Ferromagnetic quasi-atomic electrons in two-dimensional electride

Abstract

An electride, a generalized form of cavity-trapped interstitial anionic electrons (IAEs) in a positively charged lattice framework, shows exotic properties according to the size and geometry of the cavities. Here, we report that the IAEs in layer structured [Gd 2 C] 2+ •2e − electride behave as ferromagnetic elements in two-dimensional interlayer space and possess their own magnetic moments of~0.52 μ B per quasi-atomic IAE, which facilitate the exchange interactions between interlayer gadolinium atoms across IAEs, inducing the ferromagnetism in [Gd 2 C] 2+ •2e − electride. The substitution of paramagnetic chlorine atoms for IAEs proves the magnetic nature of quasi-atomic IAEs through a transition from ferromagnetic [Gd 2 C] 2+ •2e − to antiferromagnetic Gd 2 CCl caused by attenuating interatomic exchange interactions, consistent with theoretical calculations. These results confirm that quasi-atomic IAEs act as ferromagnetic elements and trigger ferromagnetic spin alignments within the antiferromagnetic [Gd 2 C] 2+ lattice framework. These results present a broad opportunity to tailor intriguing ferromagnetism originating from quasi-atomic interstitial electrons in low-dimensional materials.

Quantum electron liquid and its possible phase transition

“…It is notable from the geometrical aspect that the theoretical maximum density of the electrons on the surface can be as high as ~ 9.5 × 10 14 cm −2 , which is expected from the concentration of IAEs in a single interlayer space of the 2D electrides with the bulk electron density of 1.4 × 10 22 ~ 2.9 × 10 22 cm −3 (ref. [19][20][21]. Through the experiments, the uncharted high-density pure 2D electron system with the concentration of ~ 2.0 × 10 14 cm −2 is confirmed to be realised on the surface of 2D [Gd2C] 2+ •2e − electride at high temperatures around 10 K, extending the phase diagram of pure 2D electrons to the quantum regime (Fig.…”

“…While the IAEs have the local maxima between cationic layers, the ELF on the surface spreads up to ~ 3 Å from the outermost Gd atoms, revealing the existence of loosely confined 2D electrons. In experiments using the 2D [Gd2C] 2+ •2e − electride 21 (Extended Data Fig. 1), we verify the pure 2D quantum electrons by exposing the localised IAEs on the surface of the outermost cationic layer via in-situ cleaving at 10 K under ultra-high vacuum (UHV) better than 4 × 10 −11 Torr.…”

“…Such decoupling is possible when electrons are captured on the positively charged surface of solid matter. Such quantum electrons can be found at the surface of 2D electride crystals [19][20][21] , which consist of positively charged cationic layers and counter-anionic electrons located in the interlayer space. The interstitial anionic electrons (IAEs) are localised at the interstitial space between cationic layers, not bound to the atomic orbitals of neighbouring cations.…”

“…2a). While the latter and other complex bands are of IAEs and cationic layers, respectively 21 , the parabolic band comes from the surface electrons above the cationic layer and has a 2D nature supported by a negligible dispersion along the kz-axis and an isotropic nature by a circular Fermi surface topology in the kx-ky plane (Extended Data Figs. 2d and 3ac).…”

How Many Electrons Holds a Molecular Electride?

“…21 The group of Hosono has been the most active in the search for new (inorganic) electrides with appealing applications, but other groups have recently joint the quest. Nowadays, there is a large collection of electrides, which can be classified in terms of the shape of the lattice voids where electrons are trapped: zero-dimensional electrides, 22 one-dimensional electrides, [23][24][25][26] two-dimensional electrides, [27][28][29][30][31][32][33][34] three-dimensional ones, [35][36][37][38][39][40] and electride nanoparticles. 41,42 In Table 1, we have collected all the experimental realizations of electrides, indicating which of them are stable at room temperature, whether they are organic or inorganic, and the number of dimensions of the isolated electron cavity.…”