Spin Exchange Research Articles

Comprehensive analysis of the magnetic field closed-loop control system in SERF atomic magnetometer

Benefiting from the capability to measure and suppress magnetic field interferences in situ, the closed-loop magnetometer system has garnered significant attention. In this paper, the low-pass filtering link is analyzed theoretically and experimentally for the first time within the framework of the single-beam spin exchange relaxation free atomic magnetometer system (the object to be controlled). The analysis not only elucidates its impact on the closed-loop system but also establishes optimal operating parameters through a comprehensive consideration of factors such as steady-state error, bandwidth, and other metrics. A comparison and analysis of the direct output signal of the system with the controller output signal reveal the necessity of using the controller output as the closed-loop system’s output, supported by the amplitude and frequency response characteristics of the output signal. The paper introduces evaluation indicators essential for comparing the long-term measurement stability of open- and closed-loop systems, and it explores the correlation between the output signals of the open- and closed-loop systems and the cardio-magnetic input signals. Finally, the calibration methods for multi-channel closed-loop magnetometers are discussed.

Enhancing Intrinsic Magnetic Hardness by Modulating Antagonistic Interactions in the Rare-Earth-Free Magnetic Solid Solution Hf2 Fe1-δ Ru5-x Irx+δ B2.

The quinary members in the solid solution Hf2 Fe1-δ Ru5-x Irx+δ B2 (x=1-4, VE=63-66) have been investigated experimentally and computationally. They were synthesized via arc-melting and analyzed by EDX and X-ray diffraction. Density functional theory (DFT) calculations predicted a preference for magnetic ordering in all members, but with a strong competition between ferro- and antiferromagnetism arising from interchain Fe-Fe interactions. The spin exchange and magnetic anisotropy energies predicted the lowest magnetic hardness for x=1 and 3 and the highest for x=2. Magnetization measurements confirm the DFT predictions and demonstrate that the antiferromagnetic ordering (TN =55-70 K) found at low magnetic fields changed to ferromagnetic (TC =150-750 K) at higher fields, suggesting metamagnetic behavior for all samples. As predicted, Hf2 FeRu3 Ir2 B2 has the highest intrinsic coercivity (Hc =74 kA/m) reported to date for Ti3 Co5 B2 -type phases. Furthermore, all coercivities outperform that of ferromagnetic Hf2 FeIr5 B2 , indicating the importance of AFM interactions in enhancing magnetic anisotropy in these materials. Importantly, two members (x=1 and 4) maintain intrinsic coercivities in the semi-hard range at room temperature. This study opens an avenue for controlling magnetic hardness by modulating antagonistic AFM and FM interactions in low-dimensional rare-earth-free magnetic materials.

Rare earth based Mg- chalcogenides MgDy2(S/Se)4 as an emerging aspirant for spintronic and thermoelectric applications

The magnesium based spinel chalcogenides are outstanding materials for spintronic technology and energy applications. Herein, the modified Becke Johnson potential (TB-mBJ) was employed to investigate the electrical, ferromagnetism, and thermoelectric properties of MgDy2(S/Se)4 spinels comprehensively. The energy emitted during optimization as well as formation energy has both been used to demonstrate the stability of the cubic phase. The density of states, Curie temperature, exchange coupling, and spin polarization are elaborated to address the nature of ferromagnetism. Further, half metallic ferromagnetism is studied in terms of hybridization, exchange energies, and exchange constants. In contrast to the clustering effect of the internal magnetic of Dy atoms in the structure, the lowering of Dy's magnetic moment and its transferring on Mg, and S/Se sites demonstrate that the ferromagnetism is caused by the exchange of electron spin. Furthermore, thermoelectric properties were studied and various thermoelectric parameters such as electrical and thermal conductivities, Seebeck coefficient (S), and power factor (PF) of the examined spinels have been determined.

