Magnetic Properties,Magnetocaloric Effect And Transport Of Mn₅Ge₃ And Mn₃P

Refrigeration technology has become an indispensable part of modern people’s life.With the development of society and the urgent need to save energy for environmental protection.Novel refrigeration technologies are urgently needed to replace the traditional refrigeration methods.The characteristics of the magnetocaloric effect,such as environment friendliness and energy saving,high efficiency and stability,are all of great significance for both theory research and application.Electrical transport of metal and compounds has been focused as an important property of physics for a long time.Mn₅Ge₃ and Mn₃P single crystals were grown by flux method,the structure,magnetic properties,magnetocaloric effect,transport properties and special heat were investigated by x-ray diffraction（XRD）,scanning electron microscope（SEM）,energy disperse spectroscopy（EDS）,super quantum interference device magnetometer（SQUID）and physical property measurement system（PPMS）.The main results are as follows.Hexagonal structural Mn₅Ge₃ single crystals were grown by flux method with Sn flux.A second-order transition from paramagnetic to ferromagnetic state occurrs at 295 K,effective magnetization of Mn₅Ge₃ is 4.12 μB/Mn at 10 K.The easy axis is c direction and the hard axis is in the ab plane.Magnetic anisotropy constant K1 decreases with the temperature increasing.When the temperature is closed to Tc,the anisotropy field HA close to zero.The magnetic entropy of Mn₅Ge₃ poly crystals is-6.37 J/kg K.When the field equal to the anisotropy field and the field direction rotating from c axis to ab plane,the biggest rotating-magnetic entropy was obtained.With the temperature increasing the rotating magnetic entropy increased with field from 0 to 10 kOe.In comparison,with the temperature increasing the rotating magnetic entropy decreased with the field from 10 to 50 kOe.The maximum rotating magnetic entropy is-0.851 J/kg K。The transport property of Mn₅Ge₃ shows metallic conductivity.Mn₅Ge₃ has an inverse magnetoresistance near TC.Tetragonal structural Mn₃P single crystals were grown by flux method with Mn,P eutectic as the flux.A transition from paramagnetic to ferromagnetic state occurs at 28 K.A nonmonotonous dependence of its field cooling curves occurs from 26 to 30 K.The easy direction was determined to be c axis.An abnormal electron transport phenomenon occurs at 26 K which is adjoin with the magnetic-transition temperature.The specific heat of Mn₃P shows two peaks at the same temperature region either.It might be a new phase transition near the magnetic transition temperature.The attribution of the abnormal phase transition is still under further investigation.