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Entropy 2014, 16(9), 4992-5019;

Ab Initio and Monte Carlo Approaches For the Magnetocaloric Effect in Co- and In-Doped Ni-Mn-Ga Heusler Alloys

Chelyabinsk State University, Br. Kashirinykh 129, 454001 Chelyabinsk, Russia
National University of Science and Technology "MISiS", Leninskiy pr. 4, 119049 Moscow, Russia
University of Duisburg-Essen, Lotharstrasse 1, D-47048 Duisburg, Germany
Author to whom correspondence should be addressed.
Received: 25 August 2014 / Revised: 12 September 2014 / Accepted: 12 September 2014 / Published: 19 September 2014
(This article belongs to the Special Issue Entropy in Shape Memory Alloys)
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The complex magnetic and structural properties of Co-doped Ni-Mn-Ga Heusler alloys have been investigated by using a combination of first-principles calculations and classical Monte Carlo simulations. We have restricted the investigations to systems with 0, 5 and 9 at% Co. Ab initio calculations show the presence of the ferrimagnetic order of austenite and martensite depending on the composition, where the excess Mn atoms on Ga sites show reversed spin configurations. Stable ferrimagnetic martensite is found for systems with 0 (5) at% Co and a c=a ratio of 1.31 (1.28), respectively, leading to a strong competition of ferro- and antiferro-magnetic exchange interactions between nearest neighbor Mn atoms. The Monte Carlo simulations with ab initio exchange coupling constants as input parameters allow one to discuss the behavior at finite temperatures and to determine magnetic transition temperatures. The Curie temperature of austenite is found to increase with Co, while the Curie temperature of martensite decreases with increasing Co content. This behavior can be attributed to the stronger Co-Mn, Mn-Mn and Mn-Ni exchange coupling constants in austenite compared to the corresponding ones in martensite. The crossover from a direct to inverse magnetocaloric effect in Ni-Mn-Ga due to the substitution of Ni by Co leads to the appearance of a “paramagnetic gap” in the martensitic phase. Doping with In increases the magnetic jump at the martensitic transition temperature. The simulated magnetic and magnetocaloric properties of Co- and In-doped Ni-Mn-Ga alloys are in good qualitative agreement with the available experimental data. View Full-Text
Keywords: Heusler alloys; magnetocaloric effect; first-principles and Monte Carlo methods Heusler alloys; magnetocaloric effect; first-principles and Monte Carlo methods
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

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Sokolovskiy, V.; Grünebohm, A.; Buchelnikov, V.; Entel, P. Ab Initio and Monte Carlo Approaches For the Magnetocaloric Effect in Co- and In-Doped Ni-Mn-Ga Heusler Alloys. Entropy 2014, 16, 4992-5019.

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