It can be seen that the squareS(S¼Mr/Ms whereMr denotes remanence and Msdenotes the saturation magnetization) of Ni@PA66 double-layer nanotubes is obviously higher than that of Ni nanotubes.S//¼0.15 for the Ni nanotubes andS//¼0.19 for the Ni@PA66 (“//” in S// where the symbol“//” denotes that the magneticfield direction is parallel to the axis of nanotubes).