Microstructure and magnetic domain structure in Fe-Pt and Fe-Pd polytwinned alloys

Lorentz microscopy and conventional transmission electron microscopy have been used to characterize the unique magnetic domain configurations associated with the polytwinned microstructures in Fe-Pt and Fe-Pd alloys. The evolution of the domain structures during the disorder (Al)→ order (L1₀) transformation occurring in these alloys has been followed and correlated with the development of the polytwinned state. A transition from serpentine configuration to bands of lenticular domains within emerging macrotwin plates has been revealed using Lorentz microscopy. Two types of domain walls have been identified, namely, crystallographic frozen and mobile walls within the polytwinned structures. A simple model of the domain configurations and local magnetization appears to describe the salient features of the magnetic structure in the Fe-Pt and Fe-Pd alloys. Lorentz microscopy has been used to measure the thickness of the walls in the fully ordered Fe-Pd alloy, giving an approximate value of δ~50-100 Å