresistance. Room temperature “colossal” dielectric function is decreasing with lowering temperature, accompanied by disappearance of dielectric relaxation toward very low frequencies. This behaviour indicates that large dielectric constant in PCMO arises from the Schottky barriers at electrical contacts. Weak anomaly at the charge ordering temperature can also be attributed to interplay of sample and contact resistance. Magnetic field at temperatures T > 50 K shifts dielectric relaxation to higher frequencies. However, at T 50 K , where “colossal” dielectric response is already frozen, magnetic field increases dielectric constant (and function) uniformly in the whole measured frequency range. This frequency insensitivity cannot be understood from the simplest equivalent circuit that includes Schottky contacts. It indicates that dielectric response at these temperatures is completely flattened by strong magnetic correlations. We comment our results in relation with other magnetic field induced phenomena.

We show that in Pr$ _{0.5} $La$ _{0.2} $Ca$ _{0.3} $MnO$ _{3} $/YBa$ _{2} $Cu$ _{3} $O$ _{7} $ (PLCMO/YBCO) multilayers the low temperature state of YBCO is very resistive and resembles the one of a granular superconductor or a frustrated Josephson-junction network. Notably, a coherent superconducting response can be restored with a large magnetic field which also suppresses the charge-orbital order in PLCMO. This coincidence suggests that the granular superconducting state of YBCO is induced by the charge-orbital order of PLCMO. The coupling mechanism and the nature of the induced inhomogeneous state in YBCO remain to be understood., Comment: 6 pages, 4 figures. Supplementary Information as extra file

La0.7Ca0.3MnO3 optimally doped epitaxial films were grown on ferroelectric BaTiO3 substrates. Electronic transport (magnetoresistance and electroresistance) and magnetic properties showed important anomalies in the temperature interval between 60 and 150 K, below the metal-insulator transition. Scanning probe microscopy revealed changes in BaTiO3 surface morphology at those temperatures. La0.7Ca0.3MnO3 thickness is a critical factor: 120-angstrom -thick films showed large anomalies sensitive to electric poling of the BaTiO3, whereas the behavior of 150-angstrom -thick films is closer to that of the reference La0.7Ca0.3MnO3 samples grown on SrTiO3. We propose that, through inhomogenous strain and electric polarization effects, the ferroelectric substrate induces an inhomogenous spin distribution in the magnetic layer. This would imply the coexistence of in-plane and out-of-plane ferromagnetic patches in La0.7Ca0.3MnO3, possibly interspersed with antiferromagnetic regions, as it has recently been theoretically predicted. Substrate poling effects are investigated, and a magnetoelectric coupling is demonstrated.

Heteroepitaxial superlattices of [YBa${}_{2}$Cu${}_{3}$O${}_{7}$($n$)/La${}_{0.67}$Ca${}_{0.33}$MnO${}_{3}$($m$)]${}_{x}$ (YBCO/LCMO), where $n$ and $m$ are the number of YBCO and LCMO monolayers and $x$ the number of bilayer repetitions, have been grown with pulsed laser deposition on NdGaO${}_{3}$ (110) and Sr${}_{0.7}$La${}_{0.3}$Al${}_{0.65}$Ta${}_{0.35}$O${}_{3}$ (001). These substrates are well lattice matched with YBCO and LCMO and, unlike the commonly used SrTiO${}_{3}$, they do not give rise to complex and uncontrolled strain effects at low temperature. The growth dynamics and the structure have been studied in situ with reflection high-energy electron diffraction and ex situ with scanning transmission electron microscopy, x-ray diffraction, and neutron reflectometry. The individual layers are found to be flat and continuous over long lateral distances with sharp and coherent interfaces and with a well-defined thickness of the individual layer. The only visible defects are antiphase boundaries in the YBCO layers that originate from perovskite unit-cell height steps at the interfaces with the LCMO layers. We also find that the first YBCO monolayer at the interface with LCMO has an unusual growth dynamics and is lacking the CuO chain layer, while the subsequent YBCO layers have the regular Y-123 structure. Accordingly, the CuO${}_{2}$ bilayers at both the LCMO/YBCO and the YBCO/LCMO interfaces are lacking one of their neighboring CuO chain layers and, thus, half of their hole-doping reservoir. Nevertheless, from electric transport measurements on a superlattice with $n=2$ we obtain evidence that the interfacial CuO${}_{2}$ bilayers remain conducting and even exhibit the onset of a superconducting transition at very low temperature. Finally, we show from dc magnetization and neutron reflectometry measurements that the LCMO layers are strongly ferromagnetic.

