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1. Perpendicular and in-plane hole asymmetry in a strained NiFe ₂ O ₄ film

   https://doi.org/10.1088/1361-648X/abf0c5  

   Knut, R; Malik, R S; Kons, C; Shoup, J E; Radu, F; Luo, C; Kvashnin, Y O; Gupta, A; Karis, O; Arena, D A (May 2021, Journal of Physics: Condensed Matter)

   Abstract Strained materials can exhibit drastically modified physical properties in comparison to their fully relaxed analogues. We report on the x-ray absorption spectra (XAS) and magnetic circular dichroism (XMCD) of a strained NiFe 2 O 4 inverse spinel film grown on a symmetry matched single crystal MgGa 2 O 4 substrate. The Ni XAS spectra exhibit a sizable difference in the white line intensity for measurements with the x-ray electric field parallel to the film plane (normal incidence) vs when the electric field is at an angle (off-normal). A considerable difference is also observed in the Fe L 2,3 XMCD spectrum. Modeling of the XAS and XMCD spectra indicate that the modified energy ordering of the cation 3 d states in the strained film leads to a preferential filling of 3 d states with out-of-plane character. In addition, the results point to the utility of x-ray spectroscopy in identifying orbital populations even with elliptically polarized x-rays. 

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2. The crystal and defect structures of polar KBiNb ₂ O ₇

   https://doi.org/10.1039/d1dt04064b  

   Mallick, Subhadip; Zhang, Weiguo; Batuk, Maria; Gibbs, Alexandra S.; Hadermann, Joke; Halasyamani, P. Shiv; Hayward, Michael A. (February 2022, Dalton Transactions)

   KBiNb 2 O 7 was prepared from RbBiNb 2 O 7 by a sequence of cation exchange reactions which first convert RbBiNb 2 O 7 to LiBiNb 2 O 7 , before KBiNb 2 O 7 is formed by a further K-for-Li cation exchange. A combination of neutron, synchrotron X-ray and electron diffraction data reveal that KBiNb 2 O 7 adopts a polar, layered, perovskite structure (space group A 11 m ) in which the BiNb 2 O 7 layers are stacked in a (0, ½, z ) arrangement, with the K + cations located in half of the available 10-coordinate interlayer cation sites. The inversion symmetry of the phase is broken by a large displacement of the Bi 3+ cations parallel to the y -axis. HAADF-STEM images reveal that KBiNb 2 O 7 exhibits frequent stacking faults which convert the (0, ½, z ) layer stacking to (½, 0, z ) stacking and vice versa , essentially switching the x - and y -axes of the material. By fitting the complex diffraction peak shape of the SXRD data collected from KBiNb 2 O 7 it is estimated that each layer has approximately a 9% chance of being defective – a high level which is attributed to the lack of cooperative NbO 6 tilting in the material, which limits the lattice strain associated with each fault. 

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3. Crystal growth and physical properties of an antiferromagnetic molecule: trans -dibromidotetrakis(acetonitrile)chromium(III) tribromide, [CrBr ₂ (NCCH ₃ ) ₄ ](Br ₃ )

   https://doi.org/10.1107/S2052520621004662  

   Dissanayaka Mudiyanselage, Ranuri S.; Kong, Tai; Xie, Weiwei (August 2021, Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials)

