The influence of first- and second-order magnetic phase transitions on the magnetocaloric effect (MCE) and refrigerant capacity (RC) of charge-ordered Pr0.5 Sr0.5 MnO3 has been investigated. The system undergoes a paramagnetic to ferromagnetic transition at TC ∼255 K followed by a ferromagnetic charge-disordered to antiferromagnetic charge-ordered transition at TCO ∼165 K. While the first-order magnetic transition (FOMT) at TCO induces a larger MCE (6.8 J/kg K) limited to a narrower temperature range resulting in a smaller RC (168 J/kg), the second-order magnetic transition at TC induces a smaller MCE (3.2 J/kg K) but spreads over a broader temperature range resulting in a larger RC (215 J/kg). In addition, large magnetic and thermal hysteretic losses associated with the FOMT below TCO are detrimental to an efficient magnetic RC, whereas these effects are negligible below TC because of the second-order nature of this transition. These results are of practical importance in assessing the usefulness of charge-ordered manganite materials for active magnetic refrigeration, and Pr0.5 Sr0.5 MnO 3 provides an interesting case study in which the influence of first- and second-order transitions on MCE could be compared in the same system in a single experiment.
Bibliographical noteFunding Information:
The authors acknowledge work at USF supported by DOE BES Physical Behavior of Materials Program through Grant No. DE-FG02-07ER46438. H.S. also acknowledges support from USAMRMC through Grant No. W81XWH-07-1-0708. Work at UMN supported primarily by DOE (Grant No. DE-FG02-06ER46275) and NSF (Grant No. DMR-0804432) is also acknowledged.