Effect Of Doping On The Magnetocaloric Effect Of Mn-based Compounds

In recent years,energy consumption has been increasing.Among them,15% of energy consumption comes from the refrigeration sector,especially household appliances such as air conditioners and refrigerators.They are traditional refrigeration technologies that use Freon as a refrigerant,and they cause a lot of ozone destruction,so there is an urgent need for a new refrigeration technology to replace the traditional refrigeration technology.At present,magnetic refrigeration is one of the most promising refrigeration technologies that to replace traditional refrigeration technology.It has the advantages of low power consumption,low noise,environment friendly and pollution-free.Furthermore,Mn-based magnetic refrigeration materials have Magnetic phase transitions and large magnetocaloric effects are of concern.In this paper,Mn Co Ge1-x Sbx(x = 0,0.01,0.03,0.05,0.07)and(Mn Co Si)1-x(Fe2Ge)x(x = 0,0.1,0.15,0.2,0.25)alloys were synthesized by electric arc furnace melting..The main results obtained by systematically studying their crystal structure,magnetic and magnetocaloric effects are as follows:(1)Sb element doping and high temperature annealing of Mn Co Ge alloy can transform it from orthogonal martensite to hexagonal austenite,and effectively reduce the Curie temperature of the alloy.The Maxwell equation and the isothermal magnetization curve of the sample were used to calculate the magnetic entropy curve of the sample.It was found that in the Mn Co Ge1-x Sbx series alloy,the entropy change of the alloy was the largest when x = 0.1.When the applied magnetic field range was 0-5T,the isothermal magnetism of the alloy was The entropy change reached 7.3 J / kg K at 310 K Curie temperature.According to the analysis of Arrott diagrams,they all have second-order magnetic phase transition characteristics.Combined with the magnetocaloric curve analysis,they have very small thermal hysteresis and magnetic hysteresis,so they are excellent magnetic refrigeration materials.(2)For(Mn Co Si)1-x(Fe2Ge)x alloys,doping the Fe2 Ge with a stable hexagonal structure into the Mn Co Si alloy can also change its crystal structure.When x = 0.2,the alloy changes from orthogonal martensite to hexagonal austenite.At the same time,a small amount of Fe2Ge(x = 0.1)can be used to change magnetic properties of Mn Co Si alloy from antiferromagnetic to ferromagnetic,And as the doping amount of Fe2 Ge increases,the Curie temperature of the(Mn Co Si)1-x(Fe2Ge)x alloy also decreases significantly.In particular,the thermomagnetic curves of Mn Co Si alloy under different magnetic field conditions show that the temperature region occupied by the ferromagnetic phase of Mn Co Si increases with increasing magnetic field.(Mn Co Si)1-x(Fe2Ge)x series alloys with the same crystal structure have an increase in the magnetic entropy value of the alloy as x increases.The largest change in magnetic entropy in this series of alloys is at x = 0.15.For the corresponding alloy,under the magnetic field change of 0-2.5 T,the isothermal magnetic entropy change of the alloy reaches 1.78 J / kg K at the Curie temperature of 401 K.At the same time,the Arrott diagram analysis found that this series of alloys(except Mn Co Si alloys)are excellent magnetic refrigeration materials with second-order magnetic phase transitions.According to their magnetocaloric curves,it is known that their thermal hysteresis and hysteresis are very small,which is beneficial Their next application in practice.