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Effect of impurity doping at the Mn-site on magnetocaloric effect in Pr0.6Ca0.4Mn0.96B0.04O3 (B=Al, Fe, Cr, Ni, Co, and Ru)

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2 Author(s)
Kumar, V.Suresh ; Department of Physics, Faculty of Science, National University of Singapore, 2 Science Drive 3, Singapore 117542 ; Mahendiran, R.

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We report the effect of impurity doping at the Mn-site on magnetization and magnetic entropy change Sm) in Pr0.6Ca0.4Mn0.96B0.04O3 with B cations having different electronic and spin states [B=Al3+(d0), Cr3+(d3), Fe3+(d5), Co2+(d7), Ni2+(d8), and Ru4+/5+(d4/3)]. The charge ordered antiferromagnetic insulator Pr0.6Ca0.4MnO3 transforms into a ferromagnetic metal in the absence of an external magnetic field (H) for B=Cr, Ni, Co, and Ru, whereas B=Fe and Al samples remain as antiferromagnetic insulators. It is found that the applied magnetic field induced an abrupt increase in the magnetization above a critical value of H (field-induced metamagnetic transition) in the paramagnetic state for B=Cr, Ni, and Co but not for B=Ru, which has the highest Curie temperature in the series (TC=205 K). The B=Co sample shows the maximum value of the magnetic entropy (S- - m=7.37 J/kgK under ΔH=5 T), which is followed by Sm=6.77,6.0,5.07,5.04,2.72 J/kgK for B=Ni, Cr, Ru, Fe, and Al, respectively. We have also found a large magnetic entropy change (Sm=8.42 J/kgK under ΔH=5) by differential scanning calorimetric study in B=Co sample. The large ΔSm values in B=Co, Cr, and Ni compared to Ru originate from the distinct field dependence of the magnetization above TC. It is suggested that both charge-orbital fluctuations and ferromagnetic polarons exist in the paramagnetic phase of B=Co, Cr, and Ni samples in the absence of a magnetic field, and the external magnetic field suppresses charge-orbital fluctuations and enhances size of ferromagnetic polarons, which leads to observed large ΔSm values. Our study suggests that creation of charge-orbital fluctuations and ferromagnetic polarons by dilution of the Mn-site could be a simple way to enhance the magnetocaloric effect in charge ordered manganites.

Published in:

Journal of Applied Physics  (Volume:109 ,  Issue: 2 )

Date of Publication:

Jan 2011

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