Effect of Small Fe Content on the Structure, Magnetic and Magnetocaloric Properties of SmNiFe ( x = 0; 0.3 and 0.8) Intermetallic Compounds.

The SmNiFe ( x = 0; 0.3 and 0.8) were synthesized by arc melting and annealed at 1073 K for 1 week. The Rietveld refinement showed that these compounds crystallize in the PuNi-type structure ( $R\bar 3m$ -Space group) and the substitution of nickel by iron leads to an increase of the unit cell volume. The Curie temperature (T) of the SmNiFe ( x = 0; 0.3 and 0.8) samples increases from 60 K for SmNi to 230 K for SmNiFe, the enhancement of T is ruled by electronic and magnetovolumic effects. All the samples exhibit a second-order magnetic phase transition at Curie temperature T. The magnetic entropy change Δ S was estimated from isothermal magnetization curves and it decreases with the increase of Fe content from 2.3 J/kg.K ( x = 0) to 0.6 J/kg.K ( x = 0.8) at 50 kOe. The critical properties of SmNiFe (as an example) intermetallic compound at the ferromagnetic-paramagnetic (FM-PM) transition have been analyzed. The estimated critical exponents derived from the magnetic data using various methods such as modified Arrott plot, Kouvel-Fisher method and critical magnetization isotherms M( T , H). The critical exponent values for the material are in a close agreement with those predicted for the mean-field theory. The reason for this behavior may be long-range interactions between spins in this system. [ABSTRACT FROM AUTHOR]