Magnetic X-Ray Dichroism Study of the Nearest-Neighbor Spin-Spin Correlation Function and Long-Range Magnetic Order Parameter in Antiferromagnetic NiO

Alders, D.; Vogei, J.; Levelut, Claire; Peacor, Scott D.; Hibma, T.; Sacchi, M.; Tjeng, L. H.; Chen, C. T.; Laan, G. van der; Thole, B. T.; Sawatzky, G. A.

doi:10.1209/0295-5075/32/3/012

Cited by 63 publications

(52 citation statements)

References 20 publications

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“…Although quite small, this effect is however highly reproducible and is at least an order of magnitude larger than the noise. The effect can thus be trusted and, following earlier work on NiO thin films on MgO [5,20] can be associated with the occurrence of antiferromagnetic order. By plotting the intensity ratio between the two peaks at 867.7 and 868.9 eV (L 2 ratio) as a function of temperature, as done in the top panel of Fig.…”

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confidence: 73%

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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confidence: 73%

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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“…The intensity of the XMLD signal in a single cycloidal magnetic domain, obtained by a spatial average of the collinear antiferromagnetic case [35], is proportional to M 2 3/2 cos 2 (k ·Ê) + 3/2 cos 2 (ẑ ·Ê) − 1 , where M 2 is the square of the local magnetic moment, whilek andẑ are the directions of the propagation vector and of the surface normal, respectively, andÊ is the polarisation vector of the light. The signal is maximum (∝ +M 2 /2) forÊ along the propagation vector, in which case the signal from the other two domains is ∝ −5M 2 /8.…”

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confidence: 99%

Coherent Magnetoelastic Domains in Multiferroic BiFeO3 Films

et al. 2016

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The physical properties of epitaxial films can fundamentally differ from those of bulk single crystals even above the critical thickness. By a combination of non-resonant x-ray magnetic scattering, neutron diffraction and vector-mapped x-ray magnetic linear dichroism photoemission electron microscopy, we show that epitaxial (111)-BiFeO 3 films support sub-micron antiferromagnetic domains, which are magneto-elastically coupled to a coherent crystallographic monoclinic twin structure. This unique texture, which is absent in bulk single crystals, should enable control of magnetism in BiFeO 3 film devices via epitaxial strain.PACS numbers: 77.55. Nv, 68.37.Yz, 75.60.Ch, Electrical manipulation of spins in insulators is a promising route to a new generation of fast, low consumption electronics [1][2][3]. Although direct electrical control of ferromagnets is challenging, much progress has been made towards electrical switching of antiferromagnetic spins [4]. Multiferroic BiFeO 3 (BFO) is one of the most promising materials: at room temperature, BFO is both ferroelectric and antiferromagnetic, and its spins can be rotated by switching the direction of the electrical polarisation [5,6]. Thus far, a fundamental limitation towards practical BFO devices has been the lack of understanding of the interplay between ferroelectricity, ferromagnetism and lattice distortions (ferroelasticity). Using a combination of non-resonant x-ray magnetic scattering (NXMS), neutron diffraction and vectormapped x-ray magnetic linear dichroism photoemission electron microscopy (XMLD-PEEM), we show that the antiferromagnetic domain structure of 1 µm thick, epitaxial (111)-oriented BFO films displays a ≈100 nm-scale texture, dramatically different from the mm-size features in bulk single crystals. We also demonstrate that this magnetic texture is coherent (having matching topography and symmetry elements) with a pattern of monoclinic domains at the nanoscale. This texture is reminiscent of the dense polydomain states that are thermodynamically stable in ferroelectric perovskites such as PbTiO 3 in the presence of strain misfit [7]. This strongly suggests that the relaxed (111)-oriented BFO structure is not trigonal, but is a texture of coherent monoclinic micro twins. Besides providing a new pathway towards strainengineering multiferroic domains in BFO, our approach yielded a detailed picture of the interplay between magnetism and lattice over 5 orders of magnitude in length * p.g.radaelli@physics.ox.ac.uk scales, and could be applied to many classes of functional magnetic oxide devices.Below its ferroelectric Curie temperature of T C = 1103 K, bulk BFO is generally believed to possess a rhombohedrally-distorted perovskite structure with space group R3c (pictured in fig. 1(a) and (b)) [8,9], although very recent high-resolution synchrotron measurements have suggested a small monoclinic distortion [10]. The Bi 3+ and Fe 3+ cations are displaced away from their centrosymmetric positions along the (111) (pseudocubic setting) axis [11], producing a ...

