Type Of Magnetic Coupling Research Articles

Does Mn2+-Mn2+ Spin-Exchange Interaction Involve Mn2+ Luminescence of Mn2+-Doped/Concentrated Materials?

Mn2+-doped luminescent quantum dots play a vital role in the fields of optoelectronic materials and devices. The presence of five unpaired d electrons in Mn2+ ions facilitates spin-exchange interactions, profoundly influencing the spin state of the exciton and thereby impacting the optical behaviors. However, the involvement and specific effects of spin-exchange interactions on optical properties of Mn2+ in insulating bulk phosphors remain a subject of controversy, attributed to the scarcity of solid evidence and the interference of various factors. In this Perspective, we delve into the fundamentals and recent advancements concerning the Mn2+-Mn2+ spin-exchange interaction in Mn2+ luminescent materials. The discussion encompasses various aspects, such as types of magnetic coupling, the coupling mechanism in optical ground state and excited state, as well as effective measures for verification. This Perspective underscores the existing knowledge gaps in Mn2+-doped bulk phosphors, highlighting significant opportunities for further exploration and advancement in both fundamental and applied research within this domain.

Looking for a quantum spin liquid in the BaNi2(V1−xPx)2O8 spin 1 honeycomb system

ABSTRACTThe general magnetic characterisation of a series of materials in the BaNi2V2O8-BaNi2P2O8 layered honeycomb spin-1 system is reported. A change from dominantly 2-dimensional (2D) to dominantly 3-dimentional (3D) magnetic character is observed on progressing from the pure V to the pure P material. The change is continuous with composition in BaNi2(V1−xPx)2O8. But a variety of features in the temperature-dependent magnetic susceptibilities at low temperatures suggest that the magnetic system is complex. Although the Curie–Weiss temperature becomes less strongly negative on increasing the P content, an indication of increased competition between different types of magnetic coupling, the system does not appear to be approaching a quantum spin liquid state at low temperatures.

Atomic scale imaging of magnetic circular dichroism by achromatic electron microscopy.

In order to obtain a fundamental understanding of the interplay between charge, spin, orbital and lattice degrees of freedom in magnetic materials and to predict and control their physical properties1-3, experimental techniques are required that are capable of accessing local magnetic information with atomic-scale spatial resolution. Here, we show that a combination of electron energy-loss magnetic chiral dichroism 4 and chromatic-aberration-corrected transmission electron microscopy, which reduces the focal spread of inelastically scattered electrons by orders of magnitude when compared with the use of spherical aberration correction alone, can achieve atomic-scale imaging of magnetic circular dichroism and provide element-selective orbital and spin magnetic moments atomic plane by atomic plane. This unique capability, which we demonstrate for Sr2FeMoO6, opens the door to local atomic-level studies of spin configurations in a multitude of materials that exhibit different types of magnetic coupling, thereby contributing to a detailed understanding of the physical origins of magnetic properties of materials at the highest spatial resolution.

Critical behaviors of helimagnetic ordering systems relating to skyrmion

Study of critical phenomena plays a key role in developing the theory of phase transition. In this article, we mainly review some new experimental results about the critical phenomena reported recently in the helimagentic ordering materials. These materials exhibit a kind of a vortex-like spin texture so-called skyrmion phase. The skyrmion phase has great potential applications in the new spin-based storage due to the topologically protected stability, nanometric size, and current-driven motion. Generally, the skyrmion state exists in a helimagentic system due to the DzyaloshinskiiMoriya (DM) interaction which forms in the crystal structure without inversion symmetry. It usually emerges just below the helimagentic phase transition temperature TC under a certain temperature and magnetic field. In this review article, firstly, we introduce some basic concepts about the phase transition, such as critical phenomenon, critical exponents, scaling law, and universality. Secondly, we discuss two different methods which can help us to obtain the critical exponents, i.e., the iteration method based on the isothermal dc-magnetization and the fitting technique based on the magnetic entropy change. Both methods are extensively used in the current study of critical phenomena Thirdly, we analyze and outline some latest studies of critical behaviors and critical exponents for several typical helimagnetic systems with skyrmion state, such as MnSi, FeGe, Cu2OSeO3, Fe1-xCoxSi, and Fe1.5-xCoxRh0.5MoN. The B20 compound MnSi is a typical skyrmion material, which undergoes a paramagnetic-to-helimagnetic phase transition at ~30.5 K and the skyrmion phase appears just below TC as an appropriate external magnetic field is applied. Investigations show that critical exponents of MnSi belong in the universality class of a tricritical mean-field model, implying the existence of a long-rang magnetic interaction in this system. The critical behavior of MnSi reveals that its first-order phase transition can be driven into a second-order phase transition by the action of external magnetic field, where a field-induced tricritical point is found among the helimagnetic, conical, and paramagnetic phases in MnSi system. Unlike MnSi, the critical exponent of the near-room-temperature skyrmion system FeGe, which undergoes a helimagentic phase transition at 278 K, belong to the three-dimensional Heisenberg model. The critical behavior of Cu2OSeO3 is similar to that of FeGe, which indicates that the magnetic interactions in these two systems are dominated by the short-range nearestneighbor isotropic magnetic coupling. In addition, studies revealed that magnetic interaction and critical behavior of the skyrmion system can be effectively modulated by doping. The critical exponents of Fe1-xCoxSi and the newly founded skyrmion system of Fe1.5-xCoxRh0.5MoN indicated that the doping concentration of Co can change and affect their critical behaviors. In addition, it was demonstrated that the doping of Co enhanced the anisotropic magnetic coupling in Fe1-xCoxSi while it suppressed that in Fe1.5-xCoxRh0.5MoN. Fourthly, according to the universality and the scaling equations, we proposed a method to construct the detailed H-T phase diagram around the phase transition temperature in the system exhibiting field-induced phase transition. Finally, we make a brief summary and suggest our perspectives of the study of critical phenomena in helimagentic system. The results of critical behaviors indicate that although all these helimagentic systems exhibit a similar skyrmion phase, their essential magnetic interactions belong in different universality classes, indicating different types of magnetic coupling in these systems. Furthermore, the results also suggest that magnetic coupling can also be effectively tuned by the external modulation.

