I06-Nanoscience
|
Andrew
Ross
,
Romain
Lebrun
,
Lorenzo
Baldrati
,
Akashdeep
Kamra
,
Olena
Gomonay
,
Shilei
Ding
,
Felix
Schreiber
,
Dirk
Backes
,
Francesco
Maccherozzi
,
Daniel A.
Grave
,
Avner
Rothschild
,
Jairo
Sinova
,
Mathias
Klaui
Diamond Proposal Number(s):
[23819]
Abstract: We report room-temperature long-distance spin transport of magnons in antiferromagnetic thin-film hematite doped with Zn. The additional dopants significantly alter the magnetic anisotropies, resulting in a complex equilibrium spin structure that is capable of efficiently transporting spin angular momentum at room temperature without the need for a well-defined, pure easy-axis or easy-plane anisotropy. We find intrinsic magnon spin-diffusion lengths of up to 1.5 μm, and magnetic domain governed decay lengths of 175 nm for the low-frequency magnons, through electrical transport measurements demonstrating that the introduction of nonmagnetic dopants does not strongly reduce the transport length scale, showing that the magnetic damping of hematite is not significantly increased. We observe a complex field dependence of the nonlocal signal independent of the magnetic state visible, in the local magnetoresistance and direct magnetic imaging of the antiferromagnetic domain structure. We explain our results in terms of a varying and applied field-dependent ellipticity of the magnon modes reaching the detector electrode allowing us to tune the spin transport.
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Dec 2020
|
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I06-Nanoscience
|
S.
Duttagupta
,
A.
Kurenkov
,
O. A.
Tretiakov
,
G.
Krishnaswamy
,
G.
Sala
,
V.
Krizakova
,
F.
Maccherozzi
,
S. S.
Dhesi
,
P.
Gambardella
,
S.
Fukami
,
H.
Ohno
Diamond Proposal Number(s):
[20413]
Open Access
Abstract: The ability to represent information using an antiferromagnetic material is attractive for future antiferromagnetic spintronic devices. Previous studies have focussed on the utilization of antiferromagnetic materials with biaxial magnetic anisotropy for electrical manipulation. A practical realization of these antiferromagnetic devices is limited by the requirement of material-specific constraints. Here, we demonstrate current-induced switching in a polycrystalline PtMn/Pt metallic heterostructure. A comparison of electrical transport measurements in PtMn with and without the Pt layer, corroborated by x-ray imaging, reveals reversible switching of the thermally-stable antiferromagnetic Néel vector by spin-orbit torques. The presented results demonstrate the potential of polycrystalline metals for antiferromagnetic spintronics.
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Nov 2020
|
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I06-Nanoscience
|
Z.
Kašpar
,
M.
Surýnek
,
J.
Zubáč
,
F.
Krizek
,
V.
Novák
,
R. P.
Campion
,
M. S.
Wörnle
,
P.
Gambardella
,
X.
Marti
,
P.
Němec
,
K. W.
Edmonds
,
S.
Reimers
,
O. J.
Amin
,
F.
Maccherozzi
,
S. S.
Dhesi
,
P.
Wadley
,
J.
Wunderlich
,
K.
Olejník
,
T.
Jungwirth
Abstract: Antiferromagnets are of potential use in the development of spintronic devices due to their ultrafast dynamics, insensitivity to external magnetic fields and absence of magnetic stray fields. Similar to their ferromagnetic counterparts, antiferromagnets can store information in the orientations of the collective magnetic order vector. However, the readout magnetoresistivity signals in simple antiferromagnetic films are weak, and reorientation of the magnetic order vector via optical excitation has not yet been achieved. Here we report the reversible and reproducible quenching of antiferromagnetic CuMnAs into nano-fragmented domain states using either electrical or ultrashort optical pulses. The changes in the resistivity of the system approach 20% at room temperature, which is comparable to the giant magnetoresistance ratios in ferromagnetic multilayers. We also obtain a signal readout by optical reflectivity.
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Nov 2020
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I06-Nanoscience
|
Federico
Motti
,
G.
Vinai
,
Valentina
Bonanni
,
Vincent
Polewczyk
,
Paola
Mantegazza
,
Thomas
Forrest
,
Francesco
Maccherozzi
,
Stefania
Benedetti
,
Christian
Rinaldi
,
Matteo
Cantoni
,
Damiano
Cassese
,
Stefano
Prato
,
Sarnjeet S.
