Temperature and thickness dependence of magnetic moments in NiO epitaxial films

Alders, D.; Tjeng, L. H.; Voogt, F. C.; Hibma, T.; Sawatzky, G. A.; Chen, C. T.; Vogel, Jan; Sacchi, M.; Iacobucci, S.

doi:10.1103/physrevb.57.11623

Cited by 272 publications

(327 citation statements)

References 41 publications

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“…The Néel temperature of a very thin antiferromagnetic film in a FM/AFM/FM trilayer is hard to ascertain experimentally and hence we point to previous experiments. Previous measurements on epitaxial thin films of NiO indicate Néel temperatures of ϳ300 K for a 5 ML sample, 44 46 show that the ferrimagnetic ordering of the Fe 3 O 4 stabilizes the AFM ordering of the antiferromagnet, leading to Néel temperatures well over the bulk Néel temperature. Hence, it is entirely feasible that the Néel temperature of the NiO in our multilayer sample is enhanced, certainly above the thin film value of 300 K and perhaps even above the bulk value of 525 K. In fact, in many magnetic superlattices, only a single transition temperature ͑the Curie and/or the Néel temperature͒ exists for the entire structure.…”

Section: B Temperature Dependence Of the Minor Loop Shiftmentioning

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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Section: B Temperature Dependence Of the Minor Loop Shiftmentioning

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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“…An acute issue in the field of nanoscience, however, is the strong reduction of the relevant critical or ordering temperatures due to well known finite size effects [2,3,4,5]. If ways could be found to compensate for these reductions, one would immediately enlarge the materials basis for nano-technology.…”

mentioning

confidence: 99%

Image charge screening: A new approach to enhance magnetic ordering temperatures in ultrathin correlated oxide films

Altieri¹,

Finazzi

Hsieh

et al. 2009

Phys. Rev. B

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We have tested the concept of image charge screening as a new approach to enhance magnetic ordering temperatures and superexchange interactions in ultra thin films. Using a 3 monolayer NiO(100) film grown on Ag(100) and an identically thin film on MgO(100) as model systems, we observed that the Néel temperature of the NiO film on the highly polarizable metal substrate is 390 K while that of the film on the poorly polarizable insulator substrate is below 40 K. This demonstrates that screening by highly polarizable media may point to a practical way towards designing strongly correlated oxide nanostructures with greatly improved magnetic properties.PACS numbers: 75.30.Et, 78.70.Dm Transition metal oxides exhibit many spectacular magnetic and electrical properties including high temperature superconductivity and colossal magnetoresistance [1] making them particularly promising for nanoscience technology applications. An acute issue in the field of nanoscience, however, is the strong reduction of the relevant critical or ordering temperatures due to well known finite size effects [2,3,4,5]. If ways could be found to compensate for these reductions, one would immediately enlarge the materials basis for nano-technology. Current approaches to overcome these problems include the use of chemical doping, pressure, and strain [6,7,8,9,10,11].Here we propose to exploit image charge screening as a new method to compensate finite size phenomena and to enhance magnetic ordering temperatures well beyond the capability of conventional methods [6,7,8,9,10,11]. The basic idea is to bring the material in the close proximity of a strongly polarizable medium. The relevant exchange and superexchange interactions, and thus the related magnetic ordering temperatures, can then be substantially amplified by reducing the energies of the underlying virtual charge excitations as a result of the image-charge-like screening by the polarizable medium [12,13,14].To prove this concept we have chosen to measure the Néel temperature T N of a 3 monolayer (ML) NiO film epitaxially grown on a MgO(100) substrate and of an equally thin film on Ag(100). NiO on MgO and on Ag are ideal model systems for this study because of their simple crystal structure and well characterized growth properties. They have a rock-salt crystal structure with lattice constant a M gO = 4.212Å and a N iO = 4.176Å, respectively, corresponding to a lattice misfit of about 1%. This ensures a perfect layer-by-layer epitaxial growth of NiO(100) on MgO(100), with a NiO(100) film surface roughness of about 0.1Å [15]. Silver has a cubic fcc structure with a lattice constant a Ag = 4.086Å and a mismatch with respect to NiO of about 2%. When misfit dislocations are avoided by keeping the film thickness below the critical thickness for strain relaxation (about 30 ML for NiO/Ag [16]) as done in the present work, then NiO(100) films grow on Ag(100) in a nicely layered and coherent mode with a sharp interface. This was already demonstrated by Kado [17,18], but it has also been verified ...

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“…23 From these noise filtered spectra, pixels showing a qualitatively similar polarization dependence were identified and the unfiltered values for these pixels were averaged. This data was then fitted to the expected cos 2 θ dependence of the XMLD signal for each type of domain, 22,24,25 where θ denotes the angle between the E-vector and the AFM spin axis. The data in Fig.…”

mentioning

confidence: 99%

Effects of nanostructuring and substrate symmetry on antiferromagnetic domain structure in LaFeO3thin films

et al. 2011

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Temperature and thickness dependence of magnetic moments in NiO epitaxial films

Cited by 272 publications

References 41 publications

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

et al. 2006
Phys. Rev. B

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

et al. 2006
Phys. Rev. B

Image charge screening: A new approach to enhance magnetic ordering temperatures in ultrathin correlated oxide films

Effects of nanostructuring and substrate symmetry on antiferromagnetic domain structure in LaFeO3thin films

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Temperature and thickness dependence of magnetic moments in NiO epitaxial films

Cited by 272 publications

References 41 publications

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

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

Image charge screening: A new approach to enhance magnetic ordering temperatures in ultrathin correlated oxide films

Effects of nanostructuring and substrate symmetry on antiferromagnetic domain structure in LaFeO3thin films

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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

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

et al. 2006
Phys. Rev. B