I06-Nanoscience (XPEEM)
|
Hariom
Jani
,
Jheng-Cyuan
Lin
,
Jiahao
Chen
,
Jack
Harrison
,
Francesco
Maccherozzi
,
Jonathon
Schad
,
Saurav
Prakash
,
Chang-Beom
Eom
,
A.
Ariando
,
Thirumalai
Venkatesan
,
Paolo G.
Radaelli
Diamond Proposal Number(s):
[23857, 20317]
Abstract: In the quest for post-CMOS (complementary metal–oxide–semiconductor) technologies, driven by the need for improved efficiency and performance, topologically protected ferromagnetic ‘whirls’ such as skyrmions and their anti-particles have shown great promise as solitonic information carriers in racetrack memory-in-logic or neuromorphic devices. However, the presence of dipolar fields in ferromagnets, which restricts the formation of ultrasmall topological textures, and the deleterious skyrmion Hall effect, when skyrmions are driven by spin torques have thus far inhibited their practical implementation. Antiferromagnetic analogues, which are predicted to demonstrate relativistic dynamics, fast deflection-free motion and size scaling, have recently become the subject of intense focus, but they have yet to be experimentally demonstrated in natural antiferromagnetic systems. Here we realize a family of topological antiferromagnetic spin textures in α-Fe2O3—an Earth-abundant oxide insulator—capped with a platinum overlayer. By exploiting a first-order analogue of the Kibble–Zurek mechanism2, we stabilize exotic merons and antimerons (half-skyrmions)8 and their pairs (bimerons), which can be erased by magnetic fields and regenerated by temperature cycling. These structures have characteristic sizes of the order of 100 nanometres and can be chemically controlled via precise tuning of the exchange and anisotropy, with pathways through which further scaling may be achieved. Driven by current-based spin torques from the heavy-metal overlayer, some of these antiferromagnetic textures could emerge as prime candidates for low-energy antiferromagnetic spintronics at room temperature.
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Feb 2021
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I16-Materials and Magnetism
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N.
Qureshi
,
A.
Bombardi
,
S.
Picozzi
,
P.
Barone
,
E.
Lelièvre-Berna
,
X.
Xu
,
C.
Stock
,
D. F.
Mcmorrow
,
A.
Hearmon
,
F.
Fabrizi
,
P. G.
Radaelli
,
S.-W.
Cheong
,
L. C.
Chapon
Diamond Proposal Number(s):
[4073, 1803, 17569]
Abstract: We present a combined polarized neutron and x-ray scattering study on two enantiopure langasite single crystals aimed at the determination of their absolute structural and magnetic chiralities and the coupling between them. Our respective data sets unambiguously reveal two samples of opposite structural chirality, where the magnetic handedness is pinned by the structural one. Simple energy considerations of the magnetic exchange and single-ion anisotropy parameters reveal that it is not the Dzyaloshinskii-Moriya interaction but the local single-ion anisotropy on a triangular plaquette which plays a key role in stabilizing one of the two magnetic helices.
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Aug 2020
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I10-Beamline for Advanced Dichroism - scattering
|
Diamond Proposal Number(s):
[14826, 17388]
Abstract: By employing resonant x-ray microdiffraction, we image the magnetization and magnetic polarity domains of the
Y
-type hexaferrite
Ba
0.5
Sr
1.5
Mg
2
Fe
12
O
22
. We show that the magnetic polarity domain structure can be controlled by both magnetic and electric fields and that full inversion of these domains can be achieved simply by reversal of an applied magnetic field in the absence of an electric field bias. Furthermore, we demonstrate that the diffraction intensity measured in different x-ray polarization channels cannot be reproduced by the accepted model for the polar magnetic structure, known as the 2-fan transverse conical (TC) model. We propose a modification to this model, which achieves good quantitative agreement with all of our data. We show that the deviations from the TC model are large and may be the result of an internal magnetic chirality, most likely inherited from the parent helical (nonpolar) phase.