We present Lu${}_{2}$MnCoO${}_{6}$, a multiferroic member of the double perovskites that we have investigated using x-ray and neutron diffraction, specific heat, magnetization, electric polarization, and dielectric constant measurements. This material possesses a net electric polarization strongly coupled to a net magnetization below 35 K, despite the antiferromagnetic ordering of the $S=3/2$ Mn${}^{4+}$ and Co${}^{2+}$ spins in an $\ensuremath{\uparrow}\ensuremath{\uparrow}\ensuremath{\downarrow}\ensuremath{\downarrow}$ configuration along the $c$ direction. We discuss the magnetic order in terms of a condensation of domain boundaries between $\ensuremath{\uparrow}\ensuremath{\uparrow}$ and $\ensuremath{\downarrow}\ensuremath{\downarrow}$ ferromagnetic domains, with each domain boundary producing an electric polarization due to spatial inversion symmetry breaking. In an applied magnetic field the domain boundaries slide, controlling the size of the magnetization, electric polarization, and magnetoelectric coupling.

We report the observation between 40 and 120 K of anomalous magnetic hysteresis loops in thin epitaxial films of La_(0.7)Ca_(0.3)MnO_(3) grown on ferroelectric BaTiO_(3). These hysteresis loops display extremely unusual features: after switching at coercivity, the magnetization overshoots the eventual high-field value. We study the strains in the film and substrate with x-ray diffraction and propose a model of two magnetic moment populations with different magnetoelastic anisotropies. The relative weights of both populations can be estimated by comparison with twin samples of La_(0.7)Ca_(0.3)MnO_(3) films on nonferroelectric SrTiO_(3). We propose that the observed magnetization overshoots the result from differences in the magnetostriction balance as the applied magnetic field increases. The picture of a nonuniform strain field in La_(0.7)Ca_(0.3)MnO_(3) on BaTiO_(3), caused by the corrugation of the ferroelectric domains in the rhombohedric phase of BaTiO_(3), is compatible with the magnetic granular behavior observed in the temperature and field dependences of the magnetization as well as in the low temperature magnetoresistance exhibited by the epitaxial film.

The title perovskites with mixed Mn valence exhibit strong electroresistance at room temperature, which is confirmed to be not associated with heating.

We report on nonlinear current-voltage characteristics in single-crystal ${\mathrm{Pr}}_{5∕8}{\mathrm{Ca}}_{3∕8}\mathrm{Mn}{\mathrm{O}}_{3}$ and polycrystalline ${\mathrm{Pr}}_{0.6}{\mathrm{Ca}}_{0.4}\mathrm{Mn}{\mathrm{O}}_{3}$. Measurements are done with samples immersed in liquid nitrogen, aiming to reduce the effect of Joule heating. Negative differential resistance (NDR) is observed for currents as low as $1\phantom{\rule{0.3em}{0ex}}\mathrm{mA}$. Superimposed to NDR, we observe discontinuous transitions to higher or lower resistive states. These transitions are observed and studied with current passing along all three perpendicular axes of single crystal showing clear anisotropy. In polycrystal, these transitions appear to be a mixture of transitions in different current directions of the single crystal. We demonstrate that the above effects are not originated by Joule heating, and we discuss their possible origin.

We have investigated nonlinear electrical characteristics in low bandwidth manganites ${R}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3}$ with $R=\mathrm{Pr},\mathrm{Nd},\mathrm{Ho},\mathrm{Er}$ and $x=0.3\char21{}0.5$. In all these materials we observe strong nonlinear $I\char21{}V$ characteristic that is manifested in negative differential resistance (NDR) and breakdown voltages ${V}_{br}$ as low as few volts. These effects are accompanied by intense Joule heating that seems to be inseparable from the effect itself. We present different types of measurements with the aim to resolve the origin of the phenomena. Melting of insulating state is observed regardless of its origin\char22{}antiferromagnetic, charge ordered, or paramagnetic. This nonlinearity is found to have microscopic origin, indicating that it is some sort of percolation effect. Hysteretic effects also indicate that the heating is not the only cause of NDR. Enhancement of conductivity is proposed to arise from double exchange induced by local magnetic field.

