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In this work, based on structural and magnetic phase transition temperatures estimated theoretically from the first principles, the concentration phase diagram for Fe100−xAlx (15.625≤x≤31.2...

The BaFe12O19 particles were synthesized by co-precipitation and calcination. Fe5C2 nanoparticles were synthesized in an organic solvent. The BaFe12O19 and Fe5C2 particles were mixed through cryogenic ball milling. The elemental mappings indicated that two crystal phases were homogenously mixed after the milling, and the magnetic properties of BaFe12O19/Fe5C2 composites were investigated by VSM. When the mass percentage of Fe5C2 was 10%, the composite presented the optimum magnetic exchange coupling in BaFe12O19/Fe5C2 composites and the largest (BH)max (31% increase from pure BaFe12O19). As a comparison, the room temperature ball milled BaFe12O19/Fe5C2 showed less exchange coupling compared with cryogenic ball milling counterpart. Finally, the air stability of BaFe12O19/Fe5C2 composite was also investigated.

In this contribution, we review the crystal chemistry and magnetic exchange pathways in atomically well-ordered oxide garnets and spinels. While superficially the topologies of these two structures appear quite different, both are capable of accommodating a large number of magnetic elements from across the periodic table within multiple coordination environments, making them ideal for identifying new design principles. We present a comparison of the crystal chemistry for the two structures and an overview of the various magnetic properties that have been observed when one or more magnetic ions occupy the individual sublattices. We identify that the large number of degenerate superexchange pathways between each sublattice in either structure plays a critical role in producing novel magnetic behavior.

Magnetization reversal and magnetic exchange coupling of (Co/Ni)×N/Ru/(Co/Pt)×12 were investigated as a function of the temperature. The number of repeats N of the soft multilayer (Co/Ni) was varied from 4 to 8 bilayers while the number of repeats of the hard bilayers (Co/Pt) was fixed to 12. Two steps hysteresis loops were observed for coupled structure with only 4 repeats of (Co/Ni) in a wide range of temperature (25–300 K). From the shift of the minor hysteresis loop, the antiferromagnetic exchange coupling Hex was measured and then the interlayer exchange coupling Jex was calculated. A non-monotonous dependence of Jex with temperature was observed for N = 4 with a maximum Jex of 0.13 erg/cm2 at 150 K. The annealing process performed on the same structure confirms the unusual behavior of interlayer exchange coupling Jex. As the repetition number N increases to 8 bilayers the two steps hysteresis loops disappeared in the investigated temperature range, however a small kink appeared in the range of 125 and 225 K for the case of 6 bilayers. From the analysis of the coupled and uncoupled structures, it seems that the dipolar energy overcomes the antiferromagnetic coupling for thicker (Co/Ni) multilayer.

3d-4f cubane-like complexes exhibit unique structural pattern, thus become a fascinating subclass of 3d-4f complexes. In this review, we first present the structural classification and the possible synthetic strategies towards this peculiar structure, then we focus on its magnetic properties. Inside a cubane core, spin carriers are forced to be near each other yielding significant d-d, d-f, and f-f magnetic exchanges which are summarized. As multinuclear complexes, 3d-4f cubane clusters could be applied for the magnetocaloric effect (MCE), especially with the isotropic MnII and GdIII ions. Then their single-molecule magnet (SMM) properties are described. We collect reported 3d-4f cubane complexes and attempt to demonstrate the correlations of magnetic exchange, MCE, and SMM properties.

Two novel heterometallic Cu-Ln Schiff base complexes {[Ln(hfac)2Cu(L)(H2O)][Ln(hfac)4][CuL]}(LnIII = Gd 1, Tb 2, hfac = hexafluoroacetylacetone; H2L = N,N′-bis(3-methoxy-salicylidene)ethylene-1,2-diamine) have been synthesized and characterized. Structure analysis shows that both complexes consist of one binuclear [Ln(hfac)2Cu(L)(H2O)]+ cation, one Ln(hfac)4− anion and one neutral CuL unit. Magnetic measurements indicate that the magnetic exchange between the Cu(II) and Gd(III)/Tb(III) ions is ferromagnetic. Complex Tb exhibits the frequency-dependent out of phase signals indicating the slow magnetic relaxation behavior.

