arXiv subjects

Aly H. Abdeldaim

Publications and source records attributed to Aly H. Abdeldaim.

6 recordsLinked to original sources

arXiv2026

Competing collinear and non-collinear spin textures imaged by spatially-resolved REXS in Eu(Al0.4Ga0.6)4

Here, we use resonant elastic x-ray scattering (REXS) to investigate the inhomogeneity of the zero-field magnetic spin texture of Eu(Al$_{0.4}$Ga$_{0.6}$)$_4$. By using spatially-resolved REXS, we show that the two magnetic transitions at T$_{N1}$ = 17 K and T$_{N2}$ = 14 K originate from two nearly degenerate, yet distinct, orthogonal pairs of q-vectors. The corresponding phases are segregated spatially, such that one fraction of the sample comprises coexisting orthogonal spin-density-wave domains, while another fraction hosts coexisting orthogonal helical domains. Additionally, the helical state forms inversion domains indicating that the inversion symmetry is not broken prior the magnetic transition. Our results suggest that the magnetic state is single-q and revealed a large variation of spin textures across a 0.8 - 1 mm area of the sample surface. These results demonstrate clear differences between the locally and globally probed magnetic textures, typically assumed to be representative of the system as a whole, highlighting the importance of spatially-resolved probes for accurately describing the magnetic behavior of this class of materials.

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arXiv2026

Modification of Charge and Spin Textures by Light Chemical Substitution in Eu(Al$_{1-x}$Ga$_{x}$)$_4$ ($x=0.1$)

We present the results of a resonant X-ray diffraction experiment, resolving both charge and spin textures in the intermetallic topological magnet Eu(Al$_{1-x}$Ga$_{x}$)$_4$, $x$ = 0.1. Below $\approx$ 75 K the system develops a charge density wave (CDW) with propagation vector kCDW ~ (0, 0, 0.18). The CDW order parameter grows monotonically on cooling until ~ 15 K, when a sudden decrease in the CDW amplitude occurs. Pairs of magnetic satellites of the (0, 0, 8) Bragg reflection corresponding to two distinct domains, k = ($\pm δ_\text{m}$, 0, 0), k2 = (0, $\pmδ_\text{m}$, 0), $δ_\text{m} = 0.2002(4)$ were studied at the Eu L3 edge, appearing below TN = 14.8 K. Our measurement of TN is exactly coincident with the sudden drop in the CDW amplitude, which suggests strong coupling between the charge and spin orders, as observed in other compounds of the Eu(Al$_{1-x}$Ga$_{x}$)$_4$ series. Azimuthal measurements revealed a single helical spin arrangement with an elliptical envelope of $μ_\text{Y}/μ_\text{Z}$ = 1.19(6) for the k2 domain, and a tilted helical (helicoidal) spin arrangement for the k1 domain, with $μ_\text{Y}/μ_\text{Z}$ = 1.14(4) and $μ_\text{X}/μ_\text{Z}$ = 0.20(2) that may be hidden for the k2 domain due to multiple subdomains. Temperature evolution of the magnetic satellite intensities in linear and circularly polarised light found the respective ratio to be invariant with temperature, suggesting a single magnetic phase below TN. This behaviour is unlike the x = 0 material, in which a spin density wave forms first, transitioning to a helical ground state on cooling through intermediate phases. Future theoretical work on the Eu electronic ground state, supported by related experiments, will help understand the effects of Ga substitution on the evolution of the magnetic structure.

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arXiv2024

Kitaev Interactions Through an Extended Superexchange Pathway in the jeff = 1/2 Ru3+ Honeycomb Magnet, RuP3SiO11

Magnetic materials are composed of the simple building blocks of magnetic moments on a crystal lattice that interact via magnetic exchange. Yet from this simplicity emerges a remarkable diversity of magnetic states. Some reveal the deep quantum mechanical origins of magnetism, for example, quantum spin liquid (QSL) states in which magnetic moments remain disordered at low temperatures despite being strongly correlated through quantum entanglement. A promising theoretical model of a QSL is the Kitaev model, composed of unusual bond-dependent exchange interactions, but experimentally, this model is challenging to realise. Here we show that the material requirements for the Kitaev QSL survive an extended pseudo-edge-sharing superexchange pathway of Ru3+ octahedra within the honeycomb layers of the inorganic framework solid, RuP3SiO11. We confirm the requisite jeff = 1/2 state of Ru3+ in RuP3SiO11 and resolve the hierarchy of exchange interactions that provide experimental access to an unexplored region of the Kitaev model.

