Strong magnetoelectric effects in single-phase two-dimensional (2D) materials are extremely rare in nature. Here by first-principles calculations, we find a strong magnetoelectric coupling in polar stacking bilayer Hf₂S that allows the reversal of net magnetic moments with the reversal of electric dipoles. Further analysis shows that such strong magnetoelectric effects benefit from the Stoner instability of surface Hf atoms triggered by polar stacking. Moreover, an unexpectedly large out-of-plane electric polarization (which is at least two times larger than that of bilayer BN) survives in the material, despite its metallicity. The large electric polarization is ascribed to the delocalized interlayer electrons which generally present in layered electride materials. It is quite interesting that large electric polarization, metallicity and magnetism coexist in one single-phase material. Our findings reveal rich physical phenomena to be explored in 2D stacking multiferroics and suggest an alternative way of searching for strong magnetoelectric materials with ultrathin thickness.

单相二维（2D）材料中的强磁电效应在自然界中极为罕见。通过第一性原理计算，我们发现极性堆叠双层 Hf ₂ S 中存在强磁电耦合，使得净磁矩随着电偶极子的反转而反转。进一步分析表明，如此强的磁电效应得益于极性堆积引发的表面Hf原子的斯托纳不稳定性。此外，尽管材料具有金属性，但仍存在出乎意料的大面外电极化（至少比双层 BN 大两倍）。大的电极化归因于通常存在于层状电子化物材料中的离域层间电子。非常有趣的是，大的电极化、金属性和磁性同时存在于一种单相材料中。我们的研究结果揭示了二维堆叠多铁性材料中待探索的丰富物理现象，并提出了寻找超薄厚度强磁电材料的替代方法。