Single molecule magnets (SMM) are an interesting topic within the domain of materials chemistry, with possible uses for quantum computing and high density data storage. This study is concerned with the use of polarized neutron diffraction (PND) to describe

them.

If a SMM crystal sample is measured with a classical magnetometer, it would yield a simple vector sum of all site magnetizations in the crystal. To access the anisotropic magnetic susceptibility tensor of the individual sites, (PND) can be used. Neutrons will scatter as a result of both the magnetic and the nuclear strong force interaction. In a (PND) experiment we measure the combined diffraction pattern from both interactions, but want to isolate the magnetic part in order to calculate the anisotropic susceptibility tensor. I.e. we need to find the contribution from nuclear strong force separately, which can be calculated from the crystal structure. The structure is usually found using unpolarized neutron diffraction, as opposed to XRD because of the importance of scattering from light elements. However neutron diffraction experiments are significantly harder to come by, this study has investigated the effect of using a high quality XRD structure as a basis instead.

Two known molecular magnets, have been investigated: One with a Co(II) and one with a Dy(III) ion core. For both systems, susceptibility tensors are refined using both a neutron diffraction structure and different X-ray diffraction structures. The X-ray results are compared to the neutron tensor to gauge the impact on the refinement. Ultimately the goal is to decide if X-ray diffraction could be considered as a substitute for neutron diffraction when solving the crystal structure

of a molecule with the aim of finding the magnetic susceptibility.

The magnetic materials group at Diamond Light Source contains 4 world leading instruments for the study of different aspects of magnetic and strongly correlated materials.

• I06 - The Nanoscience beamline exploits the brightest region in Diamond’s spectrum, providing a high photon flux density for soft X-ray experiments. It combines microfocused soft X-rays with variable linear and circular polarisation and X-ray photoelectron emission microscopy (PEEM) to provide spectroscopic data on nanometre length scales. The intense polarised beam can be focused to a spot several microns in diameter, allowing the PEEM to probe nanomagnetism and nanostructures.
• I10 - Beamline for Advanced Dichroism Experiments (BLADE). BLADE delivers soft X-ray beam in the energy range from 0.4 to 2 keV. The research focuses on the magnetisation and the magnetic structure of novel nanostructured systems. These magnetic properties can be probed thanks to high dichroic effects in the soft X-ray region. The dichroic effect can be studied both in absorption and scattering experiments.
• I16 - Hard x-ray materials and magnetism beamline. This beamline provides high flux in the tender-hard x-ray energy regime, from 2.7-15 keV, ideal for looking at resonant edges of most 3d, 4d and 5d metals. A large kappa-diffractometer allows diffraction in a range of geometries from several sample environments including a 4K cryostat and 1T magnet. Full polarisation control and analysis is available with a double-crystal phase retarder and linear polarisation analyser.
• I21 - This is a dedicated Resonant Inelastic soft X-ray Scattering (RIXS) beamline that provides a highly monochromatised, focused and tunable X-ray beam onto materials, while detecting and energy-analysing scattered X-rays using a spatially-resolved two-dimensional detector. By studying the energy and momentum differences between the incident and the outgoing X-rays, one can obtain information such as the local lattice structure (local crystal field), electron orbitals (orbital excitations), collective lattice vibration (phonons), magnetic (spinons/magnons) and charge excitations of the material under investigation.

For more information, please come to the poster or see https://www.diamond.ac.uk/Instruments/Magnetic-Materials.html

The next proposal deadline is: Wednesday 7th October 2020

https://www.diamond.ac.uk/Users/Apply-for-Beamtime.html

The pseudogap state in high transition temperature copper oxide superconductors shows many unusual magnetic, electrical phenomenon. A principal issue is to understand the origin of the pseudogap phase in the high transition temperature copper oxide superconductors¹. An important controversial problem is whether the pseudogap phase is a crossover from the superconducting phase or a distinct phase. If it is the latter, the symmetry changing which cause of magnetic/electric order will be observed by phase transition. There are several evidences from angle-resolved photoemission spectroscopy (ARPES)² and polarized neutron diffraction³ show that the time-reversal symmetry is broken at the pseudogap phase. However, X-ray optical activity (XOA)⁴ showed not time-reversal symmetry but mirror symmetry broken.

