Exchange bias and magnetothermal properties in Fe@Mn nanocomposites

We have studied the Exchange Bias (EB) effect in nanocomposite films consisting of Fe nanoparticles (mean size ∼1.9 nm) embedded in an antiferromagnetic Mn matrix. They were produced by co-deposition through a gas aggregation cluster source and molecular beam epitaxy and have different Fe volume filling fractions (2.2% and 24.8%). The exchange field, higher in the sample with higher Fe concentration (at T=5 K, H_ex∼460 Oe for 24.8% and ∼310 Oe for 2.2% ), in both the samples decreases with increasing T, finally disappearing at T∼40 K. The EB properties have been studied in conjunction with results on the thermal dependence of the magnetic coercivity, zero-field-cooled and field-cooled magnetization and thermoremanence. The different Fe content strongly affects the magnetothermal properties, featuring superparamagnetic relaxation in the diluted sample and a reentrant ferromagnet-type transition in the concentrated one. Hence, the EB properties of the two samples have been discussed in consideration of such peculiarities of the magnetic behavior and highlighting the role of the Mn matrix.