Largely Tunable Magneto-Coloration of Monolayer 2D Materials via Size Tailoring.

Magnetically influenced light-matter interaction provides a contactless, noninvasive and power-free way for material characterization and light modulation. Shape anisotropy of active materials mainly determines the sensitivity of magneto-optic response, thereby making magnetic two-dimensional (2D) materials suitable in achieving the giant magneto-birefringence effect as discovered recently. Consequently, relationship between magneto-birefringence response and shape anisotropy of 2D materials is critical but has remained elusive, restricting its widespread applications. Here, we report the highly sensitive and largely tunable magneto-coloration via manipulating the shape-anisotropy of magnetic 2D materials. We reveal a quadratic increasing relationship between the magneto-optic Cotton-Mouton coefficient and the lateral size of 2D materials and achieve a more than one order of magnitude tunable response. This feature enables the engineerable transmissive magneto-coloration of 2D materials by tailoring their shape anisotropy. Our work deepens the understanding of the tunability of magneto-optic response by size effect of active materials, offering various opportunities for their applications in vast areas where color is concerned.