Hysteresis, microstructure, and magneto-optical recording in Co/Pt and Co/Pd multilayers

Zeper, W. B.; Kesteren, H.W. van; Jacobs, B.A.J.; Spruit, J. H. M.; Carcia, P. F.

doi:10.1063/1.349419

Cited by 136 publications

(46 citation statements)

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“…As expected the XRD measurements reveal a clear enhancement of the ͑111͒ film texture with increasing Pt seed layer thickness. Although the more perfect initial Co/ Pt growth on thicker Pt seed layers results in a well-known increase of the coercive field, 20 the perpendicular exchange-bias field remains constant at about 8 mT ͓see Fig. 2͑c͔͒.…”

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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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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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“…This means that the electron tunneling does not occur directly into the Co, but rather into the Pt surface atoms that are spin polarized, due to the exchange interaction with the underlying Co. 36 ͑ii͒ We do not expect the polarization of the electronic states to be uniform over the sample surface, because the Pt/Co multilayer is constituted of microcrystallites with a diameter of 10 to 20 nm, 34 as we also verified with STM measurements.…”

Section: Discussionmentioning

confidence: 51%

“…It is well known that tunneling is not inhibited by a contamination layer, and that Pt/Co multilayers are resistant to oxidation. 34 Nevertheless, the operation under ambient conditions adds uncertainty to the value of the surface polarization. From the previous statements, we believe that the average polarization of our sample surface should be more than an order of magnitude lower than of pure Co; however, at selected sites, we assume that a reasonable upper limit for the polarization ͉P (G t )͉ is about 0.1 .…”

Section: Discussionmentioning

confidence: 99%

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Spin-polarized tunneling with GaAs tips in scanning tunneling microscopy

1996

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We describe a model as well as experiments on spin-polarized tunneling with the aid of optical spin orientation. This involves tunnel junctions between a magnetic material and gallium arsenide ͑GaAs͒, where the latter is optically excited with circularly polarized light in order to generate spin-polarized carriers. We present a transport model that takes account of carrier capture in the semiconductor surface states, and describes the semiconductor surface in terms of a spin-dependent energy distribution function. The so-called surface spin splitting can be calculated from the balance of the polarized electron and hole flow in the semiconductor subsurface region, the polarized tunneling current across the tunnel barrier between the magnetic material and the semiconductor surface, and the spin relaxation at the semiconductor surface. We present experimental data obtained in a scanning tunneling microscope with a GaAs tip and a Pt/Co multilayer sample under ambient conditions. A helicity asymmetry of tunnel current ͑i.e., a circular-polarization-dependent tunnel current͒ was found with a magnitude of 4 pA , which was verified not to be due to variations of the optical power. According to our model and estimations, this observation can be explained by spin-polarized tunneling, with a lower limit to the semiconductor surface spin splitting and spin lifetime of 4 mV and 0.4 ns, respectively.

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“…Assuming an exchange stiffness constant (A) of 1.8 pJ m −1 (Zeper et al, 1991) the domain wall width π A/K eff is found to be 8.6 nm and the exchange length 2A/µ 0 M 2 s is found to be 4 nm. Since the cross dimensions are large compared to the film thickness, domain wall width and exchange length, the Hall cross area can in essence be considered as a thin film.…”

Section: Structure and Magnetic Properties Of The Continuous Filmmentioning

confidence: 99%

Energy barriers in patterned media

Vries¹

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Hysteresis, microstructure, and magneto-optical recording in Co/Pt and Co/Pd multilayers

Cited by 136 publications

References 25 publications

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

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

Spin-polarized tunneling with GaAs tips in scanning tunneling microscopy

Energy barriers in patterned media

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