I06-Nanoscience
|
Diamond Proposal Number(s):
[24373]
Open Access
Abstract: The remanent domain structures of composite element magnetic barcodes have been imaged using photo-emission electron microscopy with contrast from x-ray magnetic circular dichroism (XMCD-PEEM) and analysed with reference to the results of micromagnetic simulations. The magnetisation configuration at the end of wide strips is found to be perpendicular to the majority magnetisation direction. This transitions to an incomplete rotation for nominal strip widths below 300 nm and is found to affect the mechanics of magnetisation reversal for nominal strip widths below 200 nm, owing to a difference in magnetisation orientation when an external magnetic field is applied that is just smaller than the magnetic coercivity of the structures and a corresponding change in reversal dynamics. This change in domain structure as strip width decreases is consistent with both the influence of shape anisotropy and with measurements of magnetic hysteresis. The magnetisation reversal characteristics of composite element structures are found to be dependent on the relative magnetisation configurations of neighbouring strips, which in turn are found to vary stochastically upon the application and removal of a magnetic field along the easy axis of the structure. It is found that the application of a canted field is necessary to ensure sharp, consistent magnetisation reversal of bits when writing a binary code. These results confirm that either improved lithography of narrower strips or non-rectangular elements would be necessary to further increase the number of individually programmable bits in a barcode.
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Sep 2021
|
|
I06-Nanoscience
|
C.
Schmitt
,
L.
Baldrati
,
L.
Sanchez-Tejerina
,
F.
Schreiber
,
A.
Ross
,
M.
Filianina
,
S.
Ding
,
F.
Fuhrmann
,
R.
Ramos
,
F.
Maccherozzi
,
D.
Backes
,
M.-A.
Mawass
,
F.
Kronast
,
S.
Valencia
,
E.
Saitoh
,
G.
Finocchio
,
M.
Klaui
Diamond Proposal Number(s):
[22448]
Abstract: Understanding the electrical manipulation of the antiferromagnetic order is a crucial aspect to enable the design of antiferromagnetic devices working at THz frequencies. Focusing on collinear insulating antiferromagnetic
Ni
O
/
Pt
thin films as a materials platform, we identify the crystallographic orientation of the domains that can be switched by currents and quantify the Néel-vector direction changes. We demonstrate electrical switching between different T domains by current pulses, finding that the Néel-vector orientation in these domains is along [
±
5
±
5
19], different compared to the bulk
⟨
112
⟩
directions. The final state of the in-plane component of the Néel vector
n
IP
after switching by current pulses
j
along the
[
1
±
1
0
]
directions is
n
IP
∥
j
. By comparing the observed Néel-vector orientation and the strain in the thin films, assuming that this variation arises solely from magnetoelastic effects, we quantify the order of magnitude of the magnetoelastic coupling coefficient as
b
0
+
2
b
1
=
3
×
10
7
J
/
m
3
. This information is key for the understanding of current-induced switching in antiferromagnets and for the design and use of such devices as active elements in spintronic devices.
|
Mar 2021
|
|
I06-Nanoscience
|
Richard W.
Dawidek
,
Thomas J.
Hayward
,
Ian T.
Vidamour
,
Thomas J.
Broomhall
,
Guru
Venkat
,
Mohanad Al
Mamoori
,
Aidan
Mullen
,
Stephan J.
Kyle
,
Paul W.
Fry
,
Nina-Juliane
Steinke
,
Joshaniel F. K.
Cooper
,
Francesco
Maccherozzi
,
Sarnjeet S.
Dhesi
,
Lucia
Aballe
,
Michael
Foerster
,
Jordi
Prat
,
Eleni
Vasilaki
,
Matthew O. A.
Ellis
,
Dan A.
Allwood
Diamond Proposal Number(s):
[24205]
Open Access
Abstract: Emergent behaviors occur when simple interactions between a system's constituent elements produce properties that the individual elements do not exhibit in isolation. This article reports tunable emergent behaviors observed in domain wall (DW) populations of arrays of interconnected magnetic ring‐shaped nanowires under an applied rotating magnetic field. DWs interact stochastically at ring junctions to create mechanisms of DW population loss and gain. These combine to give a dynamic, field‐dependent equilibrium DW population that is a robust and emergent property of the array, despite highly varied local magnetic configurations. The magnetic ring arrays’ properties (e.g., non‐linear behavior, “fading memory” to changes in field, fabrication repeatability, and scalability) suggest they are an interesting candidate system for realizing reservoir computing (RC), a form of neuromorphic computing, in hardware. By way of example, simulations of ring arrays performing RC approaches 100% success in classifying spoken digits for single speakers.
|
Feb 2021
|
|
I06-Nanoscience
|
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.
|
Feb 2021
|
|
I06-Nanoscience
|
Diamond Proposal Number(s):
[23819]
Abstract: Tm
Fe
O
3
(TFO) is a canted antiferromagnet that undergoes a spin reorientation transition (SRT) with temperature between 82 and 94 K in single crystals. In this temperature region, the Néel vector continuously rotates from the crystallographic
c
axis (below 82 K) to the
a
axis (above 94 K). The SRT allows for a temperature control of distinct antiferromagnetic states without the need for a magnetic field, making it apt for applications working at terahertz frequencies. For device applications, thin films of TFO are required as well as an electrical technique for read-out of the magnetic state. Here, we demonstrate that orthorhombic TFO thin films can be grown by pulsed laser deposition and the detection of the SRT in TFO thin films can be accessed by making use of the all-electrical spin Hall magnetoresistance, in good agreement for the temperature range where the SRT occurs in bulk crystals. Our results demonstrate that one can electrically detect the SRT in insulators.
|
Jan 2021
|
|
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.
|
Dec 2020
|
|
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.
|
Nov 2020
|
|
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.
|
Nov 2020
|
|
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.
|
Nov 2020
|
|
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.
|
Oct 2020
|
|
