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The [Zn1–xNix(HF2)(pyz)2]SbF6 (x = 0.2; pyz = pyrazine) solid solution exhibits a zero-field splitting (D) that is 22% larger [D = 16.2(2) K (11.3(2) cm–1)] than that observed in the x = 1 material [D = 13.3(1) K (9.2(1) cm–1)]. The substantial change in D is accomplished by an anisotropic lattice expansion in the MN4 (M = Zn or Ni) plane, wherein the increased concentration of isotropic Zn(II) ions induces a nonlinear variation in M-F and M-N bond lengths. In this, we exploit the relative donor atom hardness, where M-F and M-N form strong ionic and weak coordinate covalent bonds, respectively, the latter being more sensitive to substitution of Ni by the slightly larger Zn(II) ion. In this way, we are able to tune the single-ion anisotropy of a magnetic lattice site by Zn-substitution on nearby sites. This effect has possible applications in the field of single-ion magnets and the design of other molecule-based magnetic systems.

Two new alkali vanadate carbonates with divalent transition metals have been synthesized as large single crystals via a high-temperature (600 °C) hydrothermal technique. Compound I, Rb2Mn3(VO4)2CO3, crystallizes in the trigonal crystal system in the space group P1c, and compound II, K2Co3(VO4)2CO3, crystallizes in the hexagonal space group P63/m. Both structures contain honeycomb layers and triangular lattices made from edge-sharing MO6 octahedra and MO5 trigonal bipyramids, respectively. The honeycomb and triangular layers are connected along the c-axis through tetrahedral [VO4] groups. The MO5 units are connected with each other by carbonate groups in the ab-plane by forming a triangular magnetic lattice. The difference in space groups between I and II was also investigated with Density Functional Theory (DFT) calculations. Single crystal magnetic characterization of I indicates three magnetic transitions at 77 K, 2.3 K, and 1.5 K. The corresponding magnetic structures for each magnetic transition of I were determined using single crystal neutron diffraction. At 77 K the compound orders in the MnO6-honeycomb layer in a Neel-type antiferromagnetic orientation while the MnO5 triangular lattice ordered below 2.3 K in a colinear ‘up–up–down’ fashion, followed by a planar ‘Y’ type magnetic structure. K2Co3(VO4)2CO3 (II) exhibits a canted antiferromagnetic ordering below TN = 8 K. The Curie–Weiss fit (200–350 K) gives a Curie–Weiss temperature of −42 K suggesting a dominant antiferromagnetic coupling in the Co2+ magnetic sublattices.

We study magnetic lattice and optimize parameters for the fourth generation light source SKIF (Russian acronym of Siberian Circular Photon Source) to be built in Novosibirsk. We consider several lattice cells to achieve both low emittance and large dynamic aperture. The resulting lattice provides the natural emittance of the electron beam of 75 pm for the beam energy of 3 GeV and the orbit circumference of 476 m. Only two families of chromatic sextupoles give the dynamic aperture and energy bandwidth enough for both good beam lifetime and simple effective injection.

Henmilite {${\mathrm{Ca}}_{2}\mathrm{Cu}{(\mathrm{OH})}_{4}{[\mathrm{B}{(\mathrm{OH})}_{4}]}_{2}$} is a blue calcium copper borate mineral found only in the Fuka mine, Okayama Prefecture, Japan. Crystal structure refinement, magnetic and specific heat measurements, and density functional theory (DFT) calculations are performed to clarify its magnetic properties. Synchrotron x-ray diffraction experiments reveal that the hydrogen-bonded chains are arranged in an antiferroelectric manner, doubling the unit cell along the $a$ axis. An antiferromagnetic transition is observed at 0.2 K at zero magnetic field. Furthermore, a dome-shaped antiferromagnetic ordering region exists in the temperature--magnetic-field phase diagram, indicating the presence of quantum spin fluctuations. The obtained crystal structure in combination with DFT calculations suggests that the system has a coupled two-leg ladder magnetic lattice, explaining the very low ordering temperature.

