I10-Beamline for Advanced Dichroism
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Zihan
Li
,
Shanshan
Liu
,
Jiabao
Sun
,
Jiayi
Zhu
,
Yanhui
Chen
,
Yunkun
Yang
,
Linfeng
Ai
,
Enze
Zhang
,
Ce
Huang
,
Pengliang
Leng
,
Minhao
Zhao
,
Xiaoyi
Xie
,
Yuda
Zhang
,
Nesta Benno
Joseph
,
Rajdeep
Banerjee
,
Awadhesh
Narayan
,
Jin
Zou
,
Wenqing
Liu
,
Xiaodong
Xu
,
Faxian
Xiu
Diamond Proposal Number(s):
[22532]
Abstract: Two-dimensional (2D) magnets offer valuable electrical and mechanical properties, and could be used to create 2D nanoelectromechanical systems. However, the low Curie temperature of most 2D magnets limits practical applications. Here we report van der Waals ferromagnetic low-pass filters based on wafer-scale iron germanium telluride (Fe5+xGeTe2) thin films grown by molecular-beam epitaxy. We show that the Curie temperature of the Fe5+xGeTe2 system can be continuously modulated from 260 to 380 K via in situ iron doping. Few-layer Fe5+xGeTe2 is used to fabricate planar spiral inductors, with the 2D magnetic core providing inductance enhancement of 74% at room temperature compared with an inductor without the core. Low-pass Butterworth filters are then created from inductance–capacitance circuits built with these inductors. The filters offer a broad dynamic range of around 40 dB, and the –3 dB cut-off frequency can be tuned from 18 to 30 Hz by using different inductors in the inductance–capacitance circuit.
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Mar 2023
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I10-Beamline for Advanced Dichroism
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Diamond Proposal Number(s):
[21872, 27487]
Open Access
Abstract: The topological surface states (TSSs) in topological insulators (TIs) offer exciting prospects for dissipationless spin transport. Common spin-based devices, such as spin valves, rely on trilayer structures in which a non-magnetic (NM) layer is sandwiched between two ferromagnetic (FM) layers. The major disadvantage of using high-quality single-crystalline TI films in this context is that a single pair of spin-momentum locked channels spans across the entire film, meaning that only a very small spin current can be pumped from one FM to the other, along the side walls of the film. On the other hand, using nanocrystalline TI films, in which the grains are large enough to avoid hybridization of the TSSs, will effectively increase the number of spin channels available for spin pumping. Here, we used an element-selective, x-ray based ferromagnetic resonance technique to demonstrate spin pumping from a FM layer at resonance through the TI layer and into the FM spin sink.
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Mar 2023
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I10-Beamline for Advanced Dichroism
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Diamond Proposal Number(s):
[16141]
Open Access
Abstract: Owing to the unique chemical and electronic properties arising from 3d-electrons, substitution with transition metal ions is one of the key routes for engineering new functionalities into materials. While this approach has been used extensively in complex metal oxide perovskites, metal halide perovskites have largely resisted facile isovalent substitution. In this work, it is demonstrated that the substitution of Co2+ into the lattice of methylammonium lead triiodide imparts magnetic behavior to the material while maintaining photovoltaic performance at low concentrations. In addition to comprehensively characterizing its magnetic properties, the Co2+ ions themselves are utilized as probes to sense the local electronic environment of Pb in the perovskite, thereby revealing the nature of their incorporation into the material. A comprehensive understanding of the effect of transition metal incorporation is provided, thereby opening the substitution gateway for developing novel functional perovskite materials and devices for future technologies.
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Mar 2023
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I06-Nanoscience
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Diamond Proposal Number(s):
[14135]
Abstract: The size of the orbital moment in
Fe
3
O
4
has been the subject of a long-standing and contentious debate. In this paper, we make use of ferromagnetic resonance (FMR) spectroscopy and x-ray magnetic circular dichroism (XMCD) to provide complementary determinations of the size of the orbital moment in “bulklike” epitaxial
Fe
3
O
4
films grown on yttria-stabilized zirconia (111) substrates. Annealing the 100 nm as-grown films to
1100
∘
C
in a reducing atmosphere improves the stoichiometry and microstructure of the films, allowing for bulklike properties to be recovered as evidenced by x-ray diffraction and vibrating sample magnetometry. In addition, in-plane angular FMR spectra exhibit a crossover from a fourfold symmetry to the expected sixfold symmetry of the (111) surface, together with an anomalous peak in the FMR linewidth at
∼
10
GHz; this is indicative of low Gilbert damping in combination with two-magnon scattering. For the bulklike annealed sample, a spectroscopic splitting factor
g
≈
2.18
is obtained using both FMR and XMCD techniques, providing evidence for the presence of a finite orbital moment in
Fe
3
O
4
.
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Feb 2023
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I10-Beamline for Advanced Dichroism
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Peng
Chen
,
Qi
Yao
,
Junqi
Xu
,
Qiang
Sun
,
Alexander J.
