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Under the terms of the Creative Commons Attribution License 3.0 (CC-BY).-- et al., Magnetization studies have been performed on a polycrystalline sample of Dy5Si3Ge as a function of an applied magnetic field (up to 50 kOe) and hydrostatic pressure (up to 10 kbar) in the 5-300 K temperature range. The anomalous behavior of the magnetic susceptibility indicates that a Griffiths-like phase exists at low magnetic fields and pressures up to 10 kbar. We present evidence that the high-temperature second-order ferromagnetic transition can be coupled with the low-temperature first-order crystallographic transformation into a single first-order magnetic-crystallographic transformation using a magnetic field and hydrostatic pressure as tuning parameters. The effect of pressure on the Griffiths-like phase is reported and analyzed in the framework of the complex competition between the interslab and intraslab magnetic interactions. © 2013 American Physical Society., Work at the University of Zaragoza is supported by the Spanish Ministry of Science (MAT2011-27553-C02, MAT2011-27573-C04) and Spanish DGA (Grant No. E26). Work at the Ames Laboratory is supported by the Office of Basic Energy Sciences, Materials Sciences and Engineering Division of the Office of Science of the US Department of Energy. Ames Laboratory is operated by Iowa State University of Science and Technology for the US Department of Energy under Contract No. DE-AC02-07CH11358.

et al., Magnetic and magnetocaloric properties of single-crystalline Er 5Si 4 have been investigated as a function of the applied magnetic field (up to 50 kOe) and the hydrostatic pressure (up to 10 kbar) in the 5-300 K temperature range along the three main crystallographic directions. The magnetization isotherms show a highly anisotropic behavior with the easy-magnetization direction along the b axis for the low-pressure monoclinic and high-pressure orthorhombic structures, in good agreement with previous neutron scattering experiments. Below T C, the approach to the saturation shows a steplike behavior when the magnetic field is applied along the hard directions. The steps are sharper as the pressure increases. At constant magnetic field change, increasing the pressure induces a highly anisotropic enhancement of the magnetic entropy change. An enhancement of 20% is observed along the easy axis b, where the magnetic entropy change is maximum. The different evolution of the magnitude and temperature dependence of the magnetocaloric effect along the three crystallographic directions with pressure is discussed. © 2012 American Physical Society., Work at the University of Zaragoza was supported by the Spanish Ministry of Science (MAT2008-06567-C02) and Spanish DGA (Grant No. E26). N. Marcano acknowledges Spanish CSIC (JAE-doc program) for financial support. Work at the Ames Laboratory was supported by the Office of Basic Energy Sciences,Materials Sciences and EngineeringDivision of theOffice of Science of theUSDepartment of Energy. Ames Laboratory is operated by Iowa StateUniversity of Science and Technology for the US Department of Energy under Contract No. DE-AC02-07CH11358.

et al., In order to study the crystal structure, phase relationships, and magnetic properties of the system Tb 5-xLa xSi 2Ge 2, a series of polycrystalline samples with compositions ranging from x=0 to x=5 have been synthesized and characterized in detail. At room temperature, two structures have been detected: Compounds in the concentration range 0≤x, This work was partially supported by the projects POCI/CTM/61284/2004, PTDC/CTM-NAN/115125/2009, FEDER/POCTI No. 155/94 from Fundaçao para a Ciência ex Tecnologia (FCT), Portugal. A.M.P. thanks FCT for Grant No. SFRH/BPD/63150/2009. J.N.G. thanks FCT for Grant No. SFRH/BPD/82059/2011. The financial support of the Spanish MEC (MAT2008-06567-C02) and DGA (Grant No. E26) is acknowledged. This research was supported by UT Battelle, LLC, under Contract No. DE-AC05-00OR22725 for the US Department of Energy, Office of Science.

8 páginas, 6 figuras.-- PACS number(s): 71.10.Ca, 68.47.Gh.-- et al., Metallic surface layers are fabricated by doping (100) SrTiO3 (STO) single crystals with oxygen vacancies generated by bombardment with Ar ions from an rf plasma source. The presence of oxygen vacancies is confirmed by cathodoluminescence and x-ray photoemission spectroscopy. This technique produces a surface electron gas with high values of the sheet carrier density (n2D = 2.45×1017 cm-2). A strong increase (300%) of the low-temperature magnetoresistance is observed when the magnetic field is rotated away from the surface, characteristic of orbital effects of confined electrons. We estimate the width of the confinement region to be in the 200–300 nm range. When a magnetic field is applied in the surface plane and parallel to the current direction, a large negative magnetoresistance is found below the structural transition of the STO, which is discussed in terms of spin-orbit scattering. On further reduction of temperature, there is a change to a positive magnetoresistance regime due to the scattering of charge carriers at the disordered surface region., This work was supported by Spanish MICINN Grant No. MAT 2008 06517, Consolider Ingenio Grant No. CSD2009-00013 (IMAGINE), and CAM Grant No. S2009-MAT 1756 (PHAMA).