We will present the design for the In-Situ Nanoprobe (ISN) beamline that is being developed as part of the Upgrade of the APS storage ring with an MBA magnetic lattice. The ISN will provide large working distance of 60 mm for in-situ and operando environments, and a small spot of 20 nm (25 keV) for imaging materials with small defects and functional components. To achieve both long working distance and small spot size, Kirkpatrick-Baez mirrors will be used as nanofocusing optics. The major contrast mechanisms will be XRF imaging for chemical characterization ptychography for transmission imaging with sub-10 nm resolution. Auxiliary diffraction capabilities will allow monitoring of phase change during in-situ studies. To achieve the demagnification required to achieve small spot sizes, the ISN instrument will be placed at a distance of 220 m from the x-ray source, in a satellite building outside the APS storage ring. The ISN will provide hard x-rays with photon energy between 4.8 keV and 30 keV, enabling access to the absorption edges of to most elements in the periodic system. The MBA lattice and insertion devices, coupled with the high reflectivity of the K-B mirror system, provide a very high coherent flux of above 4*1012 Ph/s at 5 keV, and 6*1012 Ph/s at 30 keV. This allows hierarchical imaging of large samples with very small spot size, as well as multidimensional imaging, such as 3D imaging and temperature change, or 2D imaging with change of several environmental parameters. The ISN will provide flow of fluids, gases, and variable temperature.

Frustrated magnets can host numerous exotic many-body quantum and topological phenomena. GeNi$_2$O$_4$ is a three dimensional $S=1$ frustrated magnet with an unusual two-stage transition to the two-dimensional antiferromagnetic ground state, while GeCu$_2$O$_4$ is a high-pressure phase with a strongly tetragonally elongated spinel structure and magnetic lattice formed by $S=1/2$ CuO$_2$ linear chains with frustrated exchange interactions and exotic magnetic behavior. Here we report on the first thin-film epitaxial stabilization of these two compounds. Developed growth mode, surface morphology, crystal structure and copper valence state were characterized by in-situ reflection high-energy electron diffraction, atomic force microscopy, X-ray reflectivity, X-ray diffraction, X-ray photoelectron spectroscopy and resonant X-ray absorption spectroscopy. Our results pave an alternative route to the comprehensive investigation of the puzzling magnetic properties of these compounds and exploration of novel emergent features driven by strain.

The quantum spin liquid (QSL) is an exotic phase of magnetic materials where the spins continue to fluctuate without any symmetry breaking down to zero temperature. Among the handful reports of QSL with spin $S\ensuremath{\ge}$ 1, examples with magnetic ions on a three-dimensional (3D) magnetic lattice are extremely rare since both larger spin and higher dimension tend to suppress quantum fluctuations. In this work, we offer a new strategy to achieve 3D QSL with high spin by utilizing two types of transition metal ions; both are magnetically active but located at crystallographically inequivalent positions. We design a 3D magnetic system ${\mathrm{Ba}}_{3}{\mathrm{NiIr}}_{2}{\mathrm{O}}_{9}$ consisting of interconnected corner-shared ${\mathrm{NiO}}_{6}$ octahedra and face-shared ${\mathrm{Ir}}_{2}{\mathrm{O}}_{9}$ dimer, both having triangular arrangements in a-b plane. X-ray absorption spectroscopy measurements confirm the presence of ${\mathrm{Ni}}^{2+}$ ($S=1)$. Our detailed thermodynamic and magnetic measurements reveal that this compound is a realization of gapless QSL state down to at least 100 mK. Ab initio calculations find a strong magnetic exchange between Ir and Ni sublattices and in-plane antiferromagnetic coupling between the dimers, resulting in dynamically fluctuating magnetic moments.

Results are presented from an experimental study of the diffraction of a superdirectional beam of surface spin waves on a weak-contrast magnon crystal formed in a film of yttrium–iron garnet using a localized spatial periodic magnetic field. Distributions of the field of the spin wave characteristic are obtained for Bragg diffraction on a magnetic lattice.

