I05-ARPES
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A. Garrison
Linn
,
Peipei
Hao
,
Kyle N.
Gordon
,
Dushyant
Narayan
,
Bryan S.
Berggren
,
Nathaniel
Speiser
,
Sonka
Reimers
,
Richard P.
Campion
,
Vít
Novák
,
Sarnjeet S.
Dhesi
,
Timur K.
Kim
,
Cephise
Cacho
,
Libor
Šmejkal
,
Tomáš
Jungwirth
,
Jonathan D.
Denlinger
,
Peter
Wadley
,
Daniel S.
Dessau
Diamond Proposal Number(s):
[24224]
Open Access
Abstract: Tetragonal CuMnAs is a room temperature antiferromagnet with an electrically reorientable Néel vector and a Dirac semimetal candidate. Direct measurements of the electronic structure of single-crystalline thin films of tetragonal CuMnAs using angle-resolved photoemission spectroscopy (ARPES) are reported, including Fermi surfaces (FS) and energy-wavevector dispersions. After correcting for a chemical potential shift of ≈− 390 meV (hole doping), there is excellent agreement of FS, orbital character of bands, and Fermi velocities between the experiment and density functional theory calculations. In addition, 2×1 surface reconstructions are found in the low energy electron diffraction (LEED) and ARPES. This work underscores the need to control the chemical potential in tetragonal CuMnAs to enable the exploration and exploitation of the Dirac fermions with tunable masses, which are predicted to be above the chemical potential in the present samples.
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May 2023
|
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I06-Nanoscience
|
Filip
Krizek
,
Sonka
Reimers
,
Zdeněk
Kašpar
,
Alberto
Marmodoro
,
Jan
Michalička
,
Ondřej
Man
,
Alexander
Edström
,
Oliver J.
Amin
,
Kevin W.
Edmonds
,
Richard P.
Campion
,
Francesco
Maccherozzi
,
Sarnjeet S.
Dhesi
,
Jan
Zubáč
,
Domink
Kriegner
,
Dina
Carbone
,
Jakub
Železný
,
Karel
Výborný
,
Kamil
Olejník
,
Vít
Novák
,
Jan
Rusz
,
Juan-Carlos
Idrobo
,
Peter
Wadley
,
Tomas
Jungwirth
Diamond Proposal Number(s):
[22437]
Open Access
Abstract: The interest in understanding scaling limits of magnetic textures such as domain walls spans the entire field of magnetism from its physical fundamentals to applications in information technologies. Here, we explore antiferromagnetic CuMnAs in which imaging by x-ray photoemission reveals the presence of magnetic textures down to nanoscale, reaching the detection limit of this established microscopy in antiferromagnets. We achieve atomic resolution by using differential phase-contrast imaging within aberration-corrected scanning transmission electron microscopy. We identify abrupt domain walls in the antiferromagnetic film corresponding to the Néel order reversal between two neighboring atomic planes. Our work stimulates research of magnetic textures at the ultimate atomic scale and sheds light on electrical and ultrafast optical antiferromagnetic devices with magnetic field–insensitive neuromorphic functionalities.
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Apr 2022
|
|
I06-Nanoscience
|
Sonka
Reimers
,
Dominik
Kriegner
,
Olena
Gomonay
,
Dina
Carbone
,
Filip
Krizek
,
Vit
Novák
,
Richard P.
Campion
,
Francesco
Maccherozzi
,
Alexander
Bjorling
,
Oliver J.
Amin
,
Luke X.
Barton
,
Stuart F.
Poole
,
Khalid A.
Omari
,
Jan
Michalička
,
Ondřej
Man
,
Jairo
Sinova
,
Tomáš
Jungwirth
,
Peter
Wadley
,
Sarnjeet S.
Dhesi
,
Kevin W.
Edmonds
Diamond Proposal Number(s):
[22437, 2714]
Open Access
Abstract: Efficient manipulation of antiferromagnetic (AF) domains and domain walls has opened up new avenues of research towards ultrafast, high-density spintronic devices. AF domain structures are known to be sensitive to magnetoelastic effects, but the microscopic interplay of crystalline defects, strain and magnetic ordering remains largely unknown. Here, we reveal, using photoemission electron microscopy combined with scanning X-ray diffraction imaging and micromagnetic simulations, that the AF domain structure in CuMnAs thin films is dominated by nanoscale structural twin defects. We demonstrate that microtwin defects, which develop across the entire thickness of the film and terminate on the surface as characteristic lines, determine the location and orientation of 180∘ and 90∘ domain walls. The results emphasize the crucial role of nanoscale crystalline defects in determining the AF domains and domain walls, and provide a route to optimizing device performance.
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Feb 2022
|
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I06-Nanoscience
|
Z.
Kaspar
,
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
|
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
|
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
|
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I06-Nanoscience
|
Peter
Wadley
,
Sonka
Reimers
,
Michal J.
Grzybowski
,
Carl
Andrews
,
Mu
Wang
,
Jasbinder S.
Chauhan
,
Bryan L.