Quantification and suppression of optical non-orthogonality and light intensity noise in all-optical hot atomic sensing systems

All-optical hot atomic sensing systems such as optical pumping magnetometers (OPM) and comagnetometers, nuclear magnetic resonance (NMR) magnetometers and gyroscopes, have the ability to sense magnetic field, anomalous field and inertial rotation, thus having a wide potential for applications in precision measurement, fundamental physics research and inertial navigation. System noise limits the minimum value of the signal that can be measured and there is coupling effect between the noises. Therefore, the quantification and suppression of various noise are challenging and should be investigated. As one of the major noises, the light intensity fluctuation of the probe light and the pump light affects the sensitivity of the all-optical hot atomic sensing systems. However, there has been no in-depth research on the quantification of the light intensity noise. In this paper, a method of measuring the light intensity noise is proposed, which can be applied to kinds of all-optical hot atomic sensing systems. For verification, the effects of probe and pump light intensity fluctuations on system noise are simulated and experimentally verified in a spin exchange relaxation free (SERF) comagnetometer. Besides, it is found that the optical non-orthogonality amplifies the probe light intensity noise by more than 3.4 times and a quantification method of optical non-orthogonality is proposed. Finally, a suppression method of the light intensity noise is presented by suppressing the optical non-orthogonality and the noise is suppressed by 59%. A universal light intensity noise quantification method is proposed for all-optical hot atomic sensing systems, and a light intensity noise suppression method is proposed for SERF comagnetometers, which can be applied to the suppression of noises coupled with atomic polarization.

Long-distance spin communication via ambipolar conductor with electron–hole spin exchange interaction

Spin accumulation in a nonmagnetic (N) metal embedded between two ferromagnetic metals is still crucial in current spintronics because long-distance spin communication via the N metal can make all-spin logic (ASL) devices feasible. Graphene is almost the only N-region material suitable for ASL devices because its low intrinsic spin–orbit coupling results in a spin diffusion length, , of over 30 µm at room temperature, but long-distance spin communication beyond remains difficult. The present study proposes a way to remove the restriction caused by . In our proposal, an ambipolar conductor, in which electron and hole contribute to electronic conduction and interact with each other, is used for the N-region in a double-heterojunction magnetic structure. When the electron–hole interaction is accompanied by spin exchange, long-distance spin communication characteristic is predicted. Approximately 70 types of ambipolar conductors, including elemental metals and metal alloys, are available. Hence, this material variation may open a new spintronics field, ambipolar spintronics, which may realize operation mechanisms that cannot be achieved using conventional single-band metals. Finally, we present a comprehensive argument on the interface-mediated coupling mechanism between spins and charges, which is the basis of the generation of the spin-coupled interface voltage.

Influence of intrinsic spin ordering in La0.6Sr0.4Co0.8Fe0.2O3-δ and Ba0.6Sr0.4Co0.8Fe0.2O3-δ towards electrocatalysis of oxygen redox reaction in solid oxide cell.

The redox reaction of oxygen (OER & ORR) forms the rate determining step of important processes like cellular respiration and water splitting. Being a spin relaxed process governed by quantum spin exchange interaction, QSEI (the ground triplet state in O2 is associated with singlet oxygen in H2O/OH-), its kinetics is sluggish and requires inclusion of selective catalyst. Functionality and sustainability of solid oxide cell involving fuel cell (FC) and electrolyzer cell (EC) are also controlled by ORR (oxygen redox reaction) and OER (oxygen evolution reaction). We suggest that, presence of inherent spin polarization within La0.6Sr0.4Co0.8Fe0.2O3-δ (LSCF6482) (15.86 emu g-1) and Ba0.6Sr0.4Co0.8Fe0.2O3-δ (BSCF6482) (3.64 emu g-1) accounts for the excellent selective electrocatalysis towards ORR and OER. QSEI forms the atomic level basis for OER/ORR which is directly proportional to spin ordering (non-zero magnetization) of the active electrocatalyst. LSCF6482 exhibits (21.5 kJ mol-1@0.8 V for ORR compared to 61 kJ mol-1@0.8 V for OER) improved ORR kinetics whereas BSCF6482 (18.79 kJ mol-1@0.8 V for OER compared to 32.19 kJ mol-1 for ORR@-0.8 V) is best suited for OER under the present stoichiometry. The findings establish the presence of inherent spin polarization of catalyst to be an effective descriptor for OER and ORR kinetics in solid oxide cell (SOC).