Ar+ post-irradiation effects on magnetic behavior of Cu+-implanted ZnO single crystals were studied. It was found that Cu+-implanted and Ar+-irradiated samples, even the primary sample, showed a magnetic moment (MM), but the saturation magnetization (MS) of Ar+ post-irradiated on Cu+ as-implanted one drastically decreased. Based on the first-principle method, it was drawn to the incomplete filling electronic configuration of the substituted Cu ion whose 3d orbital hybridized with O-2p contributing to the magnetism. The MM induced by the substituted Cu+ ion was much less than that induced by the substituted Cu2+ and Cu3+ ion, so the ratio of Cu2+,3+/Cu+ decreased after Ar+ post-irradiation, leading to the decrease of MS. The excessive concentration of O vacancy induced by post-irradiation also weakened the MM by their compensating electrons, and decreased the effective magnetic exchange coupling interaction. Cu-related clusters dissolution was also a critical reason for the reduction of MS.

Zr2Co11 thin films were deposited by sputtering. MgO thin film was deposited on the top of Zr2Co11, followed by FeCo thin film deposition and post-annealing, to have magnetic exchange coupling between Zr2Co11 and FeCo. MgO thin film worked as a diffusion barrier between Zr2Co11 and FeCo during post-annealing. The thickness of FeCo layer was controlled as 4, 8 and 12 nm, respectively. The results showed that when the FeCo thickness was 8 nm, the Zr2Co11/MgO/FeCo showed the optimum magnetic properties, with 58% increased of (BH)max over Zr2Co11, which could be attributed to the effective exchange coupling between Zr2Co11 and FeCo. The exchange coupling between Zr2Co11 and FeCo thin film was investigated by Henkel plots.

The possibility to operate on magnetic materials through the application of electric rather than magnetic fields—promising faster, more compact and energy efficient circuits—continues to spur the investigation of magnetoelectric effects. Symmetry considerations, in particular the lack of an inversion centre, characterize the magnetoelectric effect. In addition, spin–orbit coupling is generally considered necessary to make a spin system sensitive to a charge distribution. However, a magnetoelectric effect not relying on spin–orbit coupling is appealing for spin-based quantum technologies. Here, we report the detection of a magnetoelectric effect that we attribute to an electric field modulation of the magnetic exchange interaction without atomic displacement. The effect is visible in electron paramagnetic resonance absorption of molecular helices under electric field modulation and confirmed by specific symmetry properties and spectral simulation. A modulation of the magnetic exchange interaction using an electric field, in the absence of atomic displacement and not relying on spin–orbit coupling, is reported.

Controlling spin Hamiltonian parameters such as magnetic exchange and magnetic anisotropy of polynuclear clusters is of great interest in the area of single molecule magnets (SMMs). Among large pol...

Here we present a calculation scheme which allows us to obtain the electronic structure and exchange interaction parameters of low-dimensional magnetic compounds with subsequent construction of the spin model and verification of this model by comparing the simulated thermodynamic properties with experimental data. This scheme is implemented to quasi-one-dimensional (1D) perovskite $$\hbox {KCuF}_3$$ , the S = 1 spin ladder $$\hbox {Rb}_3\hbox {Ni}_2(\hbox {NO}_3)_7$$ compound, and potassium dimanganese trivanadate, $$\hbox {KMn}_2\hbox {V}_3\hbox {O}_{10}$$ , containing Mn tetramers.

Three-dimensional topological insulators (TIs) are a perfectly tuned quantum-mechanical machinery in which counterpropagating and oppositely spin-polarized conduction channels balance each other on the surface of the material. This topological surface state crosses the bandgap of the TI and lives at the interface between the topological and a trivial material, such as vacuum. Despite its balanced perfection, it is rather useless for any practical applications. Instead, it takes the breaking of time-reversal symmetry (TRS) and the appearance of an exchange gap to unlock hidden quantum states. The quantum anomalous Hall effect, which has first been observed in Cr-doped (Sb,Bi)2Te3, is an example of such a state in which two edge channels are formed at zero field, crossing the magnetic exchange gap. The breaking of TRS can be achieved by magnetic doping of the TI with transition metal or rare earth ions, modulation doping to keep the electronically active channel impurity free, or proximity coupling to a magnetically ordered layer or substrate in heterostructures or superlattices. We review the challenges these approaches are facing in the famous 3D TI (Sb,Bi)2(Se,Te)3 family and try to answer the question whether these materials can live up to the hype surrounding them., A.I.F. acknowledges funding from the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie Grant Agreement No. 796925, the FET-PROACTIVE project TOCHA under Grant Agreement No. 824140 and the H2020 European Research Council PoC project SOTMEM under Grant Agreement 899896.

