Superexchange Coupling Research Articles

Superexchange Electron Transfer and Protein Matrix in the Charge-Separation Process of Photosynthetic Reaction Centers.

In type-II reaction centers, such as photosystem II (PSII) and reaction centers from purple bacteria (PbRC), light-induced charge separation involves electron transfer from pheophytin (PheoD1) to quinone (QA), occurring near a conserved tryptophan residue (D2-Trp253 in PSII and Trp-M252 in PbRC). This study investigates the route of the PheoD1-to-QA electron transfer, focusing on the superexchange coupling (|HPheoD1···QA|) in the PSII protein environment. |HPheoD1···QA| is significantly larger for the PheoD1-to-QA electron transfer via the unoccupied molecular orbitals of D2-Trp253 ([Trp]•--like intermediate state, 0.73 meV) compared to direct electron transfer (0.13 meV), suggesting that superexchange is the dominant mechanism in the PSII protein environment. While the overall impact of the protein environment is limited, local interactions, particularly H-bonds, enhance superexchange electron transfer by directly affecting the delocalization of molecular orbitals. The D2-W253F mutation significantly decreases the electron transfer rate. The conservation of D2-Trp253/D1-Phe255 (Trp-M252/Phe-L216 in PbRC) in the two branches appears to differentiate superexchange coupling, contributing to the branches being either active or inactive in electron transfer.

Double honeycomb symmetry: Effective-field theory study

The double hexagonal lattice model is a new statistical model constructed by connecting two-dimensional hexagonal structured materials such as Graphene and Lie symmetries. The double hexagonal structure of this model appears in the G2 symmetry of Lie algebras. To investigate the magnetic properties of this new lattice model, an Ising-1/2 model was constructed with spin values σ = ±1. An effective-field theory (EFT) method was used with the differential operator technique to formulate the identity of the spin system, based on Callen's work. Different phase diagrams were established by varying the double-exchange interaction couplings and the super-exchange interaction coupling present in the model. The accurate results obtained by the EFT method were compared with those found by the mean-field approximation (MFA) method. The symmetry of the MFA diagrams was broken in the EFT diagrams. The critical temperature behavior was found to depend on the type of super-exchange ferromagnetism.

Competition between Anion-Deficient Oxide and Oxyhydride Phases during the Topochemical Reduction of LaSrCoRuO6.

Binary metal hydrides can act as low-temperature reducing agents for complex oxides in the solid state, facilitating the synthesis of anion-deficient oxide or oxyhydride phases. The reaction of LaSrCoRuO6, with CaH2 in a sealed tube yields the face-centered cubic phase LaSrCoRuO3.2H1.9. The reaction with LiH under similar conditions converts LaSrCoRuO6 to a mixture of tetragonal LaSrCoRuO4.8H1.2 and cubic LaSrCoRuO3.3H2.13. The formation of the LaSrCoRuOxHy oxyhydride phases proceeds directly from the parent oxide, with no evidence for anion-deficient LaSrCoRuO6-x intermediates, in contrast with many other topochemically synthesized transition-metal oxyhydrides. However, the reaction between LaSrCoRuO6 and LiH under flowing argon yields a mixture of LaSrCoRuO5 and the infinite layer phase LaSrCoRuO4. The change to all-oxide products when reactions are performed under flowing argon is attributed to the lower hydrogen partial pressure under these conditions. The implications for the reaction mechanism of these topochemical transformations is discussed along with the role of the hydrogen partial pressure in oxyhydride synthesis. Magnetization measurements indicate the LaSrCoRuOxHy phases exhibit local moments on Co and Ru centers, which are coupled antiferromagnetically. In contrast, LaSrCoRuO4 exhibits ferromagnetic behavior with a Curie temperature above 350 K, which can be rationalized on the basis of superexchange coupling between the Co1+ and Ru2+ centers.

Superexchange Mechanism in Coupled Triangulenes Forming Spin-1 Chains.

We show that the origin of the antiferromagnetic coupling in spin-1 triangulene chains, which were recently synthesized and measured by Mishra et al. ( Nature 2021, 598, 287-292), originates from a superexchange mechanism. This process, mediated by intertriangulene states, opens the possibility to control parameters in the effective bilinear-biquadratic spin model. We start from the derivation of an effective tight-binding model for triangulene chains using a combination of tight-binding and Hartree-Fock methods fitted to hybrid density functional theory results. Next, correlation effects are investigated within the configuration interaction method. Our low-energy many-body spectrum for NTr = 2 and NTr = 4 triangulene chains agree well with the bilinear-biquadratic spin-1 chain antiferromagnetic model when indirect coupling processes and superexchange coupling between triangulene spins are taken into account.

