Super-superexchange Interaction Research Articles

Enhanced Intralayer Ferromagnetism in CrI3 by Interfacial Super-Superexchange Interaction

Enhanced Intralayer Ferromagnetism in CrI₃ by Interfacial Super-Superexchange Interaction

Metamagnetic transitions induced by doping with non-magnetic 4+ ions in ludwigites Co5A(O2BO3)2 (A=Zr and Hf)

The novel A-doped Co3O2BO3 (A4+=Zr, Hf) ludwigites have been synthetized by the first time and investigated by X-ray diffraction, magnetization and specific heat experiments. The non-magnetic ions place mainly at sites 4 of the structure. This doping strengthens the magnetic interactions rising the magnetic transition temperatures from 42 K, for the undoped compound, to 71 K and 72 K for Zr and Hf, respectively. These magnetic transition temperature are ~ 10 K below that shown by the Sn4+-doped Co3O2BO3. As expected, all these isostructural and isovalent compounds exhibit the same magnetic features. However, low temperature specific heat experiments and magnetization curves with typical metamagnetic behavior revealed that doping with the non-magnetic open-shell ions d0 Zr and Hf preserves the two-dimensional antiferromagnetic character of the parent ludwigite Co3O2BO3 while the closed-shell d10 Sn leads to a three-dimensional magnetism. The experimental results are compatible with an antiferromagnetic structure with a ferromagnetic component for these two compounds. The difference in TN and dimensionality of these compounds are related to super-superexchange (SSE) interaction between two Co2+ mediated by the non-magnetic ion A4+. The non-magnetic closed-shell d10 ion turned out to be more effective in mediating SSE interactions between 1−2−3 magnetic layers.

Synthesis, crystal structure, Mössbauer spectroscopy, optical and magnetic properties of Cs2M2Fe(PO4)3 (M = Mn, Co, Ni, Cu) ordered pollucite structure

Four isomorphous iron phosphates Cs2M2Fe(PO4)3 (M = Mn, Co, Ni, Cu) have been synthesized as powder by conventional solid state technic and characterized by X-ray diffraction, magnetic susceptibility, diffuse reflectance and Mössbauer spectroscopies. All these compounds crystallize in the space group I4132 of the cubic system with similar cell parameters: a = 13.8268(1) Å, 13.7624(1) Å, 13.5917(1) Å or 13.5834(1) Å for M = Mn, Co, Ni or Cu, respectively and eight formula units per cell. Their structure closely related to that of pollucite, is built up from [M2/3,Fe1/3]O4 tetrahedra connected to each other through the common corners with PO4 tetrahedra. The resulting anionic three-dimensional framework leads to the formation along [1 1 1] direction, of channels where the large cesium ions occupy two independent crystallographic sites. A Mössbauer study at room temperature, confirmed the +3 oxidation state of iron and its tetrahedral coordination. Diffuse reflectance spectroscopy also confirmed the occurrence of isolated Fe3+ ions: low energy gap due to oxygen to iron (III) inter-electronic transition and absence of d-d transition linked to iron; the colorimetric properties of the compounds were shown to be mainly governed by the visible d-d transitions linked to the M2+ cation in tetrahedral coordination. Magnetic susceptibility measurements reveal that the title compounds are weakly magnetically ordered at very low temperature due to super-superexchange magnetic interaction. The thermal evolution of χm follows in a wide temperature range, a Curie-Weiss law χ = C/(T-θ) with θ = − 59, −36, −50 and −39 K for Mn, Co, Ni and Cu phases, respectively.

Ferromagnetic nature in low-dimensional S = 1 antiferromagnetic Li2Ni(WO4)2 nanoparticles

We report the magnetic behaviour of ball-milled nanoparticles of antiferromagnetic spin-1 Li2Ni(WO4)2 system by magnetic susceptibility and neutron diffraction measurements. Bulk sample shows indicators of two successive three dimensional (3D) antiferromagnetic (AF) ordering at TN1∼18K and TN2∼13K in χ(T). The magnetic susceptibility and neutron diffraction measurements indicate that no long-range magnetic order is detected when bulk sample is reduced to nano size particles, despite of the identical crystal structures. The super-super exchange interaction is proposed being disrupted as a result of cell volume expansion in nanoparticles. The Zero-Field-Cooled (ZFC) and Field-Cooled (FC) curve bifurcation and M(H) curve of nanoparticle reveal that the weak ferromagnetic behavior exists at low temperature because of spin disorder on the surface of nanoparticle.

