Abstract:
The magnetism of antiferromagnetic FeₓPt₁₋ₓ thin films x=0.27 and 0.30) epitaxially grown onto MgO (110) and a-axis sapphire (α-Al₂O₃) substrates has been studied by elastic neutron and x-ray scattering. Bulk chemically ordered FeP₃ exhibits an antiferromagnetic spin structure with a wave vector Q₁=2π/a(1/2 1/2 0) below T_(N1)∼160K. For slightly Fe-rich alloys (x≳0.26) a spin-reorientation transition to a second antiferromagnetic phase with a wave vector Q₂=2π/a(1/2 0 0) occurs below T_(N2)∼100K at the expense of Q₁. For increased Fe content (x≳0.30) the Q₁ phase is strongly suppressed with a dominant Q₂ phase. For (111)-oriented films grown on a-axis sapphire the spin structure is the same as that found in the bulk. The x=0.27 film exhibits transitions at T_(N1) and T_(N2). The film with x=0.30 exhibits an almost completely suppressed Q₁ phase and a dominant Q₂ phase with an enhanced ordering temperature of T_(N2)∼140K. In contrast FePt₃ (110) films grown onto MgO (110) exhibit only the Q₁ phase for both compositions x=0.27 and x=0.30 with the onset of the Q₂ phase suppressed. The distinct behavior of the films grown onto MgO from those grown onto a-axis sapphire and bulk FePt₃ may be explained by higher strain and defect densities incorporated in the films grown onto MgO.