Here we report the persuasive evidence of spatial-inverse symmetry and time-reversal symmetry broken by using our original machine, the generalized-high accuracy universal polarimeter(G-HAUP)^5,6. G-HAUP enables us to measure the optical rotation (OR) and the circular dichroism (CD) in addition to the linear birefringence (LB) and the linear dichroism (LD), simultaneously. When the spatial inversion symmetry is broken, reciprocal OR and CD, i.e., optical activity (OA) and natural CD (NCD), can be observed. On the other hand, when the time reversal symmetry is broken, non-reciprocal OR and CD, i.e., Faraday rotation (FR) and Magnetic-CD (MCD), can be observed.

1. Norman, M. R., Pines, D. & Kallin, C. Adv. Phys. 54, 715–733 (2005).

2. A. Kaminski et al., Nature, 416, 610 (2002)

3. S. De Almeida-Didry et al., Phys. Rev. B, 86, 020504 (2012)

4. M. Kubota et al., J. Phys. Jap., 75, 053760 (2006)

5. J. Kobayashi, T. Asahi, M. Sakurai, M. Takahashi, K. Okubo, Y. Enomoto, Phys. Rev. B, 1996, 53, 11784-11795.

6. M. Tanaka, N. Nakamura, H. Koshima, T. Asahi, J. Phys. D: Appl. Phys., 2012, 45, 175303-175310

The competing or cooperative character between different degrees of freedom lead to different ground states in strongly-correlated systems. Even simple systems, such as pure rare earth compounds, present multiple phase transitions with complex magnetic structures in some of them, resulting from a strong interplay between magnetic dipolar interaction and temperature dependence of crystal field parameters [1]. So, it is expected that some rare-earth-based compounds also have rich magnetic phase diagrams. One example is the series of intermetallic compounds RNiSi₃ (R = rare earth), which shows anisotropic antiferromagnetic ground states evolving with R [2-4]. The microscopic magnetic structures must be determined to rationalize such rich behavior. Here, resonant X-ray magnetic diffraction experiments are performed on single crystals of GdNiSi₃, TbNiSi₃ and HoNiSi₃ at zero field. The primitive magnetic unit cell matches the chemical cell below the Néel temperatures T_N = 22.2, 33.2 K, for Gd- and Tb-based compounds, respectively. The magnetic structure is determined to be the same for both compounds (magnetic space group Cmmm′) and could be fully described by a single one-dimensional irreducible representation of the Cmmm space group. It features ferromagnetic ac planes that are stacked in an antiferromagnetic + − + − pattern, with the rare-earth magnetic moments pointing along the a direction [5]. For HoNiSi₃, the situation is more complicated, since this compound show two well-defined λ-shape anomalies at T_N1 = 6.3 K and T_N2 = 10.4 K. Additionally, different components of the total magnetic moment order at different temperatures. The a component orders at T_N2, and after further cooling above T_N1, the c component orders. For this compound, our results show that at temperatures between T_N1 and T_N2 (phase II), the ordered magnetic moment points along the a-axis, while below T_N1 (phase I), the ordered magnetic moments have components both along with a and c. Remarkably, while at phase II the possible magnetic structure is the same as found in GdNiSi₃ and TbNiSi₃, at phase I two irreducible representations are needed to account the total magnetic moment direction. In this phase, the magnetic structure is consistent with C2’/m magnetic structure. Lastly, those magnetic structures contrasts with the + − − + stacking and moment direction along the b axis previously reported for YbNiSi₃ [6]. This indicates a sign reversal of the coupling constant between second-neighbor R planes as R is varied from Gd, Tb and Ho to Yb. The long b lattice parameter of GdNiSi₃ and TbNiSi₃ shows a magnetoelastic expansion upon cooling below T_N, pointing to the conclusion that the + − + − stacking is stabilized under lattice expansion. A competition between distinct magnetic stacking patterns with similar exchange energies tuned by the size of R sets the stage for the magnetic ground state instability observed along this series.

