Griffiths phase and magnetocaloric behaviors of Co-doped Nd0.6Sr0.4MnO3

Abstract

Nd_0.6Sr_0.4Mn_1-yCo_yO₃ (y = 0–0.09) compounds have been fabricated by using solid-state reactions. X-ray diffraction analyses reveal their monophase in the Imma orthorhombic structure. When y increases, there are gradual reductions of the unit-cell parameters and porosity. Concurrently, the Curie temperature (T_C) also reduces from 280 K (y = 0) to ∼232 K (y = 0.09). In the vicinity of T_C, we have observed the Griffiths phase that more develops as increasing y. The presence of this phase enhances magnetocaloric responses, corresponding to the operating range widened above 95 % and the cooling power enhanced ∼30 % for an applied field H = 30 kOe. All materials exhibit the characters of a second-order phase transition with a narrow hysteresis loop, suggesting their applicability in magnetic cooling devices operating below room temperature. A coexistence of Mn^3+,4+ and Co^3+,4+ ions is thought to establish randomly competing ferromagnetic and antiferromagnetic interactions in Nd_0.6Sr_0.4Mn_1-yCo_yO₃ compounds that widen the Griffiths phase, short-range magnetic ordering, and magnetocaloric response.