Dhesi
,
Giorgio
Rossi
,
Giancarlo
Panaccione
,
Piero
Torelli
Diamond Proposal Number(s):
[18810]
Abstract: A ferromagnetic (FM) thin film deposited on a substrate of
Pb
(
Mg
1
/
3
Nb
2
/
3
)
O
3
−
PbTiO
3
(PMN-PT) is an appealing heterostructure for the electrical control of magnetism, which would enable nonvolatile memories with ultralow-power consumption. Reversible and electrically controlled morphological changes at the surface of PMN-PT suggest that the magnetoelectric effects are more complex than the commonly used “strain-mediated” description. Here we show that changes in substrate morphology intervene in magnetoelectric coupling as a key parameter interplaying with strain. Magnetic-sensitive microscopy techniques are used to study magnetoelectric coupling in Fe/PMN-PT at different length scales, and compare different substrate cuts. The observed rotation of the magnetic anisotropy is connected to the changes in morphology, and mapped in the crack pattern at the mesoscopic scale. Ferroelectric polarization switching induces a magnetic field-free rotation of the magnetic domains at micrometer scale, with a wide distribution of rotation angles. Our results show that the relationship between the rotation of the magnetic easy axis and the rotation of the in-plane component of the electric polarization is not straightforward, as well as the relationship between ferroelectric domains and crack pattern. The understanding and control of this phenomenon is crucial to develop functional devices based on FM/PMN-PT heterostructures.
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Nov 2020
|
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I06-Nanoscience
|
M.
Ghidini
,
R.
Pellicelli
,
R.
Mansell
,
D.
Pesquera
,
B.
Nair
,
X.
Moya
,
S.
Farokhipoor
,
F.
Maccherozzi
,
C. H. W.
Barnes
,
R. P.
Cowburn
,
S. S.
Dhesi
,
N. D.
Mathur
Diamond Proposal Number(s):
[11843]
Open Access
Abstract: Magnetic vortex cores in polycrystalline Ni discs underwent non-volatile displacements due to voltage-driven ferroelectric domain switching in single-crystal BaTiO3. This behaviour was observed using photoemission electron microscopy to image both the ferromagnetism and ferroelectricity, while varying in-plane sample orientation. The resulting vector maps of disc magnetization match well with micromagnetic simulations, which show that the vortex core is translated by the transit of a ferroelectric domain wall, and thus the inhomogeneous strain with which it is associated. The non-volatility is attributed to pinning inside the discs. Voltage-driven displacement of magnetic vortex cores is novel, and opens the way for studying voltage-driven vortex dynamics.
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Oct 2020
|
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I06-Nanoscience
|
T.
Janda
,
J.
Godinho
,
T.
Ostatnicky
,
E.
Pfitzner
,
G.
Ulrich
,
A.
Hoehl
,
S.
Reimers
,
Z.
Šobáň
,
T.
Metzger
,
H.
Reichlová
,
V.
Novák
,
R. P.
Campion
,
J.
Heberle
,
P.
Wadley
,
K. W.
Edmonds
,
O. J.
Amin
,
J. S.
Chauhan
,
S. S.
Dhesi
,
F.
Maccherozzi
,
R. M.
Otxoa
,
P. E.
Roy
,
K.
Olejník
,
P.
Němec
,
T.
Jungwirth
,
B.
Kaestner
,
J.
Wunderlich
Diamond Proposal Number(s):
[22437, 16376, 20793]
Abstract: Antiferromagnets offer spintronic device characteristics unparalleled in ferromagnets owing to their lack of stray fields, THz spin dynamics, and rich materials landscape. Microscopic imaging of antiferromagnetic domains is one of the key prerequisites for understanding physical principles of the device operation. However, adapting common magnetometry techniques to the dipolar-field-free antiferromagnets has been a major challenge. Here we demonstrate in a collinear antiferromagnet a thermoelectric detection method by combining the magneto-Seebeck effect with local heat gradients generated by scanning far-field or near-field techniques. In a 20-nm epilayer of uniaxial CuMnAs we observe reversible
180
∘
switching of the Néel vector via domain wall displacement, controlled by the polarity of the current pulses. We also image polarity-dependent
90
∘
switching of the Néel vector in a thicker biaxial film, and domain shattering induced at higher pulse amplitudes. The antiferromagnetic domain maps obtained by our laboratory technique are compared to measurements by the established synchrotron-based technique of x-ray photoemission electron microscopy using x-ray magnetic linear dichroism.
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Sep 2020
|
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I06-Nanoscience
|
D.
Pesquera
,
E.
Khestanova
,
M.
Ghidini
,
S.
Zhang
,
A. P.
Rooney
,
F.
Maccherozzi
,
P.
Riego
,
S.
Farokhipoor
,
J.
Kim
,
X.