Rare earth rich intermetallic compounds of the type R₃T (R = rare earth, T = transition metal) are found to be formed by very limited elements because of negative heat of formation and these compounds are revisited several times due to various novel properties emerging out of their crystal and magnetic structures. [1] Tb₃Co is one such compound which orders below T_N = 84 K (Fig. 1) and goes through a first order magnetic transition of order to order type at ~72 K. Despite of several previous studies on this compound the reason behind the low temperature transition like feature was remain unexplained. It was revealed by our temperature dependent neutron diffraction study (Fig. 2) that the magnetic structure of this compound remains unaltered below 72 K to the lowest temperature except for some changes in intensity and moment values. The Rietveld refinement analysis to these data suggests that there is a drastic change in lattice parameters and volume around 40 K clearly suggesting a presence of strong spin-lattice coupling in this compound. Further, magnetic field dependent neutron diffraction data and the refinement analysis performed over the high angle part of these field dependent patterns confirms that there exists a change in strength of the spin-lattice coupling which is stronger at lower temperature and getting weaker at higher temperature. This is what responsible for the low temperature drop in ZFC in this compound. [2] Moreover, strong frequency dispersion in linear and nonlinear ac- susceptibility data and their various analyses confirm that Tb₃Co exhibits magnetic glassy behaviour with magnetic glass temperature coincides with first order transition temperature at 72 K. [2] Further, various time dependent dc- magnetization measurements provide evidences for the fact that the magnetic glassy behaviour persists in this compound even up to P ~ 1 GPa although the fitting to stretched exponential equation to the magnetic relaxation data infers that the glassy behaviour is weakened enough at P = 0.69 GPa and further increase in pressure has marginal effect on the glassy behaviour in this compound. [3] However, apart from shifting the transition temperatures to lower temperature (T_N by 6 K, First order transition by 15 K and low temperature transition like feature by 3 K) with increasing pressure up to 1.21 GPa, pressure is found to improve the magnetocaloric property of this compound (Fig. 3) to a large extent. The difference between -ΔS_M in presence of P ~ 1 GPa and at ambient condition is plotted in Fig. 3 and it is exhibiting a strong peak thereby inferring an enhancement of 37% in magnetocaloric effect in Tb₃Co at P ~ 1 GPa.

[1] Buschow, K. H. J. (1977) Rep. Prog. Phys 40, 1179.
[2] Goswami, S., Babu, P. D., Rawat, R. (2019). J. Phys. Condens. matter 31, 505802.
[3] Goswami, S., Babu, P. D., Rawat, R. (2019). J. Phys. Condens. matter 31, 505802.

One-dimensional spin chain systems have been attracting renewed interest in terms of a magnon/spinon-band splitting, which is found in ?-Cu₂V₂O₇ [1] and Cs₂CuCl₄ [2]. Nonreciprocal propagation of such quasiparticles is of growing interest since it may be used for spintronics device realization. A key parameter for the band splitting is an intrachain antisymmetric Dzyaloshinskii-Moriya interaction. To expand the variety of materials that can exhibit the band splitting, we have further searched for a possible quasi one-dimensional antiferromagnet. Cu₂(MoO₄)(SeO₃) is a candidate quasi one-dimensional compound, which crystallizes in a monoclinic system (space group P2₁/c) with the unit cell parameters ? = 104.675(12)˚, a = 8.148(5) Å, b = 9.023(5) Å, and c = 8.392(5) Å [3]. The Cu²⁺ ions are connected via edges of CuO₅, forming armchair-like chains along c-axis with three different bond lengths, 3.186 Å, 2.973 Å, and 3.149 Å. Due to the lack of local inversion symmetry between the shortest Cu(1)-O-Cu(2) bonds, the active DM interactions between these bonds could be expected.

We have performed single crystal magnetic susceptibility measurements and a neutron powder diffraction to characterize this compound. The magnetic susceptibility shows an anomaly at T_N ~ 23 K in all directions. The temperature dependence of the magnetic susceptibility shows a broad maximum near 50 K indicates a low-dimensionality and short-range correlation. The magnetic susceptibility was fit between 130 K < T < 300 K to the Curie-Weiss law and the Curie-Weiss temperature Θ = -68(1) K was obtained. The negative Curie-Weiss temperature confirms that the dominant exchange interaction between Cu²⁺ ions in Cu₂(MoO₄)(SeO₃) is antiferromagnetic. Moreover, the magnetic susceptibility strongly depends on the crystallographic direction suggesting that the g-factor in this compound is anisotropic. A sharp drop in the susceptibility only along c-axis is observed suggesting that the majority spins align along this direction.

A neutron powder diffraction experiment was carried out on HB2A powder diffractometer at High Flux Isotope Reactor (HFIR), Oak Ridge National Laboratory (ORNL). Ge(113) monochromator was used to select neutrons with λ = 2.41 Å. Magnetic Bragg reflections were observed below T_N on top of the structural reflections indicating the magnetic propagation vector q = (0 0 0). Magnetic structure analysis was performed using the representation analysis method; we found that Cu₂(MoO₄)(SeO₃) orders with antiferromagnetic structure, where the magnetic moments are mostly parallel (or antiparallel) to the chain direction.