Delafossite compound, CuCrO2, popularly known as transparent conducting oxide, has previously been reported to demonstrate antiferromagnetic ordering of the triangular magnetic lattice below 24 K. We find that mere 5% Ti-substitution at Cr-site, leads to short range magnetic correlations, manifested as non-analytical behaviour of H/M and other anomalies in the low magnetic field dc magnetization, ac magnetic susceptibility, time dependent magnetization, and isothermal remanent magnetization. The ac susceptibility measured at different applied frequencies do not show any frequency dependence, ruling out the glassy magnetic phase. The short-range magnetic correlations are observed over a wide temperature range starting from 180 K and below, until the system orders antiferromagnetically at 22 K. These correlations which are most pronounced at low values of applied magnetic field, get readily suppressed when the fields exceed 0.5 T. Signatures associated with these short-range correlations seem to fit a Griffiths-like phase description. The results of heat capacity measurement with and without magnetic field, provides additional information about the dimensionality of the magnetic interactions. Rietveld refinement of the X-ray diffraction data reveals that the highly anisotropic crystal structure remains unaffected with the substitution. A static disorder driven magnetic inhomogeneity arising in the triangular magnetic sublattice of Cr ions decreases the dimensionality of magnetic interactions, and seems to be the possible origin of this interesting magnetic behaviour.

In this work, hard magnetism was studied on cobalt-doped α-Fe2O3 particles, with special regard to the evolution of coercive fields as well as exchange bias fields. It was found that the coercivity of calcined sample fell into decline as temperature rose. Quite on the contrary, the sample prior to calcination exhibited a monotonical increment as increasing temperature. Further studies showed that lattice defects and voids in α-Fe2O3 host, Co-doped α-Fe2O3 colonies, FeOOH magnetic lattice, and CoFe2O4 impurity phase were responsible for such significantly distinct magnetism evolution. The exhibited large coercivity beyond 10 kOe and pronounced exchange bias field of −660 Oe enabled us to gain deep insight into the transition metal doped magnetic semiconductor and to promote its full exploitation in magnetic-relevant applications.

The magnetic properties are reported for three members of the glaserite series of compounds, Na2BaM(VO4)2, M = Mn, Mn0.6Co0.4, and Co. Large single crystals are grown using a high-temperature hydrothermal synthesis method. This structure type exhibits a triangular magnetic lattice in which M2+O6 octahedra are interconnected with nonmagnetic (VO4)3- groups. All the structures crystallize at room temperature with rigid trigonal symmetry (space group P3 m1); however, at lower temperatures both Na2BaMn(VO4)2 and Na2BaMn0.6Co0.4(VO4)2 undergo a structural transition to lower symmetry (monoclinic, C2/ c). The bulk magnetic measurements indicate that Mn- and Co-structures are antiferromagnetic and ferromagnetic, respectively. Na2BaMn0.6Co0.4(VO4)2 does not show any long-range ordering down to 0.5 K, although a broad heat capacity anomaly near 1.2 K suggests short-range magnetic order or freezing into a spin-glass-like state related to the chemical disorder and resulting competing magnetic interactions. The magnetic structures of Na2BaMn(VO4)2 and Na2BaCo(VO4)2 were determined using neutron powder diffraction. At zero magnetic field, Na2BaMn(VO4)2 possesses an antiferromagnetic structure with the moments ordered in a Neel-type arrangement and aligned along the C4 axis of the octahedra. Under applied magnetic field at 0.3 K, the evolution of the magnetic structure toward a fully polarized state is observed. Na2BaCo(VO4)2 represents a ferromagnetic (FM) magnetic structure with Co moments aligned parallel to the c-axis direction. The relationships between these structures and magnetic properties are discussed.

We report the direct observation of strong coupling between magnons and phonons in a two-dimensional antiferromagnetic semiconductor FePS_{3}, via magneto-Raman spectroscopy at magnetic fields up to 30 Tesla. A Raman-active magnon at 121 cm^{-1} is identified through Zeeman splitting in an applied magnetic field. At a field-driven resonance with a nearby phonon mode, a hybridized magnon-phonon quasiparticle is formed due to strong coupling between the two modes. We develop a microscopic model of the strong coupling in the two-dimensional magnetic lattice, which enables us to elucidate the nature of the emergent quasiparticle. Our polarized Raman results directly show that the magnons transfer their spin angular momentum to the phonons and generate phonon spin through the strong coupling. Ministry of Education (MOE) Nanyang Technological University Published version This work is mainly supported by the Singapore Ministry of Education via AcRF Tier 3 Programme “Geometrical Quantum Material” (MOE2018-T3-1-002). Q. X. acknowledges strong support from the State Key Laboratory of Low-Dimensional Quantum Physics and the start-up grant from Tsinghua University. P. S. acknowledges financial support from the Ministry of Education, Singapore, through Grant No. MOE2019-T2-2-119. A. G. D. A. gratefully acknowledges the financial support from the Presidential Postdoctoral Fellowship program of the Nanyang Technological University Singapore. Z. S. was supported by project LTAUSA19034 from Ministry of Education Youth and Sports (MEYS).

