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The $S=1/2$ spin ladder compound ${({\mathrm{C}}_{5}{\mathrm{H}}_{12}\mathrm{N})}_{2}{\mathrm{CuBr}}_{4}$ (BPCB) is studied by means of high-resolution inelastic neutron scattering. In agreement with previous studies we find a band of triplet excitations with a spin gap of $\ensuremath{\sim}0.8$ meV and a bandwidth of $\ensuremath{\sim}0.6$ meV. In addition, we observe a distinct splitting of the triplet band of $50(1)\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{eV}$ or $40(2)\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{eV}$ at the band minimum or maximum, respectively. By comparison to a strong-coupling expansion calculation of the triplet dispersion for a spin ladder with anisotropic exchange, weakly anisotropic leg interactions are identified as the dominant source of magnetic anisotropy in BPCB. Based on these results, we discuss the nature of magnetic exchange anisotropy in BPCB and in related transition-metal insulators.

The ability to tune the iron chalcogenides ${\mathrm{BaFe}}_{2}{Q}_{3}$ from Mott insulators to metals and then superconductors with applied pressure has renewed interest in low-dimensional iron chalcogenides and oxychalcogenides. We report here a combined experimental and theoretical study on the iron oxychalcogenides ${\mathrm{BaFe}}_{2}{Q}_{2}\mathrm{O}\phantom{\rule{4pt}{0ex}}(Q=\mathrm{S},\text{Se})$ and show that their magnetic behavior results from nearest-neighbor magnetic exchange interactions via oxide and selenide anions of similar strength, with properties consistent with more localized electronic structures than those of ${\mathrm{BaFe}}_{2}{Q}_{3}$ systems.

Magnetoelectric properties displayed in multiferroics are generally associated with complex magnetic orders. This complexity often results in a delicate balance between several geometrically frustrated magnetic exchange interactions. Applying pressure will thus unbalance this equilibrium and strongly affect the multiferroic properties. In this paper, we study the effect of pressure on magnetism in three particular members of the ${R\mathrm{Mn}}_{2}{\mathrm{O}}_{5}$ multiferroics ($R$ = Gd, Sm, and Nd) with interesting magnetic orders. Using powder neutron diffraction, we studied the evolution of their magnetic structures as a function of pressure. Despite their singular properties with respect to the other compositions, we demonstrate that these three members present the same pressure-induced commensurate phase (PCM) with the propagation wave vector [q${}_{\mathrm{PCM}}=(\frac{1}{2},0,\frac{1}{2})]$. Furthermore, the stabilization of the PCM phase under pressure can be explained by a similar mechanism. We ultimately conclude that the different origin of the CM and PCM phases of these three compounds are related to the competition of only two superexchange interactions, namely ${J}_{1}$ and ${J}_{6}$.

So-called ``exchange-spring magnets'' are important for synthesizing rare-earth-free permanent magnets with a high energy product, but the latter is limited by the critical thickness of the soft magnetic phase, above which exchange coupling deteriorates. Thus understanding the physics of exchange coupling is necessary to overcome that technical difficulty. This study uses experiment and theory to build up a model system that allows systematic analysis of exchange interactions in a MnGa/FeCo bilayer exchange system. The significant roles of epitaxial growth and hard/soft interfacial properties offer engineering solutions for multilayered exchange-spring magnets in $e.g.$ electric motors.

Ab initio calculations of the magnetic exchange in polynuclear lanthanide complexes are very challenging and often not feasible, due to large active spaces, the large number of required states or the necessity to include dynamical correlation into the calculations. We present an approach which allows for the computationally efficient calculation of exchange splittings in polynuclear lanthanide complexes including dynamical correlation. This is achieved by extending the local-density-fitted configuration-averaged Hartree-Fock (LDF-CAHF) method to systems with more than one group of open-shell orbitals (e.g. at different metal atoms) and combining it with linear-scaling many-state pair-natural-orbital complete active space perturbation theory of second order (PNO-CASPT2). In order to assess the performance of the method, we apply it to the asymmetric dinuclear complex [hqH2][Yb2(hq)4(NO3)3]·MeOH (hqH = 8-hydroxyquinoline).

