Abstract
A new model is proposed for the ferromagnetism associated with partially localized electron states in the Fe16N2 system that explains its giant saturation magnetization. It is demonstrated that an unusual correlation effect is introduced within the Fe–N octahedral cluster region and the effective on-site 3d–3d Coulomb interaction increases due to a substantial 3d electron charge density difference between the cluster and its surroundings, which leads to a partially localized electron configuration with a long-range ferromagnetic order. The first-principles calculation based on the LDA+U method shows that giant saturation magnetization can be achieved at sufficiently large Hubbard U values. The feature of the coexistence of the localized and itinerant electron states plays a key role in the formation of giant saturation magnetization.
Highlights
The search for material with higher saturation magnetization becomes more crucial for high magnetic-energy-product permanent magnets and extremely high areal density magnetic recordings
Interest in its magnetic properties originates from a discovery by Kim and Takahashi in 1972 [4], when they reported giant saturation magnetization (Ms = 2.58 T) observed on Fe–N films synthesized by a thermal evaporation process
When nitrogen is accommodated in the iron octahedral clusters to form interstitial compounds, the 3d down-spin electrons redistribute themselves on different iron sites due to p–d hybridization between the N site and its nearest six iron neighbors [10]
Summary
The search for material with higher saturation magnetization becomes more crucial for high magnetic-energy-product permanent magnets and extremely high areal density magnetic recordings. In the case of α -Fe16N2, calculations based on local spin density approximation (LSDA) fail to predict magnetic moments as high as claimed by experiments, even when firstprinciples methods [11] or non-local correction have been considered [12].
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