Magnetization reversal in exchange biased Co/CoO probed with anisotropic magnetoresistance

Abstract

The magnetization reversal in exchange coupled polycrystalline Co/CoO bilayers has been investigated as a function of CoO thickness using anisotropic magnetoresistance as a probe. The anisotropic magnetoresistance (AMR) was measured during the magnetization reversal and it was used to determine the orientation of the magnetization. For thin CoO layers large training effects were present; ergo the first hysteresis loop after field cooling was not the same as the second. The magnitude of the observed training was found to decrease with increasing CoO thickness. In the samples where substantial training was observed, the first magnetization reversal was dominated by nucleation of reversed domains. For the reversal from the antiparallel state back to the parallel direction, the AMR is consistent with a rotation process. In thicker CoO films where the training was less, the asymmetry was drastically reduced. A simple model that couples the antiferromagnetic grains to the ferromagnetic layer simulates qualitatively the observed magnetoresistance.

Origin of the Inverse Spin Switch Effect in Superconducting Spin Valves

“…These data show that the reversal process is coherent rotation of magnetization in the uniaxial anisotropy field of approximately 20 Oe. In the easy-axis minor loop, resistance remains nearly constant, consistent with reversal by propagation of a small number of domain walls [22]. Fig.…”

“…Due to AMR, the resistance of a Py film, R, depends on the angle, θ, between the directions of current and magnetization: R = R 0 + ∆Rcos 2 (θ). Since ∆R > 0 for Py, higher resistance corresponds to a greater fraction of magnetization parallel to the current direction [22]. Figures 1 (a) and (b) show resistance of a Py(6)/Nb(23)/Py(6)/Ir 25 Mn 75 (10) spin valve at T = 4.2 K (T > T c ) as a function of magnetic field applied in the plane of the sample parallel (easy axis) and perpendicular (hard axis) to the current direction.…”

Rotatable anisotropy driven training effects in exchange biased Co/CoO films

“…4 However, it has been reported that thin CoO films with low magnetocrystalline anisotropy can have large rotatable anisotropy. 36,43 As mentioned above, the classification of the interface UCSs has been recently examined, 23 and it has been demonstrated that although highly anisotropic, an UCS can contribute to H C and not to H EB if it is strongly coupled to the adjacent FM. Conversely, a low-anisotropy UCS will add to EB if the coupling to the FM is sufficiently weak.…”

“…Usually, jH EB j increases with the AFM thickness in this regime with low AFM layer thickness. 36 Moreover, it should also be taken into account that although our sample was grown in a similar fashion, the bilayers of Gruyters were grown on top of Si(111) substrates with hydrogen passivation, while our sample was deposited on top of a thermally-oxidized Si(100) substrate which was covered with a 10 nm thick Au buffer layer. Moreover, the blocking temperature of the samples of Gruyters is around 175 K, whereas the blocking temperature of our CoO layer is 125 K, suggesting that the formed CoO might be more hyperstoichiometric with a higher degree of polycrystallinity, i.e., more prone to nanostructuring effects.…”

Variation of domain formation in a 15 nm NiFe layer exchange coupled with NiO layers of different thicknesses

“…Many experimental and theoretical studies have shown that the existence of domains in the AF layer is necessary for the appearance of exchange bias in FM/AF bilayers. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] Theoretical models have suggested both parallel and perpendicular domain walls. Mauri et al 3 suggested that a domain wall forms in the AF layer parallel to the interface while the magnetization of the FM layer rotates.…”