Curie temperature and morphology in ultrathin Co/W(110) films

Abstract

The magnetic properties of ultrathin Co films grown on W(110) were studied as a function of Co thickness (1--5 monolayers), substrate temperature during the growth (170 K \ensuremath{\leqslant}${\mathrm{T}}_{\mathrm{s}}$\ensuremath{\leqslant}420 K), and annealing temperature (${\mathrm{T}}_{\mathrm{an}}$, 800 K) for films grown at room temperature. Magnetic results are obtained by means of in situ magneto-optical Kerr effect in static fields and small oscillating fields. The Curie temperature ${\mathrm{T}}_{\mathrm{C}}$ of 1.4--2 monolayers varies linearly from 160 to 450 K. No change of this behavior is found for depositions at 170 K${\mathrm{T}}_{\mathrm{s}}$370 K. Furthermore, we measure a large ac susceptibility ${\mathrm{\ensuremath{\chi}}}_{\mathrm{max}}$\ensuremath{\approx}3000. This indicates the good magnetic homogeneity of the film. Layers annealed to ${\mathrm{T}}_{\mathrm{an}}$>440 K show a much lower ${\mathrm{T}}_{\mathrm{C}}$ and a reduced ${\mathrm{\ensuremath{\chi}}}_{\mathrm{max}}$. Deposition at ${\mathrm{T}}_{\mathrm{s}}$>420 K yields the same behavior. This is correlated to changes in the morphology of the Co layers as observed by Auger spectroscopy.