Suppression of the perpendicular anisotropy at the CoO Néel temperature in exchange-biased CoO/[Co/Pt] multilayers

E Shipton (1) , K Chan (1) , Thomas Hauet (2) , O Hellwig (2) , Eric E. Fullerton (1)

1 UC San Diego - University of California [San Diego]
2 HGST San Jose Research Center

We performed high field torque magnetometry measurements on CoO/͓Co/Pt͔ magnetic multilayers that exhibit perpendicular exchange bias. We find that the antiferromagnet CoO layers strongly modify the uniaxial anisotropy of the multilayer structures. The strongest effects due to the CoO layers occur in the vicinity of the Néel temperature, where we observe a suppression of the first-order anisotropy and a smaller enhancement of the second-order anisotropy. This results in a nonmonotonic variation of the anisotropy with temperature and for selected samples a transition from perpendicular to in-plane and back to perpendicular anisotropy with increasing temperature. The exchange coupling of thin ferromagnetic ͑FM͒/ antiferromagnetic ͑AF͒ bilayer systems across their mutual interface can result in dramatic changes in the magnetic properties. The most common are exchange bias, i.e., a shift of the hysteresis loop as well as an increase in the coercivity when field cooled below the AF Néel temperature ͑T N ͒. 1 As a result, exchange biasing has become an important tool for controlling the magnetic orientation in magnetic devices and has been extensively studied in thin film 1,2 and nanostruc-tured geometries. 3 However, the impact of the exchange coupling on the anisotropy of the FM in the vicinity of T N and above the blocking temperature ͑T B ͒ is much less studied. The most extensive studies are for FM films coupled to AF single-crystal FeF 2 showing enhanced anisotropy even well above T N of FeF 2 .

Mots clés: magnetic recording; perpendicular anisotropy; thin film

Domaines: Science des matériaux [cond-mat.mtrl-sci]

E Shipton, K Chan, Thomas Hauet, O Hellwig, Eric E. Fullerton. Suppression of the perpendicular anisotropy at the CoO Néel temperature in exchange-biased CoO/[Co/Pt] multilayers . Applied Physics Letters, 2009, ⟨10.1063/1.3240402⟩. ⟨hal-01345335⟩