Analysis on Double Quench Characteristics and Power Burdens of HTSC elements comprising the Series Connected Magnetic Coupling Type SFCL using Additional Winding

Analysis on Double Quench Characteristics and Power Burdens of HTSC elements comprising the Series Connected Magnetic Coupling Type SFCL using Additional Winding

Strain-Induced Isostructural and Magnetic Phase Transitions in Monolayer MoN2

The change of bonding status, typically occurring only in chemical processes, could dramatically alter the material properties. Here, we show that a tunable breaking and forming of a diatomic bond can be achieved through physical means, i.e., by a moderate biaxial strain, in the newly discovered MoN2 two-dimensional (2D) material. On the basis of first-principles calculations, we predict that as the lattice parameter is increased under strain, there exists an isostructural phase transition at which the N-N distance has a sudden drop, corresponding to the transition from a N-N nonbonding state to a N-N single bond state. Remarkably, the bonding change also induces a magnetic phase transition, during which the magnetic moments transfer from the N(2p) sublattice to the Mo(4d) sublattice; meanwhile, the type of magnetic coupling is changed from ferromagnetic to antiferromagnetic. We provide a physical picture for understanding these striking effects. The discovery is not only of great scientific interest in exploring unusual phase transitions in low-dimensional systems, but it also reveals the great potential of the 2D MoN2 material in the nanoscale mechanical, electronic, and spintronic applications.

Successive spin polarizations underlying a new magnetic coupling contribution in diluted magnetic semiconductors

We propose a new type of magnetic coupling (MC) that is found in diluted magnetic semiconductors (DMSs). The origin of this is found to be the result of charge transfer processes followed by successive spin polarizations (SSPs) along successive cation–anion segments which include the impurities. The basic process underlying the SSP-based MC (SSP-MC) is the sharing of a single spin orbital by two neighboring impurities. As such, it can be considered as a localized double exchange as it is not mediated by free carriers. SSP-MC can be either ferromagnetic (SSP-FMC) or antiferromagnetic (SSP-AFMC) and, as demonstrated here, the SSP-FMC can be significantly enhanced via codoping; it can act in competition with superexchange and/or double and/or p–d exchange interactions. While the SSP-MC is not directly related to the magnitude of the magnetic moments of the impurities, it depends strongly on the energy difference of the host and impurity d-band centers, the difference of their electronegativities and rather weakly on the coupling interactions between them as well as between the cations and their mediating anions. The validity of the proposed SSP-MC as a new type of magnetic coupling is demonstrated by ab initio results for DMSs, namely ZnO, GaN, GaP, TiO2 and MoS2 monodoped (with Co, Cu and Mn) and codoped (with Co–Cu–Co and Mn–Cu–Mn).

Magnetism and electronic structure of binuclear manganese complexes in ortho-quinone ligand and polymer environments

By means of mechanochemical synthesis we obtained a coordination polymer containing binuclear manganese complexes with organic catechol∕ortho-quinone ligands. The reaction system contained polystyrene, manganese acetylacetonate, and donor-acceptor mixture catechol∕ortho-quinone. Electron paramagnetic resonance (EPR) and infrared spectroscopic data show that the binuclear manganese complex is covalently linked to the chain of polystyrene. Theoretical EPR spectrum analysis revealed a triplet state of the complex with two nonequivalent manganese ions coupled to each other by spin exchange. The type of magnetic coupling between manganese ions in this system is similar to the one in manganese based inorganic magnetic materials.

Magnetic property investigations on ZnMnO

Abstract There have been controversial reports about the type of magnetic coupling and hence ferromagnetism in ZnMnO. We have investigated the magnetic properties of ZnxMn1−xO layers grown by Molecular Beam Epitaxy (MBE) on sapphire substrates. At first sight, the investigated ferromagnetism in our ZnMnO layers deposited on Al2O3 substrates seemed trivial, but the results of extensive analyses of the layers and also data from the Al2O3 substrates used strongly indicate that the influence of the substrate on magnetic property measurements needs to be considered when confirming ferromagnetism in Mn-doped ZnO layers. Our ZnMnO layers showed a paramagnetic behaviour.

