Investigation On Metamagnetic Transition And Magnetocaloric Effect In Mn₂Sb-based Alloys

In the past few decades,refrigeration based on the magnetocaloric effects(MCEs)with phase transformation had been proposed to be an environmentally friendly and efficient alternative compared with gas-compression-based technology.Much attentions have been paid to develop materials that exhibit giant magnetic entropy changes.Usually,Mn-based intermetallics possessed large moments per Mn atom and had been attractive due to the low cost and easy processing.Among them,tetragonal Cu2Sb-type Mn2Sb was one candidate.Since crystallographic structure was not changed before and after phase transformation,small thermal hysteresis was expected in Mn2Sb system,which was beneficial for applications.In recent years,there are many researches on Mn2Sb-based alloys due to their obvious advantages mentioned above.However,seldom reports have been carried out on the effects of doping element occupancy and hydrostatic pressure,high-magnetic-field effects and interstitial effects on metamagnetic transition and magnetocaloric effect in tetragonal Mn2Sb-based system.Thus,in this work,the influences of Ge occupations at Sb and Mn sites in Mn2Sb system,hydrostatic pressure on Mn2Sbo.95Geo.05 alloys,high-magnetic-field solidification on Mn1.8Cu0.2Sb alloys and B atoms,which are introduced into Mn1.95Cu0.05Sb benchmark alloy since Cu substitution for Mn causes the FIM-AFM phase transition,have been investigated.The effects of Ge occupations at Sb and Mn sites in Mn2Sb system had been re-examined along with the influence of hydrostatic pressure.The metamagnetic phase transition from ferrimagnetic(FRI)to antiferromagnetic(AFM)state was observed in Mn2Sb1-xGex(x=0.05,0.1,0.1 5)and(Mn1-yGey)2Sb(y=0.025,0.04)alloys.The phase transition temperature,Tt,was gradually increased with increased Ge substitution for both Sb and Mn,but slightly decreased under increased hydrostatic pressure in Mn2Sb0.95Ge0.05 alloy.Meanwhile,the slope of critical field as the function of temperature was reduced with increased hydrostatic pressure and Ge substitution amount in(Mn1-yGey)2Sb(y=0.025,0.04)alloys.For a field change of 7 T,the maximum of magnetic entropy changes of 6 J·kg-1·K-1 have been achieved in Mn2Sb0.95Ge0.05 alloy,which are gradually decreased by more Ge substitution and increased hydrostatic pressure.The tetragonal Cu2Sb-type Mn1.8Cu0.2Sb alloy was prepared by solidification under zero field and high magnetic field of 12 T.No thermal hysteresis was observed.High-magnetic-field(HMF)solidification led into c-axis texture in Mn1.8Cu0.2Sb alloy.Moreover,the severity of metamagnetic transformation in a Mn1.8Cu0.2Sb alloy was steepened and the resultant magnetic entropy change was enhanced.The exchange bias at low temperature was observed.Our work demonstrated the pronounced influences of HMF solidification on the crystallographic orientation,metamagnetic phase transformation and the magnetic exchange couplings.Mn1.95Cu0.05SbBx(x=0,0.06 and 0.1)alloys had been prepared and B interstitial effects on metamagnetic transition were studied.The metamagnetic transition temperature was reduced and thermal hysteresis was widened by higher B concentration.The saturation magnetization and the magnetic entropy change were increased by moderate amount of B addition.However,too high B composition led into the sluggish metamagnetic transition.By relating with crystallographic structure,our results further indicated that the electron density of the atoms at Mn? position plays critical role on influencing the metamagnetic transition in tetragonal Cu2Sb-type Mn1.95Cu0.05Sb alloys.