Magnetic Coupling Interactions Research Articles

Exploring the low-temperature polarization and the multifield-manipulated dielectric tunability behavior of NiMn2O4

Manganese oxides with spinel structure could exhibit abundant physical effects due to the complex sublattice structure, variable valence states and the intricate roles of manganese cations in magnetic interaction. In this work, NiMn2O4 ceramic with space group of Fd3‾m is synthesized. The low-temperature polarization behavior is investigated accompanied by revealing the multi-stage dielectric relaxation. Moreover, the relaxation mechanism is confirmed through microstructure characterization, multiple-condition pyroelectric measurement and the dielectric tunability properties under electric/magnetic fields. With increasing measuring temperature, different relaxation phenomena are respectively induced by lattice distortion because of the competition among magnetic coupling interactions (below ∼135 K), electron hopping relating to the coexistence of different valence states of manganese ions (∼135–230 K), and the synergistic contribution of oxygen vacancies and domain wall effect (above ∼230 K). These results provide additional evidence for comprehensive understanding the low-temperature polarization in NiMn2O4, guiding the method design for exploring the physical origin within a wide temperature range.

Cu(II)-Ln(III) (Ln = Gd, Tb and Dy) complexes of an unsymmetrical N2O3 donor ligand: field induced SMM behaviour of Cu(II)-Tb(III) complexes.

Three new hetero-metallic CuII-LnIII complexes [(CuL)Gd(NO3)3(CH3OH)]n (1), [(CuL)Tb(NO3)3(H2O)]·[CuL] (2) and [(CuL)Dy(NO3)3(H2O)]·[CuL] (3) have been synthesized using a mono-nuclear Cu(II) complex, [CuL], of an unsymmetrically di-condensed N2O3 donor Schiff base ligand, N-(3-methoxysalicylidene)-N-(salicylidene)-1,2-ethylenediamine (H2L). Single crystal X-ray crystallography revealed that complex 1 is a nitrate bridged 1D chain of dinuclear Cu(II)-Gd(III) units whereas in 2 and 3, the dinuclear Cu(II)-Ln(III) units are co-crystallized with a [CuL] unit. The Ln(III) centers are nine coordinated with the geometry of a spherical capped square antiprism for Gd and spherical tricapped trigonal prism for Tb and Dy. The geometry of the Cu(II) center is distorted octahedral for complex 1 and distorted square planar for complexes 2 and 3. Temperature-dependent molar magnetic susceptibility measurements in 1-3 revealed the presence of overall ferromagnetic coupling between the Cu(II) and Ln(III) centers. Notably, field induced single-molecule magnet behavior was witnessed in the Tb(III) derivative (2). The ab initio calculations indicated that upon application of an external magnetic field, the tunneling in the ground state of complex 2 gets reduced and thereby field-induced SMM behaviour is observed. Besides, in the case of complex 1, BS-DFT calculations were carried out to gain further insights into the magnetic exchange coupling interactions between the Cu(II) and Gd(III) centers.

Origin of Unprecedented Formation and Reactivity of FeIV═O Species via Oxygen Activation: Role of Noncovalent Interactions and Magnetic Coupling.

Emulating the capabilities of the soluble methane monooxygenase (sMMO) enzymes, which effortlessly activate oxygen at diiron(II) centers to form a reactive diiron(IV) intermediate Q, which then performs the challenging oxidation of methane to methanol, poses a significant challenge. Very recently, one of us reported the mononuclear complex [(cyclam)FeII(CH3CN)2]2+ (1), which performed a rare bimolecular activation of the molecule of O2 to generate two molecules of FeIV═O without the requirement of external proton or electron sources, similar to sMMO. In the present study, we employed the density functional theory (DFT) calculations to investigate this unique mechanism of O2 activation. We show that secondary hydrogen-bonding interactions between ligand N-H groups and O2 play a vital role in reducing the energy barrier associated with the initial O2 binding at 1 and O-O bond cleavage to form the FeIV═O complex. Further, the unique reactivity of FeIV═O species toward simultaneous C-H and O-H bond activation process has been demonstrated. Our study unveils that the nature of the magnetic coupling between the diiron centers is also crucial. Given that the influence of magnetic coupling and noncovalent interactions in catalysis remains largely unexplored, this unexplored realm presents numerous avenues for experimental chemists to develop novel structural and functional analogues of sMMO.

