Structure and magnetocaloric properties of Ni-Mn-Z (Z = Ga, Sn, In) Heusler alloys and MnAs compounds in high magnetic fields

QUICK INFORMATION
Type
Seminar
Start Date
04-03-2020 14:30
End Date
04-03-2020 15:30
Location
Room 337, Central Building
Speaker's name
Elvina DILMIEVA
Speaker's institute
Laboratory of magnetic phenomena in microelectronics of the Kotelnikov Institute of Radio Engineering and Electronics of RAS, Moscow, RUSSIA
Contact name
Eva Jahn
Host name
A. Rogalev
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Materials with a 1-st order magnetostructural phase transition (MPT), in which there is a strong interaction between the crystal lattice and magnetic freedom degrees, are particular interest [1]. In MPT, the relationship of magnetic and structural transitions leads to the appearance of various effects, such as giant magnetoresistance, magnetocaloric effect [2], and etc. Of the currently known Heusler alloys and the MnAs compound are of great interest, because have MPT temperatures near room temperature, which increases the application in the magnetic solid-state cooling field [3].

The study of the magnetocaloric effect (MCE) is interesting, both from the point of view of the magnetism physics and the solid state thermodynamics. MCE is a powerful and widely used tool for the study of MPTs, including their mechanisms. MCE is adiabatic temperature change (∆Tad) or isothermal heat generation/absorption (∆Q) of a magnetic material when an external magnetic field is applied to it. There are indirect and direct methods for MCE studying. Indirect methods are useful for the effective selection of promising magnetic materials, and they prevail in modern MCE studies. However, indirect methods are not free from potential errors, the it can reach up to 30% [4]. In works on MCE study by direct method, the most accessible magnetic fields up to 2 T are used mainly [5]. However, for such promising materials as Heusler alloys and MnAs compounds, a 2T magnetic field is not enough to full complete a 1-st order MPT, and, accordingly, to achieve a maximum value of ΔTad. Also it should be noted that, as a rule, ∆Q is determined indirectl, by calculating on the basis of the equation derived from the 2nd thermodynamics law, and the ratio using heat capacity data in a magnetic field, which entails the accumulation of systematic errors [6]. Therefore, a direct method has been proposed for studying ∆Tad and ∆Q in high magnetic fields up to 14 T and wide temperature range [7]. In this work, it will discuss the results of MCE studying for Ni-Mn-Z (Z = In, Ga, Sn) Heusler alloys and MnAs compounds in high magnetic fields, both from a fundamental point of view and applied.

In the MPT field, the contributions from the structural and magnetic subsystems are decisive for the MCE [8]. Therefore, a more detailed study of the crystal structure and magnetic properties directly in the MPT process induced by a magnetic field will make it possible to understand the nature of the subsystems interaction and their contributions to the MCE. The structure of Heusler alloys is studied using a variety of standard techniques, which, however, have difficulties in applying of high magnetic fields. Therefore, an original device and method were proposed for studying the structural transition in high magnetic fields [9]. With the help of this device, the evolution of a magnetoinduced martensitic twin structure in high magnetic fields for poly- and single-crystal Heusler alloys of the Ni-Mn-Ga, Ni-Mn-Sn series with direct and reverse MCE is studied. The features of the its evolution and effect on the MCE are established. The revealed features make it possible to take them into account when implementing effective thermodynamic cycles, such as the Carnot cycle.

[1] Planes, А. et.al., J. Phys.: Condens. Matter. 21 (23), 233201, 1-29 (2009).

[2] J. Lyubina,” J. Phys. D: Appl. Phys. 50, 053002 (2017).

[3] V.V. Khovailo, et.al., J. Appl. Phys. 9 (10), 8483-8485 (2003).

[4] V.K. Pecharsky // J. Appl. Phys. 86, 565–575 (1999).

[5] A.G. Gamzatov, et.al., Appl. Phys. Lett. 113 (17), 172406 (2018).

[6] X. Moya et.al., Nature Materials. 13, 439-450 (2014).

[7] Y.S. Koshkid'ko, et.al., JMMM. 433, 234-238 (2017).

[8] T. Gottschall, et.al., Appl. Phys. Lett. 106, 021901 (2015).

[9] E.T. Dilmieva, et.al., Bulletin Russ. Acad. Sci.: Phys. 81 (11), 1283-1288 (2017).

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