Grutter
,
Patrick
Quarterman
,
Purnima P.
Balakrishnan
,
Christy J.
Kinane
,
Andrew J.
Caruana
,
Sean
Langridge
,
Ang
Li
,
Barat
Achinuq
,
Emily
Heppell
,
Yuchen
Ji
,
Shanshan
Liu
,
Baoshan
Cui
,
Jiuming
Liu
,
Puyang
Huang
,
Zhongkai
Liu
,
Guoqiang
Yu
,
Faxian
Xiu
,
Thorsten
Hesjedal
,
Jin
Zou
,
Xiaodong
Han
,
Haijun
Zhang
,
Yumeng
Yang
,
Xufeng
Kou
Diamond Proposal Number(s):
[30262]
Abstract: The intrinsic magnetic topological insulator MnBi2Te4 (MBT) provides a platform for the creation of exotic quantum phenomena. Novel properties can be created by modification of the MnBi2Te4 framework, but the design of stable magnetic structures remains challenging. Here we report ferromagnet-intercalated MnBi2Te4 superlattices with tunable magnetic exchange interactions. Using molecular beam epitaxy, we intercalate ferromagnetic MnTe layers into MnBi2Te4 to create [(MBT)(MnTe)m]N superlattices and examine their magnetic interaction properties using polarized neutron reflectometry and magnetoresistance measurements. Incorporation of the ferromagnetic spacer tunes the antiferromagnetic interlayer coupling of the MnBi2Te4 layers through the exchange-spring effect at MnBi2Te4/MnTe hetero-interfaces. The MnTe thickness can be used to modulate the relative strengths of the ferromagnetic and antiferromagnetic order, and the superlattice periodicity can tailor the spin configurations of the synthesized multilayers.
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Dec 2022
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I10-Beamline for Advanced Dichroism
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Diamond Proposal Number(s):
[10207]
Open Access
Abstract: X-ray magnetic circular dichroism (XMCD), which by virtue of the sum rules provides element-specific spin and orbital moments, is obtained from the difference between two polarized spectra by reversing the direction of either the light helicity or the applied magnetic field. Usually, it is tacitly assumed that these two spectra are obtained using the same absolute degree of light and magnetic polarization. This is, however, not always possible and depends on circumstances that can be beyond control. First, we recapitulate the conventional XMCD sum rule method to obtain the values of the moments and emphasize some of the complications in the case of the rare-earth
M
4
,
5
edges, such as the presence of strong core-hole
j
j
overlap, linear dichroism, and magnetic dipole term
⟨
T
z
⟩
. Instead, we propose an alternative method. Using the individual polarized x-ray absorption spectra obtained at the Ho and Dy
M
5
edges, where each of the
Δ
J
=
−
1
,
0
, and
+
1
transitions are separated by
∼
2
eV in photon energy, we are able to determine independently the degree of circular dichroism in a single spectrum. Since light is a transverse wave, we need to include, apart from the circular dichroism, also a linear dichroism contribution in order to fit the circularly polarized spectra. In the measurements on paramagnetic rare-earth dopants it was found that reversing the field produces the same degree of circular dichroism, while reversing the helicity yields a
∼
20% difference in the degree of circular dichroism.
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Dec 2022
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I10-Beamline for Advanced Dichroism
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N.-J.
Steinke
,
S. L.
Zhang
,
P. J.
Baker
,
L. B.
Duffy
,
F.
Kronast
,
J.
Krieger
,
Z.
Salman
,
T.
Prokscha
,
A.
Suter
,
S.
Langridge
,
Gerrit
Van Der Laan
,
T.
Hesjedal
Diamond Proposal Number(s):
[11503]
Abstract: Chromium-doped
Sb
2
Te
3
is a magnetic topological insulator (MTI), which belongs to the
(
Sb
,
Bi
)
2
(
Se
,
Te
)
3
family. When doped with the transition metals V, Cr, and Mn this family displays long-range ferromagnetic order above liquid nitrogen temperature and is currently intensely explored for quantum device applications. Despite the large magnetic ordering temperature, the experimental observation of dissipationless electrical transport channels, i.e., the quantum anomalous Hall effect, is limited in these materials to temperatures below
≈
2
K. Inhomogeneities in the MTI have been identified as a major concern, affecting the coupling between the Dirac states and the magnetic dopants. Nevertheless, details on the local magnetic order in these materials are not well understood. Here, we report the study of the magnetic correlations in thin films using a combination of muon spin relaxation
(
μ
SR
)
, and magnetic soft x-ray spectroscopy and imaging.