Magnetic coupling interaction-related photoluminescence behaviors in all-inorganic manganese chloride perovskites

Manganese halides, as dilute magnetic semiconductor materials, have magnetic coupling interactions that play an essential role in their photoluminescence (PL); however, such interactions remain controversial. AMnCl3 (AMC, A = K, Rb, and Cs) and their hydrates AMnCl3·2H2O (AMCH, A = K, Rb, and Cs) are both in the ABX3 configuration but exhibit a wide variety of structures with different connectivity types and dimensions. Their magnetic coupling interaction has been demonstrated. However, few studies have systematically investigated the PL in conjunction with the magnetic coupling interaction over these chloride compounds. In this paper, the effect of the magnetic coupling interaction on AMC and AMCH PL is mainly revealed by temperature-dependent PL spectra and lifetimes. The MnX6 (X6 = Cl4(H2O)2 or Cl6) cluster connection types affect the Mn2+–Mn2+ distances. The magnetic coupling interaction between MnX6 octahedrons affects the radiative transitions of manganese chlorides, which is influenced by the Mn2+–Mn2+ distance, local symmetry, and water ligand. The Mn2+–Mn2+ distance and the magnetic coupling interaction also affect their lifetimes. Variations in magnetic coupling interactions can shift emission wavelength, especially dual-emissions and near-infrared (NIR) emission at lower temperatures while A+ = K+. This work helps researchers understand the optical process of Mn2+ ions in different manganese compounds and provides new insights into the design of tailored Mn2+ ion phosphors.

Dimensional design of Fe0.9Co0.1 nano-alloys with enhanced low-frequency microwave absorption

Low-frequency microwave absorbing materials are critical for enabling radar stealth and interference resistance in gigahertz communication devices and electronic equipment. However, long-wavelength electromagnetic waves are not easily attenuated, due to the limitations of current absorbing materials, including low permeability and a lack of electromagnetic wave loss mechanisms at low frequencies. Herein, we design and prepare one- and two-dimensional Fe0.9Co0.1 nanoalloys with high permeability through an organic templating method combined with a constrained transformation strategy. We systematically investigate the impact of the anisotropy of monodisperse Fe0.9Co0.1 nanoalloys on low-frequency microwave absorption performance. The generous specific surface area of Fe0.9Co0.1 nanosheets facilitate multiple reflections and the scattering of electromagnetic waves within the absorber. This phenomenon, coupled with dielectric resonance, culminates in a maximum reflection loss value of − 48.7 dB at 4.2 GHz. More significantly, Fe0.9Co0.1 nanorods exhibit an absorption intensity of − 35.3 dB at a notably lower frequency of 2.5 GHz, outperforming existing materials, in addition to an efficient absorption bandwidth of 4.2 GHz at a thickness of only 0.7 mm. Through a combination of experimental investigations and finite element simulations, we identify that highly anisotropic magnetic nanorods demonstrate a robust magnetic coupling interaction, substantial interface polarization and quasi-antenna effect. These characteristics result in enhanced low-frequency electromagnetic losses. Our findings indicate that the high anisotropy of the Fe0.9Co0.1 nanoalloys significantly improves their microwave absorption performance, thus emphasizing their substantial potential in the development of efficient low-frequency microwave absorbers.

