Paramagnetic-ferromagnetic phase transition during growth of ultrathin Co/Cu(001) films

Schumann, F. O.; Buckley, Mary; Bland, J. A. C.

doi:10.1103/physrevb.50.16424

Cited by 31 publications

(19 citation statements)

References 24 publications

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“…This has been ascribed to a suppressed Curie temperature due to either a finite size effect and/or intermixing of Co with Cu at the interfaces. 1,18,[21][22][23] Interestingly, for the thinnest multilayer films examined in this study, 0.56 ML cobalt, a superparamagnetic response was clearly observed at room temperature, although the saturation moment was substantially reduced to ϳ30% of the bulk value. One important distinction between prior studies and the results reported here is the deposition rate.…”

Section: Resultsmentioning

confidence: 77%

Magnetic Properties of Ultrathin Laminated Co/Cu Films Prepared by Electrodeposition

Shima

Salamanca‐Riba

McMichael

et al. 2002

J. Electrochem. Soc.

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The magnetic properties of a series of electrodeposited ͓Co (x ML)/Cu (17 ML)͔ 100 multilayers have been examined as a function of the cobalt layer thickness. The multilayers were grown on Si͑100͒ covered with a highly textured Cu͑100͒ seed layer. Films with a cobalt layer thickness less than x Ͻ 1.7 monolayer equivalents ͑ML͒ exhibit superparamagnetic behavior due to the finite size of the cobalt islands comprising the discontinuous multilayer structure. In contrast, in films with x Ͼ 1.7 ML the lateral length scale becomes large enough to stabilize ferromagnetism and the giant magnetoresistance effect is observed. The influence of magnetocrystalline anisotropy is not apparent until 2.5 Ͼ x Ͼ 3.7 ML. The coercivity increases between 1.6 and 9 ML, reflecting the combined influence of the magnetocrystalline anisotropy and surface roughness.Ultrathin magnetic films have been the subject of numerous structural and magnetic studies. 1-3 Several interesting effects are known to occur as the film thickness approaches atomic dimensions, from suppression of the Curie temperature to alterations associated with the dimensionality of the system changing from 3D to zero. Multilayers which exhibit the giant magnetoresistance effect are of particular interest in light of technical applications ranging from magnetic field sensors to data recording devices. Cu/Co multilayers have received much attention as a model system due to the immiscibility of cobalt and copper in bulk alloys, the small lattice misfit between the respective face-centered cubic ͑fcc͒ structures, and large giant magnetoresistance ͑GMR͒ effects. Numerous studies of thin cobalt films, as well as Cu/Co multilayers, grown on Cu͑100͒ account for many of the recent advances in our understanding of the interaction between structure, processing, and the resulting magnetic properties ͑Ref. 4-25, and references therein͒. Although the majority of these studies have dealt with films produced by physical vapor deposition ͑PVD͒ techniques, there has also been considerable interest in producing these materials by electrodeposition. 26,27 Co/Cu multilayers have been electrodeposited onto a variety of substrates ͑e.g., Ref. 28 and 29͒ although in this paper our attention is restricted to growth on Cu͑100͒ surfaces. 26,27,[30][31][32][33][34][35][36] For example, welldefined Co/Cu multilayers have been grown on Cu͑100͒ which exhibit sixth-order Bragg scattering peaks in low-angle X-ray diffraction ͑XRD͒ experiments. 31 More recently, in situ X-ray scattering has been applied to study the evolution of epitaxy and strain relaxation in this system. 33 In order to develop magnetotransport devices based on Co/Cu multilayers, electrodeposition onto a variety of semiconducting substrates has also been explored ͑e.g., Ref. 37͒. Of particular relevance to this study are Co/Cu multilayers which have been grown on thin copper seed layer evaporated on Si͑100͒. The resulting films exhibit a strong ͑100͒ texture in the growth direction as well as fourfold symmetric texture within the plane ...

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Section: Resultsmentioning

confidence: 77%

Magnetic Properties of Ultrathin Laminated Co/Cu Films Prepared by Electrodeposition

Shima

Salamanca‐Riba

McMichael

et al. 2002

J. Electrochem. Soc.

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“…[1][2][3][4][5][6][7] One of the main reasons for this choice was the excellent layer-by-layer growth of this system. 8 Below 2 ML, however, controversial results were published about the growth of Co/Cu͑001͒.…”

