Shifted loops and coercivity from field-imprinted high-energy barriers in ferritin and ferrihydrite nanoparticles


We show that the coercive field in ferritin and ferrihydrite depends on the maximum magnetic field in a hysteresis loop and that coercivity and loop shifts depend both on the maximum and cooling fields. In the case of ferritin, we show that the time dependence of the magnetization also depends on the maximum and previous cooling fields. This behavior is associated to changes in the intraparticle energy barriers imprinted by these fields. Accordingly, the dependence of the coercive and loop-shift fields with the maximum field in ferritin and ferrihydrite can be described within the frame of a uniform-rotation model considering a dependence of the energy barrier with the maximum and the cooling fields.



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Silva, NJO; Amaral, VS; Urtizberea, A; Bustamante, R; Millan, A; Palacio, F; Kampert, E; Zeitler, U; de Brion, S; Iglesias, O; Labarta, A

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The authors acknowledge V. de Zea Bermudez for the synthesis of the organic-inorganic hybrid containing ferrihydrite nanoparticles and R. Boursier for his help with the high-field setup in Grenoble. Part of this work has been supported by EuroMagNET II under the EU Contract No. 228043. We acknowledge IFIMUP for the possibility of performing the magnetization time dependence measurements. The financial support from FCT (Grant No. PTDC/FIS/105416/2008) is gratefully recognized. The Aveiro-Zaragoza collaboration has been supported by the Integrated Spanish-Portuguese Action under the Grant No. PT2009-0131. The Aveiro-Barcelona collaboration has been supported by the Integrated Spanish-Portuguese Action under the Grant No. AIB2010PT-00099. The work in Zaragoza has been supported by the research Grants No. MAT2007-61621 and No. CONSOLIDER CSD2007-00010 from the Ministry of Education. O.I. and A.L. acknowledge funding of the Spanish MICINN through Grants No. MAT2009-08667 and No. CSD2006-00012, and Catalan DIUE through Project No. 2009SGR856. N.J.O.S. acknowledges CSIC for a I3P contract and FCT for Ciencia 2008 program, A.U. acknowledges the financial support provided by contract from the EC NoE MAGMANET, and R.B. acknowledges ICMA-CSIC for a JAE-predoc grant.

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