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.
|
|
Piriou, A., E. Giannini, Y. Fasano, C. Senatore, and O. Fischer. "Vortex phase diagram and temperature-dependent second-peak effect in overdoped Bi2Sr2CuO6+d crystals." Physical Review B 81 (2010): 144517–144524.
|
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.
|
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.
|
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.
|
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.
|
Sereni, J. G., M. Gómez Berisso, G. Schmerber, and J. P. Kappler. "Suppression of the Shastry-Sutherland phase in Ce2 Pd 2 Sn at a field-induced critical point." Physical Review B – Condensed Matter and Materials Physics 81, no. 18 (2010): 184429.
Abstract: The magnetic phase diagram of Ce2 Pd2 Sn is investigated through the field dependence of thermal, transport, and magnetic properties at low temperature. The upper transition, TM =4.8 K is slightly affected by magnetic field up to B=1 T whereas the lower one T C (B) rapidly increases from 2.1 K joining TM in a critical point at Tcr = (4.1±0.2) K for Bcr = (0.11±0.01) T. At that point, the intermediate phase, previously described as an unstable Shastry-Sutherland lattice, is suppressed. A detailed analysis around the critical point reveals a structure in the maximum of the ∂ M/∂ B (B) derivative, which may be related to a step in magnetization predicted by theory for the mentioned lattice. © 2010 The American Physical Society.
|
|
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.
|