   The synthesis, crystal structure determination, magnetic properties and bonding interaction analysis of a novel 3 d transition-metal complex, [CrBr 2 (NCCH 3 ) 4 ](Br 3 ), are reported. Single-crystal X-ray diffraction results show that [CrBr 2 (NCCH 3 ) 4 ](Br 3 ) crystallizes in space group C 2/ m (No. 12) with a symmetric tribromide anion and the powder X-ray diffraction results show the high purity of the material specimen. X-ray photoelectron studies with a combination of magnetic measurements demonstrate that Cr adopts the 3+ oxidation state. Based on the Curie–Weiss analysis of magnetic susceptibility data, the Néel temperature is found to be around 2.2 K and the effective moment (μ eff ) of Cr 3+ in [CrBr 2 (NCCH 3 ) 4 ](Br 3 ) is ∼3.8 µ B , which agrees with the theoretical value for Cr 3+ . The direct current magnetic susceptibility of the molecule shows a broad maximum at ∼2.3 K, which is consistent with the theoretical Néel temperature. The maximum temperature, however, shows no clear frequency dependence. Combined with the observed upturn in heat capacity below 2.3 K and the corresponding field dependence, it is speculated that the low-temperature magnetic feature of a broad transition in [CrBr 2 (NCCH 3 ) 4 ](Br 3 ) could originate from a crossover from high spin to low spin for the split d orbital level low-lying states rather than a short-range ordering solely; this is also supported by the molecular orbital diagram obtained from theoretical calculations. 

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4. Photocrystallography of [Ru(bpy) ₂ (dmso) ₂ ] ²⁺ reveals an O-bonded metastable state

   https://doi.org/10.1039/D3SC01526B  

   Marr, Zoe Y.; Thapa Magar, Rajani; Fournier, Bertrand; Benedict, Jason B.; Rack, Jeffrey J. (June 2023, Chemical Science)

   We report the first instance of observing the phototriggered isomerization of dmso ligands on a bis sulfoxide complex, [Ru(bpy) 2 (dmso) 2 ], in the crystalline solid state. The solid-state UV-vis spectrum of the crystal demonstrates an increase in optical density around 550 nm after irradiation, which is consistent with the solution isomerization results. Digital images of the crystal before and after irradiation display a notable color change (pale orange to red) and cleavage occurs along planes, (1̄01) and (100), during irradiation. Single crystal X-ray diffraction data also confirms that isomerization is occurring throughout the lattice and a structure that contains a mix of the S , S and O , O / S , O isomer was attained from a crystal irradiated ex situ . In situ irradiation XRD studies reveal that the percentage of the O-bonded isomer increases as a function of 405 nm exposure time. 

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5. Multifunctional Cu ₂ TSiS ₄ (T = Mn and Fe): Polar Semiconducting Antiferromagnets with Nonlinear Optical Properties

   https://doi.org/10.1021/acs.inorgchem.2c03754  

   Messegee, Zachary T; Cho, Jun Sang; Craig, Andrew J; Garlea, V Ovidiu; Xin, Yan; Kang, Chang-Jong; Proffen, Thomas E; Bhandari, Hari; Kelly, Jordan C; Ghimire, Nirmal J; et al (January 2023, Inorganic Chemistry)

   Cu2TSiS4 (T = Mn and Fe) polycrystalline and single-crystal materials were prepared with high-temperature solid-state and chemical vapor transport methods, respectively. The polar crystal structure (space group Pmn21) consists of chains of corner-sharing and distorted CuS4, Mn/FeS4, and SiS4 tetrahedra, which is confirmed by Rietveld refinement using neutron powder diffraction data, X-ray single-crystal refinement, electron diffraction, energy-dispersive X-ray spectroscopy, and second harmonic generation (SHG) techniques. Magnetic measurements indicate that both compounds order antiferromagnetically at 8 and 14 K, respectively, which is supported by the temperature-dependent (100–2 K) neutron powder diffraction data. Additional magnetic reflections observed at 2 K can be modeled by magnetic propagation vectors k = (1/2,0,1/2) and k = (1/2,1/2,1/2) for Cu2MnSiS4 and Cu2FeSiS4, respectively. The refined antiferromagnetic structure reveals that the Mn/Fe spins are canted away from the ac plane by about 14°, with the total magnetic moments of Mn and Fe being 4.1(1) and 2.9(1) μB, respectively. Both compounds exhibit an SHG response with relatively modest second-order nonlinear susceptibilities. Density functional theory calculations are used to describe the electronic band structures. 

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