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“…The XMCD signal is proportional to the atomic magnetic moments in ferromagnetically ordered samples [13]. On the contrary XLD can be due to an orbital or magnetic uniaxial anisotropy (or both), and the magnetic part (XMLD, x-ray magnetic linear dichroism) is sensitive to both FM and AFM ordering [14]. To disentangle the magnetic from the orbital part of XLD we have performed measurements at different temperatures T : above the magnetic ordering temperature only the orbital contribution survives, so in our samples XLD at high T (room T for n = 1 and 200K for n = 5, 8) have orbital character only.…”

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Evolution of magnetic phases and orbital occupation in(SrMnO3)n/(LaMnO3
Aruta¹,
Adamo
²
,
Galdi
³

et al. 2009
Phys. Rev. B
68
2
50
0
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The magnetic and electronic modifications induced at the interfaces in (SrMnO3)n/(LaMnO3)2n superlattices have been investigated by linear and circular magnetic dichroism in the Mn L2,3 x-ray absorption spectra. Together with theoretical calculations, our data demonstrate that the charge redistribution across interfaces favors in-plane ferromagnetic (FM) order and eg(x 2 − y 2 ) orbital occupation, in agreement with the average strain. Far from interfaces, inside LaMnO3, electron localization and local strain favor antiferromagnetism (AFM) and eg(3z 2 − r 2 ) orbital occupation. For n = 1 the high density of interfacial planes ultimately leads to dominant FM order forcing the residual AFM phase to be in-plane too, while for n ≥ 5 the FM layers are separated by AFM regions having out-of-plane spin orientation.PACS numbers: 75.47. Lx, 78.70.Dm, 72.10.Di, 73.21.Cd, Interfaces between different transition metal oxides (TMO) have been widely demonstrated to be sources of interesting and unexpected electronic and magnetic properties.Metallic conductivity arises, for example, at the interface between two insulators, such as LaAlO 3 /SrTiO 3 [1] and LaTiO 3 /SrTiO 3 [2], while ferromagnetism (FM) occurs at the interface between the antiferromagnet (AFM) CaMnO 3 and the paramagnet CaRuO 3 [3]. In this context, strain driven spin-orbital coupled states arising in manganites make the interfaces between these compounds very interesting for engineering unique collective states. As a matter of fact, a certain amount of theoretical and experimental studies on superlattices (SLs) composed by the two AFM insulators, SrMnO 3 (SMO) and LaMnO 3 (LMO), appeared in literature during the last years [4,5,6,7,8,9,10,11,12]. The ordered sequence of the atomic layers in the digital SMO/LMO SLs [4,5], together with the electronic reconstruction arising from the interfacial Mn 3+ /Mn 4+ mixed valence, give rise to peculiar transport, magnetic and orbital properties, when different layering and strain conditions occur. In the particular case of (SMO) n /(LMO) 2n the La:Sr ratio is 2:1, in analogy with the optimal composition of La 2/3 Sr 1/3 MnO 3 (LSMO). In such a case, the metal-insulator transition (MIT) and the magnetic properties depend on the thickness of the constituent blocks [4,5,6,7], although in a non trivial way. Indeed, saturation magnetization does not linearly decrease with n [4] and both fast and viscous spin populations are present, the latter associated to FM/AFM pinning [8]. Therefore, the development of the FM metallic phase at the interfaces is well established and the coexistance of the FM and AFM phases was inferred. However, the knowledge of the mutual dependence of the AFM and FM phases with n is still uncertain, but it could open further perspectives in the control of the low dimensional magnetic properties, thus in the engineering of the TMO magnetic heterostructures. In addition, as the role of interfacial Mn e g electrons is known to be important, the influence of strain and reduced dimensionality on the transpor...

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Magnetic X-Ray Dichroism Study of the Nearest-Neighbor Spin-Spin Correlation Function and Long-Range Magnetic Order Parameter in Antiferromagnetic NiO

Cited by 63 publications

References 20 publications

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

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

Coherent Magnetoelastic Domains in Multiferroic BiFeO3 Films

Evolution of magnetic phases and orbital occupation in(SrMnO3)n/(LaMnO3
Aruta¹,
Adamo
²
,
Galdi
³

et al. 2009
Phys. Rev. B
68
2
50
0
View full text Add to dashboard Cite

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Magnetic X-Ray Dichroism Study of the Nearest-Neighbor Spin-Spin Correlation Function and Long-Range Magnetic Order Parameter in Antiferromagnetic NiO

Cited by 63 publications

References 20 publications

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

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

Coherent Magnetoelastic Domains in Multiferroic BiFeO3 Films

Evolution of magnetic phases and orbital occupation in(SrMnO3)n/(LaMnO3Aruta1, Adamo2, Galdi3 et al. 2009Phys. Rev. B682500View full textAdd to dashboardCite

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Evolution of magnetic phases and orbital occupation in(SrMnO3)n/(LaMnO3
Aruta¹,
Adamo
²
,
Galdi
³

et al. 2009
Phys. Rev. B
68
2
50
0
View full text Add to dashboard Cite