INPLANE SPIN REORIENTATION TRANSITION IN ULTRATHIN EPITAXIAL FE(001) FILMS

We studied the growth and magnetic properties of ultrathin Fe(001) fil ms on Au(001) buffer layers grown by molecular-beam epitaxy on MgO(001 ) single crystals. Epitaxial growth could be achieved by use of a Cr s eed layer. Epitaxial quality and surface structure were verified in si tu by low-energy and reflection high-energy electron diffraction and s canning tunneling microscopy (STM). Magnetic anisotropy of Fe films in the range of 3-155 monolayers (ML) was determined by alternating grad ient magnetometry, superconducting quantum interference device, and ma gneto-optic Kerr effect. The spontaneous magnetization was always in t he film plane. Below a critical thickness of 7.3+/-0.7 ML we observe a rotation of the cubic easy axes by 45 degrees from the [100] to the [ 110] directions within the film plane. This spin reorientation transit ion is equivalent to a sign reversal of an effective fourth order anis otropy constant K-1(eff). In addition, a uniaxial in-plane anisotropy is observed, which may be attributed to the step structure of the samp les obtained from STM images. (C) 1997 American Institute of Physics.