We have investigated non-linear electrical characteristics in low bandwidth manganites R 1-x Ca x MnO 3 with R=Pr, Nd, Ho, Er and x=0.3-0.5. In all these materials we observe strong nonlinear I-V characteristic that is manifested in negative differential resistance (NDR) and breakdown voltages V br as low as few volts. These effects are accompanied by intense Joule heating that seems to be inseparable from the effect itself. We present different types of measurements with the aim to resolve the origin of the phenomena. Melting of insulating state is observed regardless of its origin - antiferromagnetic, charge ordered or paramagnetic. This nonlinearity is found to have microscopic origin, indicating that it is some sort of percolation effect. Hysteretic effects also indicate that the heating is not the only cause of NDR. Theory of phase separation gives a plausible explanation for these nonlinearities, although it appears to be diffcult to prove. Pulsed and relaxation measurements show that the effect is time-dependent, similarly to nonlinearities induced by magnetic field.

We report the detailed study of dielectric response of ${\mathrm{Pr}}_{0.6}{\mathrm{Ca}}_{0.4}\mathrm{Mn}{\mathrm{O}}_{3}$ (PCMO), a member of the manganite family showing colossal magnetoresistance. Measurements have been performed on four polycrystalline samples and four single crystals, allowing us to compare and extract the essence of dielectric response in the material. High-frequency dielectric function is found to be ${\ensuremath{\epsilon}}_{\mathrm{HF}}=30$, as expected for the perovskite material. Dielectric relaxation is found in the frequency window of $20\phantom{\rule{0.3em}{0ex}}\mathrm{Hz}\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}1\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$ at temperatures of $50--200\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ that yields to colossal low-frequency dielectric function, i.e., the static dielectric constant. The static dielectric constant is always colossal, but varies considerably in different samples from $\ensuremath{\epsilon}(0)={10}^{3}\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}{10}^{5}$. The measured data can be simulated very well by blocking (surface barrier) capacitance in series with sample resistance. This indicates that the large dielectric constant in PCMO arises from the Schottky barriers at electrical contacts. Measurements in magnetic field and with dc bias support this interpretation. Colossal magnetocapacitance observed in the title compound is thus attributed to extrinsic effects. Weak anomaly at the charge ordering temperature can also be attributed to interplay of sample and contact resistance. We comment on our results in the framework of related studies by other groups.

The anisotropic and non-linear transport properties of the quasi one-dimensional organic conductor (TMTSF)_2PF_6 have been studied by dc, radiofrequency, and microwave methods. Microwave experiments along all three axes reveal that collective transport, which is considered to be the fingerprint of the spin-density-wave condensate, also occurs in the perpendicular b' direction. The pinned mode resonance is present in the $a$ and b'-axes response, but not along the least conducting c* direction. The ac-field threshold, above which the spin-density-wave response is non-linear, strongly decreases as the temperature drops below 4 K. With increasing strength of the microwave electric field and of the radiofrequency signal, the pinned mode and the screened phason loss-peak shift to lower frequencies. In the non-linear regime, in addition to the phason relaxation mode with Arrhenius-like resistive decay, an additional mode with very long and temperature-independent relaxation time appears below 4 K. We attribute the new process to short-wavelength spin-density-wave excitations associated with discommensurations in a random commensurate N=4 domain structure., 8 pages, 10 figures, submitted to EPJ B. ***N.Biskup - Present address: Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco 28049 Madrid, Spain}

The question addressed in this paper is that of the circumstances under which it is possible to observe quantum coherence phenomena in mesoscopic magnets such as single domain particles and molecular clusters. As these phenomena are only detectable at very low temperatures we also discuss the low temperature characterisation of these magnetic systems.

We have measured the 129 Xe spin-lattice relaxation time T 1 for xenon films adsorbed on silica gel in an 8 T magnetic field at dilution refrigerator temperatures, both with and without 3 He filling the sample cell. Without 3 He , T 1 increases rapidly as the temperature is lowered. With 3 He , T 1 is considerably shortened, and is consistent with temperature-independent quantum relaxation. Using this technique, it is possible to brute-force polarize large quantities of xenon in high B / T conditions.