Thermal and Vapor Induced Triple‐Mode Luminescent Switch of Manganese (II) Halides Hybrid

AbstractIt is imminent to develop phosphors with multiple stimuli responses due to the increasing demand on anti‐counterfeiting and information encryption technologies. Here, a zero dimensional (0D) organic–inorganic hybrid (DPPE)2MnBr4·H2O (DPPE = 4,4‐Difluoropiperidine, 1), which emits green light and exhibits reversible thermo‐ and vapor‐luminescence responses to heat and organic solvents is reported. Specifically, when heated above 100 °C for 30 s, hybrid 1 transforms into yellow‐emitting hybrid 2. Upon exposure to dichloromethane (DCM), it transforms into a red‐emitting hybrid 3. Experimental analysis reveals that Mn2+‐Mn2+ magnetic coupling interactions and coordination configuration transformation are responsible for the obvious switching of photoluminescence. Owing to its extraordinary triple‐mode switching characteristics, enabling luminescence‐adjustable transformations such as green to yellow, green to red, and yellow to red emission, this metal‐halide hybrid is promising for the application in anti‐counterfeiting and information encryption.

Magnetic exchange coupling via constructing hard/soft magnetic interface for stable microwave absorption

Magnetic exchange coupling interaction at hard/soft magnetic interface can expand the frequency range of magnetic resonance, providing the stable microwave absorption performance that is insensitive to matching thickness. A novel nanocomposite, in which shell/core structured Sm2Co17/Co(Sm) hard/soft magnetic nanoparticles are embedded into Sm2O3-doped porous carbon, is prepared. The magnetic exchange coupling between hard magnetic Sm2Co17 shell and soft magnetic Co(Sm) core results in extending resonance frequency. Due to the synergistic effect of quarter-wavelength cancellation and electromagnetic loss, the nanocomposites deliver the optimal reflection loss (RLm) of −38.87 dB and effective absorption bandwidth (EAB) of 3.36 GHz at thickness of 2.5 mm and 2.7 mm, respectively, and stable microwave absorption performances (RLm ≤ -20 dB and EAB ≥ 3.0 GHz) in thickness of 2.4–3.0 mm.

Highly efficient and fast modulation of magnetic coupling interaction in the SrCoO2.5/La0.7Ca0.3MnO3 heterostructure.

Effective manipulation of magnetic properties in transition-metal oxides is one of the crucial issues for the application of materials. Up to now, most investigations have focused on electrolyte-based ionic control, which is limited by the slow speed. In this work, the interfacial coupling of the SrCoO2.5/La0.7Ca0.3MnO3 (LCMO) bilayer is effectively modulated with fast response time. After being treated with diluted acetic acid, the bilayer changes from antiferromagnetic/ferromagnetic (AFM/FM) coupling to FM/FM coupling and the Curie temperature is also effectively increased. Meanwhile, the corresponding electric transport properties are modulated within a very short time. Combined with the structure characterization and X-ray absorption measurements, we find that the top SrCoO2.5 layer is changed from the antiferromagnetic insulator to the ferromagnetic metal phase, which is attributed to the formation of the active oxygen species due to the reaction between the protons in the acid and the SrCoO2.5 layer. The bottom LCMO layer remains unchanged during this process. The response time of the bilayer with the acid treatment method is more than an order of magnitude faster than other methods. It is expected that this acid treatment method may open more possibilities for manipulating the magnetic and electric properties in oxide-based devices.

An ultrabroadband metamaterial absorber based on remarkable magnetic coupling via constructing conductive composite resonators and magnetic gradient gyroid structure

ABSTRACT Broadband electromagnetic absorbing is still a challenge due to the huge difference of waves properties in different frequency bands. Herein, based on the transmission-line theory, we propose an in-plane hybrid metamaterial absorber using coupled resonators and gradient gyroid structure to realise the ultrabroadband absorbing. The coupled resonators based on Ag–Cu alloy/ABS conductive composite serve as transmission lines to orient the dipolar magnetic field, while the gradient gyroid structure fabricated by FCI/PEEK composite boosts the strong induced magnetic field. The unique hybrid strategy contributes to the remarkable magnetic coupling interaction, which not only realises good bandwidth extending effect, but also demonstrates the enhancement of absorbing efficiency. Finally, the 3D-printed hybrid metamaterial absorber achieves the high-efficiency absorbing in 2.2–40 GHz due to the electromagnetic field coupling resonance and synergistic loss effect. This absorber shows promising potential in real-life application by reasons of the low-frequency broadband absorption and convenient manufacturing.