Radical enhanced intersystem crossing mechanism, electron spin dynamics of high spin states and their applications in the design of heavy atom-free triplet photosensitizers.

Heavy atom-free triplet photosensitizers (PSs) can overcome the high cost and biological toxicity of traditional molecular systems containing heavy atoms (such as Pt(II), Ir(III), Ru(II), Pd(II), Lu(III), I, or Br atoms) and, therefore, are developing rapidly. Connecting a stable free radical to the chromophore can promote the intersystem crossing (ISC) process through electron spin exchange interaction to produce the triplet state of the chromophore or the doublet (D) and quartet (Q) states when taking the whole spin system into account. These molecular systems based on the radical enhanced ISC (REISC) mechanism are important in the field of heavy atom-free triplet PSs. The REISC system has a simple molecular structure and good biocompatibility, and it is especially helpful for building high-spin quantum states (D and Q states) that have the potential to be developed as qubits in quantum information science. This review introduces the molecular structure design for the purpose of high-spin states. Time-resolved electron paramagnetic resonance (TREPR) is the most important characterization method to reveal the properties of these molecular systems, generation mechanism and electron spin polarization (ESP) of the high spin states. The spin polarization manipulation of high spin states and potential application in the field of quantum information engineering are also summarized. Moreover, molecular design principles of the REISC system to obtain long absorption wavelength, high triplet state quantum yield and long triplet state lifetime are introduced, as well as applications of the compounds in triplet-triplet annihilation upconversion, photodynamic therapy and bioimaging. This review is useful for the design of heavy atom-free triplet PSs based on the radical-chromophore molecular structure motif and the study of the photophysics of the compounds, as well as the electron spin dynamics of the multi electron system upon photoexcitation.

Quantum fundaments of catalysis: true electronic potential energy.

Catalysis is a quantum phenomenon enthalpically driven by electronic correlations with many-particle effects in all of its branches, including electro-photo-catalysis and electron transfer. This means that only probability amplitudes provide a complete relationship between the state of catalysis and observations. Thus, in any atomic system material), competing space-time electronic interactions coexist to define its (related) properties such as stability, (super)conductivity, magnetism (spin-orbital ordering), chemisorption and catalysis. Catalysts, reactants, and chemisorbed and transition states have the possibility of optimizing quantum correlations to improve reaction kinetics. Active sites with closed-shell orbital configurations share a maximum number of spin-paired electrons, mainly optimizing coulombic attractions and covalency and defining weakly correlated closed-shell (WCCS) structures. However, in compositions with open-shell orbital configurations, at least, quantum spin exchange interactions (QSEIopenshells) arise, stabilising unpaired electrons in less covalent bonds and differentiating non-weakly (or strongly) correlated open-shell (NWCOS) systems. In NWCOS catalysts, electronic ground states can have bonds with diverse and rival spin-orbital orderings as well as ferro-, ferri- and multiple antiferro-magnetic textures, which deeply define their activities. Particularly in inter-atomic ferromagnetic (FM) bonds, the increase in relevance of non-classical quantum potentials can significantly optimize chemisorption energies, transition states (TSs), activation energies (overpotential) and spin-dependent electron transfer (conductivity), overall implying the need for explaining the thermodynamic and kinetic origin of catalysis from its true quantum electronic energy. To do so, we use the connection between the Born-Oppenheimer approximation and Virial theorem in the treatment of electronic kinetic and potential energies. Thus, the exact fundamental interactions that decompose TSs appear. The possibility of increasing the stabilization of TSs, due to quantum correlations on NWCO catalysts, opens the possibility of simultaneously reducing chemisorption enthalpies and activation barriers of reaction mechanisms, which implies the anticipation and explanation of positive deviations from the Brønsted-Evans-Polanyi principle.