Preface

Preface This issue of the Journal of Physics, Conference Series, reports the main contributions at the 25th International Conference on the Jahn-Teller Effect held online between 14th and 18th May, 2023. The tradition of biannual symposia on the Jahn-Teller effect, beginning from the first one in Bad Honnef in 1976, was interrupted by the COVID pandemic in 2020. Seeing the participants’ health concerns, the International Steering Committee decided to have the 25th Jahn-Teller conference virtually on Zoom. Hosted by York University in Toronto, Canada, its Department of Chemistry made all the corresponding arrangements. The meeting addressed diverse conceptual, spectroscopic, and structural consequences of the vibronic coupling in polyatomic molecules, nanocrystals, impurity centers in solids, liquids, amorphous solids, and crystals. Exemplified by the Jahn-Teller and pseudo-Jahn-Teller effects, the coupling between electronic states and symmetry-breaking modes influences a variety of molecular and solid-state properties, including spectroscopy, reactivity, photochemistry, local and extended crystal structure, ferroelectricity and multiferroicity, charge and energy transport, superconductivity, molecular magnetism, qubits structure in quantum computers, and other applied fields.Eighty nine participants from fifty research institutes of seventeen countries virtually attended the meeting. Topics raised in thirty nine oral seminars and nineteen poster presentations led to vivid discussions. The conference provided opportunities to less experienced scientists for discussing the most exciting issues with the authorities that shape the current status of the theory of vibronic interactions and its experimental manifestations. All oral presentations were live-recorded and kept available on the conference page: https://jahnteller2023-yorku.ca/index.html.The sixteen papers in this issue fall into four major categories:I. General theory. In a semi-review, Isaac Bersuker explores a novel theoretical concept of the pseudo-Jahn-Teller nature of the energy barriers in chemical transformations, opening uncharted catalytic actions. Ketan Sharma et al. describe the computational perspectives of the two complementary software programs designed to evaluate spin-vibronic wave functions. Maley and Mawhinney developed a computationally robust density functional theory approach to assess the impact of Hartree-Fock exchange on critical parameters of the pseudo-Jahn-Teller effect in molecules with heavy-group carbon analogs.II. Vibronic coupling in polyatomic molecules. In this collection of articles, the Jahn-Teller- and pseudo-Jahn-Teller-induced symmetry breakings in particular molecules are investigated: population transfer from high- to low-symmetry electronic states in benzene radical cation by Hannibal et al., potential barrier for proton transfer in a series of small systems with inversion symmetry by Gorinchoy et al., group-theoretical approach to geometry optimization by finding symmetry descend path for large molecules by Breza, and computation of equilibrium geometry and dipole moment in fullerene cation C70 + by Nemes.III. Impurity systems. In this section, investigation of the Jahn-Teller effect, including experimental evaluation of vibronic constants and Jahn-Teller stabilization energy, using the temperature dependence of ultrasonic attenuation is reported in two papers of the Averkiev-Gudkov team. There is also a quite unusual study of coupling between electronic states and excited long-wave acoustic phonons as manifested by the zero-phonon line in optical absorption of the Dy atom in liquid 4He, which is presented by Hyzhnyakov et al.IV. Vibronic coupling in condensed-matter physics. In this section, the first four papers discuss the role of the Jahn-Teller symmetry breaking in magnetic exchange and super-exchange coupling. The last two papers are pretty unusual in the Jahn-Teller community. Archilla et al. discuss the role of vibronic coupling in forming the so-called crowdions and the related phenomenon of hyperconductivity in layered silicates bombarded with alpha particles. Hyzhnyakov considers the zero-phonon type of quantum diffusion in the solid and liquid phases enhanced by vibronic coupling to long-wave acoustic phonons.In the present issue, the scientific community interested in the Jahn-Teller effect and other manifestations of symmetry-breaking effects will find a reference source of essential facts and important information about the current status of this diverse field, which will inspire future studies. We want to thank the members of the International Steering Committee on the Jahn-Teller Effect for their initiative and support, the conference secretary Dr. Ekadashi Pradhan for the perfect administration of the conference website, and the York University, specifically, the Department of Chemistry, the Faculty of Science, and the Office of the Vice-President Research and Innovation, for the hospitality and financial supports of the 25th International Conference on the Jahn-Teller Effect.Isaac B. Bersuker, The University of Texas at Austin, Austin, USAVictor Polinger, University of Washington, Seattle, USATao Zeng, York University, Toronto, CanadaList of Committees is available in this pdf.