Magnetic refrigeration at room-temperature is a technology that could potentially be more environmentally friendly, efficient, and affordable than traditional refrigeration. The search for suitable materials for magnetocaloric refrigeration led to the study of double-perovskites ${\mathrm{La}}_{2}{\mathrm{MnNiO}}_{6},{\mathrm{La}}_{2}{\mathrm{MnCoO}}_{6}$, and ${\mathrm{La}}_{2}{\mathrm{MnFeO}}_{6}$. While ${\mathrm{La}}_{2}{\mathrm{MnNiO}}_{6}$ and ${\mathrm{La}}_{2}{\mathrm{MnCoO}}_{6}$ are ferromagnets with near room-temperature ${T}_{C}\mathrm{s}$, a previous theoretical study of double-perovskite ${\mathrm{La}}_{2}{\mathrm{MnFeO}}_{6}$ revealed that this material is a ferrimagnet due to strong electronic interactions in $\mathrm{Fe}\text{\ensuremath{-}}d$ orbitals. Here we investigate the double-perovskites ${\mathrm{La}}_{2}{\mathrm{MnRuO}}_{6}$ and $\mathrm{La}A{\mathrm{MnFeO}}_{6}\phantom{\rule{4pt}{0ex}}(A$ = Ba, Ca, and Sr) with density functional theory (DFT) as materials that can counteract the effects the strong repulsion present in the in $\mathrm{Fe}\text{\ensuremath{-}}d$ shells of ${\mathrm{La}}_{2}{\mathrm{MnFeO}}_{6}$ and lead to a ferromagnetic state. Our study reveals that while ${\mathrm{La}}_{2}{\mathrm{MnRuO}}_{6}$ is also a ferrimagnet, but with a higher net magnetic moment per formula than ${\mathrm{La}}_{2}{\mathrm{MnFeO}}_{6}$, doubly ordered $\mathrm{La}A{\mathrm{MnFeO}}_{6}$ are ferromagnets. By mapping the total energy of the $\mathrm{La}A{\mathrm{MnFeO}}_{6}$ compounds obtained from DFT calculations to the Ising model, we also calculate their magnetic exchange couplings. This allows us to estimate the trend in ${T}_{C}$ of the three doped ${\mathrm{La}}_{2}{\mathrm{MnFeO}}_{6}$ materials with classical Monte Carlo calculations and predict that doubly ordered ${\mathrm{LaBaMnFeO}}_{6}$ and ${\mathrm{LaSrMnFeO}}_{6}$ could be suitable materials for room-temperature magnetic refrigeration.

We revisited the anisotropy of the heavy-fermion material CeCo$_2$Ga$_8$ by measuring the electrical resistivity and magnetic susceptibility along all the principal $\mathbf{a}$-, $\mathbf{b}$- and $\mathbf{c}$-axes. Resistivity along $\mathbf{c}$-axis ($\rho_c$) shows clear Kondo coherence below about 17 K, while both $\rho_{a}$ and $\rho_{b}$ remain incoherent down to 2 K. The magnetic anisotropy is well understood within the theoretical frame of crystalline electric field effect in combination with magnetic exchange interactions. We found the anisotropy ratio of these magnetic exchange interactions, $|J_{ex}^c/J_{ex}^{a,b}|$, reaches a large value of 4-5. We, therefore, firmly demonstrate that CeCo$_2$Ga$_8$ is a quasi-one-dimensional heavy-fermion compound both electrically and magnetically, and thus provide a realistic example of \textit{Kondo chain}., Comment: 5 pages, 4 figures, 1 table

A strategy to continuously tune the exchange constant J and the critical temperature Tc in the 1D coordination polymers [Co(NCS)x(NCSe)2−x(pyridine)2]n is reported. For such mixed crystals, prepared by annealing and from solution, an increase of J and Tc with increasing selenocyanate content is observed.

In the work presented the magnetic properties of the high pressure ilmenite phase Mn_2FeSbO_6 are investigated in detail. It is shown that Mn_2FeSbO_6 ilmenite is ferrimagnetic (T_N approximate to 270 K) and exhibits a near-zero coercive field H_C. Furthermore, the Mn^2+-Mn^2+, Fe^3+-Fe^3+ and Mn^2+-Fe^3+ magnetic exchange interactions exhibit gradual and continuous variations with temperature and magnetic field. The ferrimagnetic moment is unsaturated even at 120 kOe below the theoretical value of 5 mu_B per f.u.

