Unconventional critical behavior of the magnetic refrigerant system Er 0.98 □ 0.02 Co 2 around its ferromagnetic-paramagnetic transition
Year: 2020
Type: article
Abstract: Magnetic refrigeration is a promising energy efficient and environmentally friendly refrigeration technology. The major problem in magnetic refrigeration is to find working materials with a large magnetocaloric effect (MCE) in different temperatures regions. MCE is the reversible temperature change of a magnetic materials upon the application or removal of a magnetic field. Nanoscale magnetic materials are good candidates for magnetic refrigeration due to a presence of a large MCE in the superparamagnetic system and reduced hysteresis losses. The critical behavior of Er 0.98 □ 0.02 Co 2 intermetallic system has been investigated via isothermal magnetizations around its ferromagnetic-paramagnetic (FM-PM) transition at Curie temperature T C = 62 K. This study was performed through different methods; Arrott-Noakes technique, Kouvel-Fisher analysis, and critical isotherms procedure. All these models could not explain the behavior of the studied system, which suggest that it belongs to an unconventional critical behavior. The critical exponents of the magnetization β , for the temperature dependence of the spontaneous magnetization below Curie Temperature (T C ), and γ for the magnetic susceptibility, and δ for the magnetic isotherm at T C were calculated. Based on Modified Arrott plots; Er 0.98 □ 0.02 Co 2 gives T C = 62.57 K ± 0.01 K with β = 0.68 ± 0.005 and T C = 62.59 K ± 0.01 K with γ = 0.88 ± 0.008. Using Kouvel-Fisher technique, we get T C = 62.66 K ± 0.06 K with β = 0.71 ± 0.01 and T C = 62.54 K ± 0.02 K with γ = 0.90 ± 0.06. The extracted value of δ from the critical isotherms and the Widom scaling relation are so close confirming that the obtained critical exponents are suitable and accurate within experimental error values. With 536.45 J kg −1 at 5 T of relative cooling power, Er 0.98 □ 0.02 Co 2 is very promising as magnetic refrigerant.
Source: Physica Scripta
Language: English
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W3008669264