Valley-Related\nMultipiezo Effect and Noncollinear\nSpin Current in an Altermagnet Fe<sub>2</sub>Se<sub>2</sub>O Monolayer

An altermagnet exhibits many novel physical phenomena\nbecause of\nits intrinsic antiferromagnetic coupling and natural band spin splitting,\nwhich are expected to give rise to new types of magnetic electronic\ncomponents. In this study, an Fe<sub>2</sub>Se<sub>2</sub>O monolayer\nis proven to be an altermagnet with out-of-plane magnetic anisotropy,\nand its Néel temperature is determined to be 319 K. The spin\nsplitting of the Fe<sub>2</sub>Se<sub>2</sub>O monolayer reaches 860\nmeV. Moreover, an Fe<sub>2</sub>Se<sub>2</sub>O monolayer presents\na pair of energy valleys, which can be polarized and reversed by applying\nuniaxial strains along different directions, resulting in a piezovalley\neffect. Under the strain, the net magnetization can be induced in\nthe Fe<sub>2</sub>Se<sub>2</sub>O monolayer by doping with holes,\nthereby realizing a piezomagnetic property. Interestingly, noncollinear\nspin current can be generated by applying an in-plane electric field\non an unstrained Fe<sub>2</sub>Se<sub>2</sub>O monolayer doped with\n0.2 hole/formula unit. These excellent physical properties make the\nFe<sub>2</sub>Se<sub>2</sub>O monolayer a promising candidate for\nmultifunctional spintronic and valleytronic devices.