Multiple magnetic transitions and the magnetocaloric effect in Gd1-xSmxMn2Ge2 compounds

The magnetic and magnetocaloric properties of polycrystalline samples of Gd1- xSmxMn2Ge2 have been studied. All the compounds except GdMn2Ge2 show re-entrant ferromagnetic behavior. Multiple magnetic transitions observed in these compounds are explained on the basis of the temperature dependences of the exchange strengths of the rare earth and Mn sublattices. The magnetocaloric effect is found to be positive at the re- entrant ferromagnetic transition, whereas it is negative at the antiferro-ferromagnetic transition. The Sm compounds are found to show a negative magnetocaloric effect at temperatures below the re-entrant ferromagnetic transition temperature. In SmMn2Ge2, the magnetic entropy change associated with the re-entrant transition is found to decrease with field, which may be attributed to the crystalfield effect as well as the increase in the intralayer antiferromagnetic component of the Mn sublattice. The maximum value of the isothermal magnetic entropy change in this series of compounds is found to decrease with increase in Sm concentration.