Structural and Magnetic Properties of a Chemically Ordered Manganese Alloy Film

Abstract

<p>FeMn has often been successfully used as a pinning layer in exchange bias systems. Ultrathin FeMn films have been studied little, even though the importance of the volume of a data storage system has been increasingly stressed recently. A 4ML Ni/W(110) substrate is used to establish a (slightly strained) (111) f.c.c. template upon which 3ML Fe is deposited and annealed to 580K. LEED, Auger electron spectroscopy (AES) and crystallographic channeling of Auger electrons (Directional AES) confirm that the resulting substrate has very good short and long range f.c.c. (111) order, and is Fe rich at the surface. Mn is grown sequentially to 1.6ML through multiple depositions, with annealing at 580K for 20 seconds between consecutive depositions to maintain the epitaxial structure. LEED and AES reveal that the annealing caused the Fe and Mn to form a chemically ordered FeMn alloy, while Ni is relatively inert to this thermal effect. The magnetism of each alloy film is studied in situ by the Kerr effect. The alloy films formed from 0.3 or 0.5ML of Mn have magnetic properties similar to the FeNi substrate. Alloy films formed from 0.8 to 1.6ML of Mn show a marked increase in the width of the susceptibility peak, and develop a slanted hysteresis loop with a reduced coercive field that is consistent with a Mn gradient within the film creating a wide distribution in Tc. This suggests a paramagnetic or antiferromagnetic Mn alloy formation.</p>