Magnetization-reversal processes in an ultrathin Co/Au film

Ferré, J.; Grolier, V.; Meyer, P.; Lemerle, S.; Maziewski, A.; Stefanowicz, E.; Tarasenko, S. V.; Tarasenko, V. V.; Kisielewski, M.; Renard, D.

doi:10.1103/physrevb.55.15092

Cited by 88 publications

(73 citation statements)

References 15 publications

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“…Macroscopically the major loops repeat themselves in successive cycles, however it was appreciated [3,4] that disorder induces memory in the microscopic magnetic domain configurations from one cycle of the hysteresis loop to the next, even when H sat was crossed. Successive minor loops are usually reasonably reproducible, although changes of size and shape were observed [5][6][7]. Nevertheless these finite perturbations did not undermine a generally accepted view that macroscopic hysteresis loops are repeatable.…”

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confidence: 93%

“…in which N E and P E are characteristic energies for nucleation and propagation, N V and P V are characteristic nucleation and propagation volumes (which are assumed to be roughly equal [7]). A typical activation volume V a can be estimated from an exponential field dependence of t 50 on the magnetic field [17,21] ( )…”

Section: Magnetization Reversal At Constant Magnetic Fieldmentioning

confidence: 99%

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Dynamics of successive minor hysteresis loops

2012

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Cumulative growth of successive minor hysteresis loops in Co/Pd multilayers with perpendicular anisotropy was studied in the context of time dependent magnetization reversal dynamics. We show that in disordered ferromagnets, where magnetization reversal involves nucleation, domains' expansion and annihilation, differences between the time dependencies of these processes are responsible for accumulation of nuclei for rapid domain expansion, for the asymmetry of forward and backward magnetization reversals and for the respective cumulative growth of hysteresis loops. Loops stop changing and become macroscopically reproducible when populations of upward and downward nucleation domains balance each other and the respective upward and downward reversal times stabilize. PACS: 75.60.Jk, 75.70.Cn, IntroductionReproducibility of cycling processes under identical external conditions attracts particular attention in studies of magnetic hysteresis for at least two reasons: the effect is fundamental to all magnetic storage technologies, and it can serve as a model for a wide range of type-I phase transitions. Two types of hysteresis loops are distinguished."Major" loops are obtained by sweeping the applied field beyond the saturation field H sat , above which the system is said to be fully saturated and its magnetization M(H) is a single-valued function of the applied field H; "minor" loops are obtained when the cycle is limited to fields near and below H sat . Many studies were devoted to the macroscopic and microscopic repeatability of minor and major hysteresis loops and effects of disorder on cycle-to-cycle memory [1,2]. Macroscopically the major loops repeat themselves in successive cycles, however it was appreciated [3,4] that disorder induces memory in the microscopic magnetic domain configurations from one cycle of the hysteresis loop to the next, even when H sat was crossed. Successive minor loops are usually reasonably reproducible, although changes of size and shape were observed [5][6][7]. Nevertheless these finite perturbations did not undermine a generally accepted view that macroscopic hysteresis loops are repeatable. It came therefore as a surprise when Berger et al. [8] reported major cumulative expansion of successive minor hysteresis loops in Co/Pt and Co/Pd multilayers even up to four times their initial area. The phenomenon was explained in terms of successive accumulation of small nucleation domains, i.e. microscopic areas of reversed magnetization that act as nuclei for the subsequent macroscopic magnetization reversal [8,9]. The reversals at all but the first cycle do not start anew from a fully saturated state but from a preconfigured state in which nuclei for domain expansion are locally conserved. Conservation and accumulation of the nuclei can happen if the system responds asymmetrically in forward and reverse field orientations such that small domains appear to be substantially more stable toward annihilation in an opposite field than toward expansion in a forward field.In this paper we shall de...