In this article, we apply the two-mode vibronic model to the study of the dimeric molecular mixed-valence cell for quantum cellular automata. As such, we consider a multielectron mixed valence binuclear d2−d1–type cluster, in which the double exchange, as well as the Heisenberg-Dirac-Van Vleck exchange interactions are operative, and also the local (“breathing”) and intercenter vibrational modes are taken into account. The calculations of spin-vibronic energy spectra and the “cell-cell”-response function are carried out using quantum-mechanical two-mode vibronic approach based on the numerical solution of the dynamic vibronic problem. The obtained results demonstrate a possibility of combining the function of molecular QCA with that of spin switching in one electronic device and are expected to be useful from the point of view of the rational design of such multifunctional molecular electronic devices.

Developing Fe-based amorphous alloys with high saturation flux density (Bs) have been challenging topics for a long time. Metalloid elements like B, Si, C, and P are key elements for Fe-based amorphous alloys, but the addition of multiple metalloids would significantly complicate the effects of each metalloid on saturation flux density. Herein, Fe83-85(B, C, Si)14–16P1 amorphous alloys with high Bs of 1.61–1.71 T and low coercivity (Hc) of 2.2–8.7 A/m were successfully developed. Fe and metalloids were found to have strong interrelated effects on the total magnetic moment and the strength of magnetic exchange interaction, which largely determine the Bs of Fe-based amorphous alloys. It was revealed that for Fe-rich amorphous alloys, the effects of metalloids on Bs are much more significant than that of Fe, and the effects are largely dependent on Fe content. The complementary effects of metalloids on Bs and the Fe-sensitive behavior of these effects, as well as the underlying mechanisms, have been revealed. These results pave a new way to understand the composition-property relationship, and would help design and develop high-performance Fe-based soft magnetic amorphous alloys.

The nontrivial magnetoopitcal effects are predicted to arise at the visible frequency range for monolayer transition metal dichalcogenides upon the application of magnetic exchange interactions. However, their magnetoopitcal rotation angles at the terahertz frequency range are always low, which hinders their practical applications in the terahertz magnetoopitcal devices. In this letter, we theoretically demonstrate that the magnetoopitcal effects of monolayer transition metal dichalcogenides at the terahertz frequency range can be enhanced and controlled via introducing the Rashba spin orbit coupling, whose rotation angles are comparable with those of conventional bulky magnetic materials. Such an effect originates from the change of spin-up and spin-down bands in the band structures of monolayer transition metal dichalcogenides when the Rashba spin orbit coupling and magnetic exchange interaction coexist, which enables the spin-flip intraband optical transitions and thus generates the terahertz magnetoopitcal responses. Our results open up possibilities for the use of Rashba spin orbit coupling to generate as well as control the magnetoopitcal effects in two-dimensional layered materials.

Ce3-xRhGa10+3x (x = 0.36) is a new member of the linear intergrowth structure series built up from segments of the BaAl4, AlB2 and CaF2 structure types. The compound crystallizes with a disordered variant of the Pr3NiGa10 type structure. Unlike the prototype, Ce3-xRhGa10+3x exhibits notable deficiency in rare-earth content, accompanied with significant excess of Ga atoms, corresponding to additional Ga environment of one of the Ce atoms. The novel compound is a Curie-Weiss paramagnet and orders antiferromagnetically at low temperatures. The electrical transport in Ce3-xRhGa10+3x has a metallic character, and bears contributions due to crystalline electric field, Kondo and magnetic exchange interactions.

The present study focuses on the fundamental physical principles underlying the exchange interactions between two metallic centers in magnetic insulators. Using the variational method in conjunction with the Heisenberg model, we demonstrate that the exchange symmetry is tightly related to the magnetism of the considered system and that the electrons’ distributions affect the corresponding exchange interactions.

