Coercivity mechanisms in positive exchange-biased Co films and Co/Pt multilayers

Kirk, Taryl L; Hellwig, Olav; Fullerton, Eric E.

doi:10.1103/physrevb.65.224426

Cited by 63 publications

(40 citation statements)

References 23 publications

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“…Recent experiments on model systems using synthetic antiferromagnets have shown that larger domain sizes could lead to a loop bifurcation. 13,14 In this work, we demonstrate that a bifurcated hysteresis loop can be realized in field-cooled ͑FC͒ Ni/ epitaxial-FeF 2 bilayers. In comparison, the bifurcation is absent in FC Ni/ twinned-FeF 2 and Ni/ polycrystalline-FeF 2 , which are expected to have smaller AF domain sizes.…”

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confidence: 65%

“…This is consistent with the findings in synthetic antiferromagnets where it has been shown that a loop bifurcation develops as the domain size becomes larger. 13,14 For the Ni/ epitaxial-FeF 2 bilayers studied here, the larger in-plane coherence length and the lack of orthogonal twinning encourage the formation of large domains, leading to a larger D AF than that in twinned-FeF 2 . Although the actual D AF here is yet to be determined, large AF domains ͑up to ϳmm scale͒ have been seen in bulk single crystal fluorides.…”

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confidence: 92%

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Loop bifurcation and magnetization rotation in exchange-biasedNi∕FeF2

Olamit

Arenholz

et al. 2005

Phys. Rev. B

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Exchange biased Ni/ FeF 2 films have been investigated using vector coil vibrating sample magnetometry as a function of the cooling field strength H FC . In films with epitaxial FeF 2 , a loop bifurcation develops with increasing H FC as it divides into two subloops shifted oppositely from zero field by the same amount. The positively biased subloop grows in size with H FC until only a single positively shifted loop is found.Throughout this process, the negative/positive (sub)loop shift has maintained the same discrete value. This is in sharp contrast to films with twinned FeF 2 where the exchange field gradually changes with increasing H FC . The transverse magnetization shows clear correlations with the longitudinal sub-loops. Interestingly, over 85% of the Ni reverses its magnetization by rotation, either in one step or through two successive rotations. These results are due to the single crystal nature of the antiferromagnetic FeF 2 , which breaks down into two opposite regions of large domains.

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confidence: 65%

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confidence: 92%

Loop bifurcation and magnetization rotation in exchange-biasedNi∕FeF2

Olamit

Arenholz

et al. 2005

Phys. Rev. B

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“…15 They are also consistent with loop bifurcations seen in synthetic antiferromagnets with large domain sizes. 26,27 The evolution of the subloop sizes with field cooling angle α is due to a distribution of anisotropy strengths of the AF spins. Fig.…”

Section: Loop Bifurcationmentioning

confidence: 99%

Angular dependence of exchange anisotropy on the cooling field in ferromagnet/fluoride thin films

Olamit

Schuller

et al. 2006

Phys. Rev. B

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Exchange anisotropy in ferromagnet/antiferromagnet (FM/AF) films is usually introduced along the cooling field or FM magnetization direction. Here we investigate the dependence of the exchange anisotropy, loop bifurcation, and reversal mechanism on the cooling field direction using vector magnetometry. Three types of samples (FM=Fe, Ni /AF = FeF 2 , MnF 2 ) have been studied where the AF layer is epitaxial (110), twinned (110), and polycrystalline. With an epitaxial AF which has one spin axis, the cooling field orients the exchange field along the spin axis. Applying the cooling field perpendicular to the spin axis results in bifurcated loops, whose shape evolves with the cooling field geometry and strength. With a twinned AF where there are two orthogonal spin axes, the exchange field direction is along the bisector of the spin axes that encompass the cooling field. With a polycrystalline AF, the exchange field direction is the same as the cooling field. Transverse hysteresis loops show that when the exchange field has a component perpendicular to the applied field, the magnetization reversal occurs by rotation in the direction of the perpendicular component. Our results demonstrate that in fluoride films, the exchange field is established primarily by the AF anisotropy direction, and only to a lesser extent the cooling field or the magnetization Phys. Rev. B, in press; cond-mat/0512257 2 direction. The bifurcated loops are due to a distribution of AF anisotropies and large AF domain sizes. Furthermore, the magnetization reversal process is extremely sensitive to the exchange field direction.

