Magnetic properties of the complex concentrated alloy system CoFeNi0.5Cr0.5Alx

Abstract

We study the change in magnetisation with paramagnetic Al addition in the CoFeNi 0.5 cr 0.5-Al x (x: 0, 0.5, 1, and 1.5) complex concentrated alloy. The compositions were developed utilising the Mulliken electronegativity and d-electron/atom ratio. Spherical FeCr rich nanoprecipitates are observed for X: 1.0 and 1.5 in an AlCoNi-rich matrix. A ~ 5 × increase in magnetisation (from 22 to 96 Am 2 /kg) coincides with this nanoprecipitate formation-the main magnetic contribution is determined to be from FeCr nanoprecipitates. The magnetisation increase is strange as paramagnetic Al addition dilutes the ferromagnetic Fe/Co/Ni additions. In this paper we discuss the magnetic and structural characterisation of the cofeni 0.5 cr 0.5-Al x composition and attempt to relate it to the interfacial energy. The innovation of new materials has been deemed to be the key topic for development of new technologies in our modern world. For alloys, the traditional approach has been to consider the effect of multiple dilute additions to a larger alloy matrix. New complex concentrated alloys (CCAs), which are near-equimolar multiple element alloys (> 3) challenge this view and have pushed alloy research towards the centre of phase diagrams 1,2. Multiple alloying components mean that they can possess large property permutations owing to the vast compositional space that they cover. Considerable work has been done on understanding how compositionalstructure affects mechanical properties. However, their functional properties are rarely the primary focus. As the base elements of CCAs are often CoFeNi (which is a known soft magnetic alloy), this can provide a basis for alloy design 1-5. Our motivation in this work is to therefore investigate the potential of CCAs as soft magnetic materials.

Study of dual-phase functionalisation of NiCoFeCr-Alx multicomponent alloys for the enhancement of magnetic properties and magneto-caloric effect

“…Both samples show a double magnetic transition. The transitions will be referred to as low temperature transition (LTT) and high temperature transition (HTT) where, LTT < 700 K (AlNiCo-rich matrix) and HTT > 800 K (FeCr-rich NPs) in both samples following previous analysis [22]. This is in agreement with the M(H,T) data (Fig.…”

“…We recently reported on the FeCr NPs phase segregation within AlNiCo rich matrix for CoFeNi0.5Cr0.5 with Al addition (CoFeNi0.5Cr0.5-Alx, x = 0.0, 0.5, 1.0 and 1.5) [22]. The NPs-matrix segregation is driven by the addition of Al (Fig.…”

“…The FeCr-rich phase, TC HTT decreases with increasing Al concentration (Al1.0 →Al1.5). We previously identified two possible reasons for this: 1) The phase is not purely FeCr, but there is a small change in the stoichiometry within the nanoparticles and 2) The size of the FeCr grains/particles decreases with increasing Al concentration and this causes the decrease in the TC [22]. We also find that differences in the shape and size of the HTT transition can be linked to the NPs size: After the completed HTT (μ0H = 25 mT) Al1.5 sample sees a jump in magnetisation of about 3 Am 2 kg -1 , which is less than the half of the jump of 7 Am 2 kg -1 observed in Al1.0 sample.…”

“…Thus, the FM-NPs account for the majority of the magnetism of the system. LTT dependence on stoichiometric composition of the matrix was discussed in [22]. whilst ΔM(Al1.5, 1.0 T, M(700K)-M(300K)) = 46 Am 2 kg -1 .…”

“…In the present contribution we expand on preliminary results found in [22] where the FeCr-rich nanoparticles segregation dependence on Al addition in the CoFeNi0.5Cr0.5Alx system were systematically studied. For the current research, we investigate the impact on the magnetic and magneto-caloric properties of the functionalized CoFeNi0.5Cr0.5Alx system.…”