Moya
,
M. E.
Vickers
,
N. A.
Stelmashenko
,
S. J.
Haigh
,
S. S.
Dhesi
,
N. D.
Mathur
Diamond Proposal Number(s):
[14745]
Open Access
Abstract: Epitaxial films may be released from growth substrates and transferred to structurally and chemically incompatible substrates, but epitaxial films of transition metal perovskite oxides have not been transferred to electroactive substrates for voltage control of their myriad functional properties. Here we demonstrate good strain transmission at the incoherent interface between a strain-released film of epitaxially grown ferromagnetic La0.7Sr0.3MnO3 and an electroactive substrate of ferroelectric 0.68Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 in a different crystallographic orientation. Our strain-mediated magnetoelectric coupling compares well with respect to epitaxial heterostructures, where the epitaxy responsible for strong coupling can degrade film magnetization via strain and dislocations. Moreover, the electrical switching of magnetic anisotropy is repeatable and non-volatile. High-resolution magnetic vector maps reveal that micromagnetic behaviour is governed by electrically controlled strain and cracks in the film. Our demonstration should inspire others to control the physical/chemical properties in strain-released epitaxial oxide films by using electroactive substrates to impart strain via non-epitaxial interfaces.
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Jun 2020
|
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I06-Nanoscience
|
M.
Wang
,
C.
Andrews
,
S.
Reimers
,
O. J.
Amin
,
P.
Wadley
,
R. P.
Campion
,
S. F.
Poole
,
J.
Felton
,
K. W.
Edmonds
,
B. L.
Gallagher
,
A. W.
Rushforth
,
O.
Makarovsky
,
K.
Gas
,
M.
Sawicki
,
D.
Kriegner
,
J.
Zubáč
,
K.
Olejník
,
V.
Novák
,
T.
Jungwirth
,
M.
Shahrokhvand
,
U.
Zeitler
,
S. S.
Dhesi
,
F.
Maccherozzi
Diamond Proposal Number(s):
[11846, 20793]
Abstract: We report magnetic-field-induced rotation of the antiferromagnetic Néel vector in epitaxial CuMnAs thin films. First, using soft x-ray magnetic linear dichroism spectroscopy as well as magnetometry, we demonstrate spin-flop switching and continuous spin reorientation in films with uniaxial and biaxial magnetic anisotropies, respectively, for applied magnetic fields of the order of 2 T. The remnant antiferromagnetic domain configurations are determined using x-ray photoemission electron microscopy. Next, we show that the Néel vector reorientations are manifested in the longitudinal and transverse anisotropic magnetoresistance. Dependencies of the electrical resistance on the orientation of the Néel vector with respect to both the electrical current direction and the crystal symmetry are identified, including a weak fourth-order term evident at high magnetic fields. The results provide characterization of key parameters including the anisotropic magnetoresistance coefficients, magnetocrystalline anisotropy, and spin-flop field in epitaxial films of tetragonal CuMnAs, a candidate material for antiferromagnetic spintronics.
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Mar 2020
|
|
I06-Nanoscience
|
Massimo
Ghidini
,
Rhodri
Mansell
,
Raffaele
Pellicelli
,
David
Pesquera
,
Bhaskaran
Nair
,
Xavier
Moya
,
Saeedeh
Farokhipoor
,
Francesco
Maccherozzi
,
Crispin
Barnes
,
Russell
Cowburn
,
Sarnjeet
Dhesi
,
Neil
Mathur
Diamond Proposal Number(s):
[11843]
Abstract: Using photoemission electron microscopy (PEEM) to image ferromagnetism in polycrystalline Ni disks, and ferroelectricity in their single-crystal BaTiO3 substrates, we find that voltage-driven 90 ferroelectric domain switching serves to reversibly annihilate each magnetic vortex via uniaxial compressive strain, and that the orientation of the resulting bi domain reveals the chirality of the annihilated vortex. (Micromagnetic simulations reveal that only 60% of this strain was required for annihilation.) Voltage control of magnetic vortices is novel, and should be energetically favourable with respect to the use of a magnetic field or an electrical current. In future, stray field from bi domains could be exploited to read vortex chirality. Given that core polarity can already be read via stray field, our work represents a step towards four-state low power memory applications.
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Feb 2020
|
|
I06-Nanoscience
|
Diamond Proposal Number(s):
[13723]
Abstract: A novel method of measuring the core level binding energies of multiple sized nanoparticles on the same substrate is demonstrated using the early stage of Au nanoparticle growth on reduced r-TiO2(110). This method employed in situ scanning tunneling microscopy (STM) and microfocused X-ray photoemission spectroscopy. An STM tip-shadowing method was used to synthesize patterned areas of Au nanoparticles on the substrate with different coverages and sizes. Patterns were identified and imaged using a UV photoelectron emission microscope. The Au 4f core level binding energies of the nanoparticles were investigated as a function of Au nanoparticle coverage and size. A combination of initial and final state effects modifies the binding energies of the Au 4f core levels as the nanoparticle size changes. When single Au atoms and Au3 clusters are present, the Au 4f7/2 binding energy, 84.42 eV, is similar to that observed at a high coverage (1.8 monolayer equivalent), resulting from a cancellation of initial and final state effects. As the coverage is increased, there is a decrease in binding energy, which then increases at a higher coverage to 84.39 eV. These results are consistent with a Volmer-Weber nucleation-growth model of Au nanoparticles at oxygen vacancies, resulting in electron transfer to the nanoparticles.
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Jan 2020
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