Andreev reflection study of the new magnetic superconductor Mo3Sb7 in magnetic field

Andreev reflection in contacts based on the magnetic superconductor Mo3Sb7 in a magnetic field is investigated by the point-contact method. It is found that the behavior of the order parameter in the magnetic field Delta(H) is essentially dependent on the value of Delta, which varies widely (Delta(0,0)approximate to 0.01-0.31 meV) for different contacts at practically invariant T-c. At high Delta the dependence Delta(max)(H) deviates slightly from the theoretical prediction applicable under point-contact conditions. As the order parameter decreases, the deviation starts to increase and becomes very large when Delta approaches its minimum. Proceeding from the results obtained in this study and from the temperature measurements on Mo3Sb7 performed previously, we are inclined as before to assign the compound to the class of superconductors with an anisotropic gap function. Therefore, in no way can it be considered as a conventional BCS-type superconductor. The upper critical field H-c2 similar or equal to 16.5 kOe found here is close to that obtained from magnetization measurements in other studies. According to an estimate made, the pair-breaking effect of the Pauli paramagnetism is rather weak in Mo3Sb7. (c) 2007 American Institute of Physics.