I10-Beamline for Advanced Dichroism - scattering
|
Bernd
Rellinghaus
,
Andy
Thomas
,
Moritz
Winter
,
Marein C.
Rahn
,
Alexandr S.
Sukuhanov
,
Alexander
Than
,
Sebastian
Schneider
,
Alessandro
Pignedoli
,
Maria
Azhar
,
Karin
Everschor-Sitte
,
Jochen
Geck
,
Gerrit
Van Der Laan
,
Thorsten
Hesjedal
,
Praveen
Vir
,
Claudia
Felser
,
Darius
Pohl
Diamond Proposal Number(s):
[28882]
|
Jul 2025
|
|
I16-Materials and Magnetism
|
M. C.
Rahn
,
M. N.
Wilson
,
T. J.
Hicken
,
F. L.
Pratt
,
C.
Wang
,
F.
Orlandi
,
D. D.
Khalyavin
,
P.
Manuel
,
L. S. I.
Veiga
,
A.
Bombardi
,
S.
Francoual
,
P.
Bereciartua
,
A. S.
Sukhanov
,
J. D.
Thompson
,
S. M.
Thomas
,
P. F. S.
Rosa
,
T.
Lancaster
,
F.
Ronning
,
M.
Janoschek
Open Access
Abstract: Eu
5
In
2
Sb
6
is a member of a family of orthorhombic nonsymmorphic rare-earth intermetallics that combines large localized magnetic moments and itinerant exchange with a low carrier density and perpendicular glide planes. This may result in special topological crystalline (wallpaper fermion) or axion insulating phases. Recent studies of
Eu
5
In
2
Sb
6
single crystals have revealed colossal negative magnetoresistance and multiple magnetic phase transitions. Here, we clarify this ordering process using neutron scattering, resonant elastic x-ray scattering, muon spin-rotation, and magnetometry. The nonsymmorphic and multisite character of
Eu
5
In
2
Sb
6
results in coplanar noncollinear magnetic structures with an Ising-like net magnetization along the
a
axis. A reordering transition, attributable to competing ferro- and antiferromagnetic couplings, manifests as the onset of a second commensurate Fourier component. In the absence of spatially resolved probes, the experimental evidence for this low-temperature state can be interpreted either as an unusual double-
q
structure or in a phase separation scenario. The net magnetization produces variable anisotropic hysteretic effects which also couple to charge transport. The implied potential for functional domain physics and topological transport suggests that this structural family may be a promising platform to implement concepts of topological antiferromagnetic spintronics.
|
May 2024
|
|
I16-Materials and Magnetism
|
Diamond Proposal Number(s):
[27353]
Open Access
Abstract: Magnetic topological insulators and semimetals are a class of crystalline solids whose properties are strongly influenced by the coupling between non-trivial electronic topology and magnetic spin configurations. Such materials can host exotic electromagnetic responses. Among these are topological insulators with certain types of antiferromagnetic order which are predicted to realize axion electrodynamics. Here we investigate the highly unusual helimagnetic phases recently reported in EuIn2As2, which has been identified as a candidate for an axion insulator. Using resonant elastic x-ray scattering we show that the two types of magnetic order observed in EuIn2As2 are spatially uniform phases with commensurate chiral magnetic structures, ruling out a possible phase-separation scenario, and we propose that entropy associated with low energy spin fluctuations plays a significant role in driving the phase transition between them. Our results establish that the magnetic order in EuIn2As2 satisfies the symmetry requirements for an axion insulator.
|
Jun 2023
|
|
I11-High Resolution Powder Diffraction
|
Henrik
Jacobsen
,
Hai L.
Feng
,
Andrew J.
Princep
,
Marein C.
Rahn
,
Yanfeng
Guo
,
Jie
Chen
,
Yoshitaka
Matsushita
,
Yoshihiro
Tsujimoto
,
Masahiro
Nagao
,
Dmitry
Khalyavin
,
Pascal
Manuel
,
Claire A.
Murray
,
Christian
Donnerer
,
James G.
Vale
,
Marco
Moretti Sala
,
Kazunari
Yamaura
,
Andrew T.
Boothroyd
Diamond Proposal Number(s):
[9839]
Abstract: We report on the structural, magnetic, and electronic properties of two new double-perovskites synthesized under high pressure,
Pb
2
CaOsO
6
and
Pb
2
ZnOsO
6
. Upon cooling below 80 K,
Pb
2
CaOsO
6
simultaneously undergoes a metal-to-insulator transition and develops antiferromagnetic order.