Slow magnetic relaxation behaviors and diamagnetic dilution studies of a carboxyl bridged dinuclear dysprosium(III) complex

By using a rigid bulky carboxylic ligand α-cyanocinnamic acid (CCA), a dinuclear dysprosium (III) complex [Dy2(CCA)6 (MeOH)4] (1) was synthesized. Single crystal X-ray crystallography reveals that the two eight-coordinate dysprosium ions are bridged by four deprotonated carboxyl groups, forming a centrosymmetric paddle-wheel-like structure. Dynamic magnetic property measurements indicate that comple×1 displays field-induced slow magnetic relaxation. The temperature-dependent relaxation times can be fitted using Orbach and Raman processes with parameters of n = 2.8 (2), C = 27 (8) s−1/Kn, τ0 = 5 (2) × 10−10 s and Ueff = 40 (3) cm−1. Magnetic studies on the diamagnetic YIII-diluted analogue [Dy0.206Y1.794(CCA)6 (MeOH)4] (2) reveal its slow magnetic relaxation behavior without external dc field and the antiferromagnetic coupling between the DyIII ions in 1. Fits on the obtained relaxation times of 2 lead to the parameters of n = 4.5 (3), C = 0.7 (2) s−1/Kn, τ0 = 2.8 (2) × 10−9 s and Ueff = 38 (2) cm−1. The results suggest that slow magnetic relaxation originates from the single-ion relaxation of DyIII ions. Moreover, the diamagnetic dilution can suppress other fast relaxation pathways at low temperature, on account of the elimination of magnetic coupling and dipolar interaction. Ab initio calculations were then performed on the single DyIII ion species {YDy} and indicate that the first excited Kramers doublets (KDs) lie at ca. 76 cm−1, which is slightly higher than the experimental Ueff value. The intramolecular magnetic interactions were also calculated and indicate a weak ferromagnetic dipole-diploe magnetic interaction and an antiferromagnetic exchange coupling.

Electronic Transition and Magnetic Coupling Regulation in Trimetallic Complexes Featuring a New Bridging Ligand Obtained by Oxidative Addition.

A series of trimetallic complexes [FeIII(μ-L)(py)]2MII(py)n (n = 2, MII = MnII, 1; FeII, 2; CoII, 3; ZnII, 4; n = 3, MII = CdII, 5) with a new bridging ligand L4- (deprotonated 1,2-N1,N2-bis(2-mercaptoanil) oxalimidic acid) were synthesized and fully characterized by elemental analysis, single-crystal X-ray crystallography, IR, and Mössbauer spectra. Interestingly, the bridging ligand was obtained by oxidative addition of the (gma•)3- ligand from the mononuclear precursor Fe(gma)py (gma = glyoxal-bis(2-mercaptoanil)). In the obtained complexes, the bridging ligand L4- coordinates to the terminal FeIII ions (intermediate-spin with SFe = 3/2) by the N, S atoms, and coordinate to the central metal MII ion by the four O atoms. The resonance structure of the bridging ligand can be described as the two 4π-electron delocalized systems connected by one single-bond (C1-C2), which is different from the electronic structure of the precursor Fe(gma)py. Remarkably, the magnetic coupling interaction can be regulated through the central metal. The ferromagnetic coupling constant J gradually decreases as MII changes from FeII to CoII and MnII, while the paramagnetic behaviors are presented when MII = ZnII and CdII, confirmed by the magnetic susceptibility measurements and further supported by using the PHI program. Furthermore, the bridging ligand to the terminal FeIII charge transfer (LMCT) transitions emerged in all complexes but the central FeII to terminal FeIII charge transfer (MMCT) only presented in complex 2, strongly supported by the UV/vis-NIR electronic spectra and TDDFT calculations.

Intertwining of Magnetism and Charge Ordering in Kagome FeGe.

