-
P J Ryan,
J-W Kim,
T Birol,
P Thompson,
J-H Lee,
X Ke,
P S Normile, E Karapetrova,
P Schiffer,
S D Brown,
C J Fennie,
D G Schlom
[show abstract]
[hide abstract]
ABSTRACT: Intrinsic magnetoelectric coupling describes the interaction between magnetic and electric polarization through an inherent microscopic mechanism in a single-phase material. This phenomenon has the potential to control the magnetic state of a material with an electric field, an enticing prospect for device engineering. Here, we demonstrate 'giant' magnetoelectric cross-field control in a tetravalent titanate film. In bulk form, EuTiO(3), is antiferromagnetic. However, both anti and ferromagnetic interactions coexist between different nearest europium neighbours. In thin epitaxial films, strain was used to alter the relative strength of the magnetic exchange constants. We not only show that moderate biaxial compression precipitates local magnetic competition, but also demonstrate that the application of an electric field at this strain condition switches the magnetic ground state. Using first-principles density functional theory, we resolve the underlying microscopic mechanism resulting in G-type magnetic order and illustrate how it is responsible for the 'giant' magnetoelectric effect.
Nature Communications 01/2013; 4:1334. · 7.40 Impact Factor
-
Journal of The Electrochemical Society 01/2012; 159:F436. · 2.59 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Oxygen octahedral rotations have been measured in short-period (LaNiO3)n/(SrMnO3)m superlattices using synchrotron diffraction. The in-plane and out-of-plane bond angles and lengths are found to systematically vary with superlattice composition. Rotations are suppressed in structures with m>n, producing a nearly unrotated form of LaNiO3. Large rotations are present in structures with m<n, leading to reduced bond angles in SrMnO3. The metal-oxygen-metal bond lengths decrease as rotations are reduced, in contrast to behavior previously observed in strained, single-layer films. This result demonstrates that superlattice structures can be used to stabilize nonequilibrium octahedral behavior in a manner distinct from epitaxial strain, providing a novel means to engineer the electronic and ferroic properties of oxide heterostructures.
Phys. Rev. B. 04/2011; 83(15).
-
[show abstract]
[hide abstract]
ABSTRACT: We report spin reorientation transitions in a Fe3O4/BaTiO3 heterostructure driven by strain at the structural phase transitions of BaTiO3. These spin reorientations result from the emergence of an in-plane uniaxial magnetic anisotropy. The magnetoelastic response of Fe3O4 to the variations in epitaxial strain that occur at the BaTiO3 phase transitions gives rise to the uniaxial anisotropy. The anisotropy energies calculated from the in-plane strain are in quantitative agreement with a change in the Zeeman energy.
Applied Physics Letters 03/2010; 96(9):092510-092510-3. · 3.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Epitaxial strain is a proven route to enhancing the properties of complex oxides, however, the details of how the atomic structure accommodates strain are poorly understood due to the difficulty of measuring the oxygen positions in thin films. We present a general methodology for determining the atomic structure of strained oxide films via x-ray diffraction, which we demonstrate using LaNiO3 films. The oxygen octahedral rotations and distortions have been quantified by comparing the intensities of half-order Bragg peaks, arising from the two unit cell periodicity of the octahedral rotations, with the calculated structure factor. Combining ab initio density functional calculations with these experimental results, we determine systematically how strain modifies the atomic structure of this functional oxide. Comment: 23 pages, 11 figures
02/2010;
-
S J May,
P J Ryan,
J L Robertson,
J-W Kim,
T S Santos, E Karapetrova,
J L Zarestky,
X Zhai,
S G E te Velthuis,
J N Eckstein,
S D Bader,
A Bhattacharya
[show abstract]
[hide abstract]
ABSTRACT: The disorder inherent to doping by cation substitution in the complex oxides can have profound effects on collective-ordered states. Here, we demonstrate that cation-site ordering achieved through digital-synthesis techniques can dramatically enhance the antiferromagnetic ordering temperatures of manganite films. Cation-ordered (LaMnO3)m/(SrMnO3)2m superlattices show Néel temperatures (TN) that are the highest of any La(1-x)Sr(x)MnO3 compound, approximately 70 K greater than compositionally equivalent randomly doped La(1/3)Sr(2/3)MnO3. The antiferromagnetic order is A-type, consisting of in-plane double-exchange-mediated ferromagnetic sheets coupled antiferromagnetically along the out-of-plane direction. Through synchrotron X-ray scattering, we have discovered an in-plane structural modulation that reduces the charge itinerancy and hence the ordering temperature within the ferromagnetic sheets, thereby limiting TN. This modulation is mitigated and driven to long wavelengths by cation ordering, enabling the higher TN values of the superlattices. These results provide insight into how cation-site ordering can enhance cooperative behaviour in oxides through subtle structural phenomena.
Nature Material 11/2009; 8(11):892-7. · 32.84 Impact Factor
