Tailoring Size Effects on the Exchange Bias in Ferromagnetic-Antiferromagnetic 100 nm Nanostructures (original) (raw)
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A coexistence of lateral and in-depth domain walls in antiferromagnet/ferromagnet ͑AF/FM͒ thin films exhibiting double hysteresis loops ͑DHLs͒ is demonstrated. Comparison of single and DHLs together with local and global measurements confirms the formation of two oppositely oriented domains in the AF that imprint a lateral domain structure into the FM layer. Most significantly, the magnetization reversal mechanism within each opposite domain takes place by incoherent rotation of spring-like domain walls extending through the Ni thickness. Therefore, complex three-dimensional domain walls are created perpendicular and parallel to the AF/FM interface in exchange biased systems.
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The depth dependence of the magnetization has been studied in antiferromagnet/ferromagnet (AF/FM) exchange coupled systems. Results from vector magnetometry and magneto-optical Kerr effect probing both the AF/FM and FM/air interfaces demonstrate the existence of a magnetization depth profile in FeF2/FM (FM=Fe, Ni, and Py) bilayers, contrary to the assumptions of most exchange bias models. The appearance of asymmetrical hysteresis loops below the AF Néel temperature (T_N) is explained by the creation of spring-like walls parallel to the AF/FM interface and the existence of incomplete domain walls. Changes in the reversal mechanism above T_N have also been discussed. The depth dependence of the magnetization has been studied in antiferromagnet/ferromagnet ͑AF/ FM͒ exchange coupled systems. Results from vector magnetometry and magneto-optical Kerr effect probing both the AF/FM and FM/air interfaces demonstrate the existence of a magnetization depth profile in FeF 2 /FM ͑FM= Fe, Ni, and Py͒ bilayers, contrary to the assumptions of most exchange bias models. The appearance of asymmetrical hysteresis loops below the AF Néel temperature ͑T N ͒ is explained by the creation of spring-like walls parallel to the AF/FM interface and the existence of incomplete domain walls. Changes in the reversal mechanism above T N have also been discussed.
Applied Physics Letters, 2004
Exchange bias effects have been investigated in ferromagnetic ͑FM͒-antiferromagnetic ͑AFM͒ square dots, with lateral sizes of 90 nm, sputtered on a prepatterned Si substrate. The magnetic behavior of the dots has been compared with that of a continuous FM-AFM bilayer with the same composition. Along the unidirectional direction, the dots exhibit square hysteresis loops and preserve an exchange bias field, H E , of 70 Oe at room temperature, which is about 40% smaller than H E in the continuous film. In addition, the distribution of blocking temperatures in the nanostructures is found to be shifted toward lower values with respect to that in the continuous film. These results can be interpreted assuming that the reduced lateral dimensions of the nanostructures impose some constraints on the formation and pinning of domain walls in the AFM layer.
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