Molecular Oxygen-Induced Ferromagnetism and Half-Metallicity in α-BaNaO₄: A First-Principles Study

Abstract

Molecule oxygen resembles 3d and 4f metals in exhibiting long-range spin ordering and electron strong correlated behaviors in compounds. The ferromagnetic spin ordering and half-metallicity, however, are quite elusive and have not been well acknowledged. In this article, we address this issue to study how spins will interact each other if the oxygen dimers are arranged in a different way from that in the known super-and per-oxides by first principles calculations. Based on the results of structure search, thermodynamic study and lattice dynamics, we show that tetragonal α-BaNaO4 is a stable halfmetal with a Curie temperature at 120 K, a first example in this class of compounds. Like 3d and 4f metals, the O2 dimer carries a local magnetic moment 0.5 μB due to the unpaired electrons in its π* orbitals. This compound can be regarded as forming from the O2 dimer layers stacking in a head to head way. Different from that in AO2 (A=K, Rb, Cs), the spins are both ferromagnetically coupled within and between the layers. Spin polarization occurs in π* orbitals with spin-up electrons fully occupying the valence band and spin-down electrons partially the conduction band, forming the semiconducting and metallic channels, respectively. Our results highlight the importance of geometric arrangement of O2 dimers in inducing ferromagnetism and other novel properties in O2 dimer containing compounds. ASSOCIATED CONTENT Supporting Information. Lattice parameters; elastic constants; details of estimation coupling constant; phonon spectra and band structures of BaNaOx; molecular dynamics simulations of BaNaO4; more band structure results of BaNaO4; shifted configuration of RbO2; structures and formation enthalpies of related compounds.

Realization of a Half Metal with a Record‐High Curie Temperature in Perovskite Oxides

“…Mn 2 FeReO 6 , [15] and Fe 3 O 4 [16] half metals, their spin-up (or spindown) energy gaps are usually rather small (0.4-0.9 eV). In contrast, several HMs such as LaCu 3 Co 2 Re 2 O 12 [17] and BaNaO 4 [18] exhibit relatively large energy gaps (≥1.9 eV), while their corresponding Curie temperatures are considerably lower than RT.…”

“…For example, despite the high Curie temperatures observed in NiMnSb, [ 3 ] Co 2 FeSi, [ 14 ] Mn 2 FeReO 6 , [ 15 ] and Fe 3 O 4 [ 16 ] half metals, their spin‐up (or spin‐down) energy gaps are usually rather small (0.4–0.9 eV). In contrast, several HMs such as LaCu 3 Co 2 Re 2 O 12 [ 17 ] and BaNaO 4 [ 18 ] exhibit relatively large energy gaps (≥1.9 eV), while their corresponding Curie temperatures are considerably lower than RT. If one defines a coupled parameter α = T C × E g × M N , where M N represents the normalized saturated moment of each cation, then, characterizing the synthetic performance of HMs, we find that a high T C is often incompatible with a large E g and/or M N , as shown in Figure .…”

Crystal structures and mechanical properties of osmium diboride at high pressure

“…This method can predict stable or metastable crystal structures based on a given chemical compositions under specific external conditions. So far, it has been successfully applied not only to element solids, but also to binary and ternary compounds [31][32][33][34] . Moreover, the ab initio optimizations and mechanical properties calculations for every structure generated by the CALYPSO code were performed using the VASP package 35 with the PBE generalized gradient approximation 36 .…”

Application of topological quantum chemistry in electrides

“…1. We first propose that NaBaO [32] with the SG of P4/nmm (SG #129) could be an electride with an excess electron located at the cavity 2b, since the BR of the floating bands [denoted by blue-colored lines and irreps in Fig. 4(d)] is elementary, and the average charge center is located at the cavity.…”