We present a microscopic study of the electronic and magnetic properties of the spin ladder systems Sr $$_{2}$$ Fe $$_{3}$$ Ch $$_{2}$$ O $$_{3}$$ (Ch=S, Se) based on density functional calculations and on ab initio-derived effective models. We discuss explicitly the nature of the exchange paths and provide quantitative estimates of magnetic exchange couplings. Although both compounds have similar crystal structures, the values of magnetic exchange interactions are slightly greater for S compound than Se compound. A microscopic modelling based on analysis of the electronic structure of these systems put Sr $$_{2}$$ Fe $$_{3}$$ Ch $$_{2}$$ O $$_{3}$$ (Ch=S, Se) in the interesting class of 2-D AFM spin, S = 2 ladder systems.

We present an ab initio relativistic k.p theory of the effect of magnetic exchange field on the band structure in the gap region of bulk crystals and thin films of three-dimensional layered topological insulators. For the field perpendicular to the layers (along $z$), we reveal novel unconventional scenarios of the response of the band-gap edges to the magnetization. The modification of the valence and conduction states is considered in terms of their $\Gamma$-point spin $s^z$ and total angular momentum $J^z$ on the atomic sites where the states are localized. The actual scenario depends on whether $s^z$ and $J^z$ have the same or opposite sign. In particular, the opposite sign for the valence state and the same sign for the conduction state give rise to an unconventional response in Bi$_2$Te$_3$ -- both in the bulk crystal and in ultra-thin films, which fundamentally distinguishes this topological insulator from Bi$_2$Se$_3$, where both states have the same sign. To gain a deeper insight into different scenarios in insulators with both inverted and non-inverted zero-field band structure, a minimal four-band third-order k.p model is constructed from first principles. Within this model, we analyze the field-induced band structure of the insulators and identify Weyl nodes that appear in a magnetic phase and behave differently depending on the scenario. We characterize the topology of the modified band structure by the Chern number $\mathcal{C}$ and find the unconventional response to be accompanied by a large Chern number $\mathcal{C}=\pm3$., Comment: 17 pages, 8 figures, and 7 tables

Spin-labeled cyrhetrenes [(NNCp)Re(CO)3] and [(INCp)Re(CO)3], where NNCp is nitronyl nitroxide 2-(η5-cyclopentadienyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl and INCp is the corresponding imino nitroxide, were synthesized and characterized by EPR, CV, XRD, magnetochemistry and quantum chemistry methods. The correlations between different arrangements of paramagnetic centers and the magnetic exchange interactions for three polymorphs of [(NNCp)Re(CO)3] were studied. It was concluded that high kinetic stability of nitroxide-substituted cyrhetrenes is a promising feature of compounds for the creation of multifunctional contrast agents.

The discovery of superconductivity in a d(9-delta) nickelate has inspired disparate theoretical perspectives regarding the essential physics of this class of materials. A key issue is the magnitude of the magnetic superexchange, which relates to whether cuprate-like high-temperature nickelate superconductivity could be realized. We address this question using Ni L-edge and O K-edge spectroscopy of the reduced d(9-1/3) trilayer nickelates R4Ni3O8 (where R = La, Pr) and associated theoretical modeling. A magnon energy scale of similar to 80 meV resulting from a nearest-neighbor magnetic exchange of J = 69(4) meV is observed, proving that d(9-delta) nickelates can host a large superexchange. This value, along with that of the Ni-O hybridization estimated from our O K-edge data, implies that trilayer nickelates represent an intermediate case between the infinite-layer nickelates and the cuprates. Layered nickelates thus provide a route to testing the relevance of superexchange to nickelate superconductivity.

