Epitaxial nanomagnets with intrinsic uniaxial in-plane magnetic anisotropy

Abstract

High quality epitaxial Fe films were grown on GaAs(001) by molecular beam epitaxy and magnetron sputtering. Two-dimensional arrays of circular dots with 200 nm diameter and 500 nm period were made by interferometric lithography and ion beam etching. Large area patterning (about 1 cm2) allows integral magnetic measurements with an alternating gradient magnetometer. The magnetic behavior of thick patterned films is dominated by the demagnetizing field. Ultrathin continuous films and dot arrays of these show a strong uniaxial in-plane magnetic anisotropy with the easy axis in [110] direction which is fully conserved during the patterning process. This means that two stable remanent single domain states exist in ultrathin Fe (001) sub-µm dots on GaAs(001) because (i) the magnetostatic energy is not important due to the small aspect ratio, and (ii) the Fe/GaAs(001) interface creates a strong uniaxial in-plane magnetic anisotropy. Nanomagnets with these properties seem very attractive for high density memory elements.