Nanotube magnetism

Rui, Y.C.; Skomski, R.; Sorge, K.D.; Sellmyer, D.J.
March 2004
Applied Physics Letters;3/1/2004, Vol. 84 Issue 9, p1525
Academic Journal
FePt and Fe[sub 3]O[sub 4] nanotubes are produced by hydrogen reduction in nanochannels of porous alumina templates and investigated by electron microscopy, x-ray diffraction analysis, and magnetic measurements. Loading the templates with a Fe chloride and Pt chloride mixture followed by hydrogen reduction at 560 °C leads to the formation of ferromagnetic FePt nanotubes in the alumina pores. Using a Fe nitrate solution, thermally decomposed at 250 °C and reduced in hydrogen for 2.5 h at the same temperature, yields Fe[sub 3]O[sub 4] tubes. The length of the nanotubes is about 50 μm and their diameters range from about 150 to 220 nm, depending on the thickness of the template film and the pore diameter distribution. Reflecting the different magnetocrystalline anisotropies of the compounds, the coercivities range from 0.61 kOe for Fe[sub 3]O[sub 4] to 20.9 kOe for FePt. The hysteresis is explained in terms of a tubular random-anisotropy model, which yields a diameter and anisotropy dependent transition from a curling-type mode (Fe[sub 3]O[sub 4]) to a localized mode (FePt). © 2004 American Institute of Physics.


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