ThCr2Si2C: An Antiferromagnetic Metal with a Cr2C Square Lattice.

A quaternary compound, ThCr2Si2C, was synthesized by using the arc-melting technique. The compound adopts a tetragonal CeCr2Si2C-type crystal structure. The electronic resistivity and specific heat data exhibit metallic behavior, while the magnetic susceptibility displays a pronounced broad peak at around 370 K, indicating the antiferromagnetic phase transition. The first-principles calculations suggest A-type antiferromagnetic ordering of the Cr sublattice, which is confirmed by neutron diffraction experiments. By comparing the crystal structure of ThCr2Si2C with the isostructural Cr-based compounds, the magnetic state of Cr 3d orbital is discussed in terms of the band-filling effects and indirect spin exchange interaction.

Remote entangling gate between a quantum dot spin and a transmon qubit mediated by microwave photons

Spin qubits and superconducting qubits are promising candidates for realizing solid-state quantum information processors. Designing a hybrid architecture that combines the advantages of different qubits on the same chip is a highly desirable but challenging goal. Here we propose a hybrid architecture that utilizes a high-impedance SQUID array resonator as a quantum bus, thereby coherently coupling different solid-state qubits. We employ a resonant exchange spin qubit hosted in a triple quantum dot and a superconducting transmon qubit. Since this hybrid system is highly tunable, it can operate in a dispersive regime, where the interaction between the different qubits is mediated by virtual photons. By utilizing such interactions, entangling gate operations between different qubits can be realized in a short time of 30 ns with a fidelity of up to 96.5% under realistic parameter conditions. Further utilizing this interaction, remote entangled state between different qubits can be prepared and is robust to perturbations of various parameters. These results pave the way for exploring efficient fault-tolerant quantum computation on hybrid quantum architecture platforms.

Model' spinovogo stekla dlya kvantovykh yam GaAs/AlGaAs, legirovannykh nemagnitnymi primesyami, vblizi perekhoda metall–izolyator

In a previous report, we presented experiments which suggested that ferromagnetic ordering of the spins of localized holes in GaAs/AlGaAs quantum wells could be observed when doped with shallow (Be) acceptors at impurity concentrations near the metal-insulator transition. The compensating impurity (Si) was introduced into a narrow region at the center of the barriers [4]. In this paper, we present results from magnetotransport experiments performed on similar structures, but without the compensating impurity (Si). In these samples, the compensation degree is expected to be controlled by the background defects located at the edges of the quantum wells and within the barriers. At low temperatures T ≤ 10 K, we observed isotropic, linear magnetoresistance, anomalous behavior of the Hall effect as a function of the magnetic field, and slow relaxation of resistance after the application of a magnetic field. We explain this anomalous magnetotransport as the manifestation of a ferromagnetic transition or spin glass, originating from indirect spin exchange between localized holes on impurities near the metal-insulator transition. However, we note that perfect disorder, including signs of interspin interactions, leads to unstable configurations. In what follows, we present a model in which we start with this perfect disorder, but apply a procedure to obtain a stable configuration. We show that the resulting spin structure, a “closely packed” structure of “droplets,” can reproduce the features observed in the experiment, particularly isotropic, linear magnetoresistance.