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Sep 2019
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I16-Materials and Magnetism
|
Diamond Proposal Number(s):
[15087]
Abstract: The presence of domains in ferroic materials can negatively affect their macroscopic properties and hence their usefulness in device applications. From an experimental perspective, the measurement of materials comprising multiple domains can complicate the interpretation of the material properties and their underlying mechanisms. In general,
Bi
Fe
O
3
films tend to grow with multiple magnetic domains and often contain multiple ferroelectric- and ferroelastic-domain variants. By growing (111)-oriented
Bi
Fe
O
3
films on an orthorhombic
Tb
Sc
O
3
substrate, we are able to overcome this and, by exploiting the magnetoelastic coupling between the magnetic and crystal structures, bias the growth of a given magnetic-, ferroelectric-, and structural-domain film. We further demonstrate the coupling of the magnetic structure to the ferroelectric polarization by showing that the magnetic polarity in this domain is inverted upon
180
∘
ferroelectric switching.
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Feb 2019
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I06-Nanoscience (XPEEM)
|
F. P.
Chmiel
,
N.
Waterfield Price
,
R. D.
Johnson
,
A. D.
Lamirand
,
J.
Schad
,
Gerrit
Van Der Laan
,
D. T.
Harris
,
J.
Irwin
,
M. S.
Rzchowski
,
C.-B.
Eom
,
Paolo
Radaelli
Diamond Proposal Number(s):
[16338, 15088]
Abstract: Vortices, occurring whenever a flow field ‘whirls’ around a one-dimensional core, are among the simplest topological structures, ubiquitous to many branches of physics. In the crystalline state, vortex formation is rare, since it is generally hampered by long-range interactions: in ferroic materials (ferromagnetic and ferroelectric), vortices are observed only when the effects of the dipole–dipole interaction are modified by confinement at the nanoscale1,2,3, or when the parameter associated with the vorticity does not couple directly with strain4. Here, we observe an unprecedented form of vortices in antiferromagnetic haematite (α-Fe2O3) epitaxial films, in which the primary whirling parameter is the staggered magnetization. Remarkably, ferromagnetic topological objects with the same vorticity and winding number as the α-Fe2O3 vortices are imprinted onto an ultra-thin Co ferromagnetic over-layer by interfacial exchange. Our data suggest that the ferromagnetic vortices may be merons (half-skyrmions, carrying an out-of plane core magnetization), and indicate that the vortex/meron pairs can be manipulated by the application of an in-plane magnetic field, giving rise to large-scale vortex–antivortex annihilation.
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Jun 2018
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I06-Nanoscience (XPEEM)
|
W.
Saenrang
,
B. A.
Davidson
,
F.
Maccherozzi
,
J. P.
Podkaminer
,
J.
Irwin
,
R. D.
Johnson
,
J. W.
Freeland
,
J.
Íñiguez
,
J. L.
Schad
,
K.
Reierson
,
J. C.
Frederick
,
C. A. F.
Vaz
,
L.
Howald
,
T. H.
Kim
,
S.
Ryu
,
M. V.
Veenendaal
,
P. G.
Radaelli
,
S. S.
Dhesi
,
M. S.
Rzchowski
,
C. B.
Eom
Diamond Proposal Number(s):
[12084, 13225, 11589]
Open Access
Abstract: Exploiting multiferroic BiFeO3 thin films in spintronic devices requires deterministic and robust control of both internal magnetoelectric coupling in BiFeO3, as well as exchange coupling of its antiferromagnetic order to a ferromagnetic overlayer. Previous reports utilized approaches based on multi-step ferroelectric switching with multiple ferroelectric domains. Because domain walls can be responsible for fatigue, contain localized charges intrinsically or via defects, and present problems for device reproducibility and scaling, an alternative approach using a monodomain magnetoelectric state with single-step switching is desirable. Here we demonstrate room temperature, deterministic and robust, exchange coupling between monodomain BiFeO3 films and Co overlayer that is intrinsic (i.e., not dependent on domain walls). Direct coupling between BiFeO3 antiferromagnetic order and Co magnetization is observed, with ~ 90° in-plane Co moment rotation upon single-step switching that is reproducible for hundreds of cycles. This has important consequences for practical, low power non-volatile magnetoelectric devices utilizing BiFeO3.
