Effect of the FeB Impurity on the Magnetic Properties of the Intermetallic Compound AlFe 2 B 2
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Effect of the FeB Impurity on the Magnetic Properties of the Intermetallic Compound AlFe2 B2 J. W. Lee and Chunghee Nam∗ Department of Photonics and Sensors, and Department of Electrical and Electronic Engineering, Hannam University, Daejeon 34430, Korea (Received 14 November 2019; revised 4 December 2019; accepted 10 December 2019) The effect of FeB impurities in AlFe2 B2 on its magnetic and magnetocaloric properties is studied herein. Intermetallic AlFe2 B2 was synthesized by using conventional arc-melting, and the paramagnetic Al13 Fe4 impurity was removed by using an acid treatment followed by annealing. A structural analysis via powder X-ray diffraction showed that the amount of FeB impurity depended on the acid concentration during the acid treatment. The magnetic analysis showed that the Curie temperature (TC ) increased from 302 to 306 K as the amount of the ferromagnetic phase of the FeB impurity in AlFe2 B2 increased. In addition, residual magnetization was observed temperatures above the TC of AlFe2 B2 due to the presence of FeB. The maximum magnetic entropy changes were 9.89 and 6.95 J/kg·K for AlFe2 B2 samples with and without FeB impurities, respectively. Keywords: Magnetocaloric effects, Fe-based alloy, Magnetic impurity DOI: 10.3938/jkps.77.824
I. INTRODUCTION
The magnetocaloric effect (MCE) has been proposed as an alternative refrigerant to gas refrigerant since the introduction of giant MCE Gd5 Si2 Ge2 in 1997 by Pecharsky and Gschneidner [1]. For current gas refrigerant cooling technology, problems such as environmental pollution, noise, and low efficiency must be overcome. Materials with the MCE are candidates for solving problems associated with gas refrigerants. The MCE originates from the thermodynamic characteristics that cause the heating or cooling of magnetic materials when a magnetic field is applied. For refrigeration, the cooling mechanism operates through the adiabatic demagnetization of materials with the MCE [2]. Such materials can be classified as first-order magnetic phase transition (FOMT) or second-order magnetic phase transition (SOMT) materials. Conventional FOMT materials typically exhibit a high magnetic entropy change (−ΔS). MnFe(P1−x Asx ) [3], MnAs [4], Heusler alloys [5], and LaFeSi [6] have been widely studied as examples of this phenomenon. However, problems with a narrow operating temperature range and high hysteresis loss persist for FOMT materials. The use of SOMT materials is a simple method to overcome the problems associated with FOMT materials; however, the former usually results in low a −ΔS, what is one of the main factors that determine MCE efficiency. Increasing the −ΔS for SOMT materials can ∗ E-mail:
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pISSN:0374-4884/eISSN:1976-8524
be achieved by doping [7–9], hydrogenation [10,11], and structural control [12,13]. The ternary intermetallic compound AlFe2 B2 has been developed as a novel SOMT material with the MCE and a Curie temperature (TC ) of approximately 300 K [14]. AlFe2 B2 has a structure wherein Al atoms separate the two-dimensional FeB lay