Six new cyanide-bridged CrIII–MnIII one-dimensional (1D) complexes [MnIII(salen)CrIII(bpb)(CN)2]n (1), [MnIII(5-Clsalen)CrIII(bpb)(CN)2·0.5CH3OH·H2O]n (2), [MnIII(5-Brsalen)CrIII(bpb)(CN)2·0.5CH3OH·H2O]n (3), [MnIII(5-MeOsalen)CrIII(bpb)(CN)2·H2O]n (4), [MnIII(5-Clsalen)CrIII(bpClb)(CN)2·CH3CN]n (5) and [MnIII(5-Brsalen)CrIII(bpClb)(CN)2·2H2O]n (6) have been rationally designed, controlling synthesized and structurally characterized based on [MnIII(5-R1salen)]+ and [CrIII(4-R2bpb)(CN)2]− building blocks [5-R1salen2− = N,N′-ethylenebis(5-R1-salicylideneaminato)dianion, R1 = H for salen2−, Cl for 5-Clsalen2−, Br for 5-Brsalen2− and MeO for 5-MeOsalen2−; 4-R2bpb2− = 1,2-bis(pyridine-2-carboxamido)-4-R2-benzenate, R2 = H for bpb2− and Cl for bpClb2−]. The single crystal structures of these complexes consist of alternating units of [MnIII(5-R1salen)]+ and [CrIII(4-R2bpb)(CN)2]−, forming cyanide-bridged neutral 1D complexes. Investigation over magnetic properties of these complexes reveals the whole relatively weak antiferromagnetic interactions between Mn(III) ion and Cr(III) through cyanide bridge. The magnetic susceptibilities of these complexes were fitted based on the suitable 1D CrIII–MnIII magnetic model. The magneto-structural correlation for cyanide-bridged CrIII–MnIII systems reveals that the cyanide-bridging bond angle is related to the magnitude of magnetic exchange coupling: the larger the Mn N C bond angle, the weaker antiferromagnetic interactions.

The zircon polymorph of GdCrO4 has a large magnetocaloric effect over a wide temperature range, with |ΔST| > 20 J/kg·K from 6 K to 34 K, for a magnetic field of 9 T. This unusual behaviour is very interesting on magnetic refrigeration applications, for liquefying H2 or natural gas. The mean-field approach explains that it is due to the weaker Gd-Cr magnetic exchange relative to the Cr-Cr one, while the Gd-Gd exchange is negligible. This possibility has not been sufficiently studied and opens an interesting strategy to design more efficient materials for magnetic refrigeration.

Single-molecule magnets (SMMs) have attracted attention due to their potential applications in quantum computation and information storage, and many SMMs have been reported in the past two decades. In this review, we summarize the structures and the magnetic exchange interactions of pyridine alcohol-based SMMs to give a possible relationship between structure and magnetic property, providing information to generate new molecule-based magnetic materials. According to the correlated metal centers, these SMMs are separated into three segments to discuss.

The coordination chemistry of multinuclear metal compounds is important because of their relevance to the multi-metal active sites of various metalloproteins and metalloenzymes. Multinuclear Cu-II and Mn-III compounds are of interest due to their various properties in the fields of coordination chemistry, inorganic biochemistry, catalysis, and optical and magnetic materials. Oxygen-bridged binuclear Mn-III complexes generally exhibit antiferromagnetic interactions and a few examples of ferromagnetic interactions have also been reported. Binuclear Cu-II complexes are important due to the fact that they provide examples of the simplest case of magnetic interaction involving only two unpaired electrons. Two novel dioxygen-bridged copper(II) and manganese(III) Schiff base complexes, namely bis(mu-4-bromo-2-{[(3-oxidopropyl)imino]methyl}phenolato)dicopper(II), [Cu-2(C10H10BrNO2)(2)], (1), and bis(diaqua{4,4 '-dichloro2,2'-[(1,1-dimethylethane-1,2-diyl)bis(nitrilomethanylylidene)]diphenolato}manganese(III)) bis{mu-4,4'-dichloro-2,2'-[(1,1-dimethylethane-1,2-diyl)bis(nitrilomethanylylidene)]diphenolato}bis[aquamanganese(III)] tetrakis(perchlorate) ethanol disolvate, [Mn(C18H16Cl2N2O2)(H2O)(2)](2)[Mn-2(C18H16Cl2N2O2)(2)(H2O)(2)](ClO4)(4)center dot 2C(2)H(5)OH, (2), have been synthesized and single-crystal X-ray diffraction has been used to analyze their crystal structures. The structure analyses of (1) and (2) show that each Cu-II atom is four-coordinated, with long weak Cu center dot center dot center dot O interactions of 2.8631 (13) angstrom linking the dinuclear halves of the centrosymmetric tetranucelar molecules, while each Mn-III atom is sixcoordinated. The shortest intra- and intermolecular nonbonding Mn center dot center dot center dot Mn separations are 3.3277 (16) and 5.1763 (19) angstrom for (2), while the Cu center dot center dot center dot Cu separations are 3.0237 (3) and 3.4846 (3) angstrom for (1). The magnetic susceptibilities of (1) and (2) in the solid state were measured in the temperature range 2-300 K and reveal the presence of antiferromagnetic spin-exchange interactions between the transition metal ions., Balikesir University - BAP-2015/50 European Union Erasmus Programme

Density functional theory (DFT) calculations were performed to analyse the magnetic properties of dinuclear Ni–Ni and Cu–Cu bis(phenolate)-bridged complexes with two antiferromagnetically-coupled m...