Probing chiral discrimination in biological systems using atomic force microscopy: The role of van der Waals and exchange interactions

We analyze from a theoretical perspective recent experiments where chiral discrimination in biological systems was established using Atomic Force Microscopy (AFM). Even though intermolecular forces involved in AFM measurements have different origins, i.e., electrostatic, bonding, exchange, and multipole interactions, the key molecular forces involved in enantiospecific biorecognition are electronic spin exchange and van der Waals (vdW) dispersion forces, which are sensitive to spin–orbit interaction (SOI) and space-inversion symmetry breaking in chiral molecules. The vdW contribution to chiral discrimination emerges from the inclusion of SOI and spin fluctuations due to the chiral-induced selectivity effect, a result we have recently demonstrated theoretically. Considering these two enantiospecific contributions, we show that the AFM results regarding chiral recognition can be understood in terms of a simple physical model that describes the different adhesion forces associated with different electron spin polarization generated in the (DD), (LL), and (DL) enantiomeric pairs, as arising from the spin part of the exchange and vdW contributions. The model can successfully produce physically reasonable parameters accounting for the vdW and exchange interaction strength, accounting for the chiral discrimination effect. This fact has profound implications in biorecognition where the relevant intermolecular interactions in the intermediate-distance regime are clearly connected to vdW forces.

System and approach to detecting of gastric slow wave and environmental noise suppression based on optically pumped magnetometer

Gastric slow waves (SWs) are commonly used for the quantitative assessment of gastric functional disorders. Compared with surface electrogastrography, using of magnetic signals to record SWs can achieve higher-quality signal recording. In this study, we discovered that optically pumped magnetometers (OPM) based on the spin exchange relaxation-free method have comparable weak magnetic detection capabilities to superconducting quantum interference devices but without liquid helium cooling. However, owing to the inevitable interference of low-frequency environmental drift, the characteristic features of SW are obscured, greatly increasing the difficulty in detecting gastric magnetic signals. Therefore, in this study, we constructed an OPM Magnetogastrography (OPM-MGG). We proposed an adaptive filtering architecture combined with environmental drift suppression and a non-stationary signal decomposition method for extracting SW signals. Through controlled human experiments, the results demonstrated that our testing system successfully extracted SW signals in the frequency range of 2–4 cycles per minute. The extracted SW signals exhibited consistent power and time–frequency characteristics with the reported results. This study validates the feasibility of (1) using the OPM-MGG system for capturing SW signals and (2) the proposed processing strategies for identifying ultralow-frequency SW signals. In conclusion, the OPM-MGG system and the signal extraction strategies developed in this study have the potential to provide a wearable technology for bioweak magnetic field measurements, offering new opportunities for both research and clinical applications.

Uncovering the universality of critical phenomenon in a ferromagnet Gd5Si4 prepared under high pressure

Manipulation of phase transition is of great interest not only because it can enhance the application ability of accompanying physical effects, but also because it allows us to uncover the physical connotations near the critical temperature point. In this work, we systematically examine the influence of high-pressure annealing (HPA) on critical phenomena in Gd5Si4 ferromagnet. A second-order magnetic phase transition is determined in the annealed sample under 3 GPa with a reduced Curie temperature. Various techniques including modified Arrott plot, Kouvel-Fisher method, and critical isotherm analysis are adopted to calculate critical exponents β, γ, and δ of HPA compound. Using the obtained parameters, we employ the renormalization group theory to calculate the spin exchange range, which satisfies J(r) ∼ r−4.454, exhibiting a longer-range-ordered ferromagnetic interaction. Our work indicates that HPA can manipulate the degree of order inside matter with a novel universality class, thus acquiring desired functionality through reasonable HPA treatment.

Dichotomy of heavy and light pairs of holes in the t−J model

A key step in unraveling the mysteries of materials exhibiting unconventional superconductivity is to understand the underlying pairing mechanism. While it is widely agreed upon that the pairing glue in many of these systems originates from antiferromagnetic spin correlations, a microscopic description of pairs of charge carriers remains lacking. Here we use state-of-the art numerical methods to probe the internal structure and dynamical properties of pairs of charge carriers in quantum antiferromagnets in four-legged cylinders. Exploiting the full momentum resolution in our simulations, we are able to distinguish two qualitatively different types of bound states: a highly mobile, meta-stable pair, which has a dispersion proportional to the hole hopping t, and a heavy pair, which can only move due to spin exchange processes and turns into a flat band in the Ising limit of the model. Understanding the pairing mechanism can on the one hand pave the way to boosting binding energies in related models, and on the other hand enable insights into the intricate competition of various phases of matter in strongly correlated electron systems.

