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Magnetic anisotropy and thermal stability study on FePt nanoparticle assembly

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4 Author(s)
Wu, X.W. ; Seagate Research, 1251 Waterfront Place, Pittsburgh, Pennsylvania 15222-4215 ; Guslienko, K.Y. ; Chantrell, R.W. ; Weller, D.

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The temperature dependence of the first-order magnetic anisotropy constant has been investigated for off-stoichiometric chemically ordered L10, Fe45Pt55 nanoparticle samples. A representative sample shows an anisotropy energy density of Ku=0.7×107erg/cm3 and a thermal stability factor of KuV/kBT=77 at room temperature. With decreasing temperature, from room temperature to 5 K, a 50% increase of Ku, accompanied by a 25% increase of the saturation magnetization MS is observed. The temperature dependence of Ku is explained on the basis of the spin-Hamiltonian approach with an Fe effective spin. The estimated median “magnetic” grain size, obtained from time-dependent measurements, decreases by about 15% with decreasing temperature from 298 to 100 K. This magnetic grain size reduction is attributed to the decrease of the superparamagnetic fraction in the FePt nanoparticle sample. © 2003 American Institute of Physics.

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Applied Physics Letters  (Volume:82 ,  Issue: 20 )