Recent experiments report a charge density wave (CDW) in the antiferromagnet FeGe, but the nature of the charge ordering and the associated structural distortion remains elusive. We discuss the structural and electronic properties of FeGe. Our proposed ground state phase accurately captures atomic topographies acquired by scanning tunneling microscopy. We show that the 2 × 2 × 1 CDW likely results from the Fermi surface nesting of hexagonal-prism-shaped kagome states. FeGe is found to exhibit distortions in the positions of the Ge atoms instead of the Fe atoms in the kagome layers. Using in-depth first-principles calculations and analytical modeling, we demonstrate that this unconventional distortion is driven by the intertwining of magnetic exchange coupling and CDW interactions in this kagome material. The movement of Ge atoms from their pristine positions also enhances the magnetic moment of the Fe kagome layers. Our study indicates that magnetic kagome lattices provide a material candidate for exploring the effects of strong electronic correlations on the ground state and their implications for transport, magnetic, and optical responses in materials.

Self-assembly hollow magnetoelectric composites emerging tunable property between microwave absorption and shielding with light-weight and broad bandwidth

In generally, microwave absorption and shielding are a pair of conjugate properties, which merely achieves in the same system of electro-magnetic materials. In this work, Prussian blue analogues (PBA) derived hollow CoNi@C frames embedding with reduced graphene oxide (rGO) are successfully synthesized through a facile self-assembly method. In addition to considerable dielectric loss originating from high conductivity components of C@rGO, magnetic loss is also impressive due to the dynamic magnetic coupling interaction among the closely spaced magnetic units of CoNi. Finally, the CoNi@C@rGO composite with an extremely low loading ratio of 30 wt% reveals a strong reflection loss of − 48 dB and a broad absorption bandwidth of 6.24 GHz concurrently at a thin thickness of 1.6 mm. The launch field is obviously suppressed by covering the CoNi@C@rGO coating and RCS is below − 10 dBm2 within the entire detection angles (−90°<theta<90°). Meanwhile, superior shielding effectiveness (SE) of 66.2 dB is also achieved in the CoNi@C@rGO composite at 3.59 mm. It demonstrates that our work provides an effective and facile approach to make a transformation between microwave absorption and microwave shielding in the same material system.

Conjugated coupler curvature enhances magnetic spin coupling in π-diradicals

This work computationally evidences that the functionalized buckybowls as the couplers can considerably enhance the magnetic spin coupling interaction in π-diradicals through curving the coupler to reduce its aromaticity and increase spin polarization of radical groups.

Magnetic‐Dielectric Complementary Fe‐Co‐Ni Alloy/Carbon Composites for High‐Attenuation C‐Band Microwave Absorption via Carbothermal Reduction of Solid‐Solution Precursor

AbstractFerromagnetic alloys/carbon composites with excellent electrical and magnetic properties are highly desirable as electromagnetic wave absorption materials, but achieving high‐attenuation performance in C‐band (4–8 GHz) remains a challenge. Herein, a direct carbothermal reduction of organic gluconate solid‐solution precursor method is developed to synthesize ferromagnetic Fe‐Co‐Ni alloy/carbon composites, which realize high‐attenuation electromagnetic wave absorption in C‐band. By virtue of Fe, Co, and Ni elements homogeneously dispersing at the molecular level in the solid‐solution precursor with the regulated mole ratio, serial FeCo2Ni/C, Co7Fe3/C, FeNi3/C, and Co3Ni/C composites can be deliberately prepared. First‐principles calculations and off‐axis electron holograms can clearly unravel that these Fe‐Co‐Ni alloys could perform as excellent dielectric‐magnetic complementary loss units to trigger synergistic electronic dipole polarization oscillation, magnetic moment resonance, and magnetic coupling interaction. Meanwhile, the rich alloy–carbon interfaces and conductive carbon skeleton can facilitate delightful interfacial polarization and conductive loss. Combining these positive electromagnetic energy dissipation characteristics, FeCo2Ni/C with strengthened dipole polarization oscillation and outstanding impedance matching realizes an extremely high‐attenuation absorption performance with a minimum reflection loss of −82.2 dB at 5.21 GHz. This work provides a feasible and flexible insight into producing magnetic‐dielectric complementary Fe‐Co‐Ni alloys/carbon composites with various alloy compositions as excellent electromagnetic wave absorbers.

