Effect of Bi doping on magnetic and magnetocaloric properties of La 0.7-x Bix Sr0.3 MnO3 (0x0.4)

Abstract

We investigated the effect of Bi doping on magnetic and magnetocaloric properties of La0.7-x Bix Sr0.3 MnO3 (x=0.0-0.4). It is shown that the low temperature ground state changes from a ferromagnet (x=0) to a charge-ordered antiferromagnet for x=0.4. While the paramagnetic-ferromagnetic (PM-FM) transition is second-order in x0.25, it changes into first-order for x=0.3 which is at the magnetic phase boundary. The changes in the magnetic ground state affect magnetic entropy. The magnitude of the isothermal magnetic entropy ( Δ SM ) at the FM Curie temperature increases from 4.56 J/kg K for x=0 to a maximum value of 5.02 J/kg K for x=0.05 and then decreases to nearly zero for x=0.4 at the charge order transition. In contrast to x0.25, the Δ SM of x=0.3 is magnetic history dependent and its temperature dependence exhibits a clear step at TCO =260 K followed by a plateau between 240 and 185 K. Although Δ S M =3.1 J/kg K of x=0.3 is small compared to other compositions, it has a high relative cooling power (325 J/kg) which is desirable for magnetic refrigeration over a wide temperature. The unusual magnetic and magnetocaloric properties of x=0.3 are attributed to the existence of short-range charge-orbital (CO) correlations in the PM state. It is suggested that harnessing competition between FM spin ordering and CO correlations may provide a strategy to enhance magnetic refrigeration capacity over a wide temperature range. © 2010 American Institute of Physics.