The combination of fast propagation speeds and highly localized nature has hindered the direct observation of the evolution of shock waves at the molecular scale. To address this limitation, an experimental system is designed by tuning a one-dimensional magnetic lattice to evolve benign waveforms into shock waves at observable spatial and temporal scales, thus serving as a ``magnifying glass'' to illuminate shock processes. An accompanying analysis confirms that the formation of strong shocks is fully captured. The exhibited lack of a steady state induced by indefinite expansion of a disordered transition zone points to the absence of local thermodynamic equilibrium and resurfaces lingering questions on the validity of continuum assumptions in the presence of strong shocks.

Quantum spin liquid (QSL) state in rare-earth triangular lattice has attracted much attention recently due to its potential application in quantum computing and communication. Here we report the single-crystal growth synthesis, crystal structure characterizations and magnetic properties of $A$YbSe$_{2}$ ($A$= K, Rb) compounds. The X-ray diffraction analysis shows that $A$YbSe$_{2}$ ($A$ = K and Rb) crystallizes in a trigonal space group, $R$-3$m$ (No. 166) with Z = 3. $A$YbSe$_{2}$ possesses a two-dimensional (2D) Yb-Se-Yb layered structure formed by edged-shared YbSe$_6$ octahedra. The magnetic properties are highly anisotropic for both title compounds and no long-range order is found down to 0.4 K, revealing the possible QSL ground state in these compounds. The isothermal magnetization exhibits one-third magnetization plateau when the magnetic fields are applied in $ab$-plane. Heat capacity is performed along both $ab$-plane and $c$-axis, and features the characteristic dome for triangular magnetic lattice compounds as a function of magnetic fields. Due to the change of the interlayer and intralayer distance of Yb$^{3+}$, the dome shifts to low fields from KYbSe$_2$ to RbYbSe$_2$. All these results indicate the $A$YbSe$_2$ family presents unique frustrated magnetism close to the possible QSL and noncolinear spin states., Comment: 9 pages, 7 figures

Magnets are very useful for the rapid prototyping of haptic interactions. However, it is difficult to arrange fine and complex magnetic fields rapidly. This project presents a method for fabricating complex geometric magnetic patterns by overlaying magnetic rubber sheets. By layering multiple magnetic sheets that have proper thicknesses and simple magnetic patterns, various types of magnetic lattice patterns can be generated on the top surface. Furthermore, the superposed magnetic fields can be changed dynamically by rotating the layered magnetic sheets. We demonstrate several tactile interactions by applying the superposed magnetic fields.

Here, we report the synthesis and magnetic properties of a novel, centrosymmetric, quasi-1D spin chain system La3VWS3O6, with hexagonal crystal structure (P63/m, a = 9.460 76(3), c = 5.518 09(2) Å). Pure powders were obtained by solid-state reactions from La2O3, WO3 and metal powders of V and W. X-ray powder diffraction, specific heat, magnetization, 139La-nuclear magnetic resonance (NMR), and electric resistivity measurements indicate that the compound is a low dimensional magnet with an S = 1 spin chain that exhibits no sign of magnetic ordering above 2 K. A single ion anisotropy (D/k B ~ 10 K), caused by magneto-crystalline effects, is probably responsible for a thermodynamic entropy release at lower temperatures, which concurs with 139La-NMR data. By detailed comparison with non-centrosymmetric Ba3V2S4O3, having a very similar magnetic lattice, it is obvious that the presence of crystallographic inversion symmetry has an effect on the behaviour of the magnetic chains.