[1] G. Gitgeatpong, et al., Phys. Rev. Lett. 119, 047201 (2017)

[2] K. Yu. Povarov et al., Phys. Rev. Lett. 107, 037204 (2011)

[3] S. Y. Zhang, H. et al, Inorg. Chem., 48 (24), 11809–11820 (2009)

Iron borate FeBO₃ (space group) is a known crystal which exhibits specific magnetic, magnetoacoustic, magnetooptical, and resonance properties [1,2]. It was proposed to use such crystals for monochromatization of synchrotron radiation in nuclear resonance spectroscopy as the so-called synchrotron Mössbauer source (SMS) [1,2]. The spectra of reflected radiation strongly depend on the hyperfine interactions in this crystal, while the required radiation parameters are achieved near the Néel point (T_N ~ 348,5 K) [1]. In this case, precise studies of the magnetic, electronic, and structural properties of an iron borate single crystal, especially near the Néel point, are of a great importance.

Studies were carried out by means of conventional Mössbauer spectroscopy and single crystal X-ray diffraction analysis. The iron borate single crystals were previously synthesized using the flux-growth technique [1,2]. High structural perfection of the studied FeBO₃ and⁵⁷FeBO₃ crystals was confirmed by X-ray measurements.

The Mössbauer spectra were processed in the framework of the combined magnetic and electric hyperfine interactions taking into account the nonresonant background and the effective thickness of the absorber. At T< T_N, the magnetic moments of two sublattices m₁ and m₂ lie in the basal plane of the crystal and are oriented at an angle of J ~ 179.17 [3]. It was found that the main axis of an electric field gradient (Z') is orthogonal to the moments m₁ and m₂ and does not change the orientation over the entire investigated temperature range 10-400 K (Fig.1).

The maximum entropy method was used to analyze the anisotropy of electron density distribution in FeBO₃. There is no evident of local disordering near the Fe sites below and above the the Néel point, (Fig. 2) which is consistent with Mössbauer data.

In addition, for the FeBO₃ single crystal, the hyperfine parameters were determined and the crystal structure was refined in a wide temperature range. The data obtained could be very useful for tuning pure nuclear diffraction in SMS experiments.

This study was funded by RFBR, project number 19-29-12016-mk.

[1] Smirnova, E.S., Snegirev, N.I., Lyubutin I.S. et al. (2020). Acta Cryst. B. 76, 1100.

[2] Yagupov, S., Strugatsky, M., Seleznyova, K. et al. (2018). . Cryst. Growth Des. 18, 7435.

[3] Pernet, M., Elmale, D. & Joubert, J.-C. (1970). Solid State Commun. 8, 1583–1587.

Members of the multiferroic RMn₂O₅ (R = Y, Bi and rare earth elements) family are well known for their concomitant presence of more than one order parameters at a given temperature [1]. Due to centrosymmetric structure of the mullite-type BiMn₂O₅ compound the microscopic origin of the multiferroicity was explained in terms of complex interplay between spin-ordering, highly polarizable Bi³⁺ with stereo-chemically active lone electron pair, Mn³⁺/Mn⁴⁺ charge-ordering and geometric distortions of the MnO_y coordination polyhedra. A cooperative antiferromagnetic (AFM) ordering between M³⁺ and Nd³⁺ was also observed for NdCrTiO₅ [2] and NdFeTiO₅ [3,4]. Below the respective T_N the M³⁺ cations become AFM and turn the Nd³⁺ cations into AFM along the ab plane through exchange coupling [2]. The collinearly ordered M³⁺ cations along the octahedral chain directing c-axis gives rise to magnetostriction, leading to multiferroicity in this compound [2]. In search of novel multiferroics, we report the synthesis and characterization of the mullite-type O10 phase isostructural NdMnTiO₅ compound. The crystal structural features are described using X-ray powder diffraction data Rietveld refinements. Complementary optical phonon analyses were carried out by infrared and Raman spectroscopy. The optical bandgap was obtained using both Tauc and recently introduced DASF [5-6] methods to determine type and energy of the transition, respectively. The enhancement of DC magnetic susceptibility is a common feature in rare-earth manganates. The Fisher’s heat capacity shows clear evidence of the onset of long range ordering. The large deviation between ZFC and FC susceptibility below the Néel temperature (43(1) K) indicates the presence of competing interactions and/or magnetic anisotropy in the orthorhombic system. Assuming weak interactions between Nd³⁺ and Mn³⁺ magnetic sublattices, the effective total magnetic moment was calculated from the temperature-dependent paramagnetic region, which lies close to theoretical spin-only magnetic moment values. The temperature-dependent magnetic susceptibility was modelled using the mean field approximation, where an interaction between the ordered Mn³⁺ spins and the electrons occupying the lowest lying Kramers' doublet of the Nd³⁺ cations was considered.

