Rotational hysteresis of the exchange anisotropy direction in Co∕FeMn thin films

Abstract

We have investigated the effects of rotating an applied field on the exchange anisotropy in Co/FeMn thin films. When the applied field is initially along the cooling field direction, the longitudinal hysteresis loop has a maximum coercivity and the transverse hysteresis loop is flat, indicating that the exchange field is along the cooling field direction. When the applied field angle is rotated away and then restored to the original field cooling direction, the exchange anisotropy direction has changed. The rotation of the exchange field direction trails the applied field and is hysteretic. The rotational hysteresis of the exchange field direction is due to the weak anisotropy in thin FeMn layers, and decreases with increasing FeMn thickness.

Ultra-high ferromagnetic resonance frequency in exchange-biased system

“…4. Rotatable anisotropy field reported in previous publications [15][16][17][18][19][20][21] is usually small, which is less than a hundred Oe but in our case it can reach up to 600 Oe. Due to the contribution of this huge rotatable anisotropy field, the resultant dynamic magnetic anisotropy is large even though exchange bias field is small and as a consequence [see Eq.…”

“…Rotatable anisotropy found to be associated with exchange bias long time ago [15] is an angle-independent effect and manifests itself as an isotropic shift of the system energy [16]. This phenomenon is believed to result mostly from the instabilities of AF grains or domains [16][17][18] causing rotational hysteresis in high field [19], isotropic ferromagnetic resonance field shift [16], rotation of exchange field direction [20] and also having an influence on magnetization reversal [21]. It was also found that the rotatable anisotropy is most pronounced when the AF thickness is near the critical thickness for the onset of exchange bias [17,18].…”

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

“…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. Moreover, the nature of the anisotropy can be unambiguously deduced from the angular dependence of the hysteresis loops.…”

“…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.…”

Asymmetric magnetization reversal behavior in exchange-biased NiFe∕MnPt bilayers in two different anisotropy regimes: Close and far from critical thickness

“…[3][4][5][6][7][8][9][10] Moreover, the asymmetry depends on the angle between the external field and the exchange bias direction. 3,4,11 A method to probe the magnetization reversal processes is to use experimental techniques that provide information on the vectorial character of the magnetization such as Kerr magnetometry, 4 Kerr observation, 6 or polarized neutron reflectivity. 9 The existence of transverse magnetization is interpreted as coherent magnetization rotation, 4,11 while the flatness of the transverse magnetization indicates that there are no net rotation of the ferromagnetic ͑F͒ moments in the direction perpendicular to the applied field during the magnetization reversal ͑i.e., incoherent rotation 12 or domain wall propagation͒.…”