Magnetic property investigations on Mn-doped ZnO Layers on sapphire

The need for diluted magnetic semiconductors has stimulated research on Mn-doped ZnO. However, the type of magnetic coupling (ferro/para) in ZnMnO remains an issue of debate. We have investigated the magnetic properties of Mn-doped ZnO layers grown by molecular beam epitaxy. Some samples showed a hysteresis with remnant magnetization on the order of 10−5emu, thus eventually suggesting ferromagnetism. We observed that the critical influence of the substrate substantially affects magnetic property measurements. This has to be taken into account in order to clearly confirm ferromagnetism. In our case, after subtraction of the substrate effect, there is no evidence of a ferromagnetic behavior for the ZnMnO samples.

Interface coupling in a ferromagnet/antiferromagnet bilayer

A micromagnetic model accounting for exchange, dipolar interactions, and magnetocrystalline anisotropy has been applied to simulate the magnetic structure of a low anisotropy antiferromagnetic thin film on a ferromagneticsubstrate. In particular, the influence that interface uncompensated moments have on the type of magnetic coupling between the antiferromagnetic and ferromagnetic layers has been evaluated. The long-range magnetic dipole-dipole interactions force the antiferromagnetic film to have in-plane anisotropy. For the fully magnetically compensated interface, the model gives an antiferromagnetic uniaxial anisotropy perpendicular to the magnetization of the ferromagnetic film. There is a rapid transition from perpendicular to parallel anisotropy as the amount of uncompensated moments is increased. The density of uncompensated moments necessary to induce such transition decreases as the interface exchange coupling is reduced. These predictions are compared to the experimentally observed behavior of NiO in various types of interfaces with ferromagnetic materials.

Mn site substitution of La0.67Ca0.33MnO3 with closed shell ions: Effect on magnetic transition temperature

Mn site is substituted with closed shell ions (Al, Ga. Ti, Zr and a certain combination of Zr and Al) and also with Fe and Ru ions carrying the magnetic moment (S=5/2 and 2 respectively) at a fixed concentration of 5 at. %. Substitution did not change either the crystal symmetry or the oxygen stiochiometry. All substituents were found to suppress both the metal-insulator and ferromagnetic transition temperatures (TP(r) and TC respectively) to varied extents. Two main contributions identified for the suppression are the lattice disorder arising due to difference in the ionic radii (rMn3+-rM) between the substituent (rM) and the Mn3+ ion (rMn3+) and in the case of the substituents carrying a magnetic moment, the type of magnetic coupling between the substituent and that of the neighboring Mn ion.

Theoretical Studies of Intra- and Inter- Magnetic Interactions in TMAO(1,3,5,7 - Tetramethyl - 2, 6- Diazaadamantane N, N′ - Dioxyl)

Ferromagnetic properties of TMAO organic crystal, especially α-form crystal, are studied theoretically. There are two nitroxide groups, that is, both intramolecular magnetic interaction in one molecule and inter-molecular interaction between two molecules are expected in contrast to many organic ferromagnetic crystalline species that have been reported by other groups. Obtained Jab values for intra- and inter- molecular interactions are positive and small positive for only a few pairs, respectively. Cooperation of two types of magnetic coupling is essential to realize bulk ferromagnetic behavior.

57 Fe Mössbauer spectroscopy applied to the study of rare-earth iron permanent magnets

A survey of some important applications of 57Fe Mossbauer spectroscopy to the study of local magnetic and structural characteristics of the main phases in the rare-earth-transition metal (RE–TM) class of materials used in the development of the new generations of high performance permanent magnets is presented. A brief history of the hard magnets evolution in the last decades is followed by the description and interpretation of the main effects on the hyperfine interactions revealed by the Mossbauer technique. The contribution of the distinct crystallographic iron sites to the saturation magnetization of the rare-earth iron compounds is discussed in terms of the corresponding types of magnetic coupling, based mainly on the iron–iron distances, the number of iron neighbors and the respective hyperfine fields. These features are inferred from the energy of the resonant absorption by the iron sites 4e/4c/8j1/8j2/16k1/16k2 in the Nd2Fe14B, sites 6c/9d/18f/18h in the light RE2Fe17N3 and 8f/8i/8j in the RE(Fe12-xTMx) phases. The direction of the easy axis of magnetization is discussed taking into account the effects due to the interaction between the local magnetization vector and the electric field gradients. Some other characteristics such as the occupancy of the TM atoms in the 1 : 12 compounds as well as in some hybrid (Fe +TM) 2 : 17 structures are also discussed in terms of the changes in the relative subspectral areas. The effects regarding charge transfers and lattice expansions due to the incorporation of nitrogen and also of other different interstitial elements to the 2 : 17 rhombohedral structure are discussed considering the relative changes of the isomer shifts in comparison with the alterations in the parameter due exclusively to the respective volume expansions.