Effect of hydrostatic pressure on martensitic transition, magnetic and magnetocaloric properties of Mn rich Mn-Ni-Sn Heusler alloy

Abstract

I. INTRODUCTIONIn recent years Ni-Mn-Z (Z= Ga, Sn, Sb and In) Heusler alloys have attracted enormous attention owing to their multifunctional properties such as shape memory effect, giant magnetocaloric effect (MCE) and large magnetoresistance, which result from first order martensitic transition from austenite phase to martensite phase [1][2][3] . Among these properties, MCE is the most prominent as materials showing large MCE near room temperature (RT) are being considered as promising candidates for solid state cooling technology . Magnetic and magnetocaloric properties of these alloys are strongly influenced by Mn-Mn exchange interaction, which can be altered by either chemical substitution or applying pressure . Recently effect of pressure on magnetic and magnetocaloric properties of many Ni rich Ni-Mn-Z alloys have been reported [4][5] . However, no such reports are available on Mn rich Mn-Ni-Z (Z= Ga, Sn and In) Heusler alloys . In present study, we have investigated the effect of hydrostatic pressure on martensitic transition, magnetic and magnetocaloric properties of Mn rich Mn 50 Ni 41 Sn 9 Heusler alloy . II. EXPERIMENTAL DETAILSPolycrystalline sample of Mn 50 Ni 41 Sn 9 alloy was prepared by arc melting method . RT x-ray diffraction pattern shows tetragonal structure with lattice parameters as a= b= 3 .86 Å and c= 6 .59 Å (as reported in our previous work) [6] . The magnetization measurements at different applied pressures (P) have been performed using a superconducting quantum interference device magnetometer attached with a Cu-Be clamp type pressure cell with a maximum pressure of 10 .4 kbar . Fig . 1 shows the temperature dependence of magnetization (M vs . T curves) for Mn 50 Ni 41 Sn 9 alloy measured at 100 Oe field in ZFC and FC modes, with different applied hydrostatic pressures . Inset of Fig . 1 shows M vs . T curves with an expanded scale (in martensitic transition region), for better clarity . The alloy undergoes martensitic transition with a sudden decrease in magnetization at ~ RT, which corresponds to martensitic start temperatures (M S ) and attains its minimum value at ~ 277 K, which is the martensitic finish temperature (M f ) . With the further decrease of temperature, a splitting between ZFC and FC curves has been observed, which becomes more pronounced with lowering the temperature . This splitting is attributed to the coexistence of AFM and FM exchange interactions present in the alloy . It is clear from figure that, martensitic transition temperature (M S or M f ) increases with increase in pressure, which is attributed to stabilization of martensite phase, as M S ~ 299 K for P = 0 kbar and increases to M S ~ 339 K for P = 10 .4 kbar .Unlike the effect of pressure, effect of applied magnetic field on martensitic transition temperature (as observed from the M vs . T curves, data not shown here), shows a decrease in martensitic transition temperature with applied field, which is attributed to the stabilization of austenite phase . The effect of hydrostatic pressure on MCE has been ...