Intramolecular Proton Transfer Modulation of Magnetic Spin Coupling Interaction in Photochromic Azobenzene Derivatives with an Ortho-Site Hydroxyl as a Modulator.

Proton transfer modulation in an organic diradical is apparently the most conspicuously attractive phenomenon. In this work, we have computationally designed the trans and cis forms of photochromic azobenzene- (AB-) bridged diradicals by considering AB as coupler and two nitroxide (NO) as spin sources and a -OH attaching at the ortho site as modulator. Our object is that through intramolecular proton transfer to protonate the azo-unit (-N═N-) the magnetic coupling characteristics of the designed diradicals can be modulated in their photocontrolled trans and cis forms. The calculated results indicate that PT can significantly regulate the magnetic spin coupling constants, J = -701.3 cm-1 ↔ -286.2 cm-1 for the trans form and -544.1 cm-1 ↔ -328.1 cm-1 for the cis form. In particular, we discover that these designed magnetic molecules can undergo magnetic conversion between antiferromagnetic and ferromagnetic coupling through PT, besides there is considerable increase in the magnitude of their magnetic coupling constants J, (e.g., -59.97 to 172.4 cm-1) for the trans-mode at the m/m linking site. Moreover, we discover that the nitroxide radicals at different linking positions have a significant impact and remarkably alter the magnetic spin coupling characteristics of AB-based diradicals. Besides, various radical groups are used as spin sources which corroborated our assumptions and tended to the same conclusion. This work offers a novel understanding of the spin interaction mechanism and a viable approach for the rational design of new AB-based magnets which are beneficial for further applications in the future.

Crystal and magnetic structures of the Ir(V) JeffIr = 0 double perovskite LaSrNiIrO6

LaSrNiIrO6 adopts a B-site cation-ordered double perovskite structure with a strong a–a–c ​+ ​cooperative tilting distortion (space group P21/n a ​= ​5.5931(1) Å, b ​= ​5.5676(1) Å, c ​= ​7.8850(1) Å, β ​= ​90.01(1) o). Magnetization and neutron diffraction data indicate LaSrNiIrO6 adopts a ‘type II’ antiferromagnetic structure (TN ​= ​70 ​K) in which the Ni spins are arranged in an antiferromagnetic manner with their next-nearest-neighbors, with no ordered moment observed for Ir. DFT calculations, including spin-orbit coupling effects, confirm S ​= ​1 Ni2+ and Jeff ​= ​0 Ir5+ local configurations and indicate strong Ni(3dx2−y2)1 –O(2p)–Ir(5dx2−y2)0–O(2p)–Ni(3dx2−y2)1 σ-type super-super-exchange is the dominant magnetic coupling interaction in the system.

Remarkable Magnetic Exchange Coupling via Constructing Bi‐Magnetic Interface for Broadband Lower‐Frequency Microwave Absorption

AbstractSevere lower‐frequency (2–8 GHz) microwave pollution caused by the rapid development of 5th generation (5G) communication posts significance on cutting‐edge microwave absorbers. However, the intensely coupled wave‐impedance and microwave dissipating ability dramatically hinder their performance in the exact lower‐frequency range. The rationally designed heterostructure of hard/soft ferrite composite provides an efficient solution to address the issue. In this context, core‐shell structured hard/soft BaFe(12‐x)CoxO19@Fe3O4 with abundant heterointerface is created using facile spray‐drying and subsequent solvothermal approach, where hard magnetic BaFe(12‐x)CoxO19 serves as the core and soft magnetic Fe3O4 serves as the shell, respectively. The unique core‐shell integration contributes sufficient magnetic exchange coupling interaction for strong magnetic loss beyond Snoek's limitation, which considerably boosts a lower‐frequency microwave absorption. Accordingly, the minimum reflection loss (RLmin) of typical BaFe11.6Co0.4O19@Fe3O4 microcomposite reaches −48.9 dB at the thickness of 3.5 mm, its bandwidth of reflection loss &lt; −10 dB can cover almost all the S and C bands (2.6–8 GHz). Generally, an easy and controllable pathway is conveyed in this work to encourage improved magnetic loss ability as well as decouple the wave‐impedance and microwave dissipating ability in magnetic composites, which widens the road to the development of advanced lower‐frequency magnetic absorbers.

