Magnetization reversal, asymmetry, and role of uncompensated spins in perpendicular exchange coupled systems

Abstract

International audienceSoft x-ray resonant magnetic scattering has been used to investigate the element-selective microscopic magnetization reversal behavior of room temperature perpendicular exchange coupled ferromagnetic/antiferromagnetic (F/AF) systems and to study the role of the interfacial coupling strength on it. Different nucleation processes and domain size distributions along the decreasing and increasing branches of the reversal have been found. The size of the magnetic domains during reversal depends on both the F anisotropy and F/AF coupling strength, decreasing when one of them increases. Evidence of the exchange bias (coercivity enhancement) being induced by pinned (unpinned) uncompensated AF interfacial spins is also shown

Emergence of noncollinear anisotropies from interfacial magnetic frustration in exchange-bias systems

“…In general, rotation processes are more relevant in one branch of the hysteresis loop, in which a larger density of domains during irreversible domain nucleation processes is also observed. 25,28,29,35,36 For some systems, rounded transitions in M ʈ and larger M Ќ values are found in the descending branch, 20,21,[25][26][27][28][34][35][36] where the field is applied parallel to the exchange-bias direction, while other systems display the opposite behavior. [21][22][23][24][25][29][30][31][32][33] Our results indicate that this discrepancy is related to the difference between a collinear and a noncollinear anisotropy case.…”

“…Asymmetries in the magnetization reversal have been observed for many FM/AFM systems with both in-plane [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] and perpendicular 35,36 anisotropy for the FM layer. In general, rotation processes are more relevant in one branch of the hysteresis loop, in which a larger density of domains during irreversible domain nucleation processes is also observed.…”

Exploring the limits of soft x-ray magnetic holography: Imaging magnetization reversal of buried interfaces (invited)

“…In addition, it has already been found that pinned (unpinned) uncompensated AFM spins at the interface are correlated with the exchange bias 18 (coercivity enhancement). 19 These features have been addressed in both in-plane and perpendicular 20 exchange coupled FM/AFM systems. However, a microscopic imaging of most of the aforementioned effects during magnetization reversal, i.e., in external magnetic fields, is still lacking.…”

“…The smaller domain periodicity found for the thicker sample (n ¼ 8) has been also found in perpendicular exchange-biased [Pt/Co] n / FeMn systems by means of soft x-ray magnetic scattering measurements. 20 This originates from the low dimensionality and the minimization of dipolar effects in perpendicular anisotropy systems. The domain size is determined by the balance between the magnetostatic energy, which reduces upon domain formation, and the domain wall energy.…”

Asymmetric magnetization reversal and its dual origin in Co/FeMn out-of-plane induced exchanged bias systems

“…It has been revealed that the forward and backward branches of the magnetization reversal are performed in different modes, such as the separated ways of magnetic moment rotation [5][6][7][8], the distinct nucleation sites and abilities of the inverse domain [9][10][11][12][13][14][15][16][17][18], and the unsymmetrical training and recovering effect of the pinning of the UCAS [3,[19][20][21][22]. Most AMRBs, except for the loop shift, have their particular features in the specific EB systems, which strongly depends on the structure [1,4,23,24] and measuring methods [4,[9][10][11][25][26][27][28]. The appearances of the AMRBs are so complex that the comprehension on the origin and the classification of the AMRBs is still in debate.…”