Two tetranuclear CoII clusters [Co4(L)2(µ3-Cl)2Cl2] have been prepared by using multidentate diaminobisphenolate ligands. The solid-state structures of the complexes were determined by single-crystal X-ray diffraction. The cores of the cluster compounds can be defined as a two-vertex-deficient dicubane geometry (pseudo-dicubane). In the central unit, the cobalt(II) cations are linked through phenoxide oxygen (outer bridges) and chloride anions (inner bridges), previously unprecedented in this type of cobalt cluster. The magnetic properties were studied by both experimental and computational methods. By using a combination of techniques, we were able to determine the nature and strength of the intramolecular magnetic exchange coupling mediated by the different bridging fragments between the crystallographically different cobalt(II) cations.

The binuclear copper(II) complex based on azomethine, being a condensation product of 2-aminoethanol with 1-phenyl-1,2,3-butanetrione phenylhydrazone, is structurally characterized (CIF file CCDC 1059996). The structure is compared with the structure of an analog containing the axially coordinated pyridine molecule. The influence of the axial coordination of pyridine on the magnetic exchange interaction is studied by the DFT method in the broken symmetry approach.

In the solid state the iodo-substituted bisdiselenazolyl radical 1c orders as a ferromagnet with TC = 10.5 K. With the application of pressure TC rises rapidly, reaching a value of 27.5 K at 2.4 GPa. The accompanying structural and magnetic changes have been examined by high resolution powder X-ray diffraction and by DFT calculations of magnetic exchange interactions.

Three 3D Co(II) metal–organic frameworks of the general formula [Co(DNNDC)(NN)]n were reported, where DNNDC = 1,5-dinitronaphthalene-3,7-dicarboxylate and NN = bridging or chelating dipyridyl ligands. The MOFs exhibit similar 3D [Co(DNNDC)]n frameworks in which double-carboxylate-bridged [Co(OCO)2]n chains are cross-linked by naphthalene backbones. The bridging dipyridyl ligands [4,4′-bipyridine (bpy) and 1,2-bis(4-pyridyl)ethane (bpe)] serve as additional linkers between the chains to generate a reinforced framework with new net topology, while the chelating ligand 1,10-phenanthroline (phen) reinforces the frameworks through π–π stacking and C–H⋯O interactions. Remarkably, varying the auxiliary ligand leads to a change in the sign of the magnetic exchange through the double carboxylate bridge: the MOFs with the ditopic bpy and bpe ligands show ferromagnetic interactions, while the one with the chelating phen ligand shows antiferromagnetic exchange. The difference in magnetic exchange is attributable to the subtle change in the coordination conformation of the carboxylate bridge.

The effect of the double exchange in a square-planar mixed-valence dn+1&minus, dn+1&minus, dn&minus, dn&ndash, type tetramers comprising two excess electrons delocalized over four spin cores is discussed. The detailed analysis of a relatively simple d2&minus, d2&minus, d1&minus, d1&ndash, type tetramer shows that in system with the delocalized electronic pair the double exchange is able to produce antiferromagnetic spin alignment. This is drastically different from the customary ferromagnetic effect of the double exchange which is well established for mixed-valence dimers and tetramers with one excess electron or hole. That is why the question &ldquo, Can double exchange cause antiferromagnetic spin alignment?&rdquo, became the title of this article. As an answer to this question the qualitative and quantitative study revealed that due to antiparallel directions of spins of the two mobile electrons which give competitive contributions to the overall polarization of spin cores, the system entirely becomes antiferromagnetic. It has been also shown that depending on the relative strength of the second-order double exchange and Heisenberg&ndash, Dirac&ndash, Van Vleck exchange the system has either the ground localized spin-triplet or the ground delocalized spin-singlet.

