Strong magnetization fluctuations are expected near the thermodynamic critical point of a continuous magnetic phase transition. Such critical fluctuations are highly correlated and in principle can occur at any time and length scales¹; they govern critical phenomena and potentially can drive new phases^2,3. Although critical phenomena in magnetic materials have been studied using neutron scattering, magnetic a.c. susceptibility and other techniques^4,5,6, direct real-time imaging of critical magnetization fluctuations remains elusive. Here we develop a fast and sensitive magneto-optical imaging microscope to achieve wide-field, real-time monitoring of critical magnetization fluctuations in single-layer ferromagnetic insulator CrBr₃. We track the critical phenomena directly from the fluctuation correlations and observe both slowing-down dynamics and enhanced correlation length. Through real-time feedback control of the critical fluctuations, we further achieve switching of magnetic states solely by electrostatic gating. The ability to directly image and control critical fluctuations in 2D magnets opens up exciting opportunities to explore critical phenomena and develop applications in nanoscale engines and information science.

在连续磁相变的热力学临界点附近，预计会有强烈的磁化波动。这种临界波动是高度相关的，并且原则上可以在任何时间和长度范围内发生¹；它们控制着关键现象，并有可能推动新的阶段^2,3。尽管已使用中子散射，磁化率和其他技术[ ^4,5,6]研究了磁性材料中的临界现象，但仍无法对临界磁化涨落进行直接实时成像。在这里，我们开发了一种快速灵敏的磁光成像显微镜，以实现大范围实时监视单层铁磁绝缘体CrBr _3中的临界磁化涨落。。我们直接从波动相关性中跟踪关键现象，并观察到减慢的动力学和增强的相关性长度。通过对关键波动的实时反馈控制，我们进一步仅通过静电门控即可实现磁状态的切换。直接成像和控制2D磁体的临界波动的能力为探索临界现象以及开发在纳米级引擎和信息科学中的应用提供了令人兴奋的机会。