This chapter presents a pedagogical overview on fundamental aspects of surface and interface magnetism that have implications for the understanding of a broad variety of nanoscale magnetic and spintronic phenomena. We introduce general concepts derived from electronic band structure models to explain the evolution of the spin and orbital magnetic moments, exchange interaction, and magnetic anisotropy in low-dimensional structures. Trends due to the reduced symmetry and atomic coordination are emphasized, including the effects of spin–orbit coupling and the Dzyaloshinskii–Moriya interaction. We present spin Hamiltonian models that capture the collective behavior of a magnetic lattice and enable the description of the low-energy spin excitations as well as of the onset of magnetic order as a function of temperature in systems of arbitrary size and dimension. Finally, we illustrate the magnetic behavior of exemplary surface systems, such as the surfaces of bulk crystals, ultrathin films, non-collinear spin structures, and atomically engineered spin networks, including one-dimensional atomic chains and single-atom magnets.

In layered LiNixMnyCozO2 cathode material for lithium-ion batteries, the spins of transition metal (TM) ions construct a two-dimensional triangular networks, which can be considered as a simple case of geometrical frustration. By performing neutron powder diffraction experiments and magnetization measurements, we find that long-range magnetic order cannot be established in LiNixMnyCozO2 even at low temperature of 3 K. Remarkably, the frustration parameters of these compounds are estimated to be larger than 30, indicating the existence of strongly frustrated magnetic interactions between spins of TM ions. As frustration will inevitably give rise to lattice instability, the formation of Li/Ni exchange in LiNixMnyCozO2 will help to partially relieve the degeneracy of the frustrated magnetic lattice by forming a stable antiferromagnetic state in hexagonal sublattice with nonmagnetic ions located in centers of the hexagons. Moreover, Li/Ni exchange will introduce 180{\deg} superexchange interaction, which further relieves the magnetic frustration through bringing in new exchange paths. Thus, the variation of Li/Ni exchange ratio vs. TM mole fraction in LiNixMnyCozO2 with different compositions can be well understood and predicted in terms of magnetic frustration and superexchange interactions. This provides a unique viewpoint to study the Li/Ni ions exchange in layered Li(NixMnyCoz)O2 cathode materials., Comment: 22 pages, 4 figures

In this paper, we discuss a permanent magnetic lattice for trapping and manipulating ultracold atoms and quantum degenerate gases. Considering three components of an external bias magnetic field, B1x, B1y and B1z which are applied for controlling the magnetic lattice parameters, we obtain analytic expressions for the magnetic field minima locations as well as their absolute values, curvatures of the absolute value of the magnetic field, trap frequencies and barrier heights between minima in all directions. B1z had previously been considered in numerical works, but not in analytic calculations, due to difficulty in obtaining the analytic expressions for the physical parameters and sufficiency of considering only B1x and B1y. Including the third component in this study provides further control over the magnetic lattice parameters. Also, in the presence of unavoidable bias magnetic fields with a z-component such as the Earth’s magnetic field, our analytic calculations could be useful. In numerical calculations, we have considered up to n s = 1001 square magnetic slabs in each direction of the 2D lattice.

A study of controlling the microwave mitigation properties of ferrite–carbon black/PVA composites by tuning the magnetic microstructure and spin arrangement of the ferrite particles is presented. MxCo(1−x)Fe2O4 (M: Ni2+, Mn2+ & Zn2+) nano-ferrites (NFs) were synthesized by a solvothermal method and these NFs were used to fabricate NF–CB hybrids and flexible NF–CB/PVA composite films. The magnetic force microscopy studies of the NFs reveal a unique single axis oriented domain structure for Zn-NFs and multi-domain magnetic microstructures for Mn-NFs and Ni-NFs. Mossbauer analysis of the NFs reveals highly distorted co-ordination of Fe3+ cations in Zn-NFs, whereas sub-lattice spins are canted in Mn-NFs and Ni-NFs. Despite the distorted magnetic lattice and broken coordination, the largest microwave shielding effectiveness (SE) of 32 dB is observed, over a bandwidth of 8 to 18 GHz, for Zn-NF–CB/PVA with a major contribution from absorption (SEA ∼ 25 dB). The dielectric properties and Cole–Cole plots indicate enhanced interfacial polarization in Zn-NF–CB/PVA, which is attributed to the motion of polarons across multiple heterogeneous interfaces. These polarons are thought to be generated by distorted co-ordination of Fe3+, and d–d electron transition between Co2+ Fe3+ cations at the B-site of Zn-NF. Distorted co-ordination of Fe3+ in Zn-NF along with unique single axis oriented magnetic domains play a crucial role in magnetic losses, as μ′′ is almost double in Zn-NF based composites as compared to other composites. Due to their excellent and tunable microwave absorption properties, NF–CB/PVA composites could be employed for next generation stealth applications.