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“…[2][3][4][5][6][7] Although it has been intensively studied for systems with in-plane magnetization, it has hardly been used in recent studies on perpendicular exchange bias. [8][9][10][11][12][13][14][15][16][17][18] In a recent paper, Sort et al showed that Co/ Pt multilayers with out-ofplane magnetization can be biased by growing an IrMn layer on top. 19 In this paper we present an overview on the exchange-biasing properties of IrMn in systems with perpendicular magnetic anisotropy.…”

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confidence: 99%

IrMn as exchange-biasing material in systems with perpendicular magnetic anisotropy

Dijken

Besnier

Moritz

et al. 2005

Journal of Applied Physics

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Contact between a Co/ Pt multilayer and an IrMn film leads to perpendicular exchange bias. The exchange bias field does not depend on the degree of ͑111͒ film texture and for Co/ Pt multilayers with IrMn at the bottom it can be enhanced by magnetic field annealing. The perpendicular exchange bias of the Co/ Pt-IrMn system is limited by a misalignment between the Co spins and the film normal, which is due to a negative magnetic anisotropy contribution from the Co/ IrMn interface ͑K S Co/IrMn = −0.09 mJ/ m 2 ͒. The insertion of a 3 Å thick Pt layer at the Co/ IrMn interface maximizes the perpendicular exchange-bias field. © 2005 American Institute of Physics. ͓DOI: 10.1063/1.1855699͔ Exchange-biased ferromagnetic ͑FM͒ films with in-plane magnetization are utilized in applications such as read heads, magnetic sensors, and magnetic random access memory. Exchange bias in these structures is established by contacting the FM film with an antiferromagnetic ͑AFM͒ layer and the effect manifests itself by a shift in the hysteresis loop and enhanced coercivity. 1 For practical applications, IrMn is an interesting AFM material since it combines good corrosion resistance with relatively high interfacial exchange energy, high blocking temperature ͑T B Ϸ 250°C͒, and small critical thickness. [2][3][4][5][6][7] Although it has been intensively studied for systems with in-plane magnetization, it has hardly been used in recent studies on perpendicular exchange bias. [8][9][10][11][12][13][14][15][16][17][18] In a recent paper, Sort et al. showed that Co/ Pt multilayers with out-ofplane magnetization can be biased by growing an IrMn layer on top. 19 In this paper we present an overview on the exchange-biasing properties of IrMn in systems with perpendicular magnetic anisotropy. We show that Co/ Pt multilayers with an IrMn film on top or at the bottom exhibit a considerable perpendicular exchange bias in the as-deposited state. Magnetic field annealing ͑bottom-pinned structures͒ and/or the insertion of a thin Pt layer at the Co/ IrMn interface further enhances the exchange-bias field.The Co/ Pt multilayers were deposited by dc magnetron sputtering onto thermally oxidized Si substrates. A metal shadow mask was used to define Hall bars with a linewidth of 200 m. The relatively large extraordinary Hall effect ͑EHE͒ of the Co/ Pt-IrMn structures, which depends linearly on the out-of-plane moment, was utilized to measure the exchange bias field, the coercivity, and the perpendicular magnetic anisotropy. The crystalline structure of the multilayers was characterized with x-ray diffraction ͑XRD͒. For the field annealing experiments we used a vacuum furnace ͑p Ͻ 1 ϫ 10 −6 mbar͒ and a superconducting magnet. Figure 1 clearly shows that Co/ Pt multilayers with outof-plane magnetization can exhibit perpendicular exchange bias when covered with or grown on top of an IrMn layer. In the as-deposited state the exchange-bias field is largest for Co/ Pt multilayers with IrMn on top. In this case, domain formation in the antiferromagnetic IrMn film i...

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Coercivity mechanisms in positive exchange-biased Co films and Co/Pt multilayers

Cited by 63 publications

References 23 publications

Loop bifurcation and magnetization rotation in exchange-biasedNi∕FeF2

Loop bifurcation and magnetization rotation in exchange-biasedNi∕FeF2

Angular dependence of exchange anisotropy on the cooling field in ferromagnet/fluoride thin films

IrMn as exchange-biasing material in systems with perpendicular magnetic anisotropy

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