Study of Magnetocaloric Properties of Ni-Mn-X (X = Ga, In) Heusler Alloys by Monte Carlo Technique
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1200-G09-06
Study of Magnetocaloric Properties of Ni-Mn-X (X = Ga, In) Heusler Alloys by Monte Carlo Technique Vasiliy D. Buchelnikov1, Vladimir V. Sokolovskiy1,2, Sergey V. Taskaev1 and Peter Entel2 1 Chelyabinsk State University, Br. Kashirinykh str. 129, Chelyabinsk, 454001, Russia. 2 University of Duisburg-Essen, Lotharstr. 65, Duisburg, 470848, Germany. ABSTRACT Two theoretical Monte Carlo models have been presented for description of the positive and negative magnetocaloric effects of Heusler Ni-Mn-X (X = Ga, In) alloys undergoing first order coupled magnetostructural phase transition. For both models all quantities such as temperature dependence of the magnetic contribution to the total specific heat, magnetization and isothermal magnetic entropy change are in qualitative agreement with the available experimental data. INTRODUCTION The magnetocaloric effect (MCE) characterizing the adiabatic temperature change (∆T) and change of the magnetic part of the total entropy (∆Smag) upon applying an external magnetic field is the intrinsic property of any magnetic materials. There are two types of MCE (positive and negative) which are investigated experimentally in different magnetic materials. In the case of ferro – paramagnetic (FM – PM) phase transition we observe the positive MCE (∆Smag < 0 and ∆T > 0) and the case of antiferro – ferromagnetic (AF – FM) phase transition shows us the negative one (∆Smag > 0 and ∆T < 0) [1]. Nowadays many groups of experimental and theoretical researches of the magnetocaloric properties of ferromagnetic compounds are focused on the possibility to apply these materials in the technology of magnetic refrigeration near room temperature. Some of recently reported compounds undergoing first order magnetic phase transitions and exhibiting giant positive MCE are Gd5(Si1-xGex)4, MnFeP1-xAsx and La(FexSi1-x)13 [1]. The negative MCE is experimentally observed, for example, in Fe0.49Rh0.51 alloy [2]. Recent scientific reports have shown that among the Mn-based intermetallic compounds, Heusler Ni-Mn-X (X = Ga, In, Sn, Sb) alloys are of high technological interest in respect to their magnetocaloric properties [3-5]. In these alloys both positive and negative MCE (like in Gd-GeSi, Mn-As and La-Fe-Si) are observed experimentally. The negative MCE observes in Ni-Mn-X (X = In, Sn, Sb) at the temperature of coupled magnetostructural phase transition from the mixed FM – AF austenite to the FM martensite [4, 5] phase. The positive MCE undergoes in the austenite phase during FM – PM phase transition for Ni-Mn-X (X = In, Sn, Sb) compounds, also it is possible to observe it in the area of coupled PM austenite – FM martensite phase transition for Ni-Mn-Ga alloys [3]. In this work we propose theoretical investigation of the positive and negative MCE and magnetic properties of Ni-Mn-X (X = Ga, In, Sn, Sb) alloys using classical Monte Carlo method based on simple and realistic models of the crystal lattice.
THEORETICAL MODELS In the proposed model we use a simple cubic lattice with periodic boundary condi
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