Antonio, D., M. I. Dolz, and H. Pastoriza. "Magnetization measurement of single La0.67Ca0.33MnO3 nanotubes in perpendicular magnetic fields using a micromechanical torsional oscillator." Journal of Magnetism and Magnetic Materials 322, no. 5 (2010): 488–493.
Abstract: Using a silicon micromechanical resonator as a sensitive magnetometer, the authors have studied both experimentally and theoretically the magnetic behavior of two isolated ferromagnetic nanotubes of perovskite La0.67Ca0.33MnO3. The article investigates the specific configuration where a magnetic field H is applied perpendicular to the magnetic easy axis of an isolated nanotube characterized by an uniaxial anisotropy constant K. In this situation, the magnetization M reduces the effective elastic constant kM of the resonator. This softening of the mechanical system is opposed to the hardening effect of M observed in a previous work, where H was applied parallel to the easy axis. Moreover, in this magnetic field configuration two distinct magnetization regimes are manifested, depending on the magnitude of H. For H[not double greater-than sign]2K/M the magnetization is almost parallel to the applied magnetic field and for H[double less-than sign]2K/M it is almost parallel to the easy axis of the nanotube. At a certain value of H there is a sharp transition
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Sereni, J. G., M. Gomez Berisso, N. C. Canales, M. Deppe, and C. Geibel. "Tuning ground state degeneracy and quantum criticality in Ce1-xLaxTiGe." Physica Status Solidi (B) Basic Research 247, no. 3 (2010): 707–709.
Abstract: We have tuned the paramagnetic heavy Fermion (HF) system CeTiGe to a more magnetic state and toward quantum criticality (QC) by partially substituting La for Ce. The induced volume expansion leads to a pronounced decrease of the Kondo temperature (TK), from ≈50 K in pure CeTiGe to less than 4 K at large La content. Since the former value is of the order of the crystal field splitting, while the latter is well below, the systems evolves from a large degeneracy N = 6 Kondo system at x = 0 to a conventional N = 2 Kondo system at x ≥ 0:8. There, the first excited crystal field doublets become apparent in the T dependence of the specific heat CP(T) at an excitation energy DCF ≈ 30 K. The reduction of the degeneracy is expected to enhance the decrease of TK, explaining the strong reduction by more than one order of magnitude observed in this system. The decrease of TK drives the system toward QC as evidenced by a divergence of CP(T)/T and x(T) toward low temperatures in the x = 0:8 sample. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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Sengupta, K., P. Pedrazzini, and D. Jaccard. "Superconductivity of compressed iron: Low temperature electrical transport behaviour." In Journal of Physics: Conference Series, 012180. Vol. 200., 2010.
Abstract: Resistivity of iron under pressure ( p < 17 GPa) has been measured in a new type of Bridgman cell adapted to trap Daphne oil as pressure medium. Here we have done detailed studies on the T -exponent of ? ( T ) in the low p -region of the superconducting phase (13 ? p ? 31 GPa) under magnetic field (? 8 kOe). Very large drop and quasi-complete ? ( T ) transition were observed for the first time in the low- p region of SC-dome. With the increase of magnetic field we obtained, below T SC onset , a trend that the T -exponent is increasing and reached to 1.82 at the highest applied field. Attempt has also been made to estimate the critical current density, which appears to be quite high compared to our earlier work.
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Sereni, J. G., N. Caroca-Canales, M. Kumar, N. Oeschler, M. Gómez Berisso, and C. Geibel. "CeRuGe and CeRuSi: Heavy fermion systems with some unusual features." Journal of Physics: Conference Series 200, no. 1 (2010): 012181.
Abstract: We have investigated the physical properties of CeRuSi, its homologue CeRuGe and some doped La alloys. All of them present similar properties: large paramagnetic temperatures θp ##IMG## [http://ej.iop.org/icons/Entities/approx.gif] {approx} −100 K and the level off of χ( T ) below ##IMG## [http://ej.iop.org/icons/Entities/approx.gif] {approx} 10 K in coincidence with the maximum decrease of p ( T ), which starts to drop below 25 K. The respective γ ( CeRuSi ) ##IMG## [http://ej.iop.org/icons/Entities/approxeq.gif] {approxeq} 0.18 and γ ( CeRuGe ) ##IMG## [http://ej.iop.org/icons/Entities/approxeq.gif] {approxeq} 0.15 J/molK 2 coefficients reveal a heavy fermion character, with a Kondo temperature T K ##IMG## [http://ej.iop.org/icons/Entities/approxeq.gif] {approxeq} 50 K comparable to the crystal field splitting. In both compounds a broad maximum in C P ( T )/ T is observed around 5 K, whose origin is yet not clear. In contrast to the usual behavior observed in Kondo lattice systems, when Si is replaced by Ge T K ##IMG## [http://ej.iop.org/icons/Entities/propto.gif] {propto} θ p and 1/γ practically does not decreases despite the unit cell volume of CeRuGe is about 3% larger than that of CeRuSi. We discuss possible origins for these unusual features.
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Sarkar, R., M. Baenitz, J. G. Sereni, and C. Geibel. "29Si NMR study of the heavy fermion system CeRuSi." Journal of Physics: Conference Series 200 (2010): 012173.