Competing long-range and short-range interactions in ferromagnetic semiconductors: Evidence from first principle calculations

Based on ab-initio calculations, we have investigated the structural, electronic, and magnetic properties of diluted magnetic semiconductors (Ba1−yKy)F(Zn1−xMnx)tAs with (K, Mn) substitution in the parent compounds, BaFZnAs and BaFMnAs. The coexistence of two types of magnetic exchange coupling interactions was detected via the calculation of the distance-resolved and the individual exchange parameters J(dMn0−Mni)≡Ji, where i runs over the ith nearest neighbor atom (iNN) of the reference one Mn0 distanced by dMn0−Mni. The short-range interactions (SRI), at J1 and J2, are strongly influenced by hole doping and substitutional disorder of both hole and spin co-doping. The long-range interaction (LRI), at distances beyond the 2NN, of a ferromagnetic nature, is less sensitive to hole doping, although these holes are the reason for their appearance. The results analysis showed that the dependence of the LRI on y/x doping ratio, in the co-doping system, is more systematic than on the y or x doping separately. In (BaK)F(ZnMn)As system, a peak appears in the LRI at around 1.5 of y/x doping ratio. Therefore, an estimation of the optimal hole doping for each spin doping concentration was given, where it is important to obtain the maximal ferromagnetic coupling, therefore the highest ferromagnetic ordering temperature, TC. Our findings are consistent with experiments, manifested, especially, in the saturation of the ordering temperature at large hole doping, as was obtained for the experimental TC of (BaK)(ZnMn)2As2 system. The results also show a doubling of the TC when the spin doping is doubled at high hole doping. Finally, we demonstrated via a proposed model that the SRI has the Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction nature.

Enhancing magnetic coupling through protonation of benzylideneaniline-bridged diradicals and comparison with stilbene- and azobenzene-based diradicals.

Taking nitroxide radicals as spin sources, we explore the intramolecular magnetic coupling interactions of the trans- and cis-forms of benzylideneaniline (BA)-bridged diradicals, in which the central -CH[double bond, length as m-dash]N- unit can undergo single protonation to convert to its protonated counterpart or vice versa. The calculated results for these two pairs of diradicals (protonated versus unprotonated trans and cis forms) verify that the signs of their magnetic coupling constants J do not change, but the magnitudes significantly increase after protonation. In the structure, the better conjugation of the protonated trans diradical and two reduced CCNC and CCCN torsion angles of the protonated cis one make for a more efficient spin transport, promoting the spin polarization, thus leading to larger spin couplings. In terms of mechanism, the proton-induced magnetic enhancement should be attributed to strong participation of the coupler BA through its lowest unoccupied molecular orbital (LUMO) with a lower energy level after protonation, and the small HOMO-LUMO (HOMO: highest occupied molecular orbital) gap of the coupler BA through protonation is crucial in explaining such remarkable spin-coupling enhancement. Furthermore, different linking modes of the radical groups to the couplers are also considered to confirm our conclusions. In addition, we also make a comparison of the magnetic coupling strengths among their isoelectronic analogues of BA-, AB- and stilbene-bridged nitroxide diradicals before or after protonation, and find a linear correlation among them. It should be noted that the magnetic behaviors of all these diradicals obey the spin alternation rule and singly occupied molecular orbital (SOMO) effect. This work provides helpful information for the rational design of promising magnetic molecular switches.