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Nov 2017
|
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I16-Materials and Magnetism
|
Diamond Proposal Number(s):
[12837]
Abstract: We have directly imaged reversible electrical switching of the cycloidal rotation direction (magnetic polarity) in a (111)pc−BiFeO3 epitaxial-film device at room temperature by nonresonant x-ray magnetic scattering. Consistent with previous reports, fully relaxed (111)pc−BiFeO3 epitaxial films consisting of a single ferroelectric domain are found to comprise a submicron-scale mosaic of magnetoelastic domains, all sharing a common direction of the magnetic polarity, which is found to switch reversibly upon reversal of the ferroelectric polarization without any measurable change of the magnetoelastic domain population. A real-space polarimetry map of our device clearly distinguishes between regions of the sample electrically addressed into the two magnetic states with a resolution of a few tens of micron. Contrary to the general belief that the magneto-electric coupling in BiFeO3 is weak, we find that electrical switching has a dramatic effect on the magnetic structure, with the magnetic moments rotating on average by 90° at every cycle.
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Jul 2017
|
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I16-Materials and Magnetism
|
Diamond Proposal Number(s):
[9409, 12609]
Open Access
Abstract: The magnetic ground state of Sr3ARuO6, with A=(Li,Na), is studied using neutron diffraction, resonant x-ray scattering, and laboratory characterization measurements of high-quality crystals. Combining these results allows us to observe the onset of long-range magnetic order and distinguish the symmetrically allowed magnetic models, identifying in-plane antiferromagnetic moments and a small ferromagnetic component along the c axis. While the existence of magnetic domains masks the particular in-plane direction of the moments, it has been possible to elucidate the ground state using symmetry considerations. We find that due to the lack of local anisotropy, antisymmetric exchange interactions control the magnetic order, first through structural distortions that couple to in-plane antiferromagnetic moments and second through a high-order magnetoelastic coupling that lifts the degeneracy of the in-plane moments. The symmetry considerations used to rationalize the magnetic ground state are very general and will apply to many systems in this family, such as Ca3ARuO6, with A=(Li,Na), and Ca3LiOsO6 whose magnetic ground states are still not completely understood.
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Oct 2016
|
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I06-Nanoscience (XPEEM)
I16-Materials and Magnetism
|
Diamond Proposal Number(s):
[10201]
Abstract: The physical properties of epitaxial films can fundamentally differ from those of bulk single crystals even above the critical thickness. By a combination of nonresonant x-ray magnetic scattering, neutron diffraction and vector-mapped x-ray magnetic linear dichroism photoemission electron microscopy, we show that epitaxial (111)-BiFeO3 films support submicron antiferromagnetic domains, which are magnetoelastically coupled to a coherent crystallographic monoclinic twin structure. This unique texture, which is absent in bulk single crystals, should enable control of magnetism in BiFeO3 film devices via epitaxial strain.
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Oct 2016
|
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I16-Materials and Magnetism
|
Diamond Proposal Number(s):
[5693]
Abstract: Through a combination of neutron diffraction and Landau theory we describe the spin ordering in the ground state of the quadruple perovskite manganite CaMn 7 O 12 —a magnetic multiferroic supporting an incommensurate orbital density wave that onsets above the magnetic ordering temperature, T N1 =90 K. The multi-k magnetic structure in the ground state was found to be a nearly-constant-moment helix with modulated spin helicity, which oscillates in phase with the orbital occupancies on the Mn 3+ sites via trilinear magneto-orbital coupling. Our phenomenological model also shows that, above T N2 =48 K, the primary magnetic order parameter is locked into the orbital wave by an admixture of helical and collinear spin density wave structures. Furthermore, our model naturally explains the lack of a sharp dielectric anomaly at T N1 and the unusual temperature dependence of the electrical polarization.
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May 2016
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