I11-High Resolution Powder Diffraction
|
Struan
Simpson
,
Cameron A. M.
Scott
,
Fernando
Pomiro
,
Jeremiah P.
Tidey
,
Urmimala
Dey
,
Fabio
Orlandi
,
Pascal
Manuel
,
Martin R.
Lees
,
Zih-Mei
Hong
,
Wei-Tin
Chen
,
Nicholas C.
Bristowe
,
Mark S.
Senn
Diamond Proposal Number(s):
[32893]
Open Access
Abstract: Magnetoelectric multiferroics hold great promise for the development of new sustainable memory devices. However, practical applications of many existing multiferroic materials are infeasible due to the weak nature of the coupling between the magnetic and electrical orderings, meaning new magnetoelectric multiferroics featuring intrinsic coupling between their component orderings are sought instead. Here, we apply a symmetry-informed design approach to identify and realize the new manganite perovskite CeBaMn2O6 in which magnetoelectric coupling can be achieved via an intermediary non-polar structural distortion. Through first-principles calculations, we demonstrate that our chosen prototype system contains the required ingredients to achieve the desired magnetoelectric coupling. Using high-pressure/high-temperature synthesis conditions, we have been able to synthesize the CeBaMn2O6 perovskite system for the first time. Our subsequent neutron and electron diffraction measurements reveal that the desired symmetry-breaking ingredients exist in this system on a nanoscopic length scale, enabling magnetoelectric nanoregions to emerge within the material. Through this work, we showcase the potential of the new CeBaMn2O6 perovskite material as a promising system in which to realize strong magnetoelectric coupling, highlighting the potential of our symmetry-informed design approach in the pursuit of new magnetoelectric multiferroics for next-generation memory devices.
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Aug 2024
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B18-Core EXAFS
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A.
Bandyopadhyay
,
S.
Lee
,
D. T.
Adroja
,
M. R.
Lees
,
G. B. G.
Stenning
,
P.
Aich
,
L.
Tortora
,
C.
Meneghini
,
G.
Cibin
,
A.
Berlie
,
R. A.
Saha
,
D.
Takegami
,
A.
Meléndez-Sans
,
G.
Poelchen
,
M.
Yoshimura
,
K. D.
Tsuei
,
Z.
Hu
,
T.-S.
Chan
,
S.
Chattopadhyay
,
G. S.
Thakur
,
K.-Y.
Choi
Diamond Proposal Number(s):
[33369]
Open Access
Abstract: We present an experimental investigation of the magnetic ground state in Ba4NbIr3O12, a fractional valent trimer iridate. X-ray absorption and photoemission spectroscopy show that the Ir valence lies between 3+ and 4+ while Nb is pentavalent. Combined dc/ac magnetization, specific heat, and muon spin rotation/relaxation (µSR) measurements reveal no magnetic phase transition down to 0.05 K. Despite a significant Weiss temperature (ΘW∼−15 to −25 K) indicating antiferromagnetic correlations, a quantum spin-liquid (QSL) phase emerges and persists down to 0.1 K. This state likely arises from geometric frustration in the edge-sharing equilateral triangle Ir network. Our µSR analysis reveals a two-component depolarization, arising from the coexistence of rapidly (90%) and slowly (10%) fluctuating Ir moments. Powder x-ray diffraction and Ir-L3edge x-ray absorption fine structure spectroscopy identify 8–10% Nb/Ir site-exchange, reducing frustration within part of the Ir network, and likely leading to the faster muon spin relaxation, while the structurally ordered Ir ions remain highly geometrically frustrated, giving rise to the rapidly spin-fluctuating QSL ground state. At low temperatures, the magnetic specific heat varies as 𝛾𝑇+𝛼𝑇2, indicating gapless spinon excitations, and possible Dirac QSL features with linear spinon dispersion, respectively.
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Jul 2024
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I11-High Resolution Powder Diffraction
|
Diamond Proposal Number(s):
[25166]
Open Access
Abstract: We report a new nickel hydroxyfluoride diaspore Ni(OH)F prepared using hydrothermal synthesis from NiCl2·6H2O and NaF. Magnetic characterization reveals that, contrary to other reported transition-metal hydroxyfluoride diaspores, Ni(OH)F displays weak ferromagnetism below the magnetic ordering temperature. To understand this difference, neutron diffraction is used to determine the long-range magnetic structure. The magnetic structure is found to be distinct from those reported for other hydroxyfluoride diaspores and shows an antiferromagnetic spin ordering in which ferromagnetic canting is allowed by symmetry. Furthermore, neutron powder diffraction on a deuterated sample, Ni(OD)F, reveals partial anion ordering that is distinctive to what has previously been reported for Co(OH)F and Fe(OH)F. Density functional theory calculations show that OH/F ordering can have a directing influence on the lowest energy magnetic ground state. Our results point toward a subtle interplay between the sign of magnetic exchange interactions, the electronic configuration, and anion disordering.