Abstract: A recent investigation of the low temperature properties of the paramagnetic heavy fermion system CeRuSi revealed an anomalous decrease of the coefficient C/T below 6 K, indicating a second low energy scale well below the Kondo temperature of about 50 K. We started an investigation of this unusual behavior using the local probe 29Si-NMR. Here a preliminary 29Si field sweep NMR study in the temperature 4.2-200 K is reported. 29Si-NMR powder spectra obtained at 72.9 MHz could be simulated and shift components 29Kab(T) and 29K c(T) were determined. The shift along the basal plane 29Kab(T) shows the expected behavior with a Curie-Weiss dependence at high T merging in a constant value below 15 K. In contrast the shift along the tetragonal axis reveals an anomalous T dependence below 15 K where 29Kc(T) drops by a factor of 2, confirming the presence of a further low T energy scale. We suspect this drop to be related to the anomalous decrease of C/T below 6 K and discuss possible mechanism. © 2010 IOP Publishing Ltd.
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Deppe, M., N. Caroca-Canales, J. G. Sereni, and C. Geibel. "Evidence for a metamagnetic transition in the heavy Fermion system CeTiGe." In Journal of Physics: Conference Series, 012026. Vol. 200. International Conference on Magnetism, ICM 2009 200, no. SECTION 1. Karlsruhe, 2010.
Abstract: A recent study of CeTiGe identified this compound as a paramagnetic heavy Fermion system where the full J = 5/2 multiplet is involved in the formation of the ground state. Here we present a preliminary investigation of the dc-magnetization Mdc(H) and of the magnetoresistance Ï(H) of polycrystalline CeTiGe samples in applied magnetic fields up to μ0H = 14 T. The results reveal a pronounced metamagnetic transition at a critical field μ0Hc ≈ 13.5 T at low temperatures, with a step like increase in Mdc(H) of at least 0.6 μB/Ce. The metamagnetic transition leads to a strong decrease in Ï(H). A clear hysteresis in Mdc(H) and Ï(H) indicate that in CeTiGe these metamagnetic features correspond to a true thermodynamic, first order type transition in contrast to the critical behavior observed in the canonical system CeRu2Si2. Measurements at higher temperatures showed a continuous suppression of the metamagnetic transition with increasing T, which vanishes at T ∼ 30 K. © 2010 IOP Publishing Ltd.
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Niebieskikwiat, D., N. Haberkorn, R. Guitarra, and J. Guimpel. "Magnetic properties of SrTiO3/Pr2/3Ca 1/3MnO3 multilayers." In Journal of Physics: Conference Series, 072069. Vol. 200., 2010.
Abstract: Nanoscale ferromagnetic (FM) clusters embedded within insulating (I) layers of the antiferromagnetic Pr2/3Ca1/3MnO3 (PCMO) are known to improve the magnetoresistance ratio of FM-I magnetoresistive multilayers. Here, we study the magnetic properties of perovskite superlattices comprised of five PCMO layers of variable thickness t separated by 5nm-thick spacers of SrTiO3 (STO). Several multilayers (1.5 nm ≤ t ≤ 8 nm) were grown on (001) STO substrates by magnetron sputtering. We show that the magnetic moment of PCMO due to the FM inclusions presents a maximum for t ∼ 3 nm, accompanied by an abrupt increase of coercivity and exchange bias field. The nonmagnetic nature of the neighboring STO layers demonstrates that the observed behavior is not related to any interlayer exchange coupling, but the geometrical matching between layer thickness and FM domain size is the key driver for the enhancement of the FM moment and anisotropy energy. These results open a new door for the optimization of perovskite based spintronic devices.
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Haberkorn, N., F. C. Lovey, A. M. Condó, and J. Guimpel. "Development and characterization of shape memory Cu-Zn-Al thin films." Materials Science and Engineering B: Solid-State Materials for Advanced Technology 170, no. 1-3 (2010): 5–8.
Abstract: Ternary Cu-Zn-Al alloys show good shape memory properties with narrow hysteresis and a wide range of martensitic transformation temperature (Ms), depending on the alloy composition. Thin films of Cu-Zn-Al with shape memory effect were grown for the first time using a new procedure. First Cu-Al thin films were obtained by DC sputtering on Si (1 0 0) substrates at room temperature, and second, the Cu-Al films were encapsulated and annealed in the presence of a Cu-Zn-Al bulk reference in order to fix a Zn vapour pressure. In this way a controlled amount of Zn is transported from the bulk reference into the film, in such a way that the Ms of the film becomes nearly the same as the bulk reference. The structures and microstructures of the as grown films were analysed by X-ray diffraction and transmission electron microscopy. The martensitic transformation temperature was determined by resistivity measurements.
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Sirena, M., A. Zimmers, N. Haberkorn, E. E. Kaul, L. B. Steren, J. Lesueur, T. Wolf, Y. Le Gall, J. - J. Grob, and G. Faini. "Direct observation of electronic inhomogeneities induced by point defect disorder in manganite films." Journal of Applied Physics 107 (2010): 113903.
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Fasano, Y., I. Maggio-Aprile, N. D. Zhigadlo, S. Katrych, J. Karpinski, and Ã. ˜. Fischer. "Local quasiparticle density of states of superconducting SmFeAsO1 − xFx single crystals: Evidence for spin-mediated pairing." Physical Review Letters 105 (2010): 167005–167008.
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