Wall energy and wall thickness of exchange-coupled rare-earth transition-metal triple layer stacks
Journal of Applied Physics
The room-temperature wall energy w ϭ4.0ϫ10 Ϫ3 J/m 2 of an exchange-coupled Tb 19.6 Fe 74.7 Co 5.7 /Dy 28.5 Fe 43.2 Co 28.3 double layer stack can be reduced by introducing a soft magnetic intermediate layer in between both layers exhibiting a significantly smaller anisotropy compared to Tb-FeCo and Dy-FeCo. w will decrease linearly with increasing intermediate layer thickness, d IL , until the wall is completely located within the intermediate layer for d IL у d w , where d w denotes the wall
... denotes the wall thickness. Thus, d w can be obtained from the plot w versus d IL . We determined w and d w on Gd-FeCo intermediate layers with different anisotropy behavior ͑perpendicular and in-plane easy axis͒ and compared the results with data obtained from Brillouin light-scattering measurements, where exchange stiffness, A, and uniaxial anisotropy, K u , could be determined. With the knowledge of A and K u , wall energy and thickness were calculated and showed an excellent agreement with the magnetic measurements. A ten times smaller perpendicular anisotropy of Gd 28.1 Fe 71.9 in comparison to Tb-FeCo and Dy-FeCo resulted in a much smaller w ϭ1.1ϫ10 Ϫ3 J/m 2 and d w ϭ24 nm at 300 K. A Gd 34.1 Fe 61.4 Co 4.5 with in-plane anisotropy at room temperature showed a further reduced w ϭ0.3ϫ10 Ϫ3 J/m 2 and d w ϭ17 nm. The smaller wall energy was a result of a different wall structure compared to perpendicular layers.