Effects of Ni2+ modified La0.67Ca0.33MnO3 ceramics on their temperature coefficient of resistivity and magnetoresistance properties

Element-modified La0.67Ca0.33MnO3 (LCMO) ceramics have been a major research subject in the past decades due to their various electromagnetic properties and potential applications in infrared detection and magnetic storage devices. However, its electromagnetic transport mechanism has not been fully elucidated and its properties need to be further optimized for practical applications. Here, we report the effect of Ni2+ doping on the structural, magnetic, the temperature coefficient of resistivity (TCR) and magnetoresistance (MR) properties of La0.67Ca0.33Mn1-xNixO3 (LCMNO) ceramics. All samples were synthesized by the sol-gel method and were in pure phase. XRD refinement results show a decrease in lattice constants and cell volume of LCMNO ceramics with increasing Ni2+ content. The XPS study confirms the reduction of the Mn3+/Mn4+ ratio and indicates that oxygen vacancies occur in LCMNO ceramics due to the Ni2+ doping. Curie-Weiss fitting results suggest ferromagnetic superexchange coupling between Ni2+ and Mn3+(4+) ions. The electrical transport properties of LCMNO ceramics were further investigated using the spin polaron hopping model in the high temperature range and the various competing scattering mechanisms in the low temperature range. In addition, double resistivity peak behavior is observed at x = 0.04 and 0.05. Furthermore, the TCR of the LCMNO ceramics increased to 45.4 %·K−1 (x = 0.01), while the MR increased to 67.9 % (x = 0.03), respectively. Our studies contribute to a better understanding of the electromagnetic properties of LCMNO ceramics.

Exchange Couplings and Magneto‐Structural Correlations of Trinuclear MII‐UIV‐MII (MII=Co, Ni, Cu) Complexes

AbstractThe magnetic properties of the trinuclear Schiff base complexes M2UL7 (MII=Co, Ni, Cu; L7=N,N’‐bis(3‐hydroxysalicylidene)‐2,2‐dimethyl‐1,3‐propanediamine), exhibiting the [M(μ‐O)2]2U core structure (3d‐5 f‐3d subsystem), have been investigated theoretically using scalar relativistic ZORA/DFT computations combined with the broken symmetry (BS) approach. The calculated coupling constants JMU between the adjacent M1−U and M2−U agree with the observed ferromagnetic (Ferro) character observed in the case of the Cu2UL7 complex, the antiferromagnetic (AF) character of the Ni2UL7 one is consistent with the experimentally observed AF behaviour for Co2UL7. The structural parameters, in particular the M−U distances and the M−Ob−U angles, as well as the electronic factors driving the superexchange couplings are discussed. The bond orders and the magnetic molecular orbital analyses reveal that the U(5 f) covalent contribution to the bonding within the M−O−U coordination is more important in the Co2UL7 and Ni2UL7 complexes than in the Cu2UL7 congener, thus favouring AF coupling between the transition metal and the uranium magnetic centers, in the first complexes. The analyses are supported by the study of the mixed ZnMUL7 and M2ThL7 systems, where the CoII (3d7) and NiII (3d8) paramagnetic ions are replaced by the diamagnetic ZnII(3d10) one, whereas in the second complex, the UIV(5f2) paramagnetic center is replaced by the diamagnetic ThIV(5f0) one. The Natural Populations Analyses confirm the crucial role of spin delocalization that is at work in favour of the AF vs. Ferro magnetic character of the M−U−M (M=Ni, Co) and Cu−U−Cu coordination, respectively.

Water-Mediated Charge Transfer and Electron Localization in a Co3Fe2 Cyanide-Bridged Trigonal Bipyramidal Complex.

