Low temperature magnetic force microscope study of magnetization reversal in patterned nanoislands of SrRuO ₃

SrRuO 3 is an itinerant ferromagnet (T _c ∼ 150 K) characterized by large uniaxial magnetocrystalline anisotropy (K ₁ ∼ 7.7 × 10 ⁶ erg/cm ³) and relatively low saturation magnetization (M _s = 213 emu/cm ³) - properties which make SrRuO ₃ an extremely hard magnetic material. We have patterned arrays of rectangular nanoislands of a high quality epitaxial film of SrRuO ₃ with sides ranging between 50 and 500 nm, and studied their magnetization reversal at 4 K using a low temperature magnetic force microscope. We find that the nucleation field for many of the nanoislands is very close to that expected by the Stoner-Wohlfarth model (∼ 3. 8 T) and from nanoislands which exhibit partial reversals we can determine an upper bound for the nucleation volume on the order of 100 × 100 × 10 nm ³. We also find that domain wall pinning in the nanoislands is extremely high and in some cases the depinning field exceeds ∼ 3 T.