Browsing by Author "Arenholz, E."

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Electrically controllable spontaneous magnetism in nanoscale mixed phase multiferroics
(2011-03-01)
He, Q.
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Chu, Y. -H.
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Heron, J. T.
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Yang, S. Y.
;
Liang, W. I.
Magnetoelectrics and multiferroics present exciting opportunities for electric-field control of magnetism. However, there are few room-temperature ferromagnetic-ferroelectrics. Among the various types of multiferroics the bismuth ferrite system has received much attention primarily because both the ferroelectric and the antiferromagnetic orders are quite robust at room temperature. Here we demonstrate the emergence of an enhanced spontaneous magnetization in a strain-driven rhombohedral and super-tetragonal mixed phase of BiFeO(3). Using X-ray magnetic circular dichroism-based photoemission electron microscopy coupled with macroscopic magnetic measurements, we find that the spontaneous magnetization of the rhombohedral phase is significantly enhanced above the canted antiferromagnetic moment in the bulk phase, as a consequence of a piezomagnetic coupling to the adjacent tetragonal-like phase and the epitaxial constraint. Reversible electric-field control and manipulation of this magnetic moment at room temperature is also shown.
Nanoscale characterization of emergent phenomena in multiferroics
(2012-10-01)
He, Q.
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Arenholz, E.
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Scholl, A.
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Chu, Y. -H.
;
Ramesh, R.
Multiferroics exhibit intriguing physical properties and in turn promise new device applications as a result of the coupling between their order parameters. In this review article, we introduce photoemission electron microscopy (PEEM) as a powerful tool to study multiferroicity with the capability of probing the charge, spin and orbital states of a material simultaneously with nanoscale spatial resolution and element sensitivity. Several systematical studies of ferroelectricity, antiferromagnetism, and multiferroicity using PEEM are discussed. In the end, we outline several challenges remaining in multiferroic research, and how PEEM can be employed as an important characterization tool providing critical information to understand the emergent phenomena in multiferroics. Published by Elsevier Ltd.
Observation of a three-dimensional quasi-long-range electronic supermodulation in YBa2Cu3O7 (-) (x)/La0.7Ca0.3MnO3 heterostructures
(2016-03-01)
He, Junfeng
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Shafer, Padraic
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Mion, Thomas R.
;
Vu Thanh Tra
;
He, Qing
Recent developments in high-temperature superconductivity highlight a generic tendency of the cuprates to develop competing electronic (charge) supermodulations. While coupled with the lattice and showing different characteristics in different materials, these supermodulations themselves are generally conceived to be quasi-two-dimensional, residing mainly in individual CuO2 planes, and poorly correlated along the c axis. Here we observed with resonant elastic X-ray scattering a distinct type of electronic supermodulation in YBa2Cu3O7 (- x) (YBCO) thin films grown epitaxially on La0.7Ca0.3MnO3 (LCMO). This supermodulation has a periodicity nearly commensurate with four lattice constants in-plane, eight out of plane, with long correlation lengths in three dimensions. It sets in far above the superconducting transition temperature and competes with superconductivity below this temperature for electronic states predominantly in the CuO2 plane. Our finding sheds light on the nature of charge ordering in cuprates as well as a reported long-range proximity effect between superconductivity and ferromagnetism in YBCO/LCMO heterostructures.
Orthorhombic BiFeO3
(2012-12-14)
Yang, J. C.
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He, Q.
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Suresha, S. J.
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Kuo, C. Y.
;
Peng, C. Y.
A new orthorhombic phase of the multiferroic BiFeO3 has been created via strain engineering by growing it on a NdScO3(110)(o) substrate. The tensile-strained orthorhombic BiFeO3 phase is ferroelectric and antiferromagnetic at room temperature. A combination of nonlinear optical second harmonic generation and piezoresponse force microscopy revealed that the ferroelectric polarization in the orthorhombic phase is along the in-plane < 110 >(pc) directions. In addition, the corresponding rotation of the antiferromagnetic axis in this new phase was observed using x-ray linear dichroism. DOI: 10.1103/PhysRevLett.109.247606