Magnetic and critical properties of Pr0.6Sr0.4MnO3 nanocrystals prepared by a combination of the solid state reaction and the mechanical ball milling methods

Nguyen Thi Dung, Dinh Chi Linh, Pham Duc Huyen Yen, Seong Cho Yu, Nguyen Van Dang and Tran Dang Thanh

Abstract

Influence of the crystallite size on the magnetic and critical properties of Pr_0.6Sr_0.4MnO₃ nanocrystals has been investigated. The results show that Curie temperature (T_C) and magnetization slightly decrease with decreasing average crystallite size (<D>). Based on the mean-field theory and the magnetic-field dependences of magnetization at different temperatures M(H, T), we pointed out that the ferromagnetic-paramagnetic phase transition in the samples undergoes the second-order phase transition with the critical exponents (β = 0.461-0.492, γ = 1.019-1.062, and δ = 3.071 - 3.164) close to those of the mean-field theory. However, there is a small deviation from those expected for the mean-field theory of the values of β,  γ and δ obtained for the samples. It means that short-range ferromagnetic interactions appear in the smaller particles. In other words, Pr_0.6Sr_0.4MnO₃ nanocrystals become more magnetically inhomogeneous with smaller crystallite sizes that could be explained by the presence of surface-related effects, lattice strain and distortions, which lead the strength of Mn³⁺-Mn⁴⁺ ferromagnetic interaction is decreased in the small crystallite sizes