Prakash Mani

Magnetic transitions in lattice-matched, ordered FePt3 based antiferromagnetic/ferromagnetic films

Measurements of lattice-matched antiferromagnetic/ferromagnetic films which are ideal layered systems to study exchange bias are reported. Epitaxial films of FePt3 have two kinds of antiferromagnetic ordering. The spin ordering phase with wave vector Q1=(12120) has a Neel temperature TN=160K and that with wave vector Q2=(1200) has TN=100K. Neutron diffraction confirmed the presence of Q2=(1200) antiferromagnetic ordering in 200nm Fe25Pt75 grown on MgO(100). The loop shift and coercivity of a trilayer film of CoPt3∕FePt3∕CoPt3 decrease with increasing temperature, consistent with the observed Neel temperature of FePt3. The x-ray diffraction rocking curve widths of films grown on MgO(100) and Al2O3(1120) are compared and related to the loop shifts that are observed in the films with lattice-matched antiferromagnetic/ferromagnetic interfaces.

Magnetic properties of uniaxial synthetic antiferromagnetic films

A study of the properties of uniaxial synthetic antiferromagnetic films with the structure Si(100)/Ta(5 nm)/Co(a)/NM(b)/Co(c)/Ta(10 nm) prepared by oblique sputtering is reported. Easy axis and hard axis hysteresis loops show a strong uniaxial anisotropy. The structural origin of the anisotropy is revealed by atomic force microscopy. The magnetization switching process was measured by polarized neutron reflectometry. The system exhibits biquadratic coupling, since the experimental remanence differs from that calculated by a model considering only bilinear coupling. The dependence of the critical fields on top ferromagnetic layer thickness is measured. A fit including both bilinear and biquadratic coupling qualitatively agrees with the results.