The effects of temperature and chemical environment on a pentanuclear cyanide-bridged, trigonal bipyramidal molecular paramagnet have been investigated. Using element- and oxidation state-specific near-ambient pressure X-ray photoemission spectroscopy (NAP-XPS) to probe charge transfer and second order, nonlinear vibrational spectroscopy, which is sensitive to symmetry changes based on charge (de)localization coupled with DFT, a detailed picture of environmental effects on charge-transfer-induced spin transitions is presented. The molecular cluster, Co3Fe2(tmphen)6(μ-CN)6(t-CN)6, abbrev. Co3Fe2, shows changes in electronic behavior depending on the chemical environment. NAP-XPS shows that temperature changes induce a metal-to-metal charge transfer (MMCT) in Co3Fe2 between a Co and Fe center, while cycling between ultrahigh vacuum and 2 mbar of water at constant temperature causes oxidation state changes not fully captured by the MMCT picture. Sum frequency generation vibrational spectroscopy (SFG-VS) probes the role of the cyanide ligand, which controls the electron (de)localization via the superexchange coupling. Spectral shifts and intensity changes indicate a change from a charge delocalized, Robin-Day class II/III high spin state to a charge-localized, class I low spin state consistent with DFT. In the presence of a H-bonding solvent, the complex adopts a localized electronic structure, while removal of the solvent delocalizes the charges and drives an MMCT. This change in Robin-Day classification of the complex as a function of chemical environment results in reversible switching of the dipole moment, analogous to molecular multiferroics. These results illustrate the important role of the chemical environment and solvation on underlying charge and spin transitions in this and related complexes.

Dimeric Giant Molecule Acceptors Featuring N-type Linker: Enhancing Intramolecular Coupling for High-Performance Polymer Solar Cells.

Giant molecular acceptors (GMAs) are typically designed through the conjugated linking of individual small molecule acceptors (SMAs). This design imparts an extended molecular size, elevating the glass transition temperature (Tg) relative to their SMA counterparts. Consequently, it effectively suppresses the thermodynamic relaxation of the acceptor component when blended with polymer donors to construct stable polymer solar cells (PSCs). Despite their merits, the optimization of their chemical structure for further enhancing of device performance remains challenge. Different from previous reports utilizing p-type linkers, here, we explore an n-type linker, specifically the benzothiadiazole unit, to dimerize the SMA units via a click-like Knoevenagel condensation, affording BT-DL. In comparison with B-DL with a benzene linkage, BT-DL exhibits significantly stronger intramolecular super-exchange coupling, a desirable property for the acceptor component. Furthermore, BT-DL demonstrates a higher film absorption coefficient, redshifted absorption, larger crystalline coherence, and higher electron mobility. These inherent advantages of BT-DL translate into a higher power conversion efficiency of 18.49 % in PSCs, a substantial improvement over the 9.17 % efficiency observed in corresponding devices with B-DL as the acceptor. Notably, the BT-DL based device exhibits exceptional stability, retaining over 90 % of its initial efficiency even after enduring 1000 hours of thermal stress at 90 °C. This work provides a cost-effective approach to the synthesis of n-type linker-dimerized GMAs, and highlight their potential advantage in enhancing intramolecular coupling for more efficient and durable photovoltaic technologies.

Robust Magnetoelectric Coupling in FeTiO3/Ga2O3 Non-van der Waals Heterostructures.

Magnetoelectric coupling represents a significant breakthrough for next-generation electronics, offering the ability to achieve nonvolatile magnetic control via electrical means. In this comprehensive investigation, leveraging first-principles calculations, we unveil a robust magnetoelectric coupling within multiferroic heterostructures (HSs) by ingeniously integrating a non-van der Waals (non-vdW) magnetic FeTiO3 monolayer with the ferroelectric (FE) Ga2O3. Diverging from conventional van der Waals (vdW) multiferroic HSs, the magnetic states of the FeTiO3 monolayer can be efficiently toggled between ferromagnetic (FM) and antiferromagnetic (AFM) configurations by reversing the polarization of the Ga2O3 monolayer. This intriguing phenomenon arises from polarization-dependent substantial interlayer electron transfers and the interplay between superexchange and direct-exchange magnetic couplings of the iron atoms. The carrier-mediated interfacial interactions induce crucial shifts in Fermi level positions, decisively imparting distinct electronic characteristics near the Fermi level of composite systems. These novel findings offer exciting prospects for the future of magnetoelectric technology.

