University of Minnesota scientist have confirmed the ultrahigh magnetic moment of iron-nitride material first suggested in 1972.1 The material, Fe16N2, is comprised of a single nitrogen surrounded by 6 iron atoms with two more between each cluster. The material was found to be 18% higher than the predicted limit thought to only be achievable with an iron-cobalt material. It is believed that the high magnetic moment is due to the electrons being localized within the cluster instead of following a more common free electron gas model.
In the free electron gas model, bands form as atomic density increases. These bands contain electrons all sharing a common orientation of either spin-up or spin-down. When there are an equal number of spin-up and spin-down electrons, the net magnetic moment is zero. If there is a difference in the number of electrons between bands, however, as is the case for some iron, cobalt and nickel containing materials, a net magnetic moment can be measured. The magnitude of the magnetic moment depends on the difference in population of each band. The electronic configuration of iron is [Ar] 4s2 3d6, leaving it with four unpaired electrons of the same spin while that of cobalt is [Ar] 4s2 3d7, or three unpaired electrons with the same spin. In a binary complex of iron-cobalt, there would theoretically be 7 more electrons in either the spin-up or spin-down band, leading to the theoretical limit based on this model.
Because the magnetic moment of Fe16N2 is about 18% greater than this, there has been some controversy over the results first reported by Kim et al.1 One of the reasons is due to the results being difficult to reproduce. Fe16N2 is a metastable complex, making it difficult to measure the highly magnetic Fe8N clusters. Kim’s results were later affirmed in 1990 by researchers from Hitachi2, but Jian-Ping Wang and his group at the Center for Micromagnetics and Information Technologies (MINT) are perhaps the first to give a concise explanation for the unpredictably high magnetic moment of these iron-nitride materials.3,4
Using x-ray adsorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD), Wang et al. were able to measure the highly localized 3d electrons found to exist only in chemically disordered Fe8N and ordered F16N2 phases.3 To support this observation, they also performed LDA+U simulations “to illustrate the correlation between enhanced U and giant magnetic moment.”4 While still a ways off from commercialization, these new findings could lead to the long awaited (by me) resurgence of steady progress in magnetic storage capacity.
I won’t try to recap the story. You’ll have to travel to Jalopnik to view it, in its entirety, for yourself. It is the tale of Bill Caswell and how he took a $500 beater he picked up off of Craiglist to Mexico. It is a tale of how a little ingenuity, hard work, [...]
It looks as if the headline is a bit old, but I still felt it was worth sharing and I question if the copy editor allowed this to slide on purpose. Considering the recent outing of Roy Ashburn and other right-wingers, I also wonder if they are turned-off by the size of Mr. Obama’s package [...]
