An Anomalously Large Magneto‐Optical Response in 2D Material Colloids with Assembly‐Induced Giant Magnetic Anisotropy

Abstract Exploring soft matter systems with high response sensitivity to magnetic fields has been a long‐standing issue, which can realize contactless and non‐destructive modulation of the materials’ properties. 2D material colloids have emerged as promising candidates, while current experiments suggest that their response sensitivity approaches a bottleneck. Here, a 2D material colloid is reported with anomalously large magnetic response sensitivity, in which 2D materials stack coplanarly and roll into scrolls, forming a unique assembly structure. The assembly of 2D materials generates a giant equivalent particulate magnetic susceptibility anisotropy and enhances the ordered orientation, which contributes to a record magneto‐optical coefficient of 3.2 × 10 4 m −1 T −2 , being one order of magnitude larger than the previous largest value. Thanks to this, magnetic field viewers are fabricated with a detection limit of ≈25 mT and a spatial resolution in millimeter scale. This work not only provides insight in the responsivity modulation of soft matter systems by regulating interaction among constituent units but also unlocks their applications across various fields.