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We report measurements on yttrium iron garnet (YIG) thin films grown on both gadolinium gallium garnet (GGG) and yttrium aluminum garnet (YAG) substrates, with and without thin Pt top layers. We provide three principal results: the observation of an interfacial region at the Pt/YIG interface, we place a limit on the induced magnetism of the Pt layer, and confirm the existence of an interfacial layer at the GGG/YIG interface. Polarized neutron reflectometry (PNR) was used to give depth dependence of both the structure and magnetism of these structures. We find that a thin film of YIG on GGG is best described by three distinct layers: an interfacial layer near the GGG, around 5 nm thick and nonmagnetic, a magnetic "bulk" phase, and a nonmagnetic and compositionally distinct thin layer near the surface. We theorize that the bottom layer, which is independent of the film thickness, is caused by Gd diffusion. The top layer is likely to be extremely important in inverse spin Hall effect measurements, and is most likely Y2O3 or very similar. Magnetic sensitivity in the PNR to any induced moment in the Pt is increased by the existence of the Y2O3 layer; any moment is found to be less than 0.02μB/atom. [ABSTRACT FROM AUTHOR]

Using a high-resolution differential technique we have determined the electronic specific heat coefficient γ(T)=Cel/T of Ba1-xKxFe2As2 with x=0 to 1.0, at temperatures (T) from 2 K to 380 K and in magnetic fields H=0 to 13 T. In the normal state γn(x,T) increases strongly with x at low temperature, compatible with a mass renormalization ~12 at x=1, and decreases weakly with x at high temperature. A superconducting transition is seen in all samples from x=0.2 to 1, with transition temperatures and condensation energies peaking sharply at x=0.4. Superconducting coherence lengths ξab~20 Å and ξc~3 Å are estimated from an analysis of Gaussian fluctuations. For many dopings we see features in the H and T dependencies of γs(T,H) in the superconducting state that suggest superconducting gaps in three distinct bands. A broad "knee" and a sharp mean-field-like peak are typical of two coupled gaps. However, several samples show a shoulder above the sharp peak with an abrupt onset at Tc,s and a T dependence γs(T)∝√1-T/Tc,s. We provide strong evidence that the shoulder is not due to doping inhomogeneity and suggest it is a distinct gap with an unconventional T dependence Δs(T)∝(1-T/Tc,s)0.75 near Tc,s. We estimate band fractions and T=0 gaps from three-band α-model fits to our data and compare the x dependencies of the band fractions with spectroscopic studies of the Fermi surface. [ABSTRACT FROM AUTHOR]

We present a detailed study of quantum oscillations in the antiferromagnetically ordered pnictide compound SrFe2As2 as the angle between the applied magnetic field and crystalline axes is varied. Our measurements were performed on high-quality single crystals in a superconducting magnet, and in pulsed magnetic fields up to 60 T allowing us to observe orbits from several small Fermi-surface pockets. We extract the cyclotron effective mass m* and frequency F for these orbits and track their values as the field is rotated away from the c axis. While a constant ratio of m*/F is expected for a parabolic band, we observe deviations from this behavior. We conclude that this observation points to orbits derived from a band with Dirac dispersion near the Fermi level. [ABSTRACT FROM AUTHOR]