Estudo das propriedades magnéticas e magnetocalóricas dos sistemas RCoSn (R = Dy, Ho e Er) e RNiSi (R = Nd, Tb e Dy)

Abstract

In this study, structural, magnetic and magnetocaloric properties of RCoSn (R = Dy, Ho and Er) and RNiSi (R = Nd, Tb and Dy) intermetallic compounds series were investigated. The samples were synthesized by arc melting under argon atmosphere. X-ray diffraction (XRD) analysis by Rietveld method confirm the desired crystalline structure and provide the sample unit cell parameters. Magnetization measurements for RCoSn samples showed antiferromagnetic ordering around 10 K, 7.9 K and 5 K, respectively for R=Dy, Ho and Er. An additional phase transition at Tt = 5 K and 4 K was observed for DyCoSn and HoCoSn, respectively, and a transition to spin-glass-like state for ErCoSn in Tf = 2.4 K. Two antiferromagnetic phase transitions were also observed for RNiSi series at TN = 6.4 K and Tt = 3.13 K for R=Nd, TN = 15.3 K and Tt = 3.5 K for R=Tb, and, TN = 8 K and Tt = 5 K for R=Dy. External magnetic field applied in RCoSn and RNiSi compounds induces metamagnetic transitions below TN. However, the magnetic moment values at T = 2 K and H = 50 kOe (50kOe) were lower both than the respective estimate values saturated (MS) and effective magnetic moment (eff). The difference between 50kOe and MS can be an indicative that not all antiparallel sub-lattice spins rotates toward the external magnetic field or presence of high magnetocrystalline anisotropy can be reason for the polycrystalline sample to reach the maximum value expected for free ion. The magnetocaloric effect (MCE) of studied compounds was evaluated through the isothermal magnetic entropy change (-SM). For RCoSn series, the maximum values of -SM (-SMmax) and relative cooling power (RCP) were, respectively, 10.2 J/kgK and 251.36 J/kg for DyCoSn, 10.48 J/kgK and 227,19 J/kg for HoCoSn, and 16.22 J/kgK and 326,8 J/kg1 for ErCoSn in a magnetic field variation (H) of 50 kOe. The -SMmax and RCP values found for RNiSi series were respectively, 3.14 J/kgK and 39.26 J/kg, 6.44 J/kgK and 162.17 J/kg and 6.82 J/kgK and RCP = 146.1 J/kg for R=Nd, Tb, and Dy, in H = 50 kOe. These values are comparable or even bigger than those reported in literature for others magnetocaloric compounds, in the same temperature range. The obtained results indicate that the compounds studied here presented interesting characteristics for magnetic refrigeration application in the cryogenic temperature range.