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May 2024
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B18-Core EXAFS
I11-High Resolution Powder Diffraction
|
Diamond Proposal Number(s):
[25166, 14239]
Open Access
Abstract: A Mn2+-Li-Nb disordered rock-salt oxide cathode is prepared by a solid-state reaction under 5% H2/N2, and its electrochemical property shows a high voltage plateau at 4.8 V, with irreversible structural changes in the first cycle due to O redox processes; this is supported by powder X-ray diffraction and ex-situ laboratory Mn K-edge XANES data.
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Oct 2023
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[18786]
Open Access
Abstract: The crystallization of a new series of A-site substituted lanthanum ferrite materials (La1–xREx)FeO3 was explored by the hydrothermal method at 240 °C, for rare earth (RE) = Nd, Sm, Gd, Ho, Er, Yb, and Y, with 0 ≤ x ≤ 1. The effect of elemental substitution on the morphological, structural, and magnetic properties of the materials was studied using high-resolution powder X-ray diffraction, energy dispersive spectroscopy (EDS) on the scanning electron microscope, Raman spectroscopy, and SQUID magnetometry. If the radius of the La3+ and the substituent ions is similar, such as for Nd3+, Sm3+, and Gd3+, homogeneous solid solutions are formed, with the orthorhombic GdFeO3-type structure, and a continuous evolution of Raman spectra with composition and distinct magnetic behavior from the end members. When the radius difference between substituents and La3+ is large, such as for Ho3+, Er3+, Yb3+, and Y3+, then instead of forming solid solutions, crystallization in separate phases is found. However, low levels of element mixing are found and intergrowths of segregated regions give composite particles. In this case, the Raman spectra and magnetic behavior are characteristic of mixtures of phases, while EDS shows distinctive elemental segregation. A-site replacement induces an evolution in the crystallite shape with an increasing amount of substituent ions and this is most evident for RE = Y from cube-shaped crystals seen for LaFeO3 to multipodal crystals for (La1–xYx)FeO3, providing evidence for a phase-separation-driven evolution of morphology.
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Mar 2023
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I11-High Resolution Powder Diffraction
|
Diamond Proposal Number(s):
[25166]
Open Access
Abstract: We present the synthesis of a novel binary metal oxide material: Ba7Mn4O15. The crystal structure has been investigated by high-resolution powder synchrotron X-ray diffraction in the temperature range of 100–300 K as well as by powder neutron diffraction at 10 and 80 K. This material represents an isostructural barium-substituted analogue of the layered material Sr7Mn4O15 that forms its own structural class. However, we find that Ba7Mn4O15 adopts a distinct magnetic ordering, resulting in a magnetoelectric ground state below 50 K. The likely magnetoelectric coupling mechanisms have been inferred from performing a careful symmetry-adapted refinement against the powder neutron diffraction experiments, as well as by making a comparison with the nonmagnetoelectric ground state of Sr7Mn4O15.
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Jun 2022
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B18-Core EXAFS
|
Rajesh
Tripathi
,
D. T.
Adroja
,
M. R.
Lees
,
A.
Sundaresan
,
S.
Langridge
,
A.
Bhattacharyya
,
V. K.
Anand
,
D. D.
Khalyavin
,
J.
Sannigrahi
,
G.
Cibin
,
A. D.
Hillier
,
R. I.
Smith
,
H. C.
Walker
,
Y.
Muro
,
T.
Takabatake
Diamond Proposal Number(s):
[17953]
Abstract: We report a systematic study of the
5
d
-electron-doped system
Ce
(
Fe
1
−
x
Ir
x
)
2
Al
10
(
0
≤
x
≤
0.15
)
. With increasing
x
, the orthorhombic
b
axis decreases slightly while accompanying changes in
a
and
c
leave the unit cell volume almost unchanged. Inelastic neutron scattering, along with thermal and transport measurements, reveal that for the Kondo semiconductor
CeFe
2
Al
10
, the low-temperature energy gap, which is proposed to be a consequence of strong
c
−
f
hybridization, is suppressed by a small amount of Ir substitution for Fe and that the system adopts a metallic ground state with an increase in the density of states at the Fermi level. The charge or transport gap collapses (at
x
=
0.04
) faster than the spin gap with Ir substitution. Magnetic susceptibility, heat capacity, and muon spin relaxation measurements demonstrate that the system undergoes long-range antiferromagnetic order below a Néel temperature
T
N
of 3.1(2) K for
x
=
0.15
. The ordered moment is estimated to be smaller than 0.07(1)
μ
B
/Ce, although the trivalent state of Ce is confirmed by Ce
L
3
-edge x-ray absorption near edge spectroscopy. It is suggested that the
c
−
f
hybridization gap, which plays an important role in the unusually high ordering temperatures observed in
Ce
T
2
Al
10
(
T
= Ru and Os), may not be necessary for the onset of magnetic order with a low
T
N
seen here in
Ce
(
Fe
1
−
x
Ir
x
)
2
Al
10
.
