Giant inverse magnetocaloric effect near room temperature in Co substituted NiMnSb Heusler alloys

Abstract

The effect of Co on the structural, magnetic and magnetocaloric effect (MCE) of Ni 50-x Co x Mn 38 Sb 12 (x=0,2,3,4,5) Heusler alloys was studied. Using x-ray diffraction, we show the evolution of the martensitic phase from the austenite phase. The martensitic transition temperature is found to decrease monotonically with Co concentration. Remarkable enhancement of MCE is observed near room temperature upon Co substitution. The maximum magnetic entropy change of 34 Jkg -1 K -1 was achieved in x=5 at 262 K in a field of 50 kOe and a value of 29 Jkg -1 K -1 found near room temperature. The significant increase in the magnetization associated with the reverse martensitic transition is responsible for the giant MCE in these compounds. Recently there has been a great interest in Ni-Mn based Heusler alloys because of the observation of first order martensitic transformation around room temperature. These alloys received a lot of attention for showing both magnetic shape memory effect and large magnetocaloric effect [6-8]. Among the Heusler alloys, the highest MCE has been reported in Ni 55 Mn 20 Ga 25 single crystals (∆S M = -86Jkg -1 K -1 in a field of 50kOe), which is due to the coincidence of first order structural transition and the magnetic transition [7]. Other materials showing promising MCE from the Ni-Mn family are Ni-Mn-Sn [9], Ni-Mn-In [10] and Ni 12]. All these alloys generally show inverse (negative) MCE, i.e., the entropy change is positive on applying the magnetic field. It is reported that Ni-Mn-Sb based Heusler alloys undergo first order magneto-structural transition from martensite phase (tetragonal or orthorhombic) to austenite phase (cubic), resulting

Inverse magnetocaloric effect in sol–gel derived nanosized cobalt ferrite

“…Hence, this can be termed an inverse MCE. There are reports wherein giant inverse MCE has been observed in alloys like NiMnSb Heusler alloys [28,29]. A positive entropy change has been recently reported in zinc ferrite nanoparticles [30].…”

Pressure induced magnetic and magnetocaloric properties in NiCoMnSb Heusler alloy

“…Recently, we have reported a large enhancement of MCE with Co substitution in NiMnSb. 18 In this paper, we report the effect of pressure on the magnetic and MC properties of Ni 50−x Co x Mn 38 Sb 12 . It was found that the substitution of Co for Ni reduces the martensitic transition temperature.…”

In-plane and out of plane magnetic properties in Ni46Co4Mn38Sb12 ribbons

“…[1][2][3] The magnetic properties in this system are mainly due to Mn magnetic moment as Ni moment is negligible. The Mn-Mn indirect exchange interaction (RKKY type) plays the key role behind the observed magnetic behavior in this system.…”

“…In the NiMnSb bulk system, MCE and MR properties has been studied extensively. 2,3,[5][6][7][8] Recently melt spinning technique has gained much attention as it produces strongly textured polycrystalline ribbons. There are various reports on crystallographically textured melt spun ribbons where magnetic anisotropy plays the vital role in determining the observed properties.…”

“…This composition has been chosen as the bulk alloy of this composition has been reported to show martensitic transition near room temperature. 2 Polycrystalline sample of Ni 46 Co 4 Mn 38 Sb 12 was prepared by arc melting in high purity argon atmosphere. The constituent elements were at least of 99.99% purity.…”