Two-dimensional van der Waals compounds with magnetic ions on a honeycomb lattice are hosts to a variety of exotic behavior. The magnetic interactions in one such compound, $\mathrm{Mn}\mathrm{P}{\mathrm{Se}}_{3}$, are investigated with elastic and inelastic neutron scattering. Magnetic excitations are observed in the magnetically ordered regime and persist to temperatures well above the ordering temperature, ${T}_{\text{N}}=74\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, consistent with low dimensional magnetic interactions. The inelastic neutron scattering results allow a model spin Hamiltonian to be presented that includes dominant intralayer interactions of ${J}_{1ab}=0.45$ meV, ${J}_{2ab}=0.03$ meV, ${J}_{3ab}=0.19$ meV, consistent with theoretical predictions. Despite the quasi-2D behavior, appreciable interlayer interactions of ${J}_{c}=0.031(5)$ meV are required to model the data. No evidence for anisotropy in the form of a spin gap is observed in the data collected. The measurements on $\mathrm{Mn}\mathrm{P}{\mathrm{Se}}_{3}$ are contrasted with those on $\mathrm{Mn}\mathrm{P}{\mathrm{S}}_{3}$ and reveal a large increase in the interlayer exchange interaction in $\mathrm{Mn}\mathrm{P}{\mathrm{Se}}_{3}$ that may stabilize the similar ordering temperatures in the bulk compounds.

Funding: CT and PW acknowledge support from EPSRC (EP/R031924/1) and CMY and LSF from EP/S005005/1. C.H. acknowledges support by the Austrian Science Fund (FWF) Project No. P32144-N36 and the VSC-4 of the Vienna University of Technology. The work was partially supported by the Deutsche Forschungsgemeinschaft (DFG) through Transregional Research Collaboration TRR 80 (Augsburg, Munich, and Stuttgart). Controlling and sensing spin-polarization of electrons forms the basis of spintronics. Here, we report a study of the effect of helium on the spin-polarization of the tunneling current and magnetic contrast in spin-polarized Scanning Tunneling Microscopy. We show that the magnetic contrast in SP-STM images recorded in the presence of helium depends sensitively on the tunneling conditions. From tunneling spectra and their variation across the atomic lattice we establish that the helium can be reversibly ejected from the tunneling junction by the tunneling electrons. The energy of the tunneling electrons required to eject the helium depends on the relative spin-polarization of the tip and sample, making the microscope sensitive to the magnetic exchange interactions. We show that the time-averaged spin polarization of the tunneling current is suppressed in the presence of helium and thereby demonstrate voltage control of the spin polarization of the tunneling current across the tip-sample junction. Postprint

This chapter reviews the principles and contrast mechanisms of the spin-polarized scanning tunneling microscope (SP-STM) and magnetic exchange force microscope (MExFM) and the application of these instruments to explore spin spirals and skyrmions in materials with Dzyaloshinkii-Moriya interaction.

We study electron correlation driven superconductivity on a decorated honeycomb lattice (DHL), which has a low-energy flat band. On doping, we find singlet superconductivity with extended-s, extended-d and f-wave symmetry mediated by magnetic exchange. f-wave singlet pairing is enabled by the lattice decoration. The critical temperature is predicted to be significantly higher than on similar lattices lacking flat bands. We discuss how high-temperature superconductivity could be realized in the DHL materials such as Rb3TT. 2 H2O and Mo3S7(dmit)3., 4 pages, 4 figures + Supplemental material

Reaction of 2,2'-bis-p-tBu-calix[4]arene (H8L) with MnCl2·4H2O, GdCl3·6H2O and 2,6-pyridinedimethanol (H2pdm) affords [MnIIIMnIIGdIII(H3L)(pdmH)(pdm)(MeOH)2(dmf)]·3MeCN·dmf (3·3MeCN·dmf) upon vapour diffusion of MeCN into the basic dmf/MeOH mother liquor. 3 crystallises in the tetragonal space group P41212 with the asymmetric unit comprising the entire cluster. The highly unusual core contains a triangular arrangement of MnIIIMnIIGdIII ions housed within a [MnIIIMnIIGdIII(OR)4]4- partial cubane. Magnetic susceptibility and magnetisation data reveal best fit parameters JMn(II)-Mn(III) = +0.415 cm-1, JMn(III)-Gd(III) = +0.221 cm-1, JMn(II)-Gd(III) = -0.258 cm-1 and DMn(III) = -4.139 cm-1. Theoretically derived magnetic exchange interactions, anisotropy parameters, and magneto-structural correlations for 3 are in excellent agreement with the experimental data.

