Anomaly of strain relaxation in thin ordered FePd layers

Domain wall pinning on strain relaxation defects in FePt(001)/Pt thin films

“…These steps indicate the emergence at the surface of the microtwins, here corresponding to the ͕111͖ twins described above. 14,15 Up to 20 partial dislocations pileup in a single defect. Hence, the height of these steps varies from 0 to 3 nm.…”

Magnetic domain wall pinning and coercivity in FePt/MgO and FePt/Pt thin films

“…This is due to the dipolar field that favors a vertical alignment of the DW and thus the depinning. However, it has been shown [18] that the average number of atomic layers in the microtwin increases quasi-linearly with the alloy thickness, up to approximately 25 atomic planes in 40 nm FePt layers [15]. The variation of the depinning field as a function of the width of the microtwin is shown in Fig.…”

“…On the first hand, structural studies [17,18] showed that dislocations are introduced at the beginning of the growth, in order to relax the epitaxial strain between the FePt layer and the MgO substrate. According to Halley [17], these perfect dislocations possess a 1=2½1 0 1 Burgers vector, and form a lattice with a parameter of approximately 2 nm (1.7 nm in FePd/ MgO layers, whose structural and magnetic properties are very similar to those of FePt/MgO layers).…”

Critical thickness for misfit twinning in an epilayer

“…Their results show that misfit twinning, resulting from the glide of 90°partial dislocations on successive {1 1 1} planes, is the major stress-relief mechanism. Halley et al (2002) demonstrated that the strain relaxation in ordered FePd films grown on Pd (0 0 1) substrates took place mainly through misfit twining. The lattice misfit between the ordered FePd and Pd(0 0 1) lattices is about 1%.…”