Structural evolution of MnTi0·8Ru0·2O3

Here, we present the structural studies on MnTi1-xRuxO3(x = 0, 0.2) compounds. The role of Ti ions in the magnetism of MnTiO3 was unclear so here this issue has been tried to address. The magnetic susceptibility (χ) data shows that the 3-dimensional magnetic character has been improved in the doped MnTiO3. The x = 0 compound goes paramagnetic to antiferromagnetic phase at a temperature ∼64 K followed by a broad peak at a temperature ∼100 K. But in x = 0.2 compound, the antiferromagnetic transition temperature has been shifted towards the lower temperature to ∼47.5 K with a broad peak at temperature ∼79 K. On the doping of Ru at Ti site a sharp anomaly in the temperature dependent magnetic susceptibility (χ) measurement is observed ∼47.5 K in the case of x = 0.2 compound. This sharp anomaly is attributed to the improved 3D character of magnetism which arises because of the direct exchange interaction between Mn-Ti/Ru ions in addition to the inter-layer super superexchange interaction between Mn-Mn ions via two intervening oxygen ions. It is interesting to note that even though the TN and T2D are at low temperatures compared to the x = 0 compound, the onset temperature of these two temperatures occurs at much higher temperature than as observed in x = 0 compound.

Origin of the long-wavelength magnetic modulation inCa3Co2O6

The origin of the long-wavelength incommensurate magnetic structure of Ca3Co2O6 is discussed considering possible inter-chains super-superexchange paths. The experimental value of the propagation vector k=(0,0,$\Delta$) with $\Delta$ $>$ 1 can be reproduced only if one considers the next nearest super-superexchange interaction. A spin-dimer analysis using the Extended-Huckel Tight-Binding method confirms that, despite longer interatomic Co-Co distances, the latter interaction is indeed much stronger. The stability of the observed structure with respect to certain commensurate states is discussed.

Determination of the Spin−Lattice Relevant for the Quaternary Magnetic Oxide Bi4Cu3V2O14 on the Basis of Tight-Binding and Density Functional Calculations

The quaternary magnetic oxide Bi4Cu3V2O14 consists of Cu4O8 triple chains made up of corner-sharing CuO4 square planes. To determine its spin-lattice, the spin exchange interactions of Bi4Cu3V2O14 were evaluated by performing a spin dimer analysis based on tight-binding calculations and a mapping analysis based on first principles density functional theory calculations. Both calculations show that the spin-lattice of Bi4Cu3V2O14 is not an antiferromagnetically coupled diamond chain, which results from an idealized view of the structure of the Cu4O8 triple chain and a neglect of super-superexchange interactions. The correct spin-lattice is an antiferromagnetic chain made up of antiferromagnetic linear trimers coupled through their midpoints via super-superexchange interaction, which predicts that Bi4Cu3V2O14 has an antiferromagnetic spin ground state and has no spin frustration, both in agreement with experiment.

Electronic structure of spin-12Heisenberg antiferromagnetic systems:Ba2Cu(PO4)2andSr2Cu(PO4)2

We have employed first principles calculations to study the electronic structure and magnetic properties of the low-dimensional phosphates, ${\mathrm{Ba}}_{2}\mathrm{Cu}{(\mathrm{P}{\mathrm{O}}_{4})}_{2}$ and ${\mathrm{Sr}}_{2}\mathrm{Cu}{(\mathrm{P}{\mathrm{O}}_{4})}_{2}$. Using the self-consistent tight-binding linearized muffin-tin orbital method and the $N\text{th}$ order muffin-tin orbital method, we have calculated the various intrachain as well as the interchain hopping parameters between the magnetic ions $({\mathrm{Cu}}^{2+})$ for both the compounds. We find that the nearest-neighbor intrachain hopping $(t)$ is the dominant interaction suggesting the compounds to be indeed one dimensional. Our analysis of the band dispersion, orbital projected band structures, and the hopping parameters confirms that the ${\mathrm{Cu}}^{2+}\text{\ensuremath{-}}{\mathrm{Cu}}^{2+}$ super-super exchange interaction takes place along the crystallographic $b$ direction mediated by O-P-O. We have also analyzed in detail the origin of short-range exchange interaction for these systems. Our ab initio estimate of the ratio of the exchange interaction of ${\mathrm{Sr}}_{2}\mathrm{Cu}{(\mathrm{P}{\mathrm{O}}_{4})}_{2}$ to that of ${\mathrm{Ba}}_{2}\mathrm{Cu}{(\mathrm{P}{\mathrm{O}}_{4})}_{2}$ compares excellently with available experimental results.

