Giant Near-90° Coupling in Epitaxial CoFe/Mn/CoFe Sandwich Structures

Filipkowski, M. E.; Krebs, J. J.; Prinz, G. A.; Gutierrez, C. J.

doi:10.1103/physrevlett.75.1847

Cited by 94 publications

(53 citation statements)

References 11 publications

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“…Accordingly, the picture described for FM/AF bilayers [8] is different for closely coupled multilayers where interactions between multiple ferromagnetic (FM) layers and interactions between interfaces should be taken into account. Similar considerations also apply to the magneto-optic Kerr effect (MOKE) and scanning electron microscopy with polarization analysis (SEMPA) studies [17] on Fe/Cr/Fe trilayers and magnetization and ferromagnetic resonance studies of CoFe/Mn/CoFe trilayers [10], all of which specialize to a specific type of spacer layer and do not include the multilayer interactions responsible for our GAF behavior. Our results are thus complementary yet distinct from the results of bilayer/trilayer experiments.…”

Section: Pacs Numbers: 7570pamentioning

confidence: 99%

“…In a particularly simple manifestation, two neighboring films, separated by a non-magnetic spacer layer, could have different coercive fields, thus giving rise to antiparallel alignment and a GMR effect, as the external field is cycled [6]. Randomness [7,8] and competing interactions such as biquadratic coupling [9,10] can also play a significant role. In this paper we identify a glassy antiferromagnetic (GAF) phase which by marking the influence of IEC at low temperatures implies that at higher temperatures random potential variations rather than IEC are responsible for antiparallel alignment.…”

Section: Pacs Numbers: 7570pamentioning

confidence: 99%

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Coexistence of glassy antiferromagnetism and giant magnetoresistance in Fe/Cr multilayer structures

Theodoropoulou

Hebard

Gabay

et al. 2003

Journal of Magnetism and Magnetic Materials

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Using temperature-dependent magnetoresistance and magnetization measurements on Fe/Cr multilayers that exhibit pronounced giant magnetoresistance (GMR), we have found evidence for the presence of a glassy antiferromagnetic (GAF) phase. This phase reflects the influence of interlayer exchange coupling (IEC) at low temperature (T < 140K) and is characterized by a field-independent glassy transition temperature, Tg, together with irreversible behavior having logarithmic time dependence below a "de Almeida and Thouless" (AT) critical field line. At room temperature, where the GMR effect is still robust, IEC plays only a minor role, and it is the random potential variations acting on the magnetic domains that are responsible for the antiparallel interlayer domain alignment. Given the established presence of GMR-based devices in technology, especially in the multi-billion dollar computer hard disk drive market, it may come as a surprise that there is still an incomplete scientific understanding of the GMR effect [1]. The mechanism for GMR, first observed in single crystalline (100) Fe/Cr multilayers grown by molecular beam epitaxy [2,3] and subsequently in magnetron-sputtered polycrystalline films[4], relies on spin-dependent scattering [5] and the associated dependence of resistance on the relative orientations of the magnetizations in neighboring layers. It is important to recognize that interlayer exchange coupling (IEC) is not necessarily required for a GMR effect [1]. In a particularly simple manifestation, two neighboring films, separated by a non-magnetic spacer layer, could have different coercive fields, thus giving rise to antiparallel alignment and a GMR effect, as the external field is cycled [6]. Randomness [7,8] and competing interactions such as biquadratic coupling [9,10] can also play a significant role. In this paper we identify a glassy antiferromagnetic (GAF) phase which by marking the influence of IEC at low temperatures implies that at higher temperatures random potential variations rather than IEC are responsible for antiparallel alignment.Our Fe/Cr multilayer samples have been prepared on silicon substrates by ion beam sputter deposition of separate Fe and Cr targets. Extensive characterization of the deposited multilayers showed distinct compositional and structural modulations with well-defined interfaces and a surface roughness on the order of 5Å. Ten and thirtylayer stacks with the repeat sequence [Fe(20Å)/Cr(d Cr )] are typically deposited and passivated with a 50Å-thick Cr layer. The Cr spacer thickness d Cr is varied over the range 8-12Å. The inset of Fig. 1 shows typical GMR traces at 300K and 10K for the magnetic field parallel to the planes of a [Fe(20Å)/Cr(12Å) ]×30 sample.In Fig. 1 we show a selected subset of temperaturedependent field-cooled (FC, open symbols) and zerofield-cooled (ZFC, closed symbols) magnetization data for a thirty layer sample with d Cr = 12Å and a GMR ratio ((R(0) − R(H))/R(0), Fig. 1 inset) of 20.6% at 10K. The data were taken using a SQUID magnetometer in fi...

