MAGNETIC TRANSITION IN QUASI ONE DIMENSIONAL WIRES AND THIN FILMS OF GADOLINIUM

Abstract

Thin wires of gadolinium metal have been fabricated using a step lithographic technique with cross-sectional areas from 0.87 × 10−11 cm 2 to 58 × 10−11 cm 2. The thin films of gadolinium were deposited in a ultra high vacuum system by thermal evaporation with the thickness of films in the range 200Å to 1200Å. Resistivity data of Gd thin wires does not show evidence of bulk transition at T c ≈ 293 K (bulk) at all. However, a phase transition manifested as a sharp drop in resistivity of Gd thin wires is observed around 20 K. Thin films of Gd deposited on glass and sapphire substrates were used to measure the magnetic properties using a SQUID magnetometer. Films of thickness > 500Å show ferromagnetic transition around 290 K (close to bulk) and a small peak in the magnetization around 20 K is also observed. For Gd films of thickness ~ 200Å there is no evidence of ferromagnetic transition, however, the magnetization data clearly shows a peak in the neighborhood of 20 K. It appears that in the case of very thin films and thin wires of Gd we are observing a magnetic transition around 20 K. This transition may be due to magnetic ordering of the surface which has a transition temperature much smaller than the bulk ferromagnetic T c of 293 K.