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Wladek Walukiewicz and Kin Man Yu at Berkeley Lab’s Rutherford Backscattering Spectrometry laboratory
“We were able to determine where the manganese atoms were located, what fraction of this total replaced gallium and acted as electron acceptors (meaning they created ferromagnetic-mediating holes), and what fraction was in the interstitial sites, acting as positively-charged double donors compensating for a fraction of manganese acceptors,” Walukiewicz says.
“Taking all our data together, we find that the Curie temperature of gallium manganese arsenide can be understood only by assuming that its ferromagnetism is mediated by holes residing in the impurity band, and that it is the location of the Fermi level within the impurity band that determines the Curie temperature.”
Electron spin is a quantum mechanical property arising from the magnetic moment of a spinning electron. Spin carries a directional value of either “up” or “down” and can be used to encode data in the 0s and 1s of the binary system. Walukiewicz says that understanding the factors that control the Curie temperature can serve as a guide for strategies to optimise ferromagnetic materials for spintronic applications.
“For example, with appropriate control of the manganese ions, either co-doping with donor ions, or modulation doping, we can engineer the location of the Fermi level within the impurity band to best the advantage,” he points out.
Walukiewicz says the findings of this study further suggest that it should be possible to optimise magnetic coupling and the Curie temperature for the whole family of ferromagnetic semiconductors by tuning the binding energy of the acceptor ions.
The results of this study have been published in the paper, “Controlling the Curie temperature in (Ga,Mn)As through location of the Fermi level within the impurity band” by M. Dobrowolska et al in Nature Materials, published online on 19 Feb 2012. DOIi:10.1038/nmat3250
This research was supported in part by the DOE Office of Science, and by grants from the National Science Foundation, the Natural Sciences and
March 2012
www.compoundsemiconductor.net 79
Engineering Research Council of Canada, and the Canadian Institute for Advanced Research.
Infinera boosts its customer support with a new VP
Todd Hanson has joined indium phosphide PIC innovator Infinera as the vice president of Global Professional Services
Hanson brings deep experience having worked in operations executive roles with high profile cable and service provider companies.
Infinera’s Professional Services team supports customers with deployment, technical support, training, maintenance and consulting services worldwide. These include network migrations from legacy equipment to photonic integrated circuits (PIC) based systems.
Todd Hanson brings to Infinera experience from a customer perspective. Having worked in engineering and operations, management, and executive roles at Sprint, AT&T Canada, Qwest, Frontier, and Time Warner Cable, Hanson is familiar with Infinera’s solutions and the benefits of Infinera’s services.
“As a former Infinera customer on several occasions, I personally experienced Infinera’s advanced solutions and services and quickly recognised the operational benefits in terms of simplicity and lower overall life cycle costs Infinera delivered to our network compared with others,” said Hanson. “I look forward to working with our customers to improve their networks, demonstrating the ease of operation on Infinera’s platforms and the capex and opex improvements.”
“Infinera has grown rapidly, expanding our worldwide footprint,” said Lonny Orona, Senior Vice President, customer services/product support. “Todd brings a wealth of operational experience from his leadership roles with world-class service providers that will serve our customers well. We are excited to have Todd on our team.”
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