No abstract

The relatively low Curie temperature (Tc) in recently discovered two-dimensional ferromagnetic (FM) materials has limited their potential applications in designing next generation electronics. Searching for new low-dimensional layered materials with room-temperature Tc is highly needed. Here, we report the study of layered FM materials Cr5+xTe8 (x = −0.10, 0.11, 0.56, 1) in which Tc can be well manipulated by the Cr content. Single crystalline Cr5+xTe8 samples have been synthesized and characterized by energy dispersive x-ray spectroscopy, x-ray diffraction, and magnetization measurements. We have found that Tc increases monotonically with Cr content and reaches 313 K at x = 1. While the FM coupling is enhanced with an increase in the Cr content, the antiferromagnetic (AFM) phase at low temperatures is suppressed. Due to the competition of FM and AFM phases, a wasp-waist loop is observed on isothermal magnetization curves. A magnetic flip occurs by changing the temperature and magnetic field to overcome the flipping energy barrier. Our results indicate that the Cr5+xTe8 system serves as a promising platform to tune the 2D ferromagnetism in layered materials.

By preparing a series of high-quality Fe1.1Se0.8Te0.2 films on the CaF2 substrate via pulsed laser deposition, we reveal the evolution of the structure as well as the superconductivity with the film thickness. We have found that there exists a threshold thickness above which the critical temperature T c reaches its optimal value of 23.18 K with large activation energy, promising for high-field technological applications. Most importantly, the thick films have been found in a metastable state due to the fragile balance between the increased strain energy and the large compressive stress. Once the balance is broken by an external perturbation, a unique structure avalanche happens with a large part of the film exfoliated from the substrate and curves out. The exfoliated part of the film remains a single phase, with its lattice parameter and T c recovering the bulk values. Our results clearly demonstrate the close relation between the compressive stress of the film/substrate interface and the high critical temperature observed in FeSeTe films. Moreover, this also provides an efficient way to fabricate free-standing single-phase FeSeTe crystals in the phase-separation regime.

No abstract

No abstract