Ferroelectric tunnel junctions (FTJs) have recently aroused extensive attention for applications in information storage. However, the interfacial effect regarding the metallic electrodes on tunneling electroresistance (TER) has still remained unclear in traditional FTJs. Here, we observe the TER enhancement in an all-oxide FTJ, which consists of La0.7Sr0.3MnO3 (LSMO), BaTiO3 (BTO) and Nb:SrTiO3 (NSTO). This FTJ device exhibits a giant ON/OFF current ratio of ~104 at room temperature, which is two orders of magnitude larger than that of Pt/BTO/NSTO FTJ. Using combined microscopic and spectroscopic techniques, we find that Mn-Ti cation intermixing at LSMO/BTO interface is closely associated with the polarization direction of BTO, resulting in the change of the ratio of Mn3+/Mn4+ as well as magnetic exchange interactions. Finally, the interface resistance state is tuned. In addition, the device has the long resistance retention and the high switching reproducibility. Our work emphasizes the crucial role of LSMO electrode and interfacial effect in all-oxide FTJs and provide a feasible way to design the high-performance non-volatile resistive memory devices.

The marked interplay between the crystalline, electronic, and magnetic structure of atomically thin magnets has been regarded as the key feature for designing next-generation magneto-optoelectronic devices. In this respect, a detailed understanding of the microscopic interactions underlying the magnetic response of these crystals is of primary importance. Here, we combine model Hamiltonians with multireference configuration interaction wavefunctions to accurately determine the strength of the spin couplings in the prototypical single-layer magnet CrI3. Our calculations identify the (ferromagnetic) Heisenberg exchange interaction J = −1.44 meV as the dominant term, being the inter-site magnetic anisotropies substantially weaker. We also find that single-layer CrI3 features an out-of-plane easy axis ensuing from a single-ion anisotropy A = −0.10 meV, and predict g-tensor in-plane components g x x = g y y = 1.90 and out-of-plane component g zz = 1.92. In addition, we assess the performance of a dozen widely used density functionals against our accurate correlated wavefunctions calculations and available experimental data, thereby establishing reference results for future first-principles investigations. Overall, our findings offer a firm theoretical ground to recent experimental observations.

We assess the performance of popular hybrid density functional approximations for the prediction of magnetic exchange couplings ( J ) in Fe III complexes. To this end, eleven dinuclear oxo-bridged iron(III) complexes with accurately determined J values were chosen to cover cases of weak and strong antiferromagnetic couplings ranging from −6 cm - 1 to −132 cm - 1 . Seven representative exchange-correlation functionals ranging from the hybrids PBEh and B3LYP to meta hybrids (M06, M062X), range separated functionals (HSE, LC- ω PBE), and LSDA with 30% of HF exchange were used for this assessment. These functionals have been suggested as good performers for this particular property in transition metal complexes and hence this assessment aims to narrow the interval of confidence for the particular case of Fe complexes. In addition, we examined the performance of an alternative method based on differential local spin rotations to calculate magnetic exchange coupling parameters in these complexes. Our results show that, although some of these functionals perform on par, the M06 and HSE functionals yield magnetic exchange couplings in closer agreement with experimental data, with mean absolute percentage errors of 8.6 and 9.2%, respectively.

By combining the first-principles with Monte Carlo method, we investigate the magnetic exchange interactions and the magnetic entropy changes in the vicinity of the second-order transition in $${\hbox {Ni}}_{2}{\hbox {Mn}}_{1.4}{\hbox {In}}_{0.6}{\hbox {(R)}}\,{\hbox {(R}}= \hbox {Si, Ge, Al})$$ alloys with R substituting for In atoms. The results show that the substitution of R for In atoms can lead to the reduction of the Curie temperature and an increase in the total magnetic moments of the systems. The Si substitution gives rise to the increase in the magnetic entropy changes, whereas the Ge and Al substitutions make the entropy change decrease. In addition, our calculated Curie temperatures for $$\hbox {Ni}_{2}\hbox {Mn}_{1.4}\hbox {In}_{\mathrm{0.6-x}}\hbox {Si}_{\mathrm{x}} (x = 0.04, 0.08, 0.12, 0.16)$$ are in good agreement with available experimental results.

