The historic Barnett effect describes how an inertial body with otherwise zero net magnetic moment acquires spontaneous magnetization when mechanically spinning^1,2. Breakthrough experiments have recently shown that an ultrashort laser pulse destroys the magnetization of an ordered ferromagnet within hundreds of femtoseconds³, with the spins losing angular momentum to circularly polarized optical phonons as part of the ultrafast Einstein–de Haas effect^4,5. However, the prospect of using such high-frequency vibrations of the lattice to reciprocally switch magnetization in a nearby magnetic medium has not yet been experimentally explored. Here we show that the spontaneous magnetization gained temporarily by means of the ultrafast Barnett effect, through the resonant excitation of circularly polarized optical phonons in a paramagnetic substrate, can be used to permanently reverse the magnetic state of a heterostructure mounted atop the said substrate. With the handedness of the phonons steering the direction of magnetic switching, the ultrafast Barnett effect offers a selective and potentially universal method for exercising ultrafast non-local control over magnetic order.

历史性的巴尼特效应描述了净磁矩为零的惯性体如何在机械旋转时获得自发磁化^1,2。最近的突破性实验表明，超短激光脉冲会在数百飞秒内破坏有序铁磁体的磁化强度³，作为超快爱因斯坦-德哈斯效应^4,5的一部分，自旋会失去角动量，转变成圆偏振光学声子。然而，利用晶格的这种高频振动来相互切换附近磁介质中的磁化强度的前景尚未经过实验探索。在这里，我们表明，通过超快巴尼特效应，通过顺磁基板中的圆偏振光学声子的共振激发，暂时获得自发磁化，可用于永久反转安装在所述基板顶部的异质结构的磁性状态。利用声子的旋向性来控制磁开关的方向，超快巴尼特效应为对磁序进行超快非局域控制提供了一种选择性且潜在通用的方法。