Coherent spin exchange scattering of low-energy electrons by Ni2+ ions in antiferromagnetic crystal NiO under surface wave resonance: experimental and theoretical results revisited

Coherent spin exchange scattering of low-energy electrons by Ni2+ ions in antiferromagnetic crystal NiO under surface wave resonance: experimental and theoretical results revisited

Study of ferromagnetism, and thermoelectric behavior of double perovskites K2Z(Cl/Br)6 (Z = Ta, W, Re) for spintronic, and energy application

Spintronic is the developing technology which probes the properties of quantum devices with spin of electrons which reduce the size and enhance its speed. Therefore, here the role of 5d electrons and thermoelectric characteristics of double perovskites (DPs) K2ZCl/Br6 (Z = Ta, W, Re) elaborated comprehensively by density functional theory (DFT). The Heisenberg model spin polarization density (SP) has been applied to evaluate the Curie temperature (Tc) and spin polarization factor. The tolerance factor (tF) and formation energy (ΔH) have been calculated to confirm the stability of structures. Ferromagnetism has been discussed in terms of spin polarization, crystal field energy (ΔCF) and exchange energies (Δ(d), Δ(pd)). The double exchange mechanism, and exchange constants ensure the role of electrons spin in ferromagnetism instead of segregation of transition metal ions. The transferring of magnetic moments of transitions metals to nonmagnetic sites (K, Cl, Br) show the exchange of spin of electrons and integer values of total magnetic moment show 100 % spin polarization. Finally, the transport properties are studied in standings of electrical and thermal conductivities. The large value of Seebeck coefficient and power factor ensure the importance of studied DPs for thermoelectric generators.

5-Fluoro-1-Methyl-Pyrazol-4-yl-Substituted Nitronyl Nitroxide Radical and Its 3d Metal Complexes: Synthesis, Structure, and Magnetic Properties

The metal–radical approach is a well-established synthetic way toward multi-spin systems that relies on the coordination of stable radical ligands with transition metal ions. The advantage offered by the use of paramagnetic ligands is that metal–radical magnetic exchange coupling is direct between the magnetic orbitals of the radical and metal ion. With the aim of further exploring this approach, crystals of four heterspin complexes, [M(hfac)2LF]2 {M = Mn, Co, or Ni and hfac = hexafluoroacetylacetonate} and [Cu(hfac)2LF]n, were obtained using a new fluorinated pyrazolyl-substituted nitronyl nitroxide radical, 4,4,5,5-tetramethyl-2-(5-fluoro-1-methyl-1H-pyrazol-4-yl)-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (LF) as a ligand. The newly synthesized complexes were fully characterized, including X-ray crystallography and magnetometry. XRD analysis revealed that complexes [M(hfac)2LF]2 have similar dimer structures in which a metal ion is in a six-coordinated environment with four O atoms from the two hfac ligands, one radical O atom, and one pyrazole N atom from ligand LF. Nonetheless, the packing patterns of the complexes were found to be considerably different. In [Mn(hfac)2LF]2, there are no magnetically important short contacts between manganese dimers. By contrast, in [Co(hfac)2LF]2 and [Ni(hfac)2LF]2, there are short contacts between non-coordinate O atoms of nitronyl nitroxide moieties. Magnetic behaviors of [M(hfac)2LF]2 showed that the M ions and the directly coordinated radicals are strongly antiferromagnetically coupled (JMn-ON = −84.1 ± 1.5 cm−1, JCo-ON = −134.3 ± 2.6 cm−1, and JNi-ON = −276.2 ± 2.1 cm−1; H^=−2JS⃑^MS⃑^NO). Notably, the magnetization of [Mn(hfac)2LF]2 having molecular structure proved to be accompanied by hysteresis. The [Cu(hfac)2LF]n complex has a chain-polymer structure with alternating magnetic fragments: three spin exchange clusters {ONO–Cu(II)–ONO} and {Cu(II)} ions. Despite the direct coordination of radicals, its magnetic properties are weakly ferromagnetic (JCu-ON = 14.8 ± 0.3 cm−1).

