Investigation Of Magnetocaloric Effect On A Site And B Site Doping In Pervoskite Manganites

New and improved magnetocaloric materials are one of the cornerstonesin the development of room temperature magnetic refrigeration. Magnetocaloriceffect has been researched since1930’s, but has received enormous attention sincethe discovery of room temperature refrigerants. Perovskite manganite exhibits aseries of optical, electrical and magnetic properties due to its strong couplingbetween the intrinsic spin, lattice, orbital and charge degrees of freedom. Meanwhile,pervoskite manganite also appears excellent magnetoresistance, catalytic andmegnetocaloric effects. The pervoskite manganites have been paid much moreattention by researchers because of their amazing properties including chemicalstability, high resistivity, low cost, light weight, non-toxic, easy minimization etc.The most important two features are that pervoskite manganites can get relativelylarge magnetic entropy change in a low magnetic filed and that their Curietemperature can be tailored readily. However, they are suffering from several defectssuch as smaller magnetic entropy change compared with other alloys and the easychange in structure affected by magnetic properties. In this work, we will investigatethe structure, magnetic properties and magnetocaloric effect of A site and B sitesubstitutions. We also try to explore the method and mechanism of the enhancedmagnetic entropy change at room temperature in a low field. It is found thatpervoskite manganite can be used as an excellent candidate for room temperaturemagnetic refrigeration materials.In this paper, metallic element doping on A site of a series of Pr0.5Sr0.5-x(Ba, Ce,Bi)xMnO3(0≤x≤0.1) samples, which based on substrate of Pr0.5Sr0.5MnO3, areprepared by standard solid state sinter method. We can find that the type of allsamples shows second order phase transition, indicating that doping differentelements can not change the properties of substrate. The Curie temperature initiallyincreases and then drop with an increasing in doping contents. However, when Cedoping content increases,it will raise Curie temperature gradually. The highest valueof TCis310K, which is favor to application at room temperature. At the same time,the value of|SM|maxwith Pr0.5Sr0.4Ce0.1MnO3is1.93J kg-1K-1about50%of the Gd(3.8J kg-1K-1), which is regarded as a good candidate for room temperature refrigerant material.B site substitution of Pr0.5Sr0.5Mn1-x(Fe, Co)xO3(x=0,0.02,0.04,0.06and0.08)samples are also prepared by standard solid state sinter method. The samples aremeasured by XRD, SEM and EDX to detect the structure and surface, and magneticproperties are texted by VSM. We can find long range anti-ferromagnetic sampleswith Fe doping gradually vanish, and when doping content x=0.06the long rangeanti-ferromagnetic reappear. With increase of doing level, because charge of Fe3+donot participate in the hopping between Mn3+and Mn4+, which is equivalent to narrowthe one electron band-width and make the charge localized. Thus long-rangeCoulomb interaction is enhanced and subsequently long-range charge orderantiferromagnetic state emerges in a special doping level.