The critical properties and magnetocaloric effect of semiconducting ferrimagnet ${\mathrm{Mn}}_{3}{\mathrm{Si}}_{2}{\mathrm{Te}}_{6}$ single crystals have been investigated by bulk magnetization and heat capacity around ${T}_{c}$. Critical exponents $\ensuremath{\beta}=0.41\ifmmode\pm\else\textpm\fi{}0.01$ with a critical temperature ${T}_{c}=74.18\ifmmode\pm\else\textpm\fi{}0.08\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and $\ensuremath{\gamma}=1.21\ifmmode\pm\else\textpm\fi{}0.02$ with ${T}_{c}=74.35\ifmmode\pm\else\textpm\fi{}0.05\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ are deduced by the Kouvel-Fisher plot, whereas $\ensuremath{\delta}=4.29\ifmmode\pm\else\textpm\fi{}0.05(3.40\ifmmode\pm\else\textpm\fi{}0.02)$ is obtained by a critical isotherm analysis at $T=74(75)\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. The magnetic exchange distance is found to decay as $J(r)\ensuremath{\approx}{r}^{\ensuremath{-}4.79}$, which lies between the mean-field and 3D Heisenberg models. Moreover, the magnetic entropy change $\ensuremath{-}\mathrm{\ensuremath{\Delta}}{S}_{M}$ features a maximum at ${T}_{c}$, i.e., $\ensuremath{-}\mathrm{\ensuremath{\Delta}}{S}_{M}^{\mathrm{max}}\ensuremath{\sim}2.53(1.67)\phantom{\rule{0.28em}{0ex}}\mathrm{J}\phantom{\rule{0.16em}{0ex}}{\mathrm{kg}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ with in-plane (out-of-plane) field change of 5 T, confirming large magnetic anisotropy. The heat capacity measurement further gives $\ensuremath{-}\mathrm{\ensuremath{\Delta}}{S}_{M}^{\mathrm{max}}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}2.94\phantom{\rule{0.28em}{0ex}}\mathrm{J}\phantom{\rule{0.16em}{0ex}}{\mathrm{kg}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ and the corresponding adiabatic temperature change $\mathrm{\ensuremath{\Delta}}{T}_{ad}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}1.14\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ with out-of-plane field change of 9 T.

Chemical oxidation of a TTF-based NiII complex with I2 produces the corresponding radical cation salt 1, [Ni2Cl2(L)2](I3)2(I5)2(I2)(H2O)2(C4H8O)3, (L=4,5-bis(2-pyridylmethylsulfanyl)-4',5'-ethylenedithiotetrathiafulvalene). The results of magnetic susceptibility measurements show the occurrence of intramolecular magnetic exchange interactions in 1. The lack of close S···S contacts, confirmed by crystal structure analysis, results in an insulating behavior

It is demonstrated that thermally induced atomic displacements from ideal lattice positions can produce considerable effect on magnetic exchange interactions and, consequently, on the Curie temperature of Fe. Thermal lattice distortion should, therefore, be accounted for in quantitatively accurate theoretical modeling of the magnetic phase transition. At the same time, this effect seems to be not very important for magnetic exchange interactions and the Curie temperature of Co and Ni.

At a superconductor-ferromagnet (S/F) interface, the F layer can introduce a magnetic exchange field within the S layer, which acts to locally spin split the superconducting density of states. The effect of magnetic exchange fields on superconductivity has been thoroughly explored at S-ferromagnet insulator (S/FI) interfaces for isotropic s-wave S and a thickness that is smaller than the superconducting coherence length. Here we report a magnetic exchange field effect at an all-oxide S/FI interface involving the anisotropic d-wave high temperature superconductor praseodymium cerium copper oxide (PCCO) and the FI praseodymium calcium manganese oxide (PCMO). The magnetic exchange field in PCCO, detected via magnetotransport measurements through the superconducting transition, is localized to the PCCO/PCMO interface with an average magnitude that depends on the presence or absence of magnetic domain walls in PCMO. The results are promising for the development of all-oxide superconducting spintronic devices involving unconventional pairing and high temperature superconductors., Comment: 12 pages, 3 figures and supplementary information

We theoretically propose a new route to control magnetic and topological orders in a broad class of insulating magnets with a DC electric field. We show from the strong-coupling expansion that magnetic exchange interactions along the electric-field direction are generally enhanced in Mott insulators. We demonstrate that several magnetic or topological ordered phases such as quantum spin liquids and Haldane-gap states can be derived if we apply a strong enough DC electric field to typical frustrated or low-dimensional magnets. Our proposal is effective especially for weak Mott insulators and magnets in the vicinity of quantum critical points, and would also be applicable for magnets under low-frequency AC electric fields such as terahertz laser pulses. A similar strategy of controlling exchange interactions can also be utilized in cold atomic systems., 7+6 pages, 4+1 figures