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Section: Pacs Numbers: 7570pamentioning

confidence: 99%

Section: Pacs Numbers: 7570pamentioning

confidence: 99%

Coexistence of glassy antiferromagnetism and giant magnetoresistance in Fe/Cr multilayer structures

Theodoropoulou

Hebard

Gabay

et al. 2003

Journal of Magnetism and Magnetic Materials

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“…The spin structure in either the FM and/or the AFM may rotate away from its easy axis at the interface and the anisotropy constants dictate the degree of twisting. In experiments on FM sandwiches coupled across both insulating 12,13 and metallic antiferromagnets, 14 noncollinear coupling has been observed over a substantial range of spacer layer thickness. The presence of atomic layer roughness in the AFM layer leads to a competition between FM coupling between the magnetic layers ͑favored by an odd number of AFM spacer layers͒ and antiferromagnetic coupling ͑favored by an even number of AFM layers͒, leading to a compromise that results in a net noncollinear coupling in order to minimize the energy.…”

Section: Introductionmentioning

confidence: 99%

Origin of the interlayer exchange coupling in[Co∕Pt]∕NiO∕[Co∕
Baruth
¹
,
Keavney
²
,
Burton
³

et al. 2006
Phys. Rev. B

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The origin of the oscillatory interlayer exchange coupling in ͓Co/ Pt͔ / NiO / ͓Co/ Pt͔ multilayers is investigated using advanced microscopy and spectroscopy techniques and micromagnetic modeling. X-ray magnetic circular dichroism ͑XMCD͒ measurements show the presence of the canting of Ni spins in the NiO film being greater for antiferromagnetically coupled multilayers than for ferromagnetically coupled ones. This behavior is consistent with the model, which assumes a different sign of the exchange coupling at the two interfaces and the antiferromagnetic layer-by-layer coupling in the NiO film. An unexpectedly short attenuation length of 4 Å for secondary electrons in NiO is measured, which has implications for the interpretation of XMCD data. Domain images obtained using XMCD-photoemission electron microscopy at the Co and Ni resonances indicate that the canting of the Ni spins occurs on both a microscopic and macroscopic scale. The average size of the domains is shown to increase with exchange coupling strength. In antiferromagnetically coupled samples, the competition between magnetostatic and interlayer exchange effects gives rise to a region of overlapping domains. The size of this region scales inversely with coupling strength. Finally, the temperature dependence of the interlayer coupling shows both reversible and irreversible effects. The irreversible effects stem from oxidation/reduction reactions at the Co/ NiO interface. The reversible effects stem from the temperature dependences of the many factors that play a role in the interlayer coupling and exhibit nonmonotonic temperature dependence.

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“…In the first work on Fe/Mn/Fe trilayers 3 Purcell et al found interlayer coupling oscillations with a two ML period but there were no sign changes, indicating an appreciable background of AF coupling. On the contrary, Filipkowski et al 4 found very strong near-90°coupling with no evidence for AF coupling in their CoFe/Mn/CoFe samples at room temperature. Also in contrast to the results in Fe/Mn/Fe trilayers, 3 the two ML period oscillations were absent in Co/Mn ͑Ref.…”