We have synthesized two divanadates M2V2O7 (M2+ = Co2+ and Cu2+), that are known to show different and complex magnetic arrangements at low temperatures and have studied their dielectric behavior. We have observed a change in the slope of the dielectric constant at the magnetic transition temperature, result which confirms the existence of magnetodielectric coupling in these two divanadates. The origin of the magnetodielectric coupling seems to be different in the Cu- and Co-compounds, although in both cases it is related to their frustrated magnetic arrangement. In Cu2V2O7, the dielectric anomaly arises from a spin canting due to the antisymmetric exchange which is allowed by structural symmetry. In the Co-divanadate, the structural symmetry does not allow antisymmetric exchange but the compound shows correlation between the behavior of the dielectric constant and inverse magnetization, which points to a dependence of its electrical polarization with the pair correlation function of neighboring magnetic spins.

The high pressure polymorph of V2O5 is investigated as example of a high-pressure material (HP-V2O5) with potential applications in electrochemical devices, such as lithium batteries. HP-V2O5 reversibly intercalates up to 2 lithium ions down to 1 Volt vs Li+/Li. The typical voltage-composition profile of HP-V2O5 shows distinct features than that of the ambient pressure polymorph, AP-V2O5. Remarkably, the specific capacity retention with cycling of HP-V2O5 // Li cells (250 Ah/Kg at a C/3.5 rate) is comparable to that of the ambient pressure polymorph. Furthermore, the measured resistivities at room temperature (10000 Ωcm in AP and 400 Ωcm in HP) reveal that HP-V2O5 is a better electronic conductor than AP-V2O5. The enhanced electronic conductivity of HP-V2O5 is an advantage for electrochemical applications.

3 pages, 3 figures., The authors report on colossal electroresistance (ER) in the ferromagnetic insulator manganite La0.9Sr0.1MnO3. The single crystal samples exhibit a transition into a low resistive state above a certain threshold current. Pulsed measurements demonstrate that this transition is not a consequence of heating. ER behaves similarly to magnetoresistance (MR) above the orbital order temperature TOO. Below TOO the MR is only 20% while ER enhances the conductivity by several orders of magnitude. Magnetic field and electric current have opposite effects on the conductivity, therefore, it seems that only the injected carriers are able to modify the ordering of eg Mn orbitals., The authors acknowledge financial support from the Ministerio de Educacion y Ciencia (MAT2005-06024-C02-01 and MAT2006-01004). One of the authors (N.B.) acknowledges the Ramon and Cajal Program from the Ministerio de Educacion y Ciencia in Spain.

The magnetic properties of LiM0.5Mn1.5O4 (M=Ni and Cu) spinels, materials of interest as electrodes for Li-ion batteries, have been studied and interpreted with the help of the first-principles calculation method. The magnetic susceptibility of the Ni compound, that behaves virtually as stoichiometric normal spinel, is consistent with the well-established magnetic model of the spinel structure that leads to ferrimagnetism. However, the Cu spinel was oxygen deficient and showed significant divergences from this model. The ferromagnetic component of this spinel was dependent on the calcining temperature and was smaller to that predicted by the magnetic model. The special crystal structure of the spinel, namely, oxygen deficiency and increased occupancy of the tetrahedral sites by Cu ions, satisfactorily explains the more complex magnetic behavior observed, further supported by the results of the first-principles electronic structure computations.

This paper reports the isolation and characterization of a soluble antigen shared by the liver and kidney of human and some other animal species. Homogenates of human liver in saline were centrifugated at 27,000 g and the supernatants were fractionated by preparative polyacrylamide gel electrophoresis. The gels were divided in sections and each was injected into rabbits; after absorption with polymerized normal human serum, the antiserum obtained by injecting one of the sections reacted only with saline extracts of human liver and kidney when tested against a variety of human tissue extracts. The absorbed antiserum, polymerized and insolubilized with glutaraldehyde, was used to purify the antigen by affinity chromatography. The purified antigen proved to be a glycoprotein containing 19 percent carbohydrate, had a molecular weight of 5.8-6.0 x 10(4) Daltons and a pI of 7.2-7.4. The antigen, relatively thermostable, was precipitated by 35-55 percent ammonium sulphate; its antigenic activity was not affected by extraction with 0.6 N perchloric acid or by incubation with ribonuclease, deoxyribonuclease or neuraminidase but was destroyed by incubation with ttypsin or chymotrypsin. Immunoperoxidase studies showed that the antigen appeared concentrated in the neclei of liver and kidney glomerular epithelial and tubular epithelial cells in humans and rats. The antigen could not be detected in human hepatomas or hypernephromas or in the rat Morris hepatoma 5123.