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

We have studied the effect of phase separation on the magnetic and magneto-caloric properties of the CoFeNi0.5Cr0.5-Alx (x= 0.0, 1.0 and, 1.5) system. Results show that a collaborative behaviour amongst FeCr-rich segregated nanoparticles (NPs) increases the saturation magnetisation (Ms) whilst the Curie temperature (Tc) is controlled by the amount of added Al. With a strong ferromagnetic coupling between segregated FeCr-NPs, the CoFeNi0.5Cr0.5-Al1.0 sample shows the highest Ms (100 Am2kg-1) with an increase of 61% over the Al-free CoFeNi0.5Cr0.5 sample. It is argued that as the ferromagnetic interaction increases in a degenerated super-spin-glass like state of the NPs the field induced phase transition is broadened whilst the magnetic entropy decreases. In turn, the CoFeNi0.5Cr0.5-Al1.0 sample shows the highest refrigerant capacity (17.1 Jkg-1 at μ0ΔH = 1.0 T), and the smallest measured magnetic entropy change (ΔSmpeak = 0.22 Jkg-1K-1). We found that the enhanced magnetic and refrigerant capacity by mean of phase separation and NPs clustering are amongst the highest reported for the multi-component alloys being investigated for energy applications in the high temperature range.