[1] A. Munoz, J.A. Alonso, M.T. Casais, M.J. Martinez-Lope, J.L. Martinez, M.T. Fernandez-Diaz (2002). Phys. Rev. B 65, 144423.

[2] J. Saha, G. Sharma, P. Patnaik (2014). J. Magn. Magn. Mater. 360,34.

[3] G. Buisson (1970). J. Phys. Chem. Solids 31, 1171.

[4] I. Yaeger (1978). J. Appl. Phys. 49, 1513.

[5] A. Kirsch, MM: Murshed, M.J. Kirkhame, A. Huq, J.F. Litterst, Th.M. Gesing (2018). J Phys. Chem. C. 122, 28280.

[6] A. Kirsch, MM: Murshed, J.F. Litterst, Th.M. Gesing (2019). J Phys. Chem. C. 123, 3161.

Keywords: Neutron; PXRD; multiferroic; crystal structure; Raman; magnetic property.

The conductive, magnetic, optical, and mechanical properties of the rare-earth RB₁₂ dodecaborides (R = Sc, Y, Tb, Dy, Ho, Er, Tm, Yb, Lu) are of significant interest both for basic research and for practical applications. The combination of metal conductivity with resistance to external influences makes them unique materials for use in extreme environmental conditions. In basic research, these compounds are conveniently used to study the properties caused by rare-earth metal ions.

The dodecaboride structure is formed by a strong framework of boron cuboctahedra (B₁₂). Metal atoms center the spacious B₂₄ cavities between the cuboctahedra and are loosely coupled to each other. The structure of rare-earth dodecaborides is most often described as cubic, sp. gr. Fm-3m. The problem complicating the characterization of the structure and properties of dodecaborides is that the B₁₂ cuboctahedra with the orbitally degenerate ground state are distorted by the cooperative Jahn-Teller effect, although to a very small extent.

The single-crystal structures of YbB₁₂, TmB₁₂, and LuB₁₂ were studied in the temperature range 88–293 K, and HoB₁₂ and ErB₁₂ - in the range 88–500 K using high-resolution X-ray diffraction data to correlate structural changes with changes in the physical properties of the studied dodecaborides. Lattice deformations caused by the cooperative Jan-Teller effect were detected. A method is used for approximating the temperature dependences of atomic displacement parameters (ADP) using the extended Debye or Einstein models [1]. The breakpoints of the temperature dependences of ADP found for HoB₁₂ ErB₁₂ and YbB₁₂, in combination with nonmonotonic changes in the lattice parameters near critical temperatures T_c, indicate phase transformations revealed by diffraction data. Lattice instability and rearrangement of the phonon spectrum near T_c are accompanied by the observed changes in physical characteristics.

The proposed method for modelling of temperature depending ADP is a sensitive structural diagnostics tool for detecting implicit phase transitions, quantum critical points, and quantum instabilities of various nature, leading to appearance of anomalies in the physical properties of crystals.

It was previously suggested that, under certain conditions, the formation of channels or stripes of conduction electrons in certain crystals could be associated with high-temperature superconductivity and colossal magnetoresistance. X-rays diffract from all types of electrons in the crystal, including conduction (delocalized) ones. The technical difficulty laying in the fact that conduction electrons have a low density and give a very weak diffraction signal was solved using special data collection and improved data processing techniques. The visualization of charge stripes in the studied dodecaborides using X-ray diffraction data was achieved by constructing difference Fourier syntheses of electron density without taking into account the crystal symmetry and by the complementary method of maximum entropy. Violations of the cubic symmetry of dodecaborides appeared in the orientation of the residual electron density in certain directions in the crystal. A correlation has been established between the anisotropic ED distribution and the anisotropy of conductivity [2].

The analysis of electron density distribution and the suggested visualization approach will provide the formation of systematic relationships between structure and physical properties and could be applicable to other crystals.