mentioning

confidence: 83%

Oscillatory interlayer coupling in Fe/Mn/Fe trilayers

et al. 1999

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Fe/Mn/Fe wedged-shape sandwiches were prepared by molecular beam epitaxy under optimal conditions. The interlayer coupling measured by magneto-optic Kerr effect is very strong for thin Mn layers. The canted angle between the magnetization vectors of the two magnetic layers in remanence increases gradually from 0°t o about 180°and then gradually reduces to 90°for Mn thicknesses from 0.62 to 1.2 nm. For Mn layer thicknesses in the range between 1.2 and 2.45 nm, the interlayer coupling is always 90°coupling, but its strength oscillates with a short period of about 2 Mn monolayers. The above coupling phenomenon can be well described by the proximity magnetism model. ͓S0163-1829͑99͒50618-8͔Recently the mechanisms which couple ferromagnetic ͑FM͒ films across antiferromagnetic ͑AF͒ metallic interlayers have been of great interest. For AF interlayers one would expect a large contribution to the coupling coming from the direct nearest-neighbor exchange inside the interlayers and across the interfaces but since they are metals the indirect interaction due to the conduction electrons could be considered in addition. We consider here AF interlayers polarized in the plane of the film with sheets alternatively parallel and antiparallel to the magnetization of the FM films as observed by Walker and Hopster 1 on overlayers of Mn grown on Fe. In the ideal case one would expect oscillations of the coupling strength with a period of two monolayers ͑ML͒, with large amplitudes and sign changes.While this behavior has been studied in much detail for Cr interlayers and even a magnetic phase diagram for the Cr interlayer was deduced 2 which explains most of the experimental results, for Mn interlayer the situation is less clear. In the first work on Fe/Mn/Fe trilayers 3 Purcell et al. found interlayer coupling oscillations with a two ML period but there were no sign changes, indicating an appreciable background of AF coupling. On the contrary, Filipkowski et al. 4 found very strong near-90°coupling with no evidence for AF coupling in their CoFe/Mn/CoFe samples at room temperature. Also in contrast to the results in Fe/Mn/Fe trilayers, 3 the two ML period oscillations were absent in Co/Mn ͑Ref. 5͒ and Fe/Mn ͑Ref. 6͒ multilayers. Furthermore, the interlayer coupling in epitaxial Co/Mn multilayers 7 was attributed to the AF order of the Mn spacer. Unfortunately, the authors did not show the dependence of the interlayer coupling on the Mn layer thickness.In view of these contradictory results the aim of the present work was to prepare samples of the best possible quality which could provide reliable information on the coupling in this interesting system. Since this work and the evaluation of the experiments will be based on the assumption that we are here dealing with AF Mn as interlayer material we will use Slonczewki's proximity magnetism model 8 for the evaluation of the experiments. It will be briefly introduced in the next paragraph and compared with the usual method to evaluate such experiments.The proximity magnetism model 8 is a ph...

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Giant Near-90° Coupling in Epitaxial CoFe/Mn/CoFe Sandwich Structures

Cited by 94 publications

References 11 publications

Coexistence of glassy antiferromagnetism and giant magnetoresistance in Fe/Cr multilayer structures

Coexistence of glassy antiferromagnetism and giant magnetoresistance in Fe/Cr multilayer structures

Origin of the interlayer exchange coupling in[Co∕Pt]∕NiO∕[Co∕
Baruth
¹
,
Keavney
²
,
Burton
³

et al. 2006
Phys. Rev. B

Oscillatory interlayer coupling in Fe/Mn/Fe trilayers

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Giant Near-90° Coupling in Epitaxial CoFe/Mn/CoFe Sandwich Structures

Cited by 94 publications

References 11 publications

Coexistence of glassy antiferromagnetism and giant magnetoresistance in Fe/Cr multilayer structures

Coexistence of glassy antiferromagnetism and giant magnetoresistance in Fe/Cr multilayer structures

Origin of the interlayer exchange coupling in[Co∕Pt]∕NiO∕[Co∕Baruth1, Keavney2, Burton3 et al. 2006Phys. Rev. B

Oscillatory interlayer coupling in Fe/Mn/Fe trilayers

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Origin of the interlayer exchange coupling in[Co∕Pt]∕NiO∕[Co∕
Baruth
¹
,
Keavney
²
,
Burton
³

et al. 2006
Phys. Rev. B