Magnetic Properties And Magnetocaloric Effects In Mn（Fe,Ni）（Si,Al） Compounds

The MnMX series compounds exhibit a magneto-structural phase transition and lead to the giant magnetocaloric effect,which has attracted extensive attention.Nevertheless,its magnetocaloric effect performance needs to be further regulated and optimized.In this work,the ratio of M and X in the MnMX series of compounds is regulated,and the crystal structure and magnetic transition are analyzed.Through a series of ratios of fixed elements,the synthesis condition is optimized,the crystal structure is analyzed,the transition temperature is regulated,and the magnetocaloric effect is studied;the ribbons were prepared by the melt-spin method,and the crystal structure and phase characteristics of ribbons were studied and analyzed.The main research are summarized as follows:1.Structural characterization of as-cast MnFe_1-xNi_xSi_0.94Al_0.06（x=0.35-0.50）series compounds and quenched at 1100℃Mn Fe_0.6Ni_0.4Si_1-xAl_x series compounds prepared by arc-melting.Mn Fe_1-xNi_xSi_0.94Al_0.06series samples mainly form Ti Ni Si-type and Ni₂In-type structure,mixed with a small amount of Mn₅Si₃-type phase.With Ni content increasing,the Curie temperatures of the compounds are 133,168,182 and 330 K,respectively.Mn Fe_0.6Ni_0.4Si_1-xAl_x（x=0-0.08）series samples all form Ti Ni Si-type structures for x<0.06,and two phase coexist at x=0.06,The sample with x=0.08 has a single Ni₂In-type structure.With the increase of Al content,the Curie temperature of this series of compounds gradually decreased.The results show that the alloys exhibit magneto-structural coupling for 0.060.53Ni_0.47Si_1-xAl_x（x=0.04,0.05,0.06）series compounds prepared by arc melting and Mn Fe_0.53Ni_0.47Si_0.94Al_0.06 samples synthesized under different conditions.The Mn Fe_0.53Ni_0.47Si_1-xAl_x series compounds are crystallized with Ti Ni Si-type structure and Ni₂In-type structure.The Curie temperatures of the samples are 317,313 and 309 K,respectively.The samples with x=0.06 have a smaller thermal hysteresis,and the magnetic phase transition is more rapid.For Mn Fe_0.53Ni_0.47Si_0.94Al_0.06 compound,the as-cast samples show the coexistence of Ti Ni Si-type and Ni₂In-type structures.The compound quenched by 1100℃ exhibits an almost single Ni₂In structure.Compared with as-cast and 1100℃ heat treatment,the samples heat-treated at 900℃ and quenched show the three-phase coexistence of Ti Ni Si-type,Ni₂In-type structure and Mn₅Si₃-type structure.The as-cast sample and the sample quenched by 1100℃ exhibited ferromagnetic behavior,while the sample quenched by 900℃ did not show any sign of ferromagnetic order.The as-cast samples exhibit a first-order ferromagnetic transition around 310 K with a small thermal hysteresis.The sample quenched at 1100℃ shows a relatively rapid ferromagnetic transition,T_C=190 K with a large thermal hysteresis of 23K at heating.The maximum isothermal magnetic entropy change is 3.8 J kg^-1 K^-1 under the magnetic field change from 0 to 3 T.3.The MnFe_0.6Ni_0.4Si_1-xAl_x（x=0.04-0.08）ribbons and the Mn Fe_0.53Ni_0.47Si_1-xAl_x（x=0.05-0.07）ribbons prepared by the melt-spin method were characterized by their structure and magnetic properties.Mn Fe_0.6Ni_0.4Si_0.96Al_0.04 ribbons were prepared at different rates.XRD analysis shows that this series compounds are all crystallized with Ni₂In-type structure with a small part of amorphous composition,Curie temperature is around 155 K,and there is no thermal hysteresis.The Mn Fe_0.6Ni_0.4Si_0.96Al_0.04 ribbons prepared at 20 rps and 60 rps rates were kept at 700℃ for 15 minutes and quenched in water.This series of thin ribbons are crystallized with Ti Ni Si-type,Ni₂In-type and Mn₅Si₃-type structure.The magnetic transition of this series ribbons is not obvious,and there is no thermal hysteresis.The Mn Fe_0.6Ni_0.4Si_1-xAl_xribbons prepared at50 rps form a Ni₂In-type structure with a small amount of amorphous components.With the increase of Al content,the Curie temperature are 157,138,132,128 K,respectively.There is no thermal hysteresis.The ribbons with x=0.06,0.07 and 0.08 kept at 1000℃ for 30 minutes and quenched in water were all crystallized with Ni₂In hexagonal structure,and the ribbon sample with x=0.04 is mainly crystallized in the Ni₂In-type structure,with a small amount of Ti Ni Si-type phase.The Mn Fe_0.53Ni_0.47Si_1-xAl_x ribbons prepared at 50 rps were kept at 1100℃ for 1 h and quenched in water.Ribbons with x=0.05、0.06 crystallize with Ni₂In-type and Ti Ni Si-type structure,and the ribbon with x=0.07 is Ni₂In-type structure.At x=0.05,the Curie temperature T_C of the ribbon sample is 316 K.For the sample with x=0.06 two phases coexist,magnetic transitions appear at 170 K and 266 K,and there is a large thermal hysteresis.A smoother transition occurs at 151 K and 248 K for x=0.04.The results show that the ribbons of Mn Fe_0.53Ni_0.47Si0.₉₄Al_0.06 undergo a magnetic transition near room temperature,but there is a large thermal hysteresis.The results show that different preparation processes have different effects on the structure formation and magnetic properties of this series of compounds.The magneto-structural coupling and the large magnetocaloric effect can be obtained through the control and optimization of the composition and preparation process.