In pursuit of new materials in the topical area of low dimensional and frustrated magnetic systems we have begun to investigate a family of materials which use the oxalate ligand as a backbone from which multiple structures can be derived through combination with magnetic spin sources and additional ligand groups. We currently focus primarily on compounds which have first row transition metals as sources of magnetic spin [1][2], which can then be coupled in two-dimensional (2d) layered lattices.

Two such examples we have synthesised are the isostructural compounds CsM^II(C₂O₄)F (M= Co or Fe). These compounds comprise a layered 2d structure where magnetic exchange coupling is suppressed between layers by the presence of large Cs⁺ ions. Within the layers, the metal atoms are arranged in a rectangular lattice with the two coupling groups segregated in opposite axial directions (along the a axis – F^- coupling, along b axis – C₂O₄^2-, oxalate coupling). The strong two dimensionality plus the very clean in-plane rectangular coupling means this system in principle maps very nicely onto a 2d Heisenberg (3D) J₁/J₁’ type of model, which should be completely free of any diagonal (J₂) exchange coupling that might geometrically frustrate the system [3]. Theoretically this should either lead to an antiferromagnetic stripe order, or with sufficient inter-chain coupling to Néel long-range order (LRO) in the plane, with possible transitions between these states with temperature [3]. Additional coupling within the layers or between the layers may also lead to frustrated ground states, and there have been several theoretical and numerical studies of these kinds of idealised systems [4].

From elastic neutron powder diffraction data, while the two materials have a near identical nuclear structure, their magnetic superstructures are quite different when measured below their transition temperatures (100-150 K). In the Fe compound, the moments are aligned such that the antiferromagnetic coupling by the F^- and C₂O₄^2- groups dominates, creating a Néel state square lattice with ferromagnetic alignment between layers. The Co material while maintaining the F^- antiferromagnetic coupling, conversely displays ferromagnetic coupling across the C₂O₄^2- group. This leads to antiferromagnetic coupling across the Cs⁺ layer. This difference in magnetic structure is currently being investigated by examining system excitations to determine the energy differences between these two states but it is known that the oxalate ligand can support both types of coupling depending on its environment [5][6]. Examining this system more closely may give insight into the mechanisms and limits which govern how systems of this type order generally and so act as a basis for explaining more complex systems which may have frustrated character.

[1] W. Yao et al., Chem. Mater., 2017, 29, 6616.

[2] K. Sustain et al., Inorg. Chem., 2019, 58, 11971.

[3] P. Sindzingre, Phys. Rev. B, 2004, 69, 094418

[4] A. Orendacova et al, Crystals, 2019, 9, 6

[5] M. Peric et al, Monatsh Chem, 2012, 143, 569-577

[6] J. Vallejo et al, Dalton T., 2010, 39, 2350-2358

Thank you to ISIS Neutron and Muon Source and the University of St Andrews for their support of this work

The synthesis of coordination compounds based on 3d cations has been of great interest not only for their various structures and topologies but also for their possible applications as functional materials in areas such as gas storage/adsorption, catalysis, magnetism, luminescence, among others. [1-3]

Two new coordination polymers based on Co^II and Ni^II, {[Co(HL)(EtOH)₂](ClO₄)}_n(1), {[Ni(HL)(EtOH)₂](ClO₄)}_n(2) (H₂L = 2-{[(E)-1H-imidazol-4-ylmethylidene]amino}benzoic acid), were synthesized using a new Schiff base ligand. Compounds 1 and 2 are isostructural presenting a one-dimensional helical chain arrangement and crystallizing in a P21/n monoclinic space group. A hexacoordinated cation with an MN₂O₄ environment is present in the cationic fragment [M(HL)(EtOH)₂]⁺ being the charge balanced by a ClO₄^- anion. Furthermore, the carboxylate group of HL^- ligand is also acting as syn-anti bridge, producing the assembly of the [M(HL)(EtOH)₂]⁺ fragments, thus generating a cationic chain growing through the b axis with an intercation M∙∙∙M distance of 5.1257(13) Å and 5.164(4) Å for 1 and 2, respectively. The M-Ox distances are in the range of 2.060(3) Å to 2.136(4) Å for 1 and 1.988(3) to 2.107(4) Å for 2. Meanwhile, the M-Ny distances are 2.076(3) Å and 2.139(3) Å for 1 and 2.041(4) Å and 2.080(4) Å for 2. The resulting MN₂O₄ moiety presents an elongated octahedral geometry with higher bond distances in the axial position corresponding to the EtOH molecules. Magnetic susceptibility characterization in the 1.8–300 K range reveals intrachain antiferromagnetic interactions for 1 and ferromagnetic interaction for 2 with the presence of the zero-field splitting phenomenon in both compounds.

