Magnetization measurements were performed on CeCoIn_5 at temperature down to 30 mK with the magnetic field applied in three different orientations: parallel, near parallel (∼ 100 rotated) and perpendicular to the ab-plane. For these three orientations we have observed crossover features in the torque/magnetization traces at fields just below Hc2, giving further evidence for the formation of a high field Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) superconducting state in CeCoIn_5 for H∥ab-plane and newly indicates that the FFLO state persists for out-of-plane field orientations. Furthermore, for the (near) parallel to ab-plane field configurations and T≤50mK, we have found an anomalous peak effect(APE) just below the crossover field when the magnetic field is sweeping down from normal to superconducting state. The dynamics of this peak suggests the existence of a metastable phase occurring in the vicinity of the FFLO phase and raises questions about the order (first or second) of the transition from FFLO to the superconducting state. None of the above features were found in a Ce_{0.98}Gd_{0.02}CoIn_{5} crystal.
@article{arxiv.cond-mat/0608722,
title = {FFLO State and Peak Effect Dynamics in CeCoIn_5: Magnetization Studies},
author = {X. Gratens and L. Mendonca Ferreira and Y. Kopelevich and N. F. Oliveira and P. G. Pagliuso and R. Movshovich and R. R. Urbano and J. L. Sarrao and J. D. Thompson},
journal= {arXiv preprint arXiv:cond-mat/0608722},
year = {2007}
}