Magnetocaloric Effect Research Of Co_0.52Fe_0.48MnP Alloy Prepared By Various Methods

Orthogonal Mn-based alloys(such as MnCoSi,MnNiGe,and MnCoGe alloys)are a special class of magnetic functional materials.In this type of alloy,Mnatoms are the main carriers of magnetic moments,and the arrangement of magnetic moments is completely determined by the Mn-Mnspacing.The alloy appears antiferromagnetic when the distance is greater than the critical value,while the alloy exhibits ferromagnetism when the distance is greater than the critical value.In the above-mentioned orthogonal phase Mn-based alloy,the Mn-Mnspacing is just around this critical value,so the external energy(such as magnetic field)can effectively affect magnetic properties of the alloy and induce magnetic phase transitions.This magnetic phase transition is accompanied by a considerable reversible magnetocaloric effect and has potential application value in magnetic refrigerators.However,due to the orthogonal TiNiSi-hexagonal Ni₂In structural phase transition of this type of alloy that undergoes a large volume change at high temperature,the prepared alloys are usually cracked or powdered,which caused difficulties in machining and greatly reduced the practicality of the alloy.In order to solve this problem,it is feasible to eliminate the structural phase transition of the alloy to prepare a dense alloy sample.This paper starts from two perspectives to obtain a dense orthogonal phase Mn-based alloy.Through the improvement of the preparation scheme,a dense and textured(Fe,Co)MnP alloy is finally obtained.The alloy exhibits a magnetic phase transition similar to that of MnCoSi alloy,and has a large reversible magnetocaloric effect.The main results obtained in the paper are as follows:(1)In this paper,Mn_0.9Co_1.1Ge_1-xP_x alloy is selected as the research object.The effect of P on the crystal structure of the alloy is observed by increasing the doping amount of P.The introduction of P easily leads to the generation of orthogonal Co₂P phases.Although the Co₂P and TiNiSi phases have similar crystal structure,the introduction of Co₂P phases cannot increase the stability of the low-temperature TiNiSi phase,which approved that P has no contribution to increasing the structural phase transition temperature.(2)In this paper,(Fe,Co)MnP alloys were prepared based on different methods.A dense and textured(Fe,Co)MnP alloy was finally obtained by the combination of powder metallurgy,smelting and directional solidification,.Compared with MnCoSi,MnNiGe and MnCoGe alloys,(Fe,Co)MnP alloys has a stable orthogonal Co₂P structure.(3)Textured(Fe,Co)MnP alloy exhibits a"dual magnetic phase transition"induced by temperature and magnetic field.This special phase change has the advantages of small driving magnetic field and low thermal hysteresis.The maximum magnetocaloric effect of directionally solidified samples is 1.585 Jkg^-1K^-1(240 K,0-2 T),which is larger than the positive CoMnSi alloy(?S_M?0.2 Jkg^-1K^-1,0-2 T)and MnCoSi_1-xGe_x alloy(?S_M?1.1 Jkg^-1K^-1,0-2 T)under the same variable field.