Electronic and magnetic structure of bulk cobalt: The α, β, and ε-phases from density functional theory calculations

Abstract

The geometric, electronic and magnetic properties of the three metallic cobalt phases: hcp(alpha), fcc(beta), and epsilon(epsilon) have been theoretically studied using periodic density functional calculations with generalized gradient approximation (GGA) and plane wave basis set. These results have been compared with those obtained with GGA+U approach which have shown a noticeable improvement with regard to experimental data. For instance, the cohesive energy values predicted by GGA are overestimated by approximately 25%, whereas GGA+U underestimate them by 14%-17%. On the other hand, magnetic moment values are underestimated in GGA while are overestimated for GGA+U approach by almost the same amount. Besides, the introduction of U parameter gives rise to an electronic redistribution in the d-band structure, which leads to variations in the magnetic properties. Moreover, a higher attention has been paid in the study of the electronic and magnetic properties of the epsilon-phase that has not described previously. These studies show that this phase possesses special properties that could lead to an unusual behavior in magnetic or catalytic applications.

Structural and Magnetic Properties of Co Thin Films on Au(111) Substrates

“…This result seems to be consistent with a similar empirical observation, conrmed by the ab initio calculations, concerning bulk Co [18].…”

“…It seems that one should expect just the opposite relation between the penalty energy for the faulty stacking and the lm thickness. The result, however, can be interpreted in terms of α-Co and β-Co possible coexistence as has been already reported in bulk Co [18], where also low energy is required for stacking fault formation. Moreover, the actual conclusion opens a new perspective with respect to possible origins of anomalous magnetic anisotropy in such systems (see: for instance, [4]).…”

“…We have assumed hcp stacking for cobalt, as α-Co is the most stable Co phase at lower temperatures [18]. The assumption is also conrmed in glancing angle X-ray diraction (GXRD) experiments for similar sandwich structures [34].…”

“…In both crystal phases ferromagnetic structure is the most stable magnetic phase. Although α-Co and β-Co can even coexist in the same sample, the rst phase is more stable at room temperature and ambient pressure [18]. For Co lms grown on Au(111) the essential question is whether the lm will continue the fcc stacking sequence of the substrate, adopt the native hcp sequence of α-Co, or form stacking faults representing a compromise between the structural tendencies of Co and Au.…”

Recent Progress of the X-ray Magnetic Circular Dichroism Technique for Element-Specific Magnetic Analysis

“…In terms of the stability of ferromagnetism, a close relation between the crystal structure and electronic states (as characterized by the band structures) has long been pointed out. 126) Intensive efforts were made, employing a number of theoretical approaches using differential functional theory calculations 127,128) and first-principle calculations [129][130][131][132][133] to explore new structural and magnetic phases at high pressures. Highpressure XMCD spectroscopy is an advantageous technique for investigating the entanglement between crystal structures, electronic states, and magnetism.…”