The magnetic properties of nanosized La1−x Ca x MnO3 (0.5 ≤ x ≤ 0.8)

Magnetic properties of La1−x Ca x MnO3 (0.5 ≤ x ≤ 0.8) samples with an equivalent average particle size ~50 nm prepared by a sol–gel method were investigated. The charge ordering (CO) transition that is observed in the bulks disappears and the ferromagnetic (FM) transition occurs in all the prepared samples. For all the samples, the spontaneous magnetization (M S) value is much lower than the corresponding theoretic value, which shows that the majority of the sample is antiferromagnetic (AFM). However, the M S value is much larger than the corresponding value reported by some other groups. The invisible of CO transition and the large M S value can be attributed to the good connection among the adjacent particles. Moreover, the exchange bias (EB) phenomenon is observed except the x = 0.5 sample. With x increasing, the M S value decreases and the EB field increases, which can be understood by considering the coexistence of FM phase with Mn3+–Mn4+ spin clusters in the shell and the AFM phase in the core of the nanoparticles.