ABSTRACT
We have carried out detailed magnetic and transport studies of the new Sr0.5Ce0.5FBiS2-xSex (0.0 ≤ x ≤ 1.0) superconductors derived by doping Se in Sr0.5Ce0.5FBiS2. Se-doping produces several effects: it suppresses semiconducting-like behavior observed in the undoped Sr0.5Ce0.5FBiS2, the ferromagnetic ordering temperature, TFM, decreases considerably from 7.5 K (in Sr0.5Ce0.5FBiS2) to 3.5 K and the superconducting transition temperature, Tc, gets enhanced slightly to 2.9-3.3 K. Thus in these Se-doped materials, TFM is marginally higher than Tc. Magnetization studies provide evidence of bulk superconductivity in Sr0.5Ce0.5FBiS2-xSex at x ≥ 0.5 in contrast to the undoped Sr0.5Ce0.5FBiS2 (x = 0) where magnetization measurements indicate a small superconducting volume fraction. Quite remarkably, as compared with the effective paramagnetic Ce-moment (~2.2 µB), the ferromagnetically ordered Ce-moment in the superconducting state is rather small (~0.1 µB) suggesting itinerant ferromagnetism. To the best of our knowledge, Sr0.5Ce0.5FBiS2-x Sex (x = 0.5 and 1.0) are distinctive Ce-based bulk superconducting itinerant ferromagnetic materials with Tc < TFM. Furthermore, a novel feature of these materials is that they exhibit a dual and quite unusual hysteresis loop corresponding to both the ferromagnetism and the coexisting bulk superconductivity.
ABSTRACT
The role of elastic strain for magnetoelectric materials and devices is twofold. It can induce ferroic orders in thin films of otherwise non-ferroic materials. On the other hand, it provides the most exploited coupling mechanism in two-phase magnetoelectric materials and devices today. Complex oxide films (perovskites, spinels) are promising for both routes. The strain control of magnetic order in complex oxide films is a young research field, and few ab initio simulations are available for magnetic order in dependence on lattice parameters and lattice symmetry. Here, an experimental approach for the evaluation of how elastic strain in thin epitaxial films alters their magnetic order is introduced. The magnetic films are grown epitaxially in strain states controlled by buffer layers onto piezoelectric substrates of 0.72Pb(Mg1/3Nb2/3)O3-0.28PbTiO3(001). As an example, the strain dependence of the ordered magnetic moment of SrRuO3 has been investigated. At a tensile strain level of approximately 1%, SrRuO3 is tetragonal, and biaxial elastic strain induces a pronounced suppression of the ordered magnetic moment. As a second example, a strain-driven transition from a ferromagnetic to a magnetically disordered phase has been observed in epitaxial La0.8Sr0.2CoO3 films.
ABSTRACT
In this paper, the electronic transport of La(0.7)(Sr,Ca)(0.3)MnO(3) films grown by pulsed laser deposition on a LaAlO(3)(001) substrate with deep parallel structured steps and a 30° symmetric bicrystal SrTiO(3)(001) substrate have been discussed. The electronic transport properties have been related to the well-known extrinsic transport of bulk manganite compounds. The spin-glass-like behavior with a characteristic peak at 20 K and domain formation at the grain boundary is observed. Further, it has been quantified from the resonant tunneling model that mixed magnetic interactions play a significant role in the manganite films deposited on step edges.
ABSTRACT
Superconducting LaFeAsO1-xFx thin films were grown on single crystalline LaAlO3 substrates with critical temperatures (onset) up to 28 K. Resistive measurements in high magnetic fields up to 40 T reveal a paramagnetically limited upper critical field mu{0}H{c2}(0) around 77 T and a remarkable steep slope of -6.2 T K-1 near T{c}. From transport measurements we observed weak-link behavior in low magnetic fields and evidence for a broad reversible regime.
ABSTRACT
We report upper critical field Bc2(T) data for disordered (arsenic-deficient) LaO0.9F0.1FeAs1-delta in a wide temperature and magnetic field range up to 47 T. Because of the large linear slope of Bc2 approximately -5.4 to -6.6 T/K near Tc approximately 28.5 K, the T dependence of the in-plane Bc2(T) shows a flattening near 23 K above 30 T which points to Pauli-limited behavior with Bc2(0) approximately 63-68 T. Our results are discussed in terms of disorder effects within [corrected] unconventional superconducting pairings.
ABSTRACT
A strain-induced change of the electrical conductivity by several orders of magnitude has been observed for ferromagnetic La(0.7)Sr(0.3)CoO(3) films. Tensile strain is found to drive the narrow-band metal highly insulating. Reversible strain applied using a piezoelectric substrate reveals huge resistance modulations including a giant piezoresistive gauge factor of 7000 at 300 K. Magnetization data recorded for statically and reversibly strained films show moderate changes. This indicates a rather weak strain response of the low-temperature Co spin state. We suggest that a strain-induced static Jahn-Teller-type deformation of the CoO(6) units may provide a localization mechanism that also has impact on electronic transport in the paramagnetic regime.
ABSTRACT
We use angle-resolved photoemission with circularly polarized excitation to demonstrate that in the 5 x 1 superstructure-free (Pb,Bi)(2)Sr(2)CaCu(2)O(8+delta) (Pb-Bi2212) material there are no signatures of time-reversal symmetry breaking in the sense of the criteria developed earlier [Nature (London) 416, 610 (2002)]]. The dichroic signal retains reflection antisymmetry as a function of temperature and doping and in all mirror planes, precisely defined by the experimental dispersion at low energies. The obtained results demonstrate that the signatures of time-reversal symmetry violation in pristine Bi2212, as determined by angle-resolved photoemission spectroscopy, are not a universal feature of all cuprate superconductors.
ABSTRACT
From detailed high-resolution measurements of the photon energy dependence of the (pi,0) superconducting-state photoemission spectrum of the bilayer Bi high-temperature superconductors, we show that the famous peak-dip-hump line shape is dominated by a superposition of spectral features originating from different electronic states which reside at different binding energies, but are each describable by essentially identical single-particle spectral functions. The previously identified bilayer-split CuO2 bands are the culprit: with the "superconducting" peak being due to the antibonding band, while the hump is mainly formed by its bonding bilayer-split counterpart.