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confidence: 93%

Section: Magnetization Reversal At Constant Magnetic Fieldmentioning

confidence: 99%

Dynamics of successive minor hysteresis loops

2012

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“…7,15,24 Nevertheless, some coherent rotation models have been proposed to explain the magnetic behavior of similar systems by introducing the inhomogeneity of magnetic parameters, such as local coercivity 25 or anisotropy 26 variations. For example, Boukari et al, 13 taking into account both K 1 and K 2 together with a distribution of K 1 , were able to fit well some of the out-of-plane loops for their Co/ Pt multilayers.…”

Section: Resultsmentioning

confidence: 99%

Cone magnetization state and exchange bias in IrMn∕Cu∕[Co∕Pt]3 multilayers

Castro

Geshev

Schmidt

et al. 2009

Journal of Applied Physics

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The effects of a Cu interlayer on the perpendicular exchange bias in IrMn/ Cu/ ͓Co/ Pt͔ 3 multilayers were investigated by focusing on the correlation between the exchange bias and the magnetic anisotropy. The in-plane magnetization hysteresis loops were interpreted in the framework of a phenomenological model based on the coherent magnetization rotation, indicating that the easy magnetization axis makes an angle of approximately 15°with the normal of the IrMn/ ͓Co/ Pt͔ 3 film. This angle decreases with the introduction of the Cu spacer thickness in the IrMn/ Cu/ ͓Co/ Pt͔ 3 system, indicating that the Cu interlayer leads to a predominant perpendicular anisotropy. Although a maximum of the out-of-plane anisotropy is found for Cu layer thickness between 4 and 5 Å, the maximum of the perpendicular exchange bias was found at 3 Å of Cu, which could be attributed to the interplay between two effects, mainly the increase in the effective perpendicular anisotropy with the Cu spacer thickness due to the reorientation of the Co moment toward the normal to the film's plane direction, and the exponential decrease in the ferromagnet/antiferromagnet exchange coupling ͑and, consequently, of the exchange bias shift field͒ with the Cu interlayer thickness.

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“…This condition is usually fulfilled for films with a polycrystalline structure. The magnetostatic energy in ultrathin films with large domains only renormalizes the anisotropy energy [7] and therefore it can be also omitted. Calculations give the following formulas for ΔS and ΔL:…”

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confidence: 99%

Coercivity of Ultrathin Magnetic Films with Perpendicular Anisotropy

et al. 2000

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The calculation of the temperature dependence of the domain wall coercivity of ultrathin magnetic films with perpendicular anisotropy is reported. In this case, the magnetization reversal is supposed to occur through domain wall motion. The proposed model takes into account thermal bending fluctuations of the domain wall , which is pinned by crystal defects such as grain boundaries. A fitting procedure, applied to recently published experimental data on the field induced domain wall velocity in Au/Co films, allows us to find out realistic values of the involved parameters.PACS numbers: 75.60. 75.60.Ch, 75.70.Ak In many experiments, which had been performed for ultrathin ferromagnetic films and multilayers, either a nonlinear or almost linear law of the coercivity decrease with the increase in the film temperature has been found (for a review see Refs. [1][2][3][4]). This decrease can be understood as coming from a mechanism of thermally activated domain wall (DW) motion. Indeed, the DW coercivity at T = 0 is determined by a value of the energy barrier which separates two different positions of a DW segment. At T > 0 the energy of thermal oscillations of the . DW segment favours to overcome the coercivity barrier and decreases its effective value.The goal of this paper is to thermodynamically examine the bending oscillation of DW and the mechanism of their movement in ultrathin magnetic films with a perpendicular anisotropy. The basis is the DW vibration model similar to that applied in Ref. [5] for the description of the bend fluctuations of long molecules.Let us suppose that a segment of the DW is pinned to two defects (or to grain boundaries) and that the distance between them is 2R. We consider a limp type of DW and a weak DW pinning regime. For T > 0 the DW can change its form owing to the effect of the temperature fluctuations. We will describe the form of the DW bend by the following equation y = b/ch(x/R) (here b is the amplitude of the DW bending). The magnetic field is directed perpendicular to the film surface.(471)

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Magnetization-reversal processes in an ultrathin Co/Au film

Cited by 88 publications

References 15 publications

Dynamics of successive minor hysteresis loops

Dynamics of successive minor hysteresis loops

Cone magnetization state and exchange bias in IrMn∕Cu∕[Co∕Pt]3 multilayers

Coercivity of Ultrathin Magnetic Films with Perpendicular Anisotropy

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