High temperature spin-glass-like transition in La_0.67Sr_0.33MnO₃ nanofibers near the Curie point

The glassy transition of superparamagnetic (SPM) (r < r₀) nanoparticle systems usually occurs at a very low temperature that greatly limits its application to high temperatures. In this work, we report a spin-glass-like (SGL) behavior near the Curie point (T_C), i.e., T₀ = 330 K, in La_0.67Sr_0.33MnO₃ (LSMO) nanofibers (NFs) composed of nanoparticles beyond the SPM size (r ≫ r₀), resulting in a significant increase of the glass transition temperature. This SGL transition near the T_C of bulk LSMO can be explained to be the scenario of locally ordered clusters embedded in a disordered host, in which the assembly of nanoparticles has a magnetic core-shell model driven by surface spin glass. The presence of a surface spin glass of nanoparticles was proved by the Almeida-Thouless line δT_f ∝ H^2/3, exchange bias, and reduced saturation magnetization of the NF system. Composite dynamics were found-that is, both the SPM and the super-spin-glass (SSG) behavior are found in such an NF system. The bifurcation of the zero-field-cooled (ZFC) and field-cooled (FC) magnetization vs. temperature curves at the ZFC peak, and the flatness of FC magnetization involve SSG, while the frequency-dependent ac susceptibility anomaly follows the Vogel-Fulcher law that implies weak dipole interactions of the SPM model. This finding can help us to find a way to search for high temperature spin glass materials.