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arXiv2022

One-Dimensional Quantum Magnetism in the S = 1/2 Mo(V) system, KMoOP2O7

We present a comprehensive experimental and ab-initio study of the $S=1/2$ Mo$^{5+}$ system, KMoOP$_2$O$_7$, and show that it realizes the $S = 1/2$ Heisenberg chain antiferromagnet model. Powder neutron diffraction reveals that KMoOP$_2$O$_7$ forms a magnetic network comprised of pairs of Mo$^{5+}$ chains within its monoclinic $P2_1/n$ structure. Antiferromagnetic interactions within the Mo$^{5+}$ chains are identified through magnetometry measurements and confirmed by analysis of the magnetic specific heat. The latter reveals a broad feature centred on $T_\textrm{N} = 0.54$ K, which we ascribe to the onset of long-range antiferromagnetic order. No magnetic Bragg scattering is observed in powder neutron diffraction data collected at 0.05 K, however, which is consistent with a strongly suppressed ordered moment with an upper limit $μ_\textrm{ord} < 0.15 μ_\textrm{B}$. The one-dimensional character of the magnetic correlations in KMoOP$_2$O$_7$ is verified through analysis of inelastic neutron scattering data, resulting in a model with $J_\textrm{1} \approx 34$ K and $J_\textrm{2} \approx -2$ K for the intrachain and interchain exchange interactions, respectively. The origin of these experimental findings are addressed through density-functional theory calculations.

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arXiv2020

Realising square and diamond lattice $S=1/2$ Heisenberg antiferromagnet models in the $α$ and $β$ phases of the coordination framework, KTi(C$_2$O$_4$)$_2\cdot$\textit{x}H$_2$O

We report the crystal structures and magnetic properties of two psuedo-polymorphs of the $S=1/2$ Ti$^{3+}$ coordination framework, KTi(C$_2$O$_4$)$_2\cdot$xH$_2$O. Single-crystal X-ray and powder neutron diffraction measurements on $α$-KTi(C$_2$O$_4$)$_2\cdot$xH$_2$O confirm its structure in the tetragonal $I4/mcm$ space group with a square planar arrangement of Ti$^{3+}$ ions. Magnetometry and specific heat measurements reveal weak antiferromagnetic interactions, with $J_1\approx7$ K and $J_2/J_1=0.11$ indicating a slight frustration of nearest- and next-nearest-neighbor interactions. Below $1.8$ K, $α$ undergoes a transition to G-type antiferromagnetic order with magnetic moments aligned along the $c$ axis of the tetragonal structure. The estimated ordered moment of Ti$^{3+}$ in $α$ is suppressed from its spin-only value to $0.62(3)~μ_B$, thus verifying the two-dimensional nature of the magnetic interactions within the system. $β$-KTi(C$_2$O$_4$)$_2\cdot$2H$_2$O, on the other hand, realises a three-dimensional diamond-like magnetic network of Ti$^{3+}$ moments within a hexagonal $P6_222$ structure. An antiferromagnetic exchange coupling of $J\approx54$ K -- an order of magnitude larger than in $α$ -- is extracted from magnetometry and specific heat data. $β$ undergoes Néel ordering at $T_N=28$ K, with the magnetic moments aligned within the $ab$ plane and a slightly reduced ordered moment of $0.79~μ_B$ per Ti$^{3+}$. Through density-functional theory calculations, we address the origin of the large difference in the exchange parameters between the $α$ and $β$ psuedo-polymorphs. Given their observed magnetic behaviors, we propose $α$-KTi(C$_2$O$_4$)$_2\cdot$xH$_2$O and $β$-KTi(C$_2$O$_4$)$_2\cdot$2H$_2$O as close to ideal model $S=1/2$ Heisenberg square and diamond lattice antiferromagnets, respectively.

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arXiv2019

Large Easy Axis Anisotropy in the One-Dimensional Magnet BaMo(PO$_4$)$_2$

We present an extensive experimental and theoretical study on the low-temperature magnetic properties of the monoclinic anhydrous alum compound BaMo(PO$_4$)$_2$. The magnetic susceptibility reveals strong antiferromagnetic interactions $θ_{CW} = -167$~K and long-range magnetic order at $T_N=22$~K, in agreement with a recent report. Powder neutron diffraction furthermore shows that the order is collinear, with the moments near the $ac$ plane. Neutron spectroscopy reveals a large excitation gap $Δ= 15$~meV in the low-temperature ordered phase, suggesting a much larger easy-axis spin anisotropy than anticipated. However, the large anisotropy justifies the relatively high ordered moment, Néel temperature, and collinear order observed experimentally, and is furthermore reproduced in a first principles calculations using a new computational scheme. We therefore propose BaMo(PO$_4$)$_2$ to host $S=1$ antiferromagnetic chains with large easy-axis anisotropy, which has been theoretically predicted to realize novel excitation continua.

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