The structural and magnetic properties of a glaserite-type Na2BaFe(VO4)2 compound, featuring a triangular magnetic lattice of Fe2+ (S = 2), are reported. Temperature dependent X-ray single crystal studies indicate that at room temperature the system adopts a trigonal P3m1 structure and undergoes a structural phase transition to a C2/c monoclinic phase slightly below room temperature (Ts = 288 K). This structural transition involves a tilting of Fe-O-V bond angles and strongly influences the magnetic correlation within the Fe triangular lattice. The magnetic susceptibility measurements reveal a ferromagnetic transition near 7 K. Single crystal neutron diffraction confirms the structural distortion and the ferromagnetic spin ordering in Na2BaFe(VO4)2. The magnetic structure of the ordered state is modeled in the magnetic space group C2'/c' that implies a ferromagnetic order of the a and c moment components and antiferromagnetic arrangement for the b components. Overall, the Fe magnetic moments form ferromagnetic layers that are stacked along the c-axis, where the spins point along one of the (111) facets of the FeO6 octahedron.

The heavy fermion ferromagnet CeRh$_6$Ge$_4$ is the first example of a clean stoichiometric system where the ferromagnetic transition can be continuously suppressed by hydrostatic pressure to a quantum critical point. In order to reveal the outcome when the magnetic lattice of CeRh$_6$Ge$_4$ is diluted with non-magnetic atoms, this study reports comprehensive measurements of the physical properties of both single crystal and polycrystalline samples of La$_x$Ce$_{1-x}$Rh$_6$Ge$_4$. With increasing $x$, the Curie temperature decreases, and no transition is observed for $x$ $>$ 0.25, while the system evolves from exhibiting coherent Kondo lattice behaviors at low $x$, to the Kondo impurity scenario at large $x$. Moreover, non-Fermi liquid behavior (NFL) is observed over a wide doping range, which agrees well with the disordered Kondo model for 0.52 $\leq$ $x$ $\leq$ 0.66, while strange metal behavior is revealed in the vicinity of $x_c$ = 0.26., 6 pages, 5 figures

Angular momentum transport is one of the cornerstones of spintronics. Spin angular momentum is not only transported by mobile charge carriers, but also by the quantized excitations of the magnetic lattice in magnetically ordered systems. In this regard, magnetically ordered insulators provide a platform for magnon spin transport experiments without additional contributions from spin currents carried by mobile electrons. In combination with charge-to-spin current conversion processes in conductors with finite spin-orbit coupling it is possible to realize all-electrical magnon transport schemes in thin film heterostructures. This review provides an insight into such experiments and recent breakthroughs achieved. Special attention is given to charge current based manipulation via an adjacent normal metal of magnon transport in magnetically ordered insulators in terms of spin-transfer torque. Moreover, the influence of two magnon modes with opposite spin in antiferromagnetic insulators on all-electrical magnon transport experiments is discussed., If you have suggestions or ideas to improve this review, please contact me via email

High-frequency electron spin resonance (ESR) measurements were carried out on a single crystal β-Cu2V2O7, where Cu–O edge-sharing chains are connected by non-magnetic VO4 tetrahedrons. Due to sizable anisotropies, analyses of bulk magnetic properties alone have not yielded any definite conclusion and the modeling of the magnetic lattice is controversial. By means of high-frequency ESR with operating frequencies of 135–405 GHz and at a temperature range of 4.2–50 K, the large g value anisotropy is determined, which removes the ambiguity of susceptibility fitting. Moreover, non-negligible exchange anisotropy is evaluated by analyzing high-field magnetization and antiferromagnetic resonance in antiferromagnetic state appearing below T N = 26 K. Based on these microscopic information, we found that alternating-chain model is the most reasonable candidate for explaining properties of the crystal. The present study shows the importance of combining macroscopic and microscopic probes in analyzing magnetic network of complex magnetic materials.