In starting off this chapter, we ask whether the findings of Chapter 2 are peculiar to the Ising model, or whether they are more generally valid, and, in particular, whether they apply to cases other than lattice configurations. We find that this is the case, which may come as a surprise, since that model fixates on spin interactions between nearest neighbors and with an externally applied magnetic field. It turns out that such an approach is representative of a whole class of models. It is therefore instructive to examine the mean field approach to critical phenomena in a broader context, again starting from a model with magnetic exchange interactions, this time in spin-rotationally invariant form in spin space.

We present the first principle density functional calculations to figure out the comparative study of the underlying spin model SrMn3P4O14 and Sr3Cu3(PO4)4. We explicitly discuss the nature of the exchange paths and provide quantitative estimates of magnetic exchange couplings for both compounds. A microscopic modeling based on analysis of the electronic structure of both systems puts them in the interesting class of weakly coupled trimer units, which makes chains S=5/2 for SrMn3P4O14 and S=1/2 for Sr3Cu3(PO4)4 that are in turn weakly coupled to each other.

We investigate the role of exchange bridges in molecular magnets. We explore their effects on the distribution of the valence electrons and their contribution to the exchange processes. The present study is focused on a spin-half dimer with nonequivalent exchange bridges. Here, we derive an effective Hamiltonian that allows for an accurate estimation of the observables associated to the magnetic properties of the magnet. Our results are compared to those obtained by means of the conventional Heisenberg model that usually fails.

Different magnetic phases have been identified in nanosized core/shell Prussian blue analogue (PBA) cubes, with a 250 nm Rb–Co–Fe phase (Rb0.48Co[Fe(CN)6]0.75[(H2O)6]0.25·0.34H2O) in the core coated by a 45 nm K–Ni–Cr phase (K0.36Ni[Cr(CN)6]0.74[(H2O)6]0.26·0.11H2O) on the shell. Three separate characteristic temperatures at 86, 69, and 67 K are associated with magnetic phases in the K–Ni–Cr shell. Two magnetic exchange paths are identified. One propagates along the three crystallographic axis directions. The other propagates along the [110] crystallographic direction for the associated Ni–Ni interactions, but not for Cr–Cr interactions. The severe Cr deficiency and the appearance of direct Ni–Ni exchange are used to understand the appearance of two separate transitions associated with magnetic ordering. A weak moment develops in the core at low temperature, corresponding to separate ordering of the Co–Fe PBA network.

The cubic NaZn 13 -type LaFe 11.2 Al 1.8−x Si x (x = 0.2, 0.3, 0.4 and 0.5) compounds with different Si content were fabricated by conventional arc-melting method, the structures of which were confirmed by powder X-ray diffraction (XRD) measurement at ambient temperature. Besides, the thermal expansion and magnetic properties of these samples were also researched by means of a strain gage and a physical property measurement system (PPMS). Significantly, it was found that the negative thermal expansion (NTE) behavior have been remarkably enhanced with substituting Al with Si atoms. Furthermore, the NTE operation-temperature window concurrently shifts toward a higher temperature region. The variable temperature XRD results indicate that LaFe 11.2 Al 1.8−x Si x retain cubic NaZn 13 -type structure when temperature varies from 20 K to 270 K, including the temperature region where NTE occurs. The further theoretical analysis combined with magnetic characterization reveal that the improvement of NTE behavior is attributed to the enhancement of Fe–Fe magnetic exchange interactions with doping Si atoms. It is noteworthy that this study displays a new pathway to improve the NTE property of La(Fe,Al) 13 -based compounds at low temperature region, which highlights the potential applications of NTE materials in cryogenic engineering.

The magnetism in several materials of the RCo 5 type is studied. A numerical calculation scheme, based on an induced magnetic ordering transition, is set up. Using this scheme, and previously reported crystalline electric and magnetic exchange fields parameters, the magnetic structure in R 1− y Y y Co 3 B 2 and R(Co 1− x Ni x ) 5 materials (R=Tb and Ho), and its temperature evolution, is calculated, and compared with the corresponding observed results. It is proposed that the magnetic order in the materials of the RCo 5 type, with R 3+ of integral J , is driven by an induced transition.