Effect of the surface anisotropy on the magnetic behavior of ultra-thin films single-domain on the spin reorientation transition regime by monte carlo simulation

In this work, Monte Carlo simulations allowed for studying the effect of the surface anisotropy on the Spin Reorientation Transition regime for single-domain ultra-thin films. The simulations included spin moments (1), exchange constant (10 meV), magnetocrystalline anisotropy (0.5 meV), and dipolar magnetic interaction (0.05 meV). We evaluated the surface anisotropy constant for K S = 0.5, 1, and 2 meV and thicknesses ranging from 3 to 11 cells. We determined the magnetothermal and hysteresis loop in- and out-plane at different angles to the plane. Analysis of Variance allows for modeling the coercivity as a function of the thickness and the applied field direction (in- and out-plane). Under these simulation conditions, the Spin Reorientation Transitions appear only at a thickness of 7 cells with K S =1 meV. The main contribution to magnetization rises out-plane at low thicknesses and in-plane at high values. However, the dominant magnetization contribution is in-plane for the thickness of 7 cells and low surface anisotropy. The magnetization is mainly oriented, out-plane for the high surface anisotropy case. However, hysteresis loops were observed independent of the applied magnetic field direction and thickness. Analysis of Variance results suggests that the thickness and the applied magnetic field direction allowed for tunning the coercivity (hard or soft magnetic materials). Sample simulated ignoring the magnetocrystalline and the surface anisotropies produce magnetic components in- and out-plane with slight differences as angle function. The combination of dipolar interactions and magnetocrystalline anisotropy showed two magnetic behaviors, a hard magnetic phase at low angles and a soft one at high angles in-plane direction. The inverse behavior results in the out-plane component. We observed the same behavior when surface anisotropy is considered. The differences are the transition angle of 50° in the first case and 30° in the second.

P and Fe doping, a strategy to develop light and magnetic responsive multifunctional materials: The case of LiMn2O4

The current work reports an unprecedented multifunctional material with optical activity and a modified magnetic response by a unique combination of doping with P and Fe into the spinel LiMn2O4. Through inductively coupled plasma – optical emission spectroscopy, X-ray absorption near-edge spectroscopy, X-ray diffraction and scanning transmission electron microscopy, the chemical composition, oxidation state and the crystalline structure are determined. Solid-state UV-Vis spectroscopy, magnetic susceptibility and electronic conductivity reveal the critical importance of the interaction between iron and phosphorus when simultaneously doping the crystalline structure of LiMn2O4. The presence of Fe and P considerably increases charge carrier concentration as a mechanism for enhancing electronic conductivity. Fe and P doping also creates Fe-Fe spin interactions that allow double electron optical excitations. This opens a pathway to create multifunctional materials for light-assisted charging lithium-ion batteries. P doping also induces the formation of magnetic clusters arising from the Fe-O-Fe, Fe-O-Mn and Mn-O-Mn spin exchange interactions. The magnetic response of the materials is strongly influenced by the relative amount of Fe in octahedral or tetrahedral sites of the spinel structure. Such ferrimagnetic behaviour has not been reported before LiMn2O4 doped with Fe or P separately. The potential applicability of this newly identified magnetic feature was demonstrated by a significant capacity gain when a lithium-ion cell is exposed to a static external magnetic field.