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.
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Feb 2021
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I06-Nanoscience
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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.
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Feb 2021
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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.
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Jan 2021
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I06-Nanoscience
|
Diamond Proposal Number(s):
[17588]
Open Access
Abstract: A procedure to build the optical conductivity tensor that describes the full magneto-optical response of the system from experimental measurements is presented. Applied to the Fe L2,3-edge of a 38.85 nm Fe3O4/SrTiO3 (001) thin-film, it is shown that the computed polarization dependence using the conductivity tensor is in excellent agreement with that experimentally measured. Furthermore, the magnetic field angular dependence is discussed using a set of fundamental spectra expanded on spherical harmonics. It is shown that the convergence of this expansion depends on the details of the ground state of the system in question and in particular on the valence-state spin–orbit coupling. While a cubic expansion up to the third order explains the angular-dependent X-ray magnetic linear dichroism of Fe3+ well, higher-order terms are required for Fe2+ when the orbital moment is not quenched.
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Dec 2020
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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
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Abstract: The `water window', covering 2.4–4.4 nm, is an important wavelength range particularly essential to biology research. Cr/Ti multilayers are one of the promising reflecting elements in this region because the near-normal-incidence reflectivity is theoretically as high as 64% at 2.73 nm. However, due to multilayer imperfections, the reported reflectivity is lower than 3% for near-normal incidence. Here, B and C were intentionally incorporated into ultra-thin Cr/Ti soft X-ray multilayers by co-deposition of B4C at the interfaces. The effect on the multilayer structure and composition has been investigated using X-ray reflectometry, X-ray photoelectron spectroscopy, and cross-section electron microscopy. It is shown that B and C are mainly bonded to Ti sites, forming a nonstoichiometric TiBxCy composition, which hinders the interface diffusion, supresses the crystallization of the Cr/Ti multilayer and dramatically improves the interface quality of Cr/TiBxCy multilayers. As a result, the near-normal-incidence reflectivity of soft X-rays increases from 4.48% to 15.75% at a wavelength of 2.73 nm.
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Nov 2020
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I06-Nanoscience
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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
I10-Beamline for Advanced Dichroism
|
Zhongchong
Lin
,
Liang
Zha
,
Fanggui
Wang
,
Zhou
Liu
,
Rui
Wu
,
Jie
Yang
,
Mingzhu
Xue
,
Wenyun
Yang
,
Guang
Tian
,
Xiaobai
Ma
,
Liang
Qiao
,
Alexandra
Franz
,
Qi
An
,
Wenqing
Liu
,
Changsheng
Wang
,
Jinbo
Yang
Diamond Proposal Number(s):
[16538]
Abstract: The effect of Ce substitution on the structural and magnetic properties of (Nd1-δCeδ)2Fe14B (0 < δ < 1) series was systematically studied using neutron diffraction, 57Fe Mössbauer spectroscopy and X-ray magnetic circular dichroism (XMCD). An anomaly in the lattice parameters was observed in a sample with composition in the range of 0.2 < δ < 0.4, where a phase separation happens and the 2:14:1 isostructural dual-main-phases (IDMPs) appear. Outside this composition range, Ce shows a preferential occupation at the 4g site than the 4f site and a preferable Ce3+ valence state. The average magnetic moments of Nd/Ce and Fe atoms decrease with the increasing of δ. The magnitude of the Fe moments at non-equivalent sites is related to several factors, such as the Fe coordination number, the Wigner-Seitz cell volume, and the Boron atom effect. These results reveal the microscopic mechanisms for the structural and magnetic properties of Ce-substitution Nd2Fe14B, providing perspective on developing the next-generation low-cost and high-performance permanent magnetic materials.
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Nov 2020
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