Magnetic anisotropy and thermal stability study on FePt nanoparticle assembly

Wu, X. W.; Guslienko, K. Y.; Chantrell, R. W.; Weller, D.
May 2003
Applied Physics Letters;5/19/2003, Vol. 82 Issue 20, p3475
Academic Journal
The temperature dependence of the first-order magnetic anisotropy constant has been investigated for off-stoichiometric chemically ordered L1[sub 0], Fe[sub 45]Pt[sub 55] nanoparticle samples. A representative sample shows an anisotropy energy density of K[sub u] = 0.7 × 10[sup 7] erg/cm³ and a thermal stability factor of K[sub u] F/k[sub B] T= 77 at room temperature. With decreasing temperature, from room temperature to 5 K, a 50% increase of K[sub u], accompanied by a 25% increase of the saturation magnetization M[sub S] is observed. The temperature dependence of K[sub u] 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.


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