Reentrant superconductivity in HoNi 5 -NbN-HoNi 5 nanostructures

Abstract

Superconductivity (S) and ferromagnetism (F) are probed through transport and magnetization measurements in nanometer scale HoNi5-NbN (F-S) bilayers and HoNi5-NbN-HoNi5 (F-S-F) trilayers. The choice of materials has been made on the basis of their comparable ordering temperatures and strong magnetic anisotropy in HoNi5. We observe the normal state reentrant behavior in resistance vs. temperature plots of the F-S-F structures just below the superconducting transition in the limited range of HoNi5 layer thickness dHN ($20\ \text{nm}<d_{HN}<80\ \text{nm}$ ) when $d_{\textit{NbN}}$ is fixed at${}\simeq 10\ \text{nm}$ . The reentrance is quenched by increasing the out-of-plane ($H_{\perp}$ ) magnetic field and transport current where as in-plane ($H_{\parallel}$ ) field of $\leq 1500\ \text{Oe}$ has no effect on the reentrance. The origin of the reentrant behavior seen here in the range $T_{\textit{Curie}}/T_C \leq 0.92$ is attributed to a delicate balance between the magnetic exchange energy and the condensation energy in the interfacial regions of the trilayer.