[1] F. J. Teixeira, L. S. Flores, L. B.L. Escobar, T.C. dos Santos, M. I. Yoshida, M.S. Reis, Stephen Hill, C. M. Ronconi, C. C. Corrêa, Inorg. Chim. Acta 511 (2020).

[2] Y. N. Belokon, V. I. Maleev, M. North, V. A. Larionov, T. F. Savel’yeva, A. Nijland, Y. V. Nelyubina://doi.org/10.1021./cs400409d.

[3] R. Jangir, M. Ansari, D. Kaleeswaran, G. Rajaraman, M. Palaniandavar, R. Murugavel, ACS Catal. 9 (2019) 10940-10950.

The authors acknowledge FONDECYT 1211394, Proyecto Anillo CONICYT ACT 1404 grant, CONICYT FONDEQUIP/PPMS/EQM130086-UNAB, Chilean-French International Associated Laboratory for Multifunctional Molecules and Materials-LIAM3-CNRS N°102 and CEDENNA, Financiamiento Basal, AFB180001.

Dense coordination polymers combine the functional properties typical of the traditional inorganic solid state, such as magnetism, with the remarkable tunability and flexibility that arises from the incorporation of molecular components. They therefore offer the opportunity to discover unusual behaviour that arises from the coupling of these properties. [1] Thiocyanate compounds have the potential for rich optical and magnetic properties, but both their chemistry and magnetism remain comparatively unexplored.

Metal framework compounds involving bridging thiocyanate ligands have started to establish themselves as a rewarding family of materials for magnetic studies, as the thiocyanate acts as an effective superexchange pathway between metal centres. [2] In addition, the asymmetric bonding requirements of the nitrogen and sulphur termini can often result in unconventional framework topologies. This, in turn, can lead to unusual magnetic structures and spin textures in the compounds.

Here will be presented three isomorphous metal thiocyanate frameworks, CsM(NCS)₃, where M = Ni, [3] Mn and Co; of which the latter two are new materials. The structures of these materials have been determined by single crystal X-ray diffraction to be post-perovskite two-dimensional frameworks with interplanar Cs counterions. Bulk magnetic susceptibility measurements revealed all the materials magnetically order between 6 and 16 K, with complex, non-collinear orderings. Following these results, neutron diffraction experiments of both single crystal and powder samples have been carried out to explore the unusual magnetic features further.

[1] W. Li, et al., Nat. Rev. Mater., 2017, 2, 16099.

[2] E. Bassey, et al., Inorg. Chem., 2020, 59, 11627 – 11639.

[3] M. Fleck, Acta Crystallogr. C60, i63 (2004).

Polynuclear coordination complexes with transition metal ions in intramolecular spin communications have been sought by both synthetic and theoretical chemists to step forward towards a new generation of magnets. In this context, manganese carboxylates are attractive systems owing to the variable oxidation states of the metal and the diversity of the carboxylate linker which impart unique characteristics to the frameworks. Manganese (II) compounds in the high spin ground state (S=5/2) are particularly important due to the possibility of the strong exchange interaction between the 3d-electrons. The magnetic centers with varying unpaired electrons provide a variety of magnetic ordering-spin frustrated multiferroics to single-molecule magnetism. Our group is adopting a crystal engineering approach to assemble high nuclear manganese clusters with varying coordination assemblies and explore the influence of selected aromatic dicarboxylic acids in different polar aprotic solvents on spin-exchange interactions. In this presentation, we discuss our strategy on the structural design of new manganese carboxylate coordination polymers and the influence of nonbonding interaction on overall assembly and its antiferromagnetic behavior.

As in the smaller doping range (0.0 ≤ x ≤ 0.5) [1,2], Nd_1-xSr_xFeO₃ adopts an orthorhombic (space group: Pnma) ABO₃ perovskite structure at room temperature, for all compositions within 0.1 ≤ x ≤ 0.9.

Magnetization measurements from 5K to 700K show weak antiferromagnetic behaviour and paramagnetism following the typical Curie-Weiss law above 600K. Assuming that the spin state of the Fe site is (LS Fe³⁺_y IS Fe³⁺_1-y)_1-x LS Fe⁴⁺_x, the ratio of intermediate spin (IS) Fe³⁺ gradually decreases as x increases, and it decreases rapidly when x≧0.6. This decrease in the ratio of IS Fe³⁺ with the increase in x is expected to show a large correlation with the relaxation of the FeO₆ octahedron distortion.