Entropy-stabilized oxides possess a large configurational entropy that allows for the unique ability to include typically immiscible concentrations of species in different configurations. Particularly in oxides, where the physical behavior is strongly correlated to stereochemistry and electronic structure, entropic stabilization creates a unique platform to tailor the interplay of extreme structural and chemical disorder to realize unprecedented functionalities. Here, we control stereochemically driven structural disorder in single crystalline, rocksalt, (MgCoNiCuZn)O-type entropy-stabilized oxides through the incorporation of ${\mathrm{Cu}}^{2+}$ cations. We harness the disorder to tune the degree of glassiness in the antiferromagnetic structure. Structural distortions driven by the Jahn-Teller effect lead to a difference in valence on the Co cation sites, which extends to dilution and disorder of the magnetic lattice. A spin glass model reveals that the fractional spin ordering of the magnetic lattice can be tuned by \ensuremath{\sim}65%. These findings demonstrate entropy-stabilization as a tool for control of functional phenomena.

International audience; We have shown a new design strategy which exploits different oxyanions in a Ruddlesden-Popper (RP)-type phase to modulate the local crystal structure and magnetic lattice. Material (Sr4Fe2(SO4)0.5O6.5) with the larger voluminous oxyanion (SO4, S-O distance = 1.49 Å) as separating blocks between magnetic FeO layers shows a two-dimensional magnetic lattice. A three-dimensional magnetic lattice and spin reorientation transition is observed for the Sr4Fe2(CO3)O6, having CO3 (C-O distance = 1.25 Å), a smaller oxyanion, as a separating layer. Using mixed oxyanions (SO4 and CO3) in the central perovskite block of the RP3 phase, we have demonstrated a facile strategy to modulate the local crystal structure. The modulated displacement of the magnetic cations, which can break the local centrosymmetry, is suggested to originate the magnetodielectric effect near the magnetic ordering temperatures (higher than room temperature). Further, all CO3 containing samples show magnetodielectric coupling below room temperature due to the spin reorientation transition. The room temperature magnetodielectric effect coupled to the targeted local modulation of the crystal structure by oxyanions (in the absence of second-order Jahn-Teller active "distortion centers") opens a new door to the design of new multifunctional materials with the possibility for the room temperature application. © 2019 American Chemical Society.

International audience; We report the synthesis, structure and physical properties of a hitherto unreported brownmillerite compound Sr2ScFeO5. We haveshown a new ordering sequence of the interlayer iron tetrahedralchains. Reduced dimensionality of the magnetic lattice and the frustration in the two dimensional iron tetrahedral chains originate complex magnetic and magneto-dielectric effects. Our study high-lights a novel approach to tailor the magnetic lattice in bulk oxides

This article reviews the development in our laboratory of magnetic lattices comprising periodic arrays of magnetic microtraps created by patterned magnetic films to trap periodic arrays of ultracold atoms. Recent achievements include the realisation of multiple Bose-Einstein condensates in a 10 \(\mu\)m-period one-dimensional magnetic lattice; the fabrication of sub-micron-period square and triangular magnetic lattice structures suitable for quantum tunnelling experiments; the trapping of ultracold atoms in a sub-micron-period triangular magnetic lattice; and a proposal to use long-range interacting Rydberg atoms to achieve spin-spin interactions between sites in a large-spacing magnetic lattice.

