Hard-axis magnetization of ultrathin Ni(111) films on W(110): An experimental method to measure the magneto-optic Kerr effect in ultrahigh vacuum

A set up to measure the magneto-optic Kerr rotation in ultrahigh vacuum from ultrathin ferromagnetic films in magnetic fields of up to 1.4 T is described. Hard-axis-magnetization loops of 10 to 30 {} thin Ni(111) films are recorded in situ with the magnetic field applied normal to the film plane. The anisotropy energy of 10-{} Ni(111) is {}-10⁶ erg/cm³ at room temperature, more than 1 order of magnitude larger than in the bulk. Square hysteresis loops are recorded with the field parallel to the film plane. This yields an easy axis of magnetization in the plane oriented along the W(100) direction. The shape of the hard-axis loops depends critically on the perfect alignment of the applied field with respect to the film normal.