Ferromagnetism is usually deemed incompatible with superconductivity. Consequently, the coexistence of superconductivity and ferromagnetism is usually observed only in elegantly designed multi-ingredient structures in which the two competing electronic states originate from separate structural components. Here we report the use of surface molecular adsorption to induce ferromagnetism in two-dimensional superconducting NbSe2, representing the freestanding case of the coexistence of superconductivity and ferromagnetism in one two-dimensional nanomaterial. Surface-structural modulation of the ultrathin superconducting NbSe2 by polar reductive hydrazine molecules triggers a slight elongation of the covalent Nb-Se bond, which weakens the covalent interaction and enhances the ionicity of the tetravalent Nb with unpaired electrons, yielding ferromagnetic ordering. The induced ferromagnetic momentum couples with conduction electrons generating unique correlated effects of intrinsic negative magnetoresistance and the Kondo effect. We anticipate that the surface molecular adsorption will be a powerful tool to regulate spin ordering in the two-dimensional paradigm.

中文翻译：

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表面分子吸附触发二维NbSe2中超导性和铁磁性的共存。

铁磁性通常被认为与超导不相容。因此，通常仅在设计精美的多成分结构中观察到超导性和铁磁性的共存，在该结构中，两个相互竞争的电子态源自单独的结构组件。在这里，我们报道了利用表面分子吸附在二维超导NbSe2中诱导铁磁性，这代表了一种二维纳米材料中超导性和铁磁性共存的独立情况。极性还原肼分子对超薄超导NbSe2的表面结构调节会触发共价Nb-Se键的轻微伸长，从而削弱共价相互作用并增强四价Nb与不成对电子的离子性，产生铁磁有序。感应的铁磁动量与传导电子耦合，产生固有负磁阻和近藤效应的独特关联效应。我们预期表面分子吸附将是调节二维范式中自旋有序的有力工具。