Abstract
The development of materials that are non-magnetic in the bulk but exhibit two-dimensional (2D) magnetism at the surface is at the core of spintronics applications. Here, we present the valence-fluctuating material EuIr2Si2, where in contrast to its non-magnetic bulk, the Si-terminated surface reveals controllable 2D ferromagnetism. Close to the surface the Eu ions prefer a magnetic divalent configuration and their large 4f moments order below 48 K. The emerging exchange interaction modifies the spin polarization of the 2D surface electrons originally induced by the strong Rashba effect. The temperature-dependent mixed valence of the bulk allows to tune the energy and momentum size of the projected band gaps to which the 2D electrons are confined. This gives an additional degree of freedom to handle spin-polarized electrons at the surface. Our findings disclose valence-fluctuating rare-earth based materials as a very promising basis for the development of systems with controllable 2D magnetic properties which is of interest both for fundamental science and applications.
Highlights
Its proximity to the center of the lanthanide period makes elemental europium highly interesting for the elaboration of novel materials with rich and exotic properties that are governed by the 4f electrons and their interactions.[1,2,3] In solids the rare earth atoms are usually in the trivalent state which in the case of Eu results in a 4f 6(5d6s)[3] configuration
We consider a Si-terminated crystal of EuIr2Si2 and focus on the properties of the Si-Ir-Si-Eu (SISE) block forming the surface
It can immediately be seen that in contrast to the general expectation both PE spectra are characterized by a pronounced Eu2+ signal close to the Fermi energy EF
Summary
Its proximity to the center of the lanthanide period makes elemental europium highly interesting for the elaboration of novel materials with rich and exotic properties that are governed by the 4f electrons and their interactions.[1,2,3] In solids the rare earth atoms are usually in the trivalent state which in the case of Eu results in a 4f 6(5d6s)[3] configuration. When the system moves into the magnetically ordered regime, the M surface state experiences a strong exchange-induced splitting due to coupling with the 4f moments in the fourth layer below the Si surface.[17,18,19] Note that in contrast to EuIr2Si2 the mentioned RERh2Si2 compounds are bulk antiferromagnets (AFM) in which rare-earth FM planes are stacked antiferromagnetically along the c axis.
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