Abstract
Near the point of equiatomic composition, both FeRh and FeCo bulk alloys exhibit a CsCl-type (B2) chemically ordered phase that is related to specific magnetic properties, namely a metamagnetic anti-ferromagnetic/ferromagnetic transition near room temperature for FeRh and a huge magnetic moment for the FeCo soft alloy. In this paper, we present the magnetic and structural properties of nanoparticles of less than 5 nm diameter embedded in an inert carbon matrix prepared by mass-selected low-energy cluster-beam deposition technique. We obtained a CsCl-type (B2) chemically ordered phase for annealed nanoalloys. Using different experimental measurements, we show how decreasing the size affects the magnetic properties. FeRh nanoparticles keep the ferromagnetic order at low temperature due to surface relaxation affecting the cell parameter. In the case of FeCo clusters, the environment drastically affects the intrinsic properties of this system by reducing the magnetization in comparison to the bulk.
Highlights
Magnetic bimetallic nanoparticles (NPs) are very attractive systems from a fundamental point of view and because of their various areas of use [1,2]
We present a comparative study performed on FeRh and FeCo nanocrystal assemblies prepared by massselected low-energy cluster-beam deposition (MS-LECBD) embedded in a carbon matrix
We have obtained completely opposite thermal evolutions for the magnetic moments in CsCl-type (B2) chemically ordered FeRh and FeCo nanocrystal assemblies prepared by MS-LECBD
Summary
Magnetic bimetallic nanoparticles (NPs) are very attractive systems from a fundamental point of view and because of their various areas of use [1,2]. The binary phase diagrams of bulk materials of iron and transition metals show a wide range of different properties, in particular magnetic properties [3]. Near the point of equiatomic composition, both FeRh and FeCo bulk alloys present a CsCl-type (B2) chemically ordered phase at room temperature (Figure 1) with the competition between several magnetic orderings for FeRh and a huge magnetic moment for soft FeCo according to the Slater–Pauling graph. We show how the competition between the stable bimetallic NPs structure and their chemical affinity with the environment affects their intrinsic magnetic properties compared to their bulk counterparts
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