|
Oct 2021
|
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B18-Core EXAFS
|
Diamond Proposal Number(s):
[14239]
Abstract: The rutiles (M,Ru)O2 (M = Mg, Zn, Co, Ni, Cu) are formed directly under hydrothermal conditions at 240 °C from potassium perruthenate and either peroxides of zinc or magnesium, or poorly crystalline oxides of cobalt, nickel or copper. The polycrystalline powders consist of lath-shaped crystallites, tens of nanometres in maximum dimension. Powder neutron diffraction shows that the materials have expanded a axis and contracted c axis compared to the parent RuO2, but there is no evidence of lowering of symmetry to other AO2-type structures, supported by Raman spectroscopy. Rietveld refinement shows no evidence for oxide non-stoichiometry and provides a formula (MxRu1-x)O2 with 0.14 < x < 0.2, depending on the substituent metal. This is supported by energy-dispersive X-ray analysis on the transmission electron microscope, while Ru K-edge XANES spectroscopy shows that upon inclusion of the substituent the average Ru oxidation state is increased to balance charge. Variable temperature magnetic measurements provide evidence for atomic homogeneity of the mixed metal materials, with suppression of the high temperature antiferromagnetism of RuO2 and increased magnetic moment. The new rutiles all show enhanced electrocatalysis compared to reference RuO2 materials for oxygen evolution in 1 M H2SO4 electrolyte at 60 °C, with higher specific and mass activity (per Ru) than a low surface area crystalline RuO2, and with less Ru dissolution over 1000 cycles compared to an RuO2 with a similar surface area. Magnesium substitution provides the optimum balance between stability and activity, despite leaching of the Mg2+ into solution, and this was proved in membrane electrode assemblies.
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Jun 2020
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B18-Core EXAFS
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Diamond Proposal Number(s):
[13841]
Abstract: The oxyhydroxide Ga2.52V2.48O7.33(OH)0.67 is prepared by reaction between Ga metal and Na3VO4 in a 1:1 monoethanolamine:water mixture at 240 °C. Powder neutron diffraction shows the material to be isostructural with the minerals nolanite and akdalaite, with cations occupying tetrahedral and octahedral interstitial sites in a hexagonal close-packed array of oxide/hydroxide (P63mc, a = 5.7906(2) Å, c = 9.2550(5) Å). Rietveld refinement against the data shows that Ga preferentially occupies tetrahedral sites, as well as some octahedral sites, and hence all V is octahedrally coordinated. The oxidation state of vanadium is confirmed as close to V3+ using V K-edge X-ray absorption near-edge structure spectroscopy, consistent with the refined chemical composition. The material is metastable, dehydrating around 300 °C and then decomposing above 500 °C, as shown by thermogravimetric analysis and thermodiffraction. The oxide Ga2.52V2.48O8 produced after dehydration at 300 °C is shown to contain a larger proportion of V4+ than the parent oxyhydroxide, to ensure charge balance, but the essential hexagonal structure is maintained. Variable temperature magnetisation measurements show that although both materials appear to obey the Curie-Weiss Law at high temperatures, at low temperatures the inverse susceptibility curves are non-linear. There is, however, no evidence for strong magnetic exchange and the extracted effective moments are consistent with the presence of more V3+ in the oxyhydroxide compared to the oxide.
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Apr 2020
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I18-Microfocus Spectroscopy
|
Open Access
Abstract: Iron is an essential element, and cornflake-style cereals are typically fortified with iron to a level up to 14 mg iron per 100 g. Even single cornflakes exhibit magnetic behaviour. We extracted iron microparticles from samples of two own-brand supermarket cornflakes using a strong permanent magnet. Synchrotron iron K-edge X-ray absorption near-edge spectroscopic data were consistent with identification as metallic iron, and X-ray diffraction studies provided unequivocal identification of the extracted iron as body-centred cubic (BCC) α-iron. Magnetometry measurements were also consistent with ca. 14 mg per 100 g BCC iron. These findings emphasise that attention must be paid to the speciation of trace elements, in relation to their bioavailability. To mimic conditions in the stomach, we suspended the iron extract in dilute HCl (pH 1.0–2.0) at 310 K (body temperature) and found by ICP-MS that over a period of 5 hours, up to 13% of the iron dissolved. This implies that despite its metallic form in the cornflakes, the iron is potentially bioavailable for oxidation and absorption into the body.
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Mar 2020
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