In-plane spin reorientation transition in ultrathin epitaxial Fe(001) films

We studied the growth and magnetic properties of ultrathin Fe(001) films 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 seed layer. Epitaxial quality and surface structure were verified in situ by low-energy and reflection high-energy electron diffraction and scanning tunneling microscopy (STM). Magnetic anisotropy of Fe films in the range of 3-155 monolayers (ML) was determined by alternating gradient magnetometry, superconducting quantum interference device, and magneto-optic Kerr effect. The spontaneous magnetization was always in the 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 transition is equivalent to a sign reversal of an effective fourth order anisotropy constant K-1(eff). In addition, a uniaxial in-plane anisotropy is observed, which may be attributed to the step structure of the samples obtained from STM images. (C) 1997 American Institute of Physics.