8 páginas, 7 figuras, 1 tabla.-- PACS number(s): 75.30.Sg, 71.70.Ch, 75.30.Kz, 75.10.Dg, We present a detailed study of the temperature dependence of the electrical resistivity [ρ(T)] in the range 13–300 K for the Ho5(SixGe1-x)4 system. Three distinct ρ(T) behaviors are observed, associated with different magnetic and crystallographic structures along the series. In the samples with an antiferromagnetic phase (AFM) one observes a shoulder near the Néel temperature (TN) attributed to the formation of a gap on the Fermi surface. This gap is analyzed using a phenomenological two-band model for an AFM with distinct atomic and magnetic periodicities, and its effect seems to extend well above TN. We also found the presence of short-range magnetic clusters in the paramagnetic (PM) phase. On the ferromagnetic (FM) materials, the distinct ρ(T) scattering contributions (phonon, magnetic, and residual terms) are extracted from the measurements, with ρ(T) mainly dominated by electron spin scattering. An additional contribution is also observed, arising from the strong crystal field effect in these materials. The effect is mainly observed in the PM phase, leading to a curvature on ρ(T) in this phase. Using a two-level crystal field model the corresponding gap was estimated for the different Si/Ge ratio samples, revealing that the crystal field splitting increases linearly with Si content., Work partially supported by the projects POCI/CTM/61284/2004, PTDC/CTM/NAN/115125/2009, and FEDER/POCTI n0155/94 from Fundaçâo para a Ciência ex Tecnologia (FCT), Portugal. A.M.P. thanks FCT for Grant No. SFRH/BPD/63150/2009. C.M. acknowledges the support of the Fundación ARAID. The financial support of the Spanish MEC (MAT2008-06567-C02) and DGA (Grant No. E26) is acknowledged.

4 páginas, 3 figuras.-- PACS number(s): 75.30.Sg, 64.60.ah, 75.40.Cx, 75.50.-y.-- et al., We report on the discovery of Griffiths-like phase in several compounds of the R5(SixGe1−x)4 (R=Gd, Tb, Dy, and Ho) system, through the existence of an anomalous behavior on the reciprocal magnetic susceptibility (χ−1). We found that this anomaly is restricted to the samples which present the Gd5Si2Ge2-type (monoclinic) or the Sm5Ge4-type {orthorhombic-II [O(II)]} structural phases at room temperature. This peculiar effect originates from local disorder within the crystallographic structure, stabilized and enhanced by the competing intralayer and interlayer magnetic interactions. From this strong competition, a ratio of ∼0.5 between Néel and the Griffiths-like temperatures is always found in the O(II) structure. In addition, a universal (x,T) phase diagram is proposed with an interpretation based on percolative processes., Work partially supported by the Projects No. POCI/CTM/ 61284/2004, PTDC/CTM/NAN/115125/2009, and FEDER/ POCTI No. 155/94 from Fundação para a Ciência e Tecnologia (FCT), Portugal. A.M.P. thanks FCT for the Grant No. SFRH/BPD/63150/2009. C.M. acknowledges the support of the Fundación ARAID. The financial support of the Spanish MEC (Grant No. MAT2008-06567-C02) and DGA (Grant No. E26) is acknowledged.

7 páginas, 7 figuras.-- PACS number(s): 75.70.Rf, 75.70.Ak, 75.50.Bb.-- et al., We study the enhanced magnetic moment observed in epitaxial magnetite (Fe3O4) ultrathin films (t, This work has been financially supported by Spanish Ministry of Science through Projects No. MAT2008-06567-C02 and No. MAT2008-01077, and the Regional Government of Aragón (E-26, E-69, and E-34).

We have measured the Hall effect of polycrystalline Gd5(Si1.8Ge2.2) in the temperature range 4–360 K and in magnetic fields of up to 12 T. The Hall resistivity follows the magnetization of the material in the range studied. The anomalous Hall coefficient increases with increasing temperature and shows a sharp dip at the magnetostructural transition. Away from the dip, the Hall coefficient scales roughly with the square of the total resistivity, as expected if side-jump scattering dominates., Part of this research was supported by Project No. MAT 99-1063-C4 of Comision Interministerial de Ciencia y Tecnologia (CICYT).