arXiv subjects

H. v. Loehneysen

Publications and source records attributed to H. v. Loehneysen.

22 records · Page 2Linked to original sources

arXiv1999

Strongly Enhanced Curie Temperature in Carbon-Doped Mn5Ge3 Films

The structural and magnetic properties of Mn5Ge3Cx films prepared at elevated substrate temperatures TS are investigated. In particular, films with x >= 0.5 and TS = 680 K exhibit a strongly enhanced Curie temperature TC = 440 K compared to Mn5Ge3 with TC = 304 K. Structural analysis of these films suggests that the carbon is interstitially incorporated into the voids of Mn octahedra of the hexagonal Mn5Si3-type structure giving rise to a lattice compression. The enhanced ferromagnetic stability in connection with the lattice compression is interpreted in terms of an Mn-Mn interaction mediated by C based on a change in the electronic structure.

cond-mat.mtrl-sci↗

arXiv1999

From an antiferromagnet to a heavy-fermion system: CeCu5Au under pressure

The electrical resistivity rho(T) of single crystalline CeCu_5Au under pressure was measured in the temperature range 30mK<T<300K. Pressure suppresses the antiferromagnetic order (T_N=2.35K at ambient pressure) and drives the system into a non-magnetic heavy-fermion state above P_c=4.1(3)GPa. The electrical resistivity shows a deviation from a T^2 dependence of a Fermi-liquid in the pressure range 1.8GPa<=P<=5.15GPa. The rho(T)-curves can be compared with those of CeCu_{6-x}Au_x at different Au concentrations. Just before the long-range magnetic order vanishes, a possibly superconducting phase (at T_c=0.1K and P=3.84GPa) occurs, pointing to a coexistence of antiferromagnetic order and superconductivity. This new phase is only seen in a narrow pressure interval Delta P=0.4GPa.

cond-mat.str-el↗

arXiv1999

Critical Behavior of the Conductivity of Si:P at the Metal-Insulator Transition under Uniaxial Stress

We report new measurements of the electrical conductivity sigma of the canonical three-dimensional metal-insulator system Si:P under uniaxial stress S. The zero-temperature extrapolation of sigma(S,T -> 0) ~§- S_cmu shows an unprecidentedly sharp onset of finite conductivity at S_c with an exponent mu = 1. The value of mu differs significantly from that of earlier stress-tuning results. Our data show dynamical sigma(S,T) scaling on both metallic and insulating sides, viz. sigma(S,T) = sigma_c(T) F(§- S_cT^y) where sigma_c(T) is the conductivity at the critical stress S_c. We find y = 1/znu = 0.34 where nu is the correlation-length exponent and z the dynamic critical exponent.

cond-mat.dis-nn↗

arXiv1998

Superconducting and Magnetic Properties of Nb/Pd_1-xFe_x/Nb Triple Layers

The superconducting and magnetic properties of Nb/Pd_1-xFe_x/Nb triple layers with constant Nb layer thickness d_Nb=200 A and different interlayer thicknesses are investigated. The thickness dependence of the magnetization and of the superconducting transition temperature shows that for small iron concentration x the Pd_1-xFe_x layer is likely to be in the paramagnetic state for very thin films whereas ferromagnetic order is established for x>=0.13. The parallel critical field B_c2II(T) exhibits a crossover from two-dimensional (2D) behavior where the Nb films are coupled across the interlayer, towards a 2D behavior of coupled Nb films with increasing d_PdFe or x. This 2D-2D crossover allows a determination of the penetration depth xi_F of Cooper pairs into the Pd_1-xFe_x layer as a function of x. For samples with a ferromagnetic interlayer xi_ is found to be independent of x.

cond-mat.supr-con↗