Motivated by the recent discovery of superconductivity in doped NdNiO$_2$, we study the magnetic exchange interaction $J$ in layered $d^9$ nickelates from first principles. The mother compounds of the high-$T_{\rm c}$ cuprates belong to the charge-transfer regime in the Zaanen-Sawatzky-Allen diagram and have $J$ larger than 100 meV. While this feature makes the cuprates very different from other transition metal oxides, it is of great interest whether layered $d^9$ nickelates can also have such a large $J$. However, one complexity is that NdNiO$_2$ is not a Mott insulator due to carrier doping from the block layer. To compare the cuprates and $d^9$ nickelates on an equal basis, we study RbCa$_2$NiO$_3$ and $A_{2}$NiO$_{2}$Br$_2$ ($A$: a cation with the valence of $2.5+$), which were recently designed theoretically by block-layer engineering. These nickelates are free from the self-doping effect and belong to the Mott-Hubbard regime. We show that these nickelates share a common thread with the high-$T_{\rm c}$ cuprates in that they also have a significant exchange interaction $J$ as large as about 100 meV., Comment: 10 pages, 3 figures

We present a combined polarized neutron and x-ray scattering study on two enantiopure langasite single crystals aimed at the determination of their absolute structural and magnetic chiralities and the coupling between them. Our respective data sets unambiguously reveal two samples of opposite structural chirality, where the magnetic handedness is pinned by the structural one. Simple energy considerations of the magnetic exchange and single-ion anisotropy parameters reveal that it is not the Dzyaloshinskii-Moriya interaction but the local single-ion anisotropy on a triangular plaquette which plays a key role in stabilizing one of the two magnetic helices.

The recent development in the field of 2D magnetic materials urges reliable theoretical methodology for determination of magnetic properties. Among the available methods, ab initio four-state energy mapping based on Density Functional Theory stands out as a powerful technique to calculate the magnetic exchange interaction in the Heisenberg spin model. Although the required formulae were explained in earlier works, the considered Hamiltonian in those studies always corresponded to the specific case that J-matrix is anti-symmetric, which may be misleading in other cases. Therefore, using the most general form of the Heisenberg spin Hamiltonian, we here derive the generic formulae. With a proper choice of four different magnetic states, a single formula governs all elements of the exchange interaction matrix for any considered pair of spin sites., 8 pages, 1 figure

Tetragonal Mn-based Heusler compounds feature rich exchange interactions and exotic topological magnetic textures, such as antiskyrmions, complimented by the chiral-type Hall effects. This makes the material class interesting for device applications. We report the relation of the magnetic exchange interactions to the thickness and Mn concentration of Mn$_{x}$PtSn films, grown by magnetron sputtering. The competition of the magnetic exchange interactions determines the finite temperature magnetic texture and thereby the chiral-type Hall effects in external magnetic fields. We investigate the magnetic and transport properties as a function of magnetic field and temperature. We focus on the anomalous and chiral-type Hall effects and the behavior of the dc-magnetization, in relation to chiral spin textures. We further determine the stable crystal phase for a relative Mn concentration between 1.5 and 1.85 in the $I\overline{4}2d$ structure. We observe a spin-reorientation transition in all compounds studied, which is due to the competition of exchange interactions on different Mn sublattices. We discuss our results in terms of exchange interactions and compare them with theoretical atomistic spin calculations., 13 pages, 6 figures

The nuclear magnetic relaxation time $T_1$ in ferrimagnetic insulators is calculated by a Raman process of hyperfine interaction with a meanfield approximation. It is found that the 1/$T_1$ on one site rapidly increases near the compensation temperature $T_0$, whereas that on another site does not increase up to Curie temperature $T_c$. This is due to that the band width of soft magnon becomes comparable to $T_0$. The increasing behavior of 1/$T_1$ below $T_c$ is found also in another type ferrimagnet, which shows hump structure in the temperature dependence of magnetization instead of compensation. Also in this case, we find the rapid increase of 1/$T_1$ below $T_c$, even though the magnetization does not show the compensation. Such a coexistence of soft and hard magnons will lead to remarkable properties of ferrimagnet., 8 pages, 12 figures