Structural and magnetic dimers in the spin-gapped systemCuTe2O5

We investigated the magnetic properties of the system CuTe2O5 by susceptibility and electron spin resonance measurements. The anisotropy of the effective g-factors and the ESR linewidth indicates that the anticipated structural dimer does not correspond to the singlet-forming magnetic dimer. Moreover, the spin susceptibility of CuTe2O5 can only be described by taking into account interdimer interactions of the same order of magnitude than the intradimer coupling. Analyzing the exchange couplings in the system we identify the strongest magnetic coupling between two Cu ions to be mediated by super-super exchange interaction via a bridging Te ligand, while the superexchange coupling between the Cu ions of the structural dimer only results in the second strongest coupling.

Spin dimer and classical spin analyses of the ordered magnetic structures of alkali iron pyrophosphates NaFeP(2)O(7) and LiFeP(2)O(7).

The magnetic oxides NaFeP(2)O(7) and LiFeP(2)O(7), made up of FeO(6) octahedra containing high-spin Fe(3+)(d(5)) ions, undergo a three-dimensional antiferromagnetic ordering at low temperatures. The strengths of various Fe-O...O-Fe super-superexchange interactions of NaFeP(2)O(7) and LiFeP(2)O(7) were estimated on the basis of spin dimer analysis to probe the nature of their ordered magnetic structures. It is found that the critical factor governing the strength of a Fe-O...O-Fe super-superexchange interaction is not the Fe...Fe distance but the O...O distance. Using the spin exchange parameters thus obtained, the total spin exchange interaction energies were calculated for various ordered spin arrangements of NaFeP(2)O(7) and LiFeP(2)O(7) on the basis of classical spin analysis to confirm that the observed magnetic structures are the magnetic ground states.

Flux growth of vanadyl pyrophosphate, (VO)(2)P(2)O(7), and spin dimer analysis of the spin exchange interactions of (VO)(2)P(2)O(7) and vanadyl hydrogen phosphate, VO(HPO(4)).0.5H(2)O.

Large transparent blue crystals of vanadyl pyrophosphate, (VO)(2)P(2)O(7), were grown from a phosphorus pentoxide flux, and the single-crystal X-ray structure of (VO)(2)P(2)O(7) was determined with high precision. On the basis of spin dimer analysis, we examined the spin exchange interactions of (VO)(2)P(2)O(7) and its precursor VO(HPO(4)).0.5H(2)O. Our analysis of (VO)(2)P(2)O(7) using two high-precision crystal structures shows unambiguously that the V3-V4 chain has a larger spin gap than does the V1-V2 chain and that the super-superexchange (V-O...O-V) interaction is stronger than the superexchange (V-O-V) interaction in the V3-V4 chain while the opposite is true in the V1-V2 chain. Our analysis of VO(HPO(4)).0.5H(2)O reveals that the superexchange interaction must dominate over the super-superexchange interaction, in disagreement with the conclusion from a powder neutron scattering study of VO(DPO(4)).0.5D(2)O.

Spin dimer analysis of the anisotropic spin exchange interactions in the distorted wolframite-type oxides CuWO4, CuMoO4-III, and Cu(Mo(0.25)W0.75)O4.

The distorted wolframite-type oxides CuWO4 and CuMoO4-III have a structure in which CuO4 zigzag chains, made up of cis-edge-sharing CuO6 octahedra, run along the c-direction and hence exhibit low-dimensional magnetic properties. We examined the magnetic structures of these compounds and their isostructural analogue Cu(Mo(0.25)W0.75)O4 on the basis of the spin-orbital interaction energies calculated for their spin dimers. Our study shows that these compounds consist of two-dimensional (2D) magnetic sheets defined by one superexchange (intrachain Cu-O-Cu) and three super-superexchange (interchain Cu-O.O-Cu) paths, the strongly interacting spin units of these 2D magnetic sheets are the two-leg antiferromagnetic (AFM) ladder chains running along the (a + c)-direction, and the spin arrangement between adjacent AFM ladder chains leads to spin frustration. The similarities and differences in the magnetic structures of CuWO4, CuMoO4-III, and Cu(Mo(0.25)W0.75)O4 were discussed by examining how adjacent AFM ladder chains are coupled via the superexchange paths in the 2D magnetic sheets and how adjacent 2D magnetic sheets are coupled via another superexchange paths along the c-direction. Our study reproduces the experimental finding that the magnetic unit cell is doubled along the a-axis in CuWO(4) and along the c-axis in CuMoO4-III and predicts that the magnetic unit cell should be doubled along the a- and b-axes in Cu(Mo(0.25)W0.75)O4. In the understanding of the strength of a super-superexchange interaction, the importance of the geometrical factors controlling the overlap between the tails of magnetic orbitals was pointed out.