Four layer monolithic integrated high Tc dc SQUID magnetometer

YBa2Cu3O7−x based monolithic integrated dc SQUID magnetometers, consisting of a dc SQUID integrated with a flux transformer on a single bicrystalline substrate, have been fabricated and characterized. The devices consist of four layers, including two superconducting layers, and first realizations operate up to 73 K. A maximum voltage modulation of 32 μV is observed at 40 K. A field sensitivity of 0.17 pT/√Hz is obtained above 200 Hz at 45 K and 0.49 pT/√Hz at 1 Hz and 65 K

Inhomogenous magnetic ground state in CeAgGa

CeAgGa crystallizes in CeCu 2 Imma structure with Ag and Ga atoms randomly distributed at 8h sites. The magnetic and transport properties of the orthorhombic CeAgGa compound have been obtained from the analysis of ac magnetic susceptibility χ ac , magnetization M vs. magnetic field, specific heat C and electrical resistivity ρ. The results provide evidence for the formation of a spin-glass state with a freezing temperature T f =5.1 K. The randomness in the Ce-Ce magnetic exchange interactions seem to arise from a statistical distribution of Ag and Ga atoms on a crystallographic site of the CeAgGa crystal lattice. The results provide also evidence for the formation of ferromagnetic-like order at the temperature T C ≈ 3.6 K. Band structure calculations for a disordered system give magnetic moment similar to saturation moment obtained from magnetization measurements, however, its calculated value is insensitive on Ga/Ag off-stoichiometry in the 8h position. Complex behavior of CeAgGa Kondo-lattice compound is discussed in terms of interplaying Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions, Kondo effect and structural disorder. Copyright EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2011