Normal and inverse magnetocaloric effects in

We have investigated magnetic and magnetocaloric properties of La0.5Ca0.5Mn1−xNixO3 ( x = 0 , 0.02, 0.04, 0.06, & 0.08). It is shown that charge-ordered antiferromagnetic ground state of x = 0 is destabilized and ferromagnetism is induced by just 2% Ni substitution. The ferromagnetic Curie temperature ( T C ) decreases from T C = 220 K for x = 0 to 85 K ( x = 0.08 ) . Unusual field-induced metamagnetic transition is found above T C for x = 0.02 – 0.06 and even below T C in the parent compound ( x = 0 ) . Magnetic entropy change ( Δ S m ) was estimated from isothermal magnetization data and it is found that the parent compound ( x = 0 ) exhibits both normal (negative Δ S m ) and inverse (positive Δ S m ) magnetocaloric effects at T C and T N (Neel temperature), respectively. The Δ S m = + 6.5 J kg − 1 K − 1 at T N is twice larger than that at T C ( Δ S m = − 3 Jkg − 1 K − 1 ) for a field change ( Δ H ) of 5 T. However, all the Ni doped samples in La0.5Ca0.5Mn1−xNixO3 system show only normal magnetocaloric effect at T C . The largest MCE in the Ni doped series occurs for x = 0.04 ( Δ S m = − 3.9 Jkg − 1 K − 1 , Δ H = 5 T ) which also has the largest relative cooling power ( RCP = 235 J / kg , Δ H = 5 T ) in the series. We discuss our results in the scenario of phase separation induced by Ni substitution.