Magnetocaloric effect in Ni-Mn-Ga and Ni-Co-Mn-In Heusler alloys
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1200-G07-03
Magnetocaloric effect in Ni-Mn-Ga and Ni-Co-Mn-In Heusler alloys Vasiliy Buchelnikov1, Sergey Taskaev1, Mikhail Drobosyuk1, Vladimir Sokolovskiy1, Viktor Koledov2, Vladimir Khovaylo3, Vladimir Shavrov2, Alexander Fediy1 1
Chelyabinsk State University, Br. Kashirinykh Str. 129, Chelyabinsk, 454001, Russia.
2
Institute of Radioengineering and Electronics of RAS, Mokhovaya Str. 11/7, Moscow, 125009,
Russia 3
National University of Science and Technology “MISiS”, Leninskiy Av. 4, Moscow 119049,
Russia
ABSTRACT The positive magnetocaloric effect (MCE) in the vicinity of the Curie point in Ni2+xMn1xGa
(x=0.33, 0.36, 0.39) Heusler alloys and the negative and positive MCE near the
metamagnetostructural (MMS) transition and the Curie point, respectively, in Ni45Co5Mn36.5In13.5 Heusler alloy has been measured by a direct method. For the magnetic field change ∆H = 2 T, the maximal adiabatic temperature change ∆Tad at the Curie point in Ni2+xMn1-xGa alloys is larger than 0.6 K. For Ni45Co5Mn36.5In13.5 alloy, the maximal value of ∆Tad = 1.68 K (for the same magnetic field change, ∆H = 2 T) is observed at the MMS phase transition temperature. INTRODUCTION The MCE is the ability of magnetic materials to heat up or cool down when placed in or removed from an external magnetic field [1,2]. It has great importance in the technology of magnetic refrigeration. The magnetic materials with large values of MCE can be applied as refrigerants in the magnetic cooling devices such as industrial and household refrigerators, air conditioners, heat pumps and other cooling devices. Recent experimental studies have shown that Ni-Mn-X (X=Ga, In, Sn, Sb) Heusler alloys are attractive for the application in magnetic refrigeration [3]. Moreover, these materials exhibit unique functional properties such as shape memory effect, giant magnetic-field-induced strains, and large magnetoresistance [3,4]. Both negative and positive MCE have experimentally been observed in Ni-Mn-X (X= In, Sn, Sb) Heusler alloys [3]. In case of the positive MCE, the adiabatic temperature change is positive (∆Tad > 0) whereas the magnetic entropy change is
negative (∆Sm < 0) when the applied magnetic field increases from H1 to H2. The positive MCE is observed near the magnetic phase transition (the Curie point) from a paramagnetic to a ferromagnetic state. In case of the negative MCE, the adiabatic temperature change is negative (∆Tad < 0) whereas the magnetic entropy change is positive (∆Sm > 0). Such effect is observed at coupled MMS phase transition, i.e. at the transition, for example, from a high-temperature ferromagnetic phase to a low-temperature antiferromagnetic (or paramagnetic, or mixed ferroantiferromagnetic) phase. In this work we study experimentally both positive and negative MCE in Ni2+xMn1-xGa (x=0.33, 0.36, 0.39) and Ni45Co5Mn36.5In13.5 Heusler compounds that undergo second-order magnetic phase transitions, second-order magnetic and first order MMS phase transitions, respectively.
EXPERIMENTAL DETAILS Polycrystalline ingots with Ni2+xMn
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