Pb
2
ZnOsO
6
, on the other hand, remains a paramagnetic metal down to 2 K. The key difference between the two compounds lies in their crystal structures. The Os atoms in
Pb
2
ZnOsO
6
are arranged on an approximately face-centered cubic lattice with strong antiferromagnetic nearest-neighbor exchange couplings. The geometrical frustration inherent to this lattice prevents magnetic order from forming down to the lowest temperatures. In contrast, the unit cell of
Pb
2
CaOsO
6
is heavily distorted up to at least 500 K including antiferroelectriclike displacements of the Pb and O atoms despite metallic conductivity above 80 K. This distortion relieves the magnetic frustration, facilitating magnetic order which, in turn, drives the metal-insulator transition. Our results suggest that the phase transition in
Pb
2
CaOsO
6
is spin driven and could be a rare example of a Slater transition.
|
Dec 2020
|
|
I16-Materials and Magnetism
|
Priscila
Rosa
,
Yuanfeng
Xu
,
Marein
Rahn
,
Jean
Souza
,
Satya
Kushwaha
,
Larissa
Veiga
,
Alessandro
Bombardi
,
Sean
Thomas
,
Marc
Janoschek
,
Eric
Bauer
,
Mun
Chan
,
Zhijun
Wang
,
Joe
Thompson
,
Neil
Harrison
,
Pascoal
Pagliuso
,
Andrei
Bernevig
,
Filip
Ronning
Diamond Proposal Number(s):
[18991]
Open Access
Abstract: Here we investigate antiferromagnetic Eu5In2Sb6, a nonsymmorphic Zintl phase. Our electrical transport data show that Eu5In2Sb6 is remarkably insulating and exhibits an exceptionally large negative magnetoresistance, which is consistent with the presence of magnetic polarons. From ab initio calculations, the paramagnetic state of Eu5In2Sb6 is a topologically nontrivial semimetal within the generalized gradient approximation (GGA), whereas an insulating state with trivial topological indices is obtained using a modified Becke−Johnson potential. Notably, GGA + U calculations suggest that the antiferromagnetic phase of Eu5In2Sb6 may host an axion insulating state. Our results provide important feedback for theories of topological classification and highlight the potential of realizing clean magnetic narrow-gap semiconductors in Zintl materials.
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Jul 2020
|
|
I05-ARPES
I11-High Resolution Powder Diffraction
|
J.-R.
Soh
,
F.
De Juan
,
M. G.
Vergniory
,
N. B. M.
Schröter
,
M. C.
Rahn
,
D. Y.
Yan
,
J.
Jiang
,
M.
Bristow
,
P. A.
Reiss
,
J. N.
Blandy
,
Y. F.
Guo
,
Y. G.
Shi
,
T. K.
Kim
,
A.
Mccollam
,
S. H.
Simon
,
Y.
Chen
,
A. I.
Coldea
,
A. T.
Boothroyd
Diamond Proposal Number(s):
[19234, 18786]
Abstract: We report theoretical and experimental evidence that
EuCd
2
As
2
in magnetic fields greater than 1.6 T applied along the
c
axis is a Weyl semimetal with a single pair of Weyl nodes. Ab initio electronic structure calculations, verified at zero field by angle-resolved photoemission spectra, predict Weyl nodes with wave vectors
k
=
(
0
,
0
,
±
0.03
)
×
2
π
/
c
at the Fermi level when the Eu spins are fully aligned along the
c
axis. Shubnikov–de Haas oscillations measured in fields parallel to
c
reveal a cyclotron effective mass of
m
∗
c
=
0.08
m
e
and a Fermi surface of extremal area
A
ext
=
0.24
nm
−
2
, corresponding to 0.1% of the area of the Brillouin zone. The small values of
m
∗
c
and
A
ext
are consistent with quasiparticles near a Weyl node. The identification of
EuCd
2
As
2
as a model Weyl semimetal opens the door to fundamental tests of Weyl physics.
