Temperature dependence of the training effect in electrodeposited Co/CoO nanotubes

Abstract

High aspect ratio Co/CoO nanotubes (NTs) were obtained by potentiostatic electrodeposition of Co inside nanoporous alumina templates followed by the natural oxidation of their inner walls. Magnetic measurements performed at low temperatures after field cooling the samples from above its blocking temperature (T B $ 220 K), evidenced the existence of exchange bias (EB) coupling between the Co ferromagnetic outer wall and the CoO antiferromagnetic inner wall of the NTs. A decrease in the magnitude of the EB field was measured at T < T B when cycling the Co/CoO NT arrays through consecutive hysteresis loops. This decrease is known as the training effect (TE) and is here studied in the 6 K T < T B temperature range. The TE was fitted using the recursive Binek formula, giving small values for the characteristic decay rate of the training behavior, and evidencing a decrease of EB with increasing antiferromagnetic layer thickness. A phenomenological theory for the temperature dependence of the TE in exchange biased systems was applied for the first time to core-shell nanotubular structures. The good agreement obtained between the experimental results and the theoretical data, provided a strong confirmation of the qualitative correctness of the spin configuration relaxation model used in these systems.

A Comparative Study of Magnetic Properties of Large Diameter Co Nanowires and Nanotubes

“…One of most recent results on Co-based nanowires is the unidirectional propagation (i.e., magnetization ratchet) of the magnetization reversal irrespective of the longitudinal applied field direction [ 19 ]. Additionally, attractive for applications is the exchange bias obtained by the oxidation or coating of the inner surface in Co core-shell nanotubes, which offer additional tailoring capabilities due to their hollow geometry [ 13 , 20 ].…”

Electrochemical synthesis and magnetism of magnetic nanotubes

“…The physical parameter g is proportional to the inverse square of the coupling constant between the AFM and FM layers. The good-quality fit obtained for g(T) in the studied Co/CoO NT arrays indicates the qualitative accuracy of the spin configuration relaxation model used in these systems (Proenca et al, 2013d). Thermal evolution of the training effect was also measured for the same system (Proenca et al, 2013d), and fitted using a phenomenological theory developed by Binek et al (2005).…”

Modeling the Training Effect in Exchange‐Biased Bilayers for Large Numbers of Magnetization Reversal Cycles

“…The Binek model has been used in diverse publications since. Mostly, 5-20 field cycles are measured, while the systems vary in a broad range of material combinations, such as Co/NiO/[Co/ Pt], [29] La 0.7 Sr 0.3 MnO 3 /SrRuO 3 , [30] Ba 2 ScRuO 6 , [31] Co/CoO, [9,32] or NiFe 2 O 4 /NiO. [33] A slight modification of the Binek model, with an additional higher-order term, was proposed by Wu et al who fitted 10 cycles of magnetization reversal in Co/CoO.…”