We present experimental evidence that ferromagnetic order at room temperature in ultrathin epitaxial Co(001) layers on Cu(001) substrates is stabilized by in-plane magnetic anisotropies. All relevant anisotropy contributions have been determined as a function of Co layer thickness with and without an additional Cu overlayer.

• Received 23 June 1992

DOI:https://doi.org/10.1103/PhysRevLett.69.3674