|
Nov 2019
|
|
I16-Materials and Magnetism
|
Diamond Proposal Number(s):
[14024]
Open Access
Abstract: We study the magnetic structure of the “stuffed” (Tb-rich) pyrochlore iridate Tb2+xIr2−xO7−y, using resonant elastic x-ray scattering (REXS). In order to disentangle contributions from Tb and Ir magnetic sublattices, experiments were performed at the Ir L3 and Tb M5 edges, which provide selective sensitivity to Ir 5d and Tb 4f magnetic moments, respectively. At the Ir L3 edge, we found the onset of long-range k = 0 magnetic order below TIr N ∼71K, consistent with the expected signal of all-in all-out (AIAO) magnetic order. Using a single-ion model to calculate REXS crosssections, we estimate an ordered magnetic moment of µIr 5d ≈ 0.34(3)µB at 5K. At the Tb M5 edge,long-range k = 0 magnetic order appeared below ∼ 40K, also consistent with an AIAO magnetic structure on the Tb site. Additional insight into the magnetism of the Tb sublattice is gleaned from measurements at the M5 edge in applied magnetic fields up to 6T, which is found to completely suppress the Tb AIAO magnetic order. In zero applied field, the observed gradual onset of the Tb sublattice magnetisation with temperature suggests that it is induced by the magnetic order on the Ir site. The persistence of AIAO magnetic order, despite the greatly reduced ordering temperature and moment size compared to stoichiometric Tb2Ir2O7, for which TIr N = 130K and µIr 5d = 0.56µB, indicates that stuffing could be a viable means of tuning the strength of electronic correlations, thereby potentially offering a new strategy to achieve topologically non-trivial band crossings in pyrochlore iridates.
|
May 2019
|
|
I11-High Resolution Powder Diffraction
|
Diamond Proposal Number(s):
[13284]
Abstract: We have performed inelastic neutron-scattering measurements on a powder sample of the superconductor lithium iron selenide hydroxide Li 1−x Fe x ODFe 1−y Se(x≃0.16,y≃0.02,T c =41K) . The spectrum shows an enhanced intensity below T c over an energy range of 0.64×2Δ<E<2Δ , where Δ is the superconducting gap, and has maxima at the wave vectors Q 1 ≃1.46 and Q 2 ≃1.97Å −1 . The behavior of this feature is consistent with the spin-resonance mode found in other unconventional superconductors, and in particular strongly resembles the spin resonance observed in the spectrum of another molecular-intercalated iron selenide Li 0.6 (ND 2 ) 0.2 (ND 3 ) 0.8 Fe 2 Se 2 . The signal can be described with a characteristic two-dimensional wave-vector (π,0.67π) in the Brillouin zone of the iron square lattice, consistent with the nesting vector between electron Fermi sheets.
|
Oct 2016
|
|
|
|
Abstract: Using resonant magnetic x-ray scattering we address the unresolved nature of the magnetic ground state and the low-energy effective Hamiltonian of Sm2Ir2O7, a prototypical pyrochlore iridate with a finite temperature metal-insulator transition. Through a combination of elastic and inelastic measurements, we show that the magnetic ground state is an all-in–all-out (AIAO) antiferromagnet. The magnon dispersion indicates significant electronic correlations and can be well described by a minimal Hamiltonian that includes Heisenberg exchange [J=27.3(6) meV ] and Dzyaloshinskii-Moriya interactions [D=4.9(3) meV ], which provides a consistent description of the magnetic order and excitations. In establishing that Sm2Ir2 O7 has the requisite inversion symmetry preserving AIAO magnetic ground state, our results support the notion that pyrochlore iridates may host correlated Weyl semimetals.
|
Jul 2016
|
|
I05-ARPES
|
L. X.
Yang
,
Z. K.
Liu
,
Y.
Sun
,
H.
Peng
,
H. F.
Yang
,
T.
Zhang
,
Binbin
Zhou
,
Y
Zhang
,
Y. F.
Guo
,
Marein
Rahn
,
D.
Prabhakaran
,
Z.
Hussain
,
S. K.
Mo
,
C.
Felser
,
B.
Yan
,
Y. L.
Chen
Diamond Proposal Number(s):
[13177]
Abstract: Three-dimensional (3D) topologicalWeyl semimetals (TWSs) represent a state of quantum matter with unusual electronic structures that resemble both a ‘3D graphene’ and a topological insulator. Their electronic structure displays pairs of Weyl points (through which the electronic bands disperse linearly along all three momentum directions) connected by topological surface states, forming a unique arc-like Fermi surface (FS). Each Weyl point is chiral and contains half the degrees of freedom of a Dirac point, and can be viewed as a magnetic monopole in momentum space. By performing angle-resolved photoemission spectroscopy on the non-centrosymmetric compound TaAs, here we report its complete band structure, including the unique Fermi-arc FS and linear bulk band dispersion across the Weyl points, in agreement with the theoretical calculations1, 2. This discovery not only confirms TaAs as a 3DTWS, but also provides an ideal platform for realizing exotic physical phenomena (for example, negative magnetoresistance, chiral magnetic effects and the quantum anomalous Hall effect) which may also lead to novel future applications.
|
Aug 2015
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