Reentrant superconductivity in a composite formed by YBa${}_2$Cu${}_3$O${}_{7-\delta }$ and Ammonium Terbium Oxalate

We present a study of reentrant behavior in a composite formed by a Hight-T${}_c$ superconductor, YBa${}_2$Cu${}_3$O${}_{7-\delta }$ and Ammonium Terbium Oxalate, Tb(H${}_2$O)(C${}_2$O${}_4$)${}_2$ $\cdot$NH${}_4$. The composite has a transition temperature about 92 K, and it presents a reentrant behaviour resulting of the coexistence between superconductivity and magnetism. According to this study the values and shape of the critical magnetic fields were dramatically reduced in a similar form as in other known reentrant superconductors.