Using the first-principles calculations, we investigate the structural, electronic, and magnetic properties of 3d transition metal (TM) (TM = Co, Cu, Mn, Fe, and Ni) atoms substitutional doping of SnSe monolayer. Magnetism is observed for Co, Mn, Fe, and Ni doping. In particular, Mn- and Fe-substituted systems exhibit large magnetic moment of 5.0 and 4.0μB at a very low impurity concentration. Then, we study the magnetic coupling in these two substituted systems. The magnetic coupling between two Mn atoms prefers to antiferromagnetic (AFM) owing to the super exchange between d states of two Mn atoms. Interestingly, both AFM and ferromagnetic (FM) coupling are observed in two-Fe-doped systems. Due to the strong spin–orbit coupling between Fe-3d and Se-4p, a long-range FM interaction is found in the Fe-substituted system. Our results demonstrate potential applications of TM-substituted SnSe for spintronics and magnetic storage devices.

Metal-organic frameworks represent the ultimate chemical platform on which to develop a new generation of designer magnets. In contrast to the inorganic solids that have dominated permanent magnet technology for decades, metal-organic frameworks offer numerous advantages, most notably the nearly infinite chemical space through which to synthesize predesigned and tunable structures with controllable properties. Moreover, the presence of a rigid, crystalline structure based on organic linkers enables the potential for permanent porosity and postsynthetic chemical modification of the inorganic and organic components. Despite these attributes, the realization of metal-organic magnets with high ordering temperatures represents a formidable challenge, owing largely to the typically weak magnetic exchange coupling mediated through organic linkers. Nevertheless, recent years have seen a number of exciting advances involving frameworks based on a wide range of metal ions and organic linkers. This review provides a survey of structurally characterized metal-organic frameworks that have been shown to exhibit magnetic order. Section 1 outlines the need for new magnets and the potential role of metal-organic frameworks toward that end, and it briefly introduces the classes of magnets and the experimental methods used to characterize them. Section 2 describes early milestones and key advances in metal-organic magnet research that laid the foundation for structurally characterized metal-organic framework magnets. Sections 3 and 4 then outline the literature of metal-organic framework magnets based on diamagnetic and radical organic linkers, respectively. Finally, Section 5 concludes with some potential strategies for increasing the ordering temperatures of metal-organic framework magnets while maintaining structural integrity and additional function.

Materials showing reversible magnetocaloric effect near room temperature are desirable for green refrigeration technology. The compounds in the magnetic Heusler family displaying significant magnetocaloric effect driven by first-order magnetostructural transitions are in vogue. Comparatively, Heusler compounds undergoing second-order magnetic transition near room temperature are less explored in the context of discovering significant magnetocaloric effects, though they can offer certain advantages like less energy cost and hysteresis loss. Using density-functional theory in conjunction with model Hamiltonians, we explore potential room-temperature magnetocaloric materials near second-order magnetic transition by cosubstitution in the Ni-Mn-Sb family. Our investigation on two cosubstituted families, ${\mathrm{Ni}}_{2\ensuremath{-}x}{\mathrm{Fe}}_{x}{\mathrm{Mn}}_{1+z\ensuremath{-}y}{\mathrm{Cu}}_{y}{\mathrm{Sb}}_{1\ensuremath{-}z}$ and ${\mathrm{Ni}}_{2\ensuremath{-}x}{\mathrm{Co}}_{x}{\mathrm{Mn}}_{1+z\ensuremath{-}y}{\mathrm{Cu}}_{y}{\mathrm{Sb}}_{1\ensuremath{-}z}$, discovers significant numbers of compounds with second-order phase transition near room temperature exhibiting significant changes in magnetic entropy, comparable to that observed in the compounds showing inverse magnetocaloric effect near a first-order magnetostructural transition. We provide a systematic way to select potential reversible magnetocaloric compounds and analyze our results from their electronic structures and magnetic exchange interactions.

