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Momentum transfer resolved memory in a magnetic system with perpendicular anisotropy

Description: We have used resonant, coherent soft x-ray scattering to measure wave vector re- solved magnetic domain memory in Co/Pd multilayers. The technique uses angular cross correlation functions and can be applied to any system with circular annuli of constant values of scattering wave vector q. In our Co/Pd film, the memory exhibits a maximum at q = 0.0384 nm-1 near initial reversal that decreases in magnitude as the magnetization is further reversed. The peak is attributed to bubble domains that nucleate reproducibly near initial reversal and which grow into a labyrinth domain structure that is not reproduced from one magnetization cycle to the next.
Date: January 28, 2011
Creator: Seu, Keoki; Roy, Sujoy; Su, Run; Parks, Daniel; Shipton, Erik; Fullerton, Eric et al.
Partner: UNT Libraries Government Documents Department

Domain wall dynamics in a spin-reorientation transition system Au/Co/Au

Description: We report measurements of domain wall dynamics in an ultrathin Au/Co/Au system that exhibits a spin reorientation phase transition as a function of temperature.The domain walls exhibit cooperative motion throughout the temperature range of 150 - 300 K. The decay times were found to exhibit a maximum at the transition temperature. The slowdown has been explained as due to formation of a double well in the energy landscape by the different competing interactions. Our results show that the complex, slow dynamics can provide a more fundamental understanding of magnetic phase transitions.
Date: May 14, 2009
Creator: Roy, Sujoy; Seu, Keoki; Turner, Joshua J.; Park, Sungkyun; Kevan, Steve & Falco, Charles M.
Partner: UNT Libraries Government Documents Department

Delocalization and hybridization enhance the magnetocaloric effect in Ni2Mn0.75Cu0.25Ga

Description: In view of the looming energy crisis facing our planet, attention increasingly focuses on materials potentially useful as a basis for energy saving technologies. The discovery of giant magnetocaloric (GMC) compounds - materials that exhibit especially large changes in temperature as the externally applied magnetic field is varied - is one such compound 1. These materials have potential for use in solid state cooling technology as a viable alternative to existing gas based refrigeration technologies that use choro-fluoro - and hydro-fluoro-carbon chemicals known to have a severe detrimental effect on human health and environment 2,3. Examples of GMC compounds include Gd5(SiGe)4 4, MnFeP1-xAsx 5 and Ni-Mn-Ga shape memory alloy based compounds 6-8. Here we explain how the properties of one of these compounds (Ni2MnGa) can be tuned as a function of temperature by adding dopants. By altering the free energy such that the structural and magnetic transitions coincide, a GMC compound that operates at just the right temperature for human requirements can be obtained 9. We show how Cu, substituted for Mn, pulls the magnetic transition downwards in temperature and also, counterintuitively, increases the delocalization of the Mn magnetism. At the same time, this reinforces the Ni-Ga chemical bond, raising the temperature of the martensite-austenite transition. At 25percent doping, the two transitions coincide at 317 K.
Date: November 26, 2008
Creator: Roy, Sujoy; Blackburn, E.; Valvidares, S. M.; Fitzsimmons, M. R.; Vogel, Sven C.; Khan, M. et al.
Partner: UNT Libraries Government Documents Department