Emerging 2D-ferromagnetism and strong spin-orbit coupling at the surface of valence-fluctuating EuIr2Si2

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 EuIr 2 Si 2 , where in contrast to its nonmagnetic 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.

Relativistic splitting of surface states at Si-terminated surfaces of the layered intermetallic compoundsRT2Si2(R=rare earth;TNechaev1, Krasovskii2 2018Phys. Rev. B140280View full textAdd to dashboardCite

“…Regarding the behavior of the transition-metal surface states, our k•p results are in full accord with the ARPES measurements on RT 2 Si 2 (with R = Gd, Ho, Eu and T= Rh, Ir) magnetic compounds and corresponding ab initio calculations [11,12,21]. Since the low-temperature magnetic phases of these compounds undergo a transition to paramagnetic phases when the temperature is increased, this was suggested to be a way to gradually tune the splitting of the states and their spin orientation in a given compound [11,12].…”

“…We then consider the surface states of our model as a prototype of those of a paramagnetic phase of an RT 2 Si 2 compound and tune the relative strength of the competing spin-orbit and exchange interactions in order to illustrate how the surface states at the Si-terminated surface are influenced by the ferromagnetically ordered 4f moments of the subsurface rare-earth layer in a magnetic phase of this compound. The modification of the surface electronic structure suggested by the model is in full accord with the experimental ARPES (angle-resolved photoemission spectroscopy) observations and the corresponding ab initio calculations for magnetic phases of the RT 2 Si 2 compounds [11,12,21].…”

Crystal Growth of Materials with the ThCr2Si2 Structure Type

“…After the discovery of strong ferromagnetism at the surface of the antiferromagnetic EuRh 2 Si 2 by ARPES, [22] this opened the way for a systematic investigation of the surface states in LnRh 2 Si 2 and LnIr 2 Si 2 using this technique. [23][24][25][26][27] These surface states were found to be strongly modified by the internal magnetic fields from the ordered rare earth ions underneath and for a thorough understanding of these effects it is essential to characterize the magnetic ground state in great detail.…”

Photoelectron diffraction for probing valency and magnetism of 4f -based materials: A view on valence-fluctuating EuIr2Si2

“…Discovered in 1986, EuIr 2 Si 2 has recently reappeared as a focus of research interest due to its explicit ferromagnetic properties at the Si-terminated surface, where both spin-orbit coupling and exchange magnetic interaction are involved [14]. The layered structure of this compound is composed of Si-Ir-Si trilayer blocks which separate valence-fluctuating Eu layers.…”