Unraveling Rigidified Superexchange Couplings in Organic Donor–Acceptor Polymers for Boosting the Photocatalytic Reduction of Nitrate

Unraveling Rigidified Superexchange Couplings in Organic Donor–Acceptor Polymers for Boosting the Photocatalytic Reduction of Nitrate

Superexchange coupling of donor qubits in silicon

Superexchange coupling of donor qubits in silicon

Influence of the oxygen vacancy and Ag-doping on the magnetic and electronic properties of the SrFeO3 material

SrFeO3 is a perovskite-type oxide applied in the development of magnetic material. This article discusses the influence of vacancy and transition metal doping on this functional material electronic properties. The quantum DFT/HSE06 approach simulated the magnetic property and super-exchange coupling on defective- and non-defective SrFeO3 structures. The results depict the structural deformation after defects and the origin of Jahn-Teller distortion. The electronic data suggests a p-type semiconductivity for all materials investigated, allied to a reasonable charge carrier stability, indicating the electrocatalytic activity of the O-vacancy and Ag-doped SrFeO3. In particular, the insertion of the defects affects the magnetic orderings energy, enabling a magnetic states engineering.

CoX2Y4: a family of two-dimensional magnets with versatile magnetic order.

Two-dimensional (2D) magnetic materials offer a promising platform for nanoscale spintronics and for exploration of novel physical phenomena. Here, we predict a diverse range of magnetic orders in cobalt-based 2D single septuple layers CoX2Y4, namely, CoBi2Te4, CoBi2Se2Te2, CoBi2Se4, and CoSb2Te4. Notably, CoBi2Te4 presents intrinsic non-collinear antiferromagnetism (AFM), while the others display collinear AFM. The emergence of AFM in all CoX2Y4 materials is attributed to the antiferromagnetic 90° Co-Te(Se)-Co superexchange coupling. The origin of non-collinear/collinear orders lies in competing Heisenberg exchange interactions within the Co triangular lattice. A pivotal factor governing the non-collinear order of CoBi2Te4 is the vanishingly small ratio of exchange coupling between next-nearest neighbour Co and the nearest neighbour Co (J2/J1 ∼ 0.01). Furthermore, our investigation into strain effects on CoX2Y4 lattices demonstrates the tunability of the magnetic state of CoSb2Te4 from collinear to non-collinear. Our prediction of the unique non-collinear AFM in 2D suggests the potential for observing extraordinary magnetic phenomena in 2D, including non-collinear scattering and magnetic domain walls.

Subphthalocyanine semiconducting cocrystals with efficient super-exchange coupling

The SubPc-12H-12F cocrystal was constructed with almost identical packings of SubPc-6F(β). This study proved that the super-exchange coupling can both improve the charge carrier mobility and expand the charge transport channels in cocrystals.

Exchange coupling effect at Cuprate-Manganite superlattices driven by dimensionality

The strongly correlated of multi-degrees of freedoms at transition metal oxide heterointerfaces greatly enriches its physical properties and expands the relevant application fields. It has been reported that dimensionality is an effective method to tune the properties of oxide heterostructure. SCO films display structural transformation from planar-type to chain-type with the change of thickness. In this text, the high quality of SCO/LCMO superlattices are deposited by pulsed laser deposition system. And the interfacial exchange coupling effect is effectively manipulated by controlling the dimensionality of SCO layer. Combined with XAS measurement, it is found that the charge transfer would occur at heterointerface. When the SCO layer is thin, the interfacial superexchange coupling supported by charge transfer generates a weak magnetic moment to pin the ferromagnetic LCMO layer. The charge transfer would decrease as the SCO layer is thicken. Meanwhile, the long-range antiferromagnetic order in thicken SCO layer can interacted with LCMO layer and resulted in the exchange bias effect. This experiment confirms the important role of dimensionality to tune properties in multifunctional oxide heterostructure.

Nonfullerene Acceptor Featuring Unique Self-Regulation Effect for Organic Solar Cells with 19 % Efficiency.