Magnetic skyrmions have been the focus of intense research due to their potential applications in ultrahigh-density data and logic technologies, as well as for the unique physics arising from their antisymmetric exchange term and topological protections. In this work we prepare a chiral jammed state in chemically disordered (Fe, Co)Si consisting of a combination of randomly oriented magnetic helices, labyrinth domains, rotationally disordered skyrmion lattices, and/or isolated skyrmions. Using small angle neutron scattering, we demonstrate a symmetry-breaking magnetic field sequence which disentangles the jammed state, resulting in an ordered, oriented skyrmion lattice. The same field sequence was performed on a sample of powdered $\mathrm{C}{\mathrm{u}}_{2}\mathrm{OSe}{\mathrm{O}}_{3}$ and again yields an ordered, oriented skyrmion lattice, despite the relatively noninteracting nature of the grains. Micromagnetic simulations confirm the promotion of a preferred skyrmion lattice orientation after field treatment, independent of the initial configuration, suggesting this effect may be universally applicable. Energetics extracted from the simulations suggests that approaching a magnetic hard axis causes the moments to diverge away from the magnetic field, increasing the Dzyaloshinskii-Moriya energy, followed subsequently by a lattice reorientation. The ability to facilitate an emergent ordered magnetic lattice with long-range orientation in a variety of materials despite overwhelming internal disorder enables the study of skyrmions even in imperfect powdered or polycrystalline systems and greatly improves the ability to rapidly screen candidate skyrmion materials.

Interaction-driven metal–insulator transitions or Mott transitions are widely observed in condensed matter systems. In multi-orbital systems, many-body physics is richer in which an orbital-selective metal–insulator transition is an intriguing and unique phenomenon. Here we use first-principles calculations to show that a magnetic transition (from paramagnetic to long-range magnetically ordered) can simultaneously induce an orbital-selective insulator–metal transition in rock-salt ordered double perovskite oxides A2BB′O6, where B is a non-magnetic ion (Y3+ and Sc3+) and B′ a magnetic ion with a d3 electronic configuration (Ru5+ and Os5+). The orbital-selectivity originates from geometrical frustration of a face-centered-cubic lattice on which the magnetic ions B′ reside. Including realistic structural distortions and spin-orbit interaction do not affect the transition. The predicted orbital-selective transition naturally explains the anomaly observed in the electric resistivity of Sr2YRuO6. Implications of other available experimental data are also discussed. This work shows that by exploiting geometrical frustration on non-bipartite lattices, new electronic/magnetic/orbital-coupled phase transitions can occur in correlated materials that are in the vicinity of metal–insulator phase boundary. First-principle calculations shed new light on orbital-selective Mott transitions in magnetic perovskites, providing new insight and explaining existing data. A Mott transition is a metal–insulator transition whereby electric-field screening causes the potential felt by electrons to become strongly peaked, making the electrons localized. In multi-orbital systems an orbital-selective Mott transition can occur: electrons become localized on some orbitals but remain itinerant on the others. Hanghui Chen from New York University Shanghai in China uses first-principle calculations to show that a magnetic transition can induce an orbital-selective Mott transition in an ordered double perovskite oxide, in which the occurrence of long-range magnetic order makes electrons in one orbital metallic while leaving the others insulating. This is related to geometrical frustration in the magnetic lattice, and structural distortions and spin-orbit interactions do not affect the transition.

We conduct an extensive study of nonlinear localized modes (NLMs), which are temporally periodic and spatially localized structures, in a two-dimensional array of repelling magnets. In our experiments, we arrange a lattice in a hexagonal configuration with a light-mass defect, and we harmonically drive the center of the chain with a tunable excitation frequency, amplitude, and angle. We use a damped, driven variant of a vector Fermi-Pasta-Ulam-Tsingou lattice to model our experimental setup. Despite the idealized nature of this model, we obtain good qualitative agreement between theory and experiments for a variety of dynamical behaviors. We find that the spatial decay is direction-dependent and that drive amplitudes along fundamental displacement axes lead to nonlinear resonant peaks in frequency continuations that are similar to those that occur in one-dimensional damped, driven lattices. However, we observe numerically that driving along other directions results in asymmetric NLMs that bifurcate from the main solution branch, which consists of symmetric NLMs. We also demonstrate both experimentally and numerically that solutions that appear to be time-quasiperiodic bifurcate from the branch of symmetric time-periodic NLMs., New Journal of Physics, 23 (4), ISSN:1367-2630

The most effective way to increase the brilliance of synchrotron light sources is the reduction of beam emittance. Following the recent developments in low emittance lattice design, a new sub-nm emittance lattice based on implementation of multi-band achromat concept and application of longitudinal gradient bending magnets was developed for CANDLE storage ring. The paper presents the main design considerations, linear and non-linear beam dynamics aspects of the new lattice proposed.