Section: Introductionmentioning

confidence: 99%

“…The complicate structure of films below 2 ML resulted in controversial works on the magnetic properties such as the Curie temperature (T c ) and the type of magnetic ordering ͑ferromagnetism, superparamagnetism, etc.͒. For example, it was reported that 1.6 ML is the thickness for the onset of room-temperature ferromagnetism 4,7 and below 1.6 ML Co/Cu͑001͒ is in a paramagnetic state because of the absence of magnetic anisotropy. 4 Later on, a clear jump of about 100 K in the Curie temperature (T c ) at a critical coverage d c of about 1.8 ML Co/Cu͑001͒ was observed.…”

Section: Introductionmentioning

confidence: 99%

Metastable magnetic properties of Co/Cu(001) films below theTcjump

et al. 2002

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The growth of the first two monolayers of Co on Cu͑001͒ has received considerable attention within experiment and theory, and it is now well understood. Here we deal with the magnetic properties of these films which are less clear. Below a critical coverage of 1.8 monolayers, Co islands are formed as single-domain ferromagnets which couple via long-range dipolar forces. They show metastable magnetic properties upon soft heat treatment. At the percolation threshold of 1.8 monolayers the islands overlap and a direct island interaction is switched on which produces a Curie temperature jump ͑T C jump͒ of about 100 K. The experimental observations are supported by model calculations for an ensemble of ferromagnetic islands below and above the percolation threshold.

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“…A similar mechanism for long-range order was proposed for Co/Cu͑001͒. 2 For further study of the magnetic interaction in nanometer-scale structures, however, these random networks of magnetic islands are not suitable for macroscopic measurements of spatially averaged quantities because of inhomogeneities in the lateral size and the thickness of the magnetic islands. In order to study the size and shape dependence of the magnetic interaction, controlled fabrication of ordered nanometer-scale structures is required.…”

Section: Introductionmentioning

confidence: 78%

Growth and magnetism ofConanometer-scale dots squarely arranged on aCu(001)−c(2×2)
Komori
¹
,
Lee
²
,
Nakatsuji
³

et al. 2001
Phys. Rev. B
39
0
10
0
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We have studied the growth and magnetism of two-dimensionally coupled nanometer-scale Co dots which are squarely arranged on a Cu(001)-c(2ϫ2)N surface. The morphology was analyzed by scanning tunneling microscopy, and the magnetization was studied using the magneto-optical Kerr effect. Well-ordered arrays of two monolayer ͑ML͒ thick Co dots interconnected by narrow 1 ML thick Co films can be grown by adjusting the deposited amount of Co. Here we used selective growth of Co at the clean Cu area of the surface, which consists of 5ϫ5 nm 2 N-adsorbed c(2ϫ2) patches separated by clean Cu lines of a few nm in width. The observed ferromagnetism in these arrays is considered to be mediated by narrow monolayer thick Co films on clean Cu lines. When the average thickness of Co exceeds 1.5 ML, 2 ML thick Co dots are connected with each other, and 1 ML Co films grow on the c(2ϫ2)N patches. For Co films with an average thickness between 1.8 ML and 2.1 ML, the magnetization is almost constant between 150 K and 370 K, and increases with decreasing temperature from 150 K. This result suggests that polarization is induced in the 1 ML Co film on c(2ϫ2)N patches below 150 K.

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Paramagnetic-ferromagnetic phase transition during growth of ultrathin Co/Cu(001) films

Cited by 31 publications

References 24 publications

Magnetic Properties of Ultrathin Laminated Co/Cu Films Prepared by Electrodeposition

Magnetic Properties of Ultrathin Laminated Co/Cu Films Prepared by Electrodeposition

Metastable magnetic properties of Co/Cu(001) films below theTcjump

Growth and magnetism ofConanometer-scale dots squarely arranged on aCu(001)−c(2×2)
Komori
¹
,
Lee
²
,
Nakatsuji
³

et al. 2001
Phys. Rev. B
39
0
10
0
View full text Add to dashboard Cite

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Paramagnetic-ferromagnetic phase transition during growth of ultrathin Co/Cu(001) films

Cited by 31 publications

References 24 publications

Magnetic Properties of Ultrathin Laminated Co/Cu Films Prepared by Electrodeposition

Magnetic Properties of Ultrathin Laminated Co/Cu Films Prepared by Electrodeposition

Metastable magnetic properties of Co/Cu(001) films below theTcjump

Growth and magnetism ofConanometer-scale dots squarely arranged on aCu(001)−c(2×2)Komori1, Lee2, Nakatsuji3 et al. 2001Phys. Rev. B390100View full textAdd to dashboardCite

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Growth and magnetism ofConanometer-scale dots squarely arranged on aCu(001)−c(2×2)
Komori
¹
,
Lee
²
,
Nakatsuji
³

et al. 2001
Phys. Rev. B
39
0
10
0
View full text Add to dashboard Cite