μ
SR
provides two key quantities for understanding the microscopic magnetic behavior: The magnetic volume fraction, i.e., the percentage of the material that is ferromagnetically ordered, and the relaxation rate, which is sensitive to the magnetic static
(
≈
μ
s
)
and dynamic disorder. By choosing different implantation depths for the muons, one can further discriminate between near-surface and bulk properties. No evidence for a surface enhancement of the magnetic ordering is observed, but, instead, we find evidence of small magnetically ordered clusters in a paramagnetic background, which are coupled. The significant magnetic field shift that is present in all samples indicates a percolation transition that proceeds through the formation and growth of magnetically ordered spin clusters. We further find that fluctuations are present even at low temperatures, and that there appears to be a transition between superparamagnetism and superferromagnetism.
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Dec 2022
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B18-Core EXAFS
I10-Beamline for Advanced Dichroism
|
Diamond Proposal Number(s):
[24930, 22629]
Open Access
Abstract: The spectroscopic g-factor of epitaxial thin film Yttrium Iron Garnet (YIG) has been studied using a combination of ferromagnetic resonance spectroscopy and x-ray magnetic circular dichroism. The values obtained by the two techniques are found, within experimental error, to be in agreement using Kittel’s original derivation for the g-factor. For an insulating material with an entirely Fe3+ configuration, a spin mixing correction to Kittel’s derivation of the spectroscopic g-factor, as recently shown by Shaw et al. [Phys. Rev. Lett. 127, 207201 (2021)] for metallic systems, is not required and demonstrates that the spin mixing parameter is small in YIG due to negligible spin–orbit coupling.
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Sep 2022
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I10-Beamline for Advanced Dichroism
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Diamond Proposal Number(s):
[19173]
Abstract: We present an investigation on the structural and magnetic properties of the interfaces of
Fe
3
O
4
/
MgO
(
001
)
and
Fe
3
O
4
/
NiO
/
MgO
(
001
)
by extracting cation-selective magneto-optical depth profiles by means of x-ray resonant magnetic reflectivity in combination with charge-transfer multiplet simulations of x-ray magnetic circular dichroism data. For
Fe
3
O
4
/
MgO
(
001
)
, the magneto-optical depth profiles at the
Fe
2
+
oct
and the
Fe
3
+
oct
resonant energies follow exactly the structural profile, while the magneto-optical depth profile at the
Fe
3
+
tet
resonance is offset by
3.2
±
1.3
Å from the interface, consistent with a
B
-site interface termination of
Fe
3
O
4
with fully intact magnetic order. In contrast, for
Fe
3
O
4
/
NiO
(
001
)
, the magneto-optical depth profiles at the
Fe
2
+
oct
and the
Ni
2
+
resonances agree with the structural profile, but the interface positions of the magneto-optical depth profiles at the
Fe
3
+
oct
and the
Fe
3
+
tet
resonances are spatially shifted by
3.3
±
1.4
and
2.7
±
0.9
Å, respectively, not consistent with a magnetically ordered stoichiometric interface. This may be related to an intermixed
(
Ni
,
Fe
)
O
layer at the interface. The dichroic depth profile at the Ni
L
3
edge might hint at uncompensated magnetic moments throughout the NiO film.
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Jun 2022
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I10-Beamline for Advanced Dichroism
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Xiaoqian
Zhang
,
Wenqing
Liu
,
Wei
Niu
,
Qiangsheng
Lu
,
Wei
Wang
,
Ali
Sarikhani
,
Xiaohua
Wu
,
Chunhui
Zhu
,
Jiabao
Sun
,
Mitchel
Vaninger
,
Paul. F.
Miceli
,
Jianqi
Li
,
David J.
Singh
,
Yew San
Hor
,
Yue
Zhao
,
Chang
Liu
,
Liang
He
,
Rong
Zhang
,
Guang
Bian
,
Dapeng
Yu
,
Yongbing
Xu
Diamond Proposal Number(s):
[22532]
Abstract: One of the most promising avenues in 2D materials research is the synthesis of antiferromagnets employing 2D van der Waals (vdW) magnets. However, it has proven challenging, due in part to the complicated fabrication process and undesired adsorbates as well as the significantly deteriorated ferromagnetism at atomic layers. Here, the engineering of the antiferromagnetic (AFM) interlayer exchange coupling between atomically thin yet ferromagnetic CrTe2 layers in an ultra-high vacuum-free 2D magnetic crystal, Cr5Te8 is reported. By self-introducing interstitial Cr atoms in the vdW gaps, the emergent AFM ordering and the resultant giant magnetoresistance effect are induced. A large negative magnetoresistance (10%) with a plateau-like feature is revealed, which is consistent with the AFM interlayer coupling between the adjacent CrTe2 main layers in a temperature window of 30 K below the Néel temperature. Notably, the AFM state has a relatively weak interlayer exchange coupling, allowing a switching between the interlayer AFM and ferromagnetic states at moderate magnetic fields. This work represents a new route to engineering low-power devices that underpin the emerging spintronic technologies, and an ideal laboratory to study 2D magnetism.
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May 2022
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