To clarify the correlation between the crystal structure and magnetic structure of Nd1-xSrxFeO3 (0.1 ≤ x ≤ 0.9) in more detail, powder neutron diffraction (PND) data of the Nd_1-xSr_xFeO₃ (0.1 ≤ x ≤ 0.9) samples were collected at room temperature with the medium resolution neutron powder diffractometer (MEREDIT), part of the CANAM infrastructure, at the Nuclear Physics Institute, Czech Republic. All Rietveld refinements were carried out using the GSAS-Ⅱ suite of programs [1].

It is confirmed that the FeO6 octahedron distortion is relaxed as x increases and approaches the crystal structure of the pseudo-cubic. Fig 1 shows the evolution of Fe-O-Fe angles with x in Nd_1-xSr_xFeO₃ (0.1 ≤ x ≤ 0.9).

The materials present antiferromagnetic order, with magnetic moment of Fe decreasing from ~ 3.2 µB for x = 0.1 to ~0.2 µB for x = 0.9. With 0.1 ≤ x ≤ 0.4, the magnetic spins are oriented in the c-axis direction (BNS Magnetic Space Group: Pn'ma'), while for 0.5 ≤ x ≤ 0.9 they appear to be in the a-axis direction (BNS Magnetic Space Group: Pnma). The magnetic structures for Nd_0.9Sr_0.1FeO₃ and Nd_0.5Sr_0.5FeO₃ are shown in fig 2. Crystal and magnetic structures were drawn using VESTA [2].

Low-dimensional magnetic crystals display highly anisotropic interactions between the magnetic moments, yielding interesting magnetic [1], electronic [2], and optical properties [3]. The ground and excited states of low-dimensional magnetic systems attract interest with increasing spin dimension andor decreasing spin values [4]. Materials containing isolated chains might work as models for (1D) S=1/2 Heisenberg systems and Ising spin chains. These models can be used for shedding light on the understanding of magnetic exchange interaction in highly correlated systems. When a geometrical distribution of the magnetic moments is such that it constrains the exchange interactions, the interaction energy is difficult to be minimized, causing the appearance of a complex electronic structure. This often leads to magnetic frustrations. Magnetic frustrations have an impact beyond magnetism, such as multiferroic and high-temperature conductivity behaviors [5,6]. Intermetallic systems are prone to have magnetic frustration, having a high potential for finding new electronic phenomena [7]. The system R₂TGe₆ often displays complex modulated magnetic structures, which can be elucidated by neutron scattering, while the nuclear structure is solved by X-rays or electron diffraction. The accurate structure elucidation of complex magnetic structures is crucial for understanding these structures. Currently, the sole program that handles complex magnetic structures and can combine X-ray, electron, and neutron diffraction is Jana2006 [8]. New features for the analysis of complex magnetic structures are being developed and require neutron diffraction data of such structures. We synthesized some of the compounds from the R₂TGe₆ system, aiming at acquiring neutron diffraction data for testing and further developing the new tools for magnetic structures in Jana2006.

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[2] G. C. Xu, W. Zhang, X. M. Ma, Y. H. Chen, L. Zhang, H. L. Cai, Z. M. Wang, R. G. Xiong, S. Gao. (2011) J. Am. Chem. Soc. 133, 14948.

[3] A. Kandasamy, R. Siddeswaran, P. Murugakoothan, P. S. Kumar, R. Mohan. (2007) Cryst. Growth Des. 7, 183.

[4] A. P. Ramirez. (1994) Annu. Rev. Mater. Sci. 24, 453.

[5] M. Mostovoy. (2008) Nature Mater. 7, 269.

[6] P. W. Anderson. (1987) Science 235, 4793.

[7] S. Arsenjević, J. M. Ok, P. Robinson, S. Ghannadzeh, M. I. Katsnelson, J. S. Kim, N. E. Hussey. (2016) Phys. Rev. Lett. 116, 087202.

[8] V. Petřiček, M. Dušek, L. Palatinus. (2014) Z. Kristallogr. 229, 345.

This work was financially supported by the project Mobility MSM100102001 of the Czech Academy of Sciences and by the Project 19-07931Y of the Czech Science Foundation.