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Magnetic and magnetotransport behavior of RFe5Al7 (R= Gd and Dy): Observation of re-entrant inverse-magnetocaloric phenomenon and asymmetric magnetoresistance behavior

We have compared and contrasted magnetic, magnetocaloric and magnetoresistive properties of Gd and Dy members of the rare-earth (R) series RFe5Al7, crystallizing in ThMn12 structure, known to order antiferromagnetically. Among other observations, we would like to emphasize on the following novel findings: (i) There are multiple sign-crossovers in the temperature (T) dependence of isothermal entropy change (DeltaS) in the case of Dy compound; in addition to nil DeltaS at the magnetic compensation point known for two-magnetic-sublattice systems, there is an additional sign-crossover at low temperatures, as though there is a re-entrant inverse magnetocaloric phenomenon. Corresponding sign reversals could also be observed in the magnetoresistance data. (ii) The plots of magnetoresistance versus magnetic field are found to be highly asymmetric with the reversal of the direction of magnetic-field (H) well below TN for both compounds, similar to that known for an antiferromagnetic tunnel junctions. We attribute these to subtle changes in spin orientations of R and Fe moments induced by T and H.