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![Fig. 1 (a) View along [110] direction of versiliaite, showing...](publication/304400605/figure/fig1/AS:378686567141378@1467297321979/a-View-along-110-direction-of-versiliaite-showing-rutile-like-edge-sharing-octahedra_Q320.jpg)
Versiliaite and apuanite are two minerals containing Fe(2+) and Fe(3+) in a low-dimensional structure exhibiting chains of edge-linked FeO6 octahedra. The chemistry of these minerals has not been fully examined because of their rarity. We demonstrate that chemical synthesis of these minerals is possible to allow measurement of their magnetic proper...
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The correlation of the microstructure and the magnetic properties of Ni2MnAl0.5Ga0.5 and Ni2MnAl Heusler alloys is studied in samples of distinct L21 order states by neutron powder diffraction and small-angle scattering. The extracted correlation lengths of the structural and magnetic order agree over all annealing states, which implies the structu...
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... Our results could be potentially observed in magnetic compounds characterized by parallel lattice planes with spin lying on a Cairo lattice and having strong horizontal and weak vertical interactions. These materials are currently matter of research interest [4,5,[61][62][63][64][65], although monitoring the spin dynamics remain a challenging task. ...
We combine experiments and numerical simulations to investigate the low
energy states and the emergence of topological defects in an artificial colloidal ice in
the Cairo geometry. This type of geometry is characterized by a mixed coordination
(z), with coexistence of both z = 3 and z = 4 vertices. We realize this particle ice by
confining field tunable paramagnetic colloidal particles within a lattice of topographic
double wells at a one to one filling using optical tweezers. By raising the interaction
strength via an applied magnetic field, we find that the ice rule breaks down, and
positive monopoles with charge q = +2 accumulate in the z = 4 vertices and are
screened by negative ones (q = −1) in the z = 3. The resulting, strongly coupled
state remains disordered. Further, via analysis of the mean chirality associated to
each pentagonal plaquette, we find that the disordered ensemble for this geometry is
massively degenerate and it corresponds to a frustrated antiferrotoroid.
... The plateau is accompanied by a characteristic magnetization jump in specific parameter regions. Not only theoretical studies but also experimental reports have been reported [10][11][12][13][14] for candidate materials of the Cairo-pentagonal-lattice system such as Bi 2 Fe 4 O 9 , Bi 4 Fe 5 O 13 F, and DyMn 2 O 5 . The S = 1/2 Ising models on the Cairo-pentagonal lattice were studied [15][16][17]. ...
We study the S = 1/2 Heisenberg antiferromagnet on the floret pentagonal lattice by numerical diagonalization method. This system shows various behaviours that are different from that of the Cairo-pentagonal-lattice antiferromagnet. The ground-state energy without magnetic field and the magnetization process of this system are reported. Magnetization plateaux appear at one-ninth height of the saturation magnetization, at one-third height, and at seven-ninth height. The magnetization plateaux at one-third and seven-ninth heights come from interactions linking the sixfold-coordinated spin sites. A magnetization jump appears from the plateau at one-ninth height to the plateau at one-third height. Another magnetization jump is observed between the heights corresponding to the one-third and seven-ninth plateaux; however the jump is away from the two plateaux, namely, the jump is not accompanied with any magnetization plateaux. The jump is a peculiar phenomenon that has not been reported.
... The latter recalls the exactly solvable dimer ground state of the Shastry-Sutherland lattice [15] largely investigated for its exotic physics [16,17]. These findings stimulated further theoretical [18][19][20][21][22][23][24] and experimental [25][26][27][28] studies on pentagon-based physics, even spreading beyond the field of magnetism. In spite of this interest, an experimental determination of the Hamiltonian of the prototypical material Bi 2 Fe 4 O 9 has never been reported yet that would solely ascertain the crucial influence of frustration on its exotic properties. ...
A peculiar non collinear magnetic order is known to be stabilized in Bi2Fe4O9 materializing a Cairo pentagonal lattice. Using inelastic neutrons scattering, we have measured the spin wave excitations in the magnetically ordered state. The magnetic excitations have been modeled to determine the frustrated superexchange interactions at the origin of the spin arrangement and of a frustration induced excited state. Moreover, our analysis has revealed a hierarchy in the interactions. This leads to a paramagnetic state (close to the N\'eel temperature) constituted of strongly coupled antiferromagnetic pairs of spins separated by much less correlated spins. This inhomogeneous spin liquid produces two types of response to an applied magnetic field associated with the two nonequivalent Fe sites, as observed in the magnetization density distributions obtained using polarized neutrons.
... Discussion -The main picture emerging from the experimental data presented here is that the interlayer Fe3 spins in Bi 4 Fe 5 O 13 F play a dual role, on one hand mediating the 3D ordering and on the other driving a reorientation of the order in the planes. While details of this transition require further dedicated theoretical work, on the experimental side the effect of the Fe3 spins is crucial for the design of new Cairo-lattice magnets, because interlayer magnetic sites, which are often introduced for the sake of stabilizing the crystal structure [53], are not innocent and in fact play decisive role for the magnetic order within the Cairo planes. ...
Using a combination of neutron diffraction and M\"ossbauer spectroscopy, we unravel the sequence of magnetic orders observed in the frustrated Cairo pentagonal magnet Bi$_4$Fe$_5$O$_{13}$F. These orders include two orthogonal magnetic structures with opposite vector chiralities, and an intermediate, partly disordered collinear phase. Stabilization of the collinear phase by quantum fluctuations was predicted theoretically, but Bi$_4$Fe$_5$O$_{13}$F is very far from the relevant parameter regime. Based on ab initio band-structure calculations, we propose that the unusual evolution of the ordered states is driven by the strong single-ion anisotropy on the interlayer Fe$^{3+}$ spins, which are located between the Cairo planes. These spins then play a dual role, on one hand mediating the 3D order and on the other driving a reorientation between the two orthogonal configurations having opposite vector chiralities, with the collinear order naturally emerging as an intermediate phase.
The research field of magnetic frustration is dominated by triangle-based lattices but exotic phenomena can also be observed in pentagonal networks. A peculiar noncollinear magnetic order is indeed known to be stabilized in Bi2Fe4O9 materializing a Cairo pentagonal lattice. We present the spin wave excitations in the magnetically ordered state, obtained by inelastic neutron scattering. They reveal an unconventional excited state related to local precession of pairs of spins. The magnetic excitations are then modeled to determine the superexchange interactions for which the frustration is indeed at the origin of the spin arrangement. This analysis unveils a hierarchy in the interactions, leading to a paramagnetic state (close to the Néel temperature) constituted of strongly coupled dimers separated by much less correlated spins. This produces two types of response to an applied magnetic field associated with the two nonequivalent Fe sites, as observed in the magnetization distributions obtained using polarized neutrons.
We show that interlayer spins play a dual role in the Cairo pentagonal magnet Bi4Fe5O13F, on one hand mediating the three-dimensional magnetic order, and on the other driving spin-reorientation transitions both within and between the planes. The corresponding sequence of magnetic orders unraveled by neutron diffraction and Mössbauer spectroscopy features two orthogonal magnetic structures described by opposite local vector chiralities, and an intermediate, partly disordered phase with nearly collinear spins. A similar collinear phase has been predicted theoretically to be stabilized by quantum fluctuations, but Bi4Fe5O13F is very far from the relevant parameter regime. While the observed in-plane reorientation cannot be explained by any standard frustration mechanism, our ab initio band-structure calculations reveal strong single-ion anisotropy of the interlayer Fe3+ spins that turns out to be instrumental in controlling the local vector chirality and the associated interlayer order.