The blend nanomorphology of electron-donor (D) and -acceptor (A) materials is of vital importance to achieving highly efficient organic solar cells. Exogenous additives especially aromatic additives are always needed to further optimize the nanomorphology of blend films, which is hardly compatible with industrial manufacture. Herein, we proposed a unique approach to meticulously modulate the aggregation behavior of NFAs in both crystal and thin film nanomorphology via self-regulation effect. Nonfullerene acceptor Z9 was designed and synthesized by tethering phenyl groups on the inner side chains of the Y6 backbone. Compared with Y6, the tethered phenyl groups participated in the molecular aggregation via the π-π stacking of phenyl-phenyl and phenyl-2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (IC-2F) groups, which induced 3D charge transport with phenyl-mediated super-exchange electron coupling. Moreover, ordered molecular packing with suitable phase separation was observed in Z9-based blend films. High power conversion efficiencies (PCEs) of 19.0 % (certified PCE of 18.6 %) for Z9-based devices were achieved without additives, indicating the great potential of the self-regulation strategy in NFA design.

Magnetic and spectroscopic properties of chloride-bridged guanidinate dilanthanide complexes

The guanidinate ligand scaffold offers a unique combination of hard anionic charges, steric tunability, and electronic modulation, rendering it an ideal candidate for the molecular design of lanthanide complexes. Here, we present two dilanthanide chloride complexes [{(Me3Si)2NC(NiPr)2}2Ln(μ–Cl)]2 (Ln = Gd (1), and Tb (2)) where each metal ion is ligated to two guanidinate anions and bridged to the other metal ion by two chloride ligands. The isostructural complexes 1 and 2 were synthesized through salt metathesis reactions and characterized through single–crystal X–ray diffraction analysis, IR and UV–Vis spectroscopy, and SQUID magnetometry. The half-filled f-electron valence shell of GdIII ion allows an accurate study of magnetic coupling through fitting of the dc magnetic susceptibility data to a spin–only Hamiltonian, affording values of J = -0.0242 cm−1 and g = 2.0192. The operative superexchange coupling mechanism was confirmed through broken–symmetry density functional theory calculations, which additionally provide insight into the spectral analysis of 1.

Symmetry-driven half-integer conductance quantization in Cobalt–fulvalene sandwich nanowire

Precise manipulation and monitoring spin transport in one-dimensional (1D) systems is a long-sought goal in the field of nano-spintronics. Based on first-principles calculations, we report the observation of half-integer conductance quantization in the Cobalt-fulvalene sandwich nanowire. Compared with a pure monatomic Cobalt wire, the introduction of fulvalene molecules leads to three important features: Firstly, the strong coupling between the fulvalene and the Cobalt prevents the contamination of the ambient air, ensuring both chemical and physical stabilities; Secondly, the fulvalene symmetry-selectively filters out most of the d-type orbitals of the Cobalt while leaving a single d-type orbital to form an open spin channel around the Fermi level, which offers a mechanism to achieve the observed half-integer conductance; Thirdly, it maintains a superexchange coupling between adjacent Co atoms to achieve a high Curie temperature. Spin transport calculations show that this half-metallic nanowire can serve as a perfect spin filter or a spin valve device, thus revealing the potential of Cobalt-fulvalene sandwich nanowire as a promising building block of high-performance spintronics technology.

Competition between magnetic interactions and structural instabilities leading to itinerant frustration in the triangular lattice antiferromagnet LiCrSe2

LiCrSe2 constitutes a recent valuable addition to the ensemble of two-dimensional triangular lattice antiferromagnets. In this work, we present a comprehensive study of the low temperature nuclear and magnetic structure established in this material. Being subject to a strong magnetoelastic coupling, LiCrSe2 was found to undergo a first order structural transition from a trigonal crystal system (Pbar{3}m1) to a monoclinic one (C2/m) at Ts = 30 K. Such restructuring of the lattice is accompanied by a magnetic transition at TN = 30 K. Refinement of the magnetic structure with neutron diffraction data and complementary muon spin rotation analysis reveal the presence of a complex incommensurate magnetic structure with a up-up-down-down arrangement of the chromium moments with ferromagnetic double chains coupled antiferromagnetically. The spin axial vector is also modulated both in direction and modulus, resulting in a spin density wave-like order with periodic suppression of the chromium moment along the chains. This behavior is believed to appear as a result of strong competition between direct exchange antiferromagnetic and superexchange ferromagnetic couplings established between both nearest neighbor and next nearest neighbor Cr3+ ions. We finally conjecture that the resulting magnetic order is stabilized via subtle vacancy/charge order within the lithium layers, potentially causing a mix of two co-existing magnetic phases within the sample.