Evolution of magnetic domain reversal with temperature in Co/Pt multilayers observed by magneto-optical Kerr imaging

The evolution of magnetic domain structures with temperature during magnetic reversal in Co(4 A)/Pt(t(Pt)) multilayers with perpendicular anisotropy has been investigated using magneto-optical Kerr imaging. Relatively large Pt layer thicknesses (t(Pt)=43 and 63 A) are chosen for this study because the interlayer coupling strength in the multilayers varies from weak at room temperature to strong at low temperatures. A Co/Pt multilayer with strong interlayer coupling (t(Pt)=11 A) is also studied as a comparison. Kerr imaging during magnetic reversal shows a transformation of domain patterns with temperature which correlates directly with the enhancement of interlayer exchange coupling with decreasing temperature, as well as the conversion from domain-wall-propagation-dominant reversal at room temperature to nucleation-dominant reversal at low temperatures. The enhanced interlayer coupling at low temperatures leads to the entire multilayer switching as a single ferromagnet; while at higher temperatures, when the interlayer coupling weakens, quasi-independent layer-by-layer magnetic reversal is observed. The transformation from propagation- to nucleation-dominant magnetic reversal can be understood by the competition between activation energies for domain nucleation and propagation, Zeeman energy, and thermal energy.