Gallagher
,
Richard P.
Campion
,
Kevin W.
Edmonds
,
Sarnjeet S.
Dhesi
,
Francesco
Maccherozzi
,
Vit
Novak
,
Joerg
Wunderlich
,
Tomas
Jungwirth
Diamond Proposal Number(s):
[16376]
Abstract: Antiferromagnets have several favourable properties as active elements in spintronic devices, including ultra-fast dynamics, zero stray fields and insensitivity to external magnetic fields1. Tetragonal CuMnAs is a testbed system in which the antiferromagnetic order parameter can be switched reversibly at ambient conditions using electrical currents2. In previous experiments, orthogonal in-plane current pulses were used to induce 90° rotations of antiferromagnetic domains and demonstrate the operation of all-electrical memory bits in a multi-terminal geometry3. Here, we demonstrate that antiferromagnetic domain walls can be manipulated to realize stable and reproducible domain changes using only two electrical contacts. This is achieved by using the polarity of the current to switch the sign of the current-induced effective field acting on the antiferromagnetic sublattices. The resulting reversible domain and domain wall reconfigurations are imaged using X-ray magnetic linear dichroism microscopy, and can also be detected electrically. Switching by domain-wall motion can occur at much lower current densities than those needed for coherent domain switching.
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Mar 2018
|
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I06-Nanoscience
|
P.
Wadley
,
K. W.
Edmonds
,
M. R.
Shahedkhah
,
R. P.
Campion
,
B. L.
Gallagher
,
J.
Železný
,
J.
Kuneš
,
V.
Novák
,
T.
Jungwirth
,
V.
Saidl
,
P.
Němec
,
F.
Maccherozzi
,
S. S.
Dhesi
Diamond Proposal Number(s):
[9993]
Open Access
Abstract: Using x-ray magnetic circular and linear dichroism techniques, we demonstrate a collinear exchange coupling between an epitaxial antiferromagnet, tetragonal CuMnAs, and an Fe surface layer. A small uncompensated Mn magnetic moment is observed which is antiparallel to the Fe magnetization. The staggered magnetization of the 5 nm thick CuMnAs layer is rotatable under small magnetic fields, due to the interlayer exchange coupling. This allows us to obtain the x-ray magnetic linear dichroism spectra for different crystalline orientations of CuMnAs in the (001) plane. This is a key parameter for enabling the understanding of domain structures in CuMnAs imaged using x-ray magnetic linear dichroism microscopy techniques.
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Sep 2017
|
|
I06-Nanoscience
|
M. J.
Grzybowski
,
P.
Wadley
,
K. W.
Edmonds
,
R.
Beardsley
,
V.
Hills
,
R. P.
Campion
,
B. L.
Gallagher
,
J. S.
Chauhan
,
V.
Novak
,
T.
Jungwirth
,
F.
Maccherozzi
,
S. S.
Dhesi
Diamond Proposal Number(s):
[12504]
Abstract: The magnetic order in antiferromagnetic materials is hard to control with external magnetic fields. Using x-ray magnetic linear dichroism microscopy, we show that staggered effective fields generated by electrical current can induce modification of the antiferromagnetic domain structure in microdevices fabricated from a tetragonal CuMnAs thin film. A clear correlation between the average domain orientation and the anisotropy of the electrical resistance is demonstrated, with both showing reproducible switching in response to orthogonally applied current pulses. However, the behavior is inhomogeneous at the submicron level, highlighting the complex nature of the switching process in multidomain antiferromagnetic films.
|
Feb 2017
|
|
I06-Nanoscience
|
V.
Saidl
,
P.
Němec
,
Peter
Wadley
,
Victoria
Hills
,
R. P.
Campion
,
V.
Novák
,
K. W.
Edmonds
,
Francesco
Maccherozzi
,
S. S.
Dhesi
,
B. L.
Gallagher
,
F.
Trojánek
,
J.
Kuneš
,
J.
Železný
,
P.
Malý
,
T.
Jungwirth
Diamond Proposal Number(s):
[9993]
Abstract: Recent breakthroughs in the electrical detection and manipulation of antiferromagnets have opened a new avenue in the research of non-volatile spintronic devices. Antiparallel spin sublattices in antiferromagnets, producing zero dipolar fields, lead to insensitivity to magnetic field perturbations, multi-level stability, ultrafast spin dynamics and other favourable characteristics, and may find utility in fields ranging from magnetic memories to optical signal processing. However, the absence of a net magnetic moment and ultrashort magnetization dynamics timescales make antiferromagnets notoriously difficult to study using common magnetometers or magnetic resonance techniques. Here, we demonstrate the experimental determination of the Néel vector in a thin film of antiferromagnetic CuMnAs (refs 9,10), a prominent material used in the first realization of antiferromagnetic memory chips10. We use a table-top femtosecond pump–probe magneto-optical experiment that is considerably more accessible than the traditionally employed large-scale-facility techniques such as neutron diffraction11 and X-ray magnetic dichroism measurements.
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Jan 2017
|
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