The peculiarities of structure and static magnetic properties of composites based on epoxy resins with microparticles of iron oxide FeOx, which are used as model materials for magnetic detection, have been investigated. The [FeNi/Cu]5/[Cu/[Cu/FeNi]5 film element with transverse magnetic anisotropy is used as a sensing element of the prototype of detector of weak magnetic fields operating on the basis of the magnetoimpedance (MI) effect. It is shown that there is a linear dependence of the specific magnetization on the concentration of microparticles in the range of 0–70 wt % despite notable differences in the structure of composites. Using the MI prototype of the weak field detector, a linear dependence of the change of the MI effect on the concentration of FeOx microparticles in the frequency range of 80–260 MHz is found. It is shown that the esigned composites and film elements based on permalloy are complementary in terms of their functional properties and can be used as a model pair for magnetic detection.