Magnetic and magnetocaloric properties of Py/Gd/CoFe/IrMn stacks

We explore whether it is possible to enhance the magnetocaloric effect (MCE) in layered systems, where a refrigerant (weak ferromagnet) is sandwiched by strong ferromagnets, by magnetizing the spacer with the effective field that results from its exchange coupling to the surroundings. Temperature variation around the Curie point of the spacer (T_C) leads to a change in interlayer coupling between strongly ferromagnetic surroundings, which manifests in increasing the switching field and/or the coercivity of the softer from the surroundings. In order to verify the hypothesis above, we have prepared layered stacks of Py(10 nm)/Gd(x nm)/Co₉₀Fe₁₀(7 nm)/Ir₂₀Mn₈₀(15 nm) (Py = Ni₈₀Fe₂₀ is permalloy) with the Gd spacer in thickness varied from x = 20 nm to x = 5 nm. In this system we clarified how the magnetization switching in the Py layer was sensitive to temperature varied in the range between 300 K and 50 K. We have found that strong enough exchange between the Py and Gd layers emerges only at low temperatures (T < 100 K) which are far from T_C. This feature provides an understanding of the observed magnetocaloric properties of the system under study.