We report the control of the interplane magnetic exchange coupling in CaIrO3 perovskite thin films and superlattices with SrTiO3. By analyzing the anisotropic magneto-transport data, we demonstrate...

Using density functional calculations, we present a comprehensive study of the electronic and magnetic properties of the quantum spin chain materials ${\mathrm{K}}_{2}{\mathrm{CuSO}}_{4}{\mathrm{Cl}}_{2}$ and ${\mathrm{K}}_{2}{\mathrm{CuSO}}_{4}{\mathrm{Br}}_{2}$. With the first-principles linear response method, we calculate the magnetic exchange parameters, and the theoretical values are in a quantitatively good agreement with experiments. Depending on the signs and magnitudes of the interchain magnetic exchange interactions, we find that the magnetic order of ${\mathrm{K}}_{2}{\mathrm{CuSO}}_{4}{\mathrm{Br}}_{2}$ along the $b$ axis is antiferromagnetic, while ${\mathrm{K}}_{2}{\mathrm{CuSO}}_{4}{\mathrm{Cl}}_{2}$ has strong frustration along the $b$ axis. Based on the obtained magnetic exchange parameters, we successfully reproduce the experimental spin-wave dispersion. We also calculate Dzyaloshinskii-Moriya interactions, which are found to dominate in these compounds compared to the interchain magnetic exchange interactions. Finally, we obtain the phase diagram for these two materials using Monte Carlo simulations. Our results are consistent with previous experiments, giving a complete explanation of the magnetic structure.

Quantum fluctuations are ubiquitous in physics. Ranging from conventional examples like the harmonic oscillator to intricate theories on the origin of the universe, they alter virtually all aspects of matter, including superconductivity, phase transitions, and nanoscale processes. As a rule of thumb, the smaller the object, the larger its impact. This poses a serious challenge to modern nanotechnology, which aims at total control via atom-by-atom engineered devices. In magnetic nanostructures, high stability of the magnetic signal is crucial when targeting realistic applications in information technology, e.g., miniaturized bits. Here we show that zero-point spin fluctuations play an important role in determining the fundamental magnetic exchange interactions that dictate the nature and stability of the magnetic state. Based on the fluctuation-dissipation theorem, we show that quantum fluctuations correctly account for the large overestimation of the interactions as obtained from conventional static first-principles frameworks, filling in an important gap between theory and experiment [Zhou et al., Nat. Phys. 6, 187 (2010); Khajetoorians et al., Nat. Phys. 8, 497 (2012)]. Our analysis further reveals that zero-point spin fluctuations tend to promote the noncollinearity and stability of chiral magnetic textures such as skyrmions, a counterintuitive quantum effect that inspires practical guidelines for designing disruptive nanodevices., This work was supported by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (ERC-consolidator Grant No. 681405, DYNASORE). J.I.-A. acknowledges funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie Grant Agreement No. 839237.

Exchange coupling constants (J) are fundamental to the understanding of spin spectra of magnetic systems. Here, we investigate the broken-symmetry (BS) approaches of Noodleman and Yamaguchi in conjunction with coupled cluster (CC) methods to obtain exchange couplings. J values calculated from CC in this fashion converge smoothly toward the full configuration interaction result with increasing level of CC excitation. We compare this BS-CC scheme to the complementary equation-of-motion CC approach on a selection of bridged molecular cases and give results from a few other methodologies for context.

Designing high potential cathodes for Na-ion batteries, which are comparable in performance to Li-ion cathodes, remains a challenging task. Through comprehensive density functional calculations, we disentangle the relationship between the cathode potential and the ionicity of $TM-O$ bonds in $O3$ $NaTMO_2$ compounds in which TM ions is a fourth- or fifth-row transition metal. We demonstrate that the magnetic exchange interaction and the local distortions in the coordination environment of TM ions play more significant roles in determining the cathode potential of the $TM^{3+}$ $\to$ $TM^{4+}+ e^-$ reaction than the ionicity of the $TM-O$ bonds in these compounds. These results indicate that designing cathode materials solely based on empirical electronegativity values to achieve high potential may not be a feasible strategy without taking into account a detailed structural assessment., Comment: 5 pages, 3 figures, 1 table, journal article

L10-Mn55Ga45 was synthesized by arc melting, followed by posted annealing. FeCo nanoparticles were synthesized by a wet chemistry process. L10-Mn55Ga45/FeCo composites were synthesized by cryogenic ball milling. In three different bathes, the FeCo mass percentage was controlled as 5%, 10% and 15%, respectively. The magnetic exchange coupling between FeCo and L10-Mn55Ga45 was investigated by VSM. The results showed that when FeCo was 5% and 10%, effective exchange coupling and increased maximum energy product were observed in the composites. However, when the FeCo mass percentage was increased to 15%, both magnetic exchange coupling and maximum energy products were reduced in the composite.

