Intriguing strain-governed magnetic phase transitions in 2D vanadium porphyrin sheets.

The strain effect on the magnetic response of 2D materials as spintronic devices is always important in actual applications. Due to the intriguing electronic and magnetic properties of two-dimensional (2D) vanadium porphyrin (V-PP) sheets, we studied the strain-induced magnetic coupling changes in 2D V-PP sheets by using the density functional theory method and found intriguing magnetic variation characters. The calculated results indicate that biaxial strain can modulate the magnetic moments of the central transition metal vanadium atoms and more importantly can induce phase transitions among three magnetic modes with four magnetic states (ferromagnetic (FM), ferrimagnetic (FIM), and two antiferromagnetic (AFM: AFM1 featuring a parallel spin lattice versus AFM2 featuring a crossing spin lattice)) with unique conversion pathways due to their different responses to the strain. As the compressive strain increases, the magnetic characteristics of 2D-VPP transitions as FM → FIM → AFM1 with two critical points (-4.7% and -6%), while the tensile strain can induce the original FM coupling to transition to another AFM state (FM → AFM2) at 5.3%. Analyses of the density of states, spin densities, and Bader charges reveal that the rich magnetic response properties of the system originate from the electron transfer between the central V and the porphyrin ligand induced by strain. This work provides intriguing information regarding the strain-induced magnetic phase transition mechanism and also presents a viable development direction to design 2D porphyrin magnetic semiconductors and spintronic devices.