La(Fe, Si)13-based compounds are well-known magnetocaloric materials, which show a pronounced negative thermal expansion (NTE) around the Curie temperature but have not been considered as NTE materials for industrial applications. The NaZn13-type LaFe13-xSix and LaFe11.5-xCoxSi1.5 compounds were synthesized, and their linear NTE properties were investigated. By optimizing the chemical composition, the sharp volume change in La(Fe, Si)13-based compounds was successfully modified into continuous expansion. By increasing the amount of Co dopant in LaFe11.5-xCoxSi1.5, the NTE shifts toward a higher temperature region, and also the NTE operation-temperature window becomes broader. Typically, the linear NTE coefficient identified in the LaFe10.5Co1.0Si1.5 compound reaches as much as -26.1 × 10(-6) K(-1), with an operation-temperature window of 110 K from 240 to 350 K, which includes room temperature. Such control of the specific composition and the NTE properties of La(Fe, Si)13-based compounds suggests their potential application as NTE materials.

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Two-dimensional (2D) organic materials with stable electron spin polarization, ferromagnetic ordering and half-metallicity are quite promising for spintronics, due to their long spin coherence length and mechanical flexibility. Here, using porphyrin molecules as building blocks, we propose a novel 2D periodic organic nanomaterial (2D-polyporphyrin) from first-principles calculations. The recent experimental progress on the one-dimensional (1D) Zn-porphyrin arrays hints the plausibility of these 2D polyporphyrin frameworks.We show that electron spin-polarization can be achieved in both metal-free and transition-metalembedded 2D-polyporphyrins. Cr-polyporphyrin (Cr-PP) in particular has stable ferromagnetic ordering with a Curie temperature (T c ) of about 187 K as indicated by the Monte Carlo simulations based on the 2D Ising model, which is much higher than that reported in the 2D Mn-phthalocyanine framework. The ferromagnetic Cr-PP nanosheet can be tuned to half-metallic by electron doping. The present work opens up an avenue for the development of 2D organic nanostructures with stable ferromagnetism and halfmetallicity.

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