With density functional calculations, the enhancement of magnetic exchange energy (MEE) of two-dimensional (2-d) diluted magnetic semiconductor (DMS) δ–(Zn,Cr)S with shape deformation was investigated. The increase of lattice parameter c (perpendicular to the Cr layer) and decrease of a (parallel to the Cr layer) had a significant effect on the increase of MEE. Both PBE and LDA + U methods could enhance the MEE to a significant extent, which makes it superior to other δ-DMS found in initial research. The main mechanism by which increase the MEE is to vary the hole-states across the Fermi level with shape deformation, based on Zener's double exchange (DE) mechanism. This enriches the research into 2-d FM materials, which are candidates for next-generation electronic and optoelectronic applications.

τ-MnAl thin film was deposited by DC magnetron sputtering. Co thin film was deposited on the surface of τ-MnAl thin film by Plasma Enhanced Atomic Layer Deposition (PEALD). In three parallel experiments, the Co layer thickness is controlled as 2, 4 and 6 nm, respectively. The surface chemical states of as-deposited τ-MnAl and Co thin films were determined by XPS. The magnetic properties of both τ-MnAl and τ-MnAl/Co thin films were investigated by VSM. The results showed that when the Co layer thickness was 2 and 4 nm, effective magnetic exchange coupling was occurring between τ-MnAl and Co, which was indicated by smooth magnetic hysteresis loops and enhanced (BH)max. However, when the Co layer thickness was increased to 6 nm, the magnetic exchange coupling between MnAl and Co was reduced, which was indicated by the kinks in the magnetic hysteresis loop and decreased (BH)max.

In this work, the structural and magnetic properties in ZnCr2−xGaxO4 were investigated. In ZnCr2−xGaxO4, Ga3+ ions substitute partial Cr3+ ions and occupy the B sites. ZnCr2O4 undergoes a paramagnetic-antiferromagnetic transition at 12 K. In ZnCr2−xGaxO4, the antiferromagnetic short-range correlation occurs below 60 K above $T_{\mathrm {N}}$ . The Ga3+ doping weakens the antiferromagnetic nearest-neighbor exchange interaction (J1) and induces ferromagnetic next-nearest-neighbor exchange interaction (J2) among the B site magnetic ions. The generation of the ferromagnetic J2 is ascribed to structure distortion induced by the Ga3+ doping.

Antisymmetric magnetic exchange interaction−so-called Dzyaloshinskii-Moriya interaction (DMI)−governs intriguing magnetic phenomena in spintronic materials. A sizeable DMI causes chiral magnetic phenomena such as the formation of chiral magnetic domain walls and the topological magnetic skyrmions. Since the stability and functionality of these chiral objects are largely attributed to the strength of the DMI, an unambiguous determination of the DMI is essential for engineering the chiral spintronic applications. Here, we review recent progresses on the measurement schemes of the DMI strengths and related phenomena.

For the first time, in ferromagnetic nanocomposites Co/СoO/Al2O3 formed by two-crucible electron beam evaporation with deposition on a policor substrate, the magnetic exchange bias was observed. It is associated with the magnetic interaction of the ferromagnetic metal core of Co nanoparticles with antiferromagnetic CoO layer on their surface. The low value of magnetic exchange bias is attributed to the small thickness of the CoO shell, inasmuch as the energy of exchange magnetic anisotropy, which decreases with diminishing the antiferromagnetic CoO layer thickness, cannot provide a significant increase of the coercive force when changing the magnetic field direction. The ferromagnetic nanocomposites with the magnetic exchange bias can be used as a bias magnetic layer for magnetoresistive sensors.