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.
- Kim, T.K. and Takahashi. M, Appl. Phys. Lett., 20, 492 (1972)
- Sugita, Y., et al., J. Appl. Phys. 76, 6637 (1994)
- Liu, X. Q. et al., arxiv: 0909.4480v1 (2009)
- Ji, N. et al., arxiv: 0909.4478v1 (2009)
IBM Continues their forward march in bringing about the end of an era, one that began in the 1960s at Bell Laboratories where the first transistor was made. Oddly enough, what began with germanium quickly transitioned to silicon and the semiconductor industry that we know of today. Though there are patents for transistors dating back to the early 1920s, it wasn’t until Shockley’s work, expanding on that of Bardeen and Brattain, that we came to have the transistors that we know and love today. But it seems that all of that may soon be coming to an end, with the rapid research taking place in the fields of plasmonics and especially graphene.
We all want faster, more efficient, machines but we are starting to reach the limits of what can be done with silicon and silicon based electronics. Replacements are being research, such as the PlasMOStor DOI: 10.1021/nl803868k suggested by Henry Atwater, but it would be nice to have alternatives that offer more of a drop-in replacement for the infrastructure we currently have. That is where graphene comes in. Graphene, for those of you wondering, is a single layer of graphite – the stuff in pencils – and has become one of the latest buzzwords in the field. A better description graphene is offered by A. K. Geim et. al.
Graphene is a flat monolayer of carbon atoms tightly packed into a two-dimensional (2D) honeycomb lattice, and is a basic building block for graphitic materials of all other dimensionalities. It can be wrapped up into 0D fullerenes, rolled into 1D nanotubes or stacked into 3D graphite.[1]
And now IBM has managed to demonstrate a 100GHz transistor fashioned from this same material. If memory serves, that is about 10x faster than the fastest silicon transistor to be demonstrated. We are still a ways off from having graphene based CPUs, GPUs and APUs, but they are coming and with the blistering rate at which IBM has been moving I would say they’ll be here sooner than any of us expects.
- Geim, A. K. and Novoselov, K. S. (2007). “The rise of graphene”. Nature Materials 6 (3): 183–191. doi:10.1038/nmat1849. http://onnes.ph.man.ac.uk/nano/Publications/Naturemat_2007Review.pdf.
And here you though pencil lead was only good for writing. As it turns out, when you take graphite and whittle it down to a two-dimensional structure, the stuff becomes pretty amazing. Terahertz amazing, as in the stuff is predicted to allow us to replace silicon-based microelectronics with parts that are 100-1000 times faster. It is pretty impressive stuff, especially if it can do the job more cheaper and more efficiently than silicon. I won’t abandon my hopes for light based computing, but instead of silicon waveguides (DOI: 10.1021/nl803868k), maybe I should start to look into ways to create the same device using graphene. To summarize, for those keeping track of the latest in graphene news, we have IBM coming out with their announcement of finally being able to open a bandgap for graphene field-effect transistors (FETs) and now Penn State can fabricate sheets of pure graphene on 100mm wafers. It still involves silicon and the sizes are about 200mm off from what is currently used in the industry, but we’re getting there and we are getting there fast.
A new report has been released suggesting that dolphins should enjoy the classification of ‘person’. This is based largely, in part, on the work of zoologist, Lori Marino, and professor of psychology, Diana Reiss. Their work, of course, builds off the large body of research already looking into dolphin intelligence and their findings replace chimpanzees as the planets second most intelligent mammal with dolphins. Their full findings are to be present next month at a conference in San Diego where they conclude “that the new evidence about dolphin intelligence makes it morally repugnant to mistreat them.” They will also be joined by Thomas White, professor of ethics, who has suggested that dolphins, as ‘non-human persons’, should be afforded basic rights. Read the rest of this entry »