We have synthesized a single crystalline YC electride of centimeter-scale by floating-zone method and successfully characterized its anisotropic electrical and magnetic properties. In-plane resistivity upturn at low temperature together with anisotropic behavior of negative magnetoresistance is ascribed to the stronger suppression of spin fluctuation along in-plane than that along the c-axis, verifying the existence of magnetic moments preferred for the c-axis. A superior magnetic moment along the c-axis to that along the in-plane direction strongly demonstrates the anisotropic magnetism of YC electride containing a magnetically easy axis. It is clarified from the theoretical calculations that the anisotropic nature of the YC electride originates from strongly localized anionic electrons with an inherent magnetic anisotropy in the interlayer spaces.

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.

Electrides have emerged as promising materials with exotic properties, such as extraordinary electron-donating ability. However, the inevitable instability of electrides, which is caused by inherent excess electrons, has hampered their widespread applications. We report that a self-passivated dihafnium sulfide electride ([Hf2S]2+∙2e−) by double amorphous layers exhibits a strong oxidation resistance in water and acid solutions, enabling a persistent electrocatalytic hydrogen evolution reaction. The naturally formed amorphous Hf2S layer on the cleaved [Hf2S]2+∙2e− surface reacts with oxygen to form an outermost amorphous HfO2 layer with ~10-nm thickness, passivating the [Hf2S]2+∙2e− electride. The excess electrons in the [Hf2S]2+∙2e− electride are transferred through the thin HfO2 passivation layer to water molecules under applied electric fields, demonstrating the first electrocatalytic reaction with excellent long-term sustainability and no degradation in performance. This self-passivation mechanism in reactive conditions can advance the development of stable electrides for energy-efficient applications.

We use first-principles total-energy calculations based on density functional theory to study the site occupancy and magnetic properties of Al-substituted M -type strontium hexaferrite SrFe12−xAlxO19 with x = 0.5 and x = 1.0. We find that the non-magnetic Al 3+ ions preferentially replace Fe 3+ ions at two of the majority spin sites, 2a and 12k, eliminating their positive contribution to the total magnetization causing the saturation magnetization Ms to be reduced as Al concentration x is increased. Our formation probability analysis further provides the explanation for increased magnetic anisotropy field when the fraction of Al is increased. Although Al 3+ ions preferentially occupy the 2a sites at a low temperature, the occupation probability of the 12k site increases with the rise of the temperature. At a typical annealing temperature (> 700 • C) Al 3+ ions are much more likely to occupy the 12k site than the 2a site. Although this causes the magnetocrystalline anisotropy K1 to be reduced slightly, the reduction in Ms is much more significant. Their combined effect causes the anisotropy field Ha to increase as the fraction of Al is increased, consistent with recent experimental measurements.[4] decreased coercivity. However, the coercivity of the M-type hexaferrites is not increased significantly by these cation substitutions, and is still much smaller than that of Nd-Fe-B magnet [15].Al substitution in the M-type hexaferrite has been more effective in enhancing coercivity [16][17][18][19][20]. Particularly, Wang et al synthesized Al-doped SFO SrFe 12−x Al x O 19 (SFAO) with Al content of x = 0 − 4 using glycinnitrate method and subsequent annealing in a temperature over 700 • C obtaining the largest coercivity of 17.570 kOe, which is much larger than that of SFO (5.356 kOe) and exceeds even the coercivity of the Nd 2 Fe 17 B (15.072 kOe) [1]. Wang and co-workers also observed that the coercivity of the SFAO increases with increasing Al concentration at a fixed annealing temperature. These results call for a systematic understanding, from first principles, of why certain combinations of dopants lead to particular results. This theoretical understanding will be essential in systematically tailoring the properties of SFO.

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The site preference and magnetic properties of Zn, Sn and Zn-Sn substituted M-type strontium hexaferrite (SrFe12O19) have been investigated using first-principles total energy calculations based on density functional theory. The site occupancy of substituted atoms were estimated by calculating the substitution energies of different configurations. The distribution of different configurations during the annealing process at high temperature was determined using the formation probabilities of configurations to calculate magnetic properties of substituted strontium hexaferrite. We found that the magnetization and magnetocrystalline anisotropy are closely related to the distributions of Zn-Sn ions on the five Fe sites. Our calculation show that in SrFe11.5Zn0.5O19, Zn atoms prefer to occupy 4f1, 12k, and 2a sites with occupation probability of 78%, 19% and 3%, respectively, while in SrFe11.5SnO19, Sn atoms occupy the 12k and 4f2 sites with occupation probability of 54% and 46%, respectively. We also found that in SrFe11Zn0.5Sn0.5O19, (Zn,Sn) atom pairs prefer to occupy the (4f1, 4f2), (4f1, 12k) and (12k, 12k) sites with occupation probability of 82%, 8% and 6%, respectively. Our calculation shows that the increase of magnetization and the reduction of magnetic anisotropy in Zn-Sn substituted M-type strontium hexaferrite as observed experimentally is due to the occupation of (Zn,Sn) pairs at the (4f1, 4f2) sites. arXiv:1811.04101v2 [cond-mat.mtrl-sci]

The first-principles density functional theory has been used to study Ga/In-substituted strontium hexaferrite (SrFe12O19). Based on the calculation of the substitution energy of Ga and In in SrFe12O19 and the formation probability analysis, we conclude that in SrFe12−xGaxO19 the substituted Ga atoms prefer to occupy the 12k, 2a, and 4f1 sites, while In atoms in SrFe12−xInxO19 occupy the 12k, 4f2, and 4f1 sites. We used the site occupation probabilities to calculate the magnetic properties of the substituted SrFe12O19. It was found that as the fraction of Ga atoms in SrFe12−xGaxO19 increases, the saturation magnetization (Ms) as well as magnetic anisotropy energy (MAE) decrease, while the anisotropy field (Ha) increases. In the case of SrFe12−xInxO19, Ms, MAE, and Ha decrease with an increase of the concentration of In atoms.

Recently, the two dimensional (2D) materials have become a potential candidates for various technological applications in spintronics and optoelectronics soon after the discovery of graphene from the mechanical exfoliation of graphite. In the present study, the structural, electronic, and phase stability of layered quasi-2D ZnSb compounds have been tuned using the first principle calculations based on density functional theory