Magnetic properties of ferrimagnetic minerals have been studied in detail over the years. By contrast, the magnetic properties of paramagnetic minerals containing rare earth elements (REE) remain largely unexplored, even though the presence of particular rare-earth ions can give rise to complex magnetic behavior due to their unpaired 4f electrons. Consequently, filling this knowledge gap is becoming increasingly important in light of the enormous interest these minerals have attracted in recent years because of their economic value. The primary goal of this study is to characterize the intrinsic magnetic behavior of selected REE minerals at the grain scale and in relation to their crystal structures.Six REE-bearing minerals from various Swedish localities were investigated: monazite-(Ce), xenotime-(Y), ferriallanite-(Ce), bastnäsite-(Ce), cerite-(CeCa) and fluorapatite. Electron microprobe analysis and X-ray diffraction methods were used to determine mineral chemistry and confirm crystal structures. Magnetic properties were characterized via field- and temperature- dependent magnetization measurements.Field-dependent magnetization measured at 2 K revealed the absence of a hysteresis loop in all minerals except ferriallanite-(Ce), which exhibits a small hysteresis loop. This behavior is primarily attributed to the presence of Fe2+ and Fe3+ ions in ferriallanite-(Ce). The preliminary results show that the effective magnetic moments (μ_eff) obtained from temperature-dependent measurements are in good agreement with calculated free-ion magnetic moments (μ_calc), suggesting that paramagnetic rare-earth ions represent a major contribution to the observed magnetism.These results provide fundamental knowledge of the intrinsic magnetic properties of selected REE-bearing minerals and improve our understanding of their crystal-chemical controls on their magnetism. Moreover, these insights form a basis for further interdisciplinary studies exploring the potential of designing novel functional materials inspired by naturally occurring compositions.

Li₃V₂(PO₄)₃ (LVP) is a promising cathode material for lithium-ion batteries, yet its poor electronic conductivity limits electrochemical performance. In this work, LVP/C composites were synthesized via a CTAB-assisted solution combustion method using sucrose as a secondary carbon source. The optimized sample (LVPS20) exhibits reduced particle size, a uniform nanoscale carbon coating, and a continuous three-dimensional conductive carbon matrix. These structural features significantly enhance lithium-ion diffusion and electronic conductivity. As a result, LVP-S20 delivers a high initial discharge capacity of 119.5 mAh g−1 at 0.1C and excellent cycling stability with 97.1% capacity retention after 1000 cycles at 10C. Electrochemical kinetic analysis reveals that the LVP-S20 electrode possesses an enhanced lithium-ion diffusion coefficient of 8.24 × 10−9 cm2s−1, indicating accelerated Li+ transport within the electrode. The improved electrochemical performance is attributed to the morphology refinement and optimized carbon structure.

Mn4Ta2O9 (MTO) is a magnetoelectric material with Ising-like antiferromagnetism (AFM) in which an applied magnetic field (H) induces electric polarization and an applied electric field produces magnetization. Here, we report results from our detailed investigations of the temperature (T) and H dependence of magnetization (M) and heat capacity of MTO. These results show AFM ordering in MTO below T-N similar to 102 K followed by additional transitions near T-S1 similar to 50 K and T-S2 similar to 20 K. The M vs H variations at 3 K show the presence of weak ferromagnetism (FM) below T-S1 superposed on AFM, with coercivity becoming zero for T >= T-S1. This weak FM for T <= T-S1 is likely due to two inequivalent Mn2+ ions present in MTO. The magnetic susceptibility chi vs T data for T> T-N is used to determine two dominant AFM exchange constants J(2)/k(B) = -11.3 K and J(3)/k(B) = -22.9 K, which are in good agreement with those determined from the first-principles density-functional theory (DFT + U) calculations. It is argued that the H-induced transition observed at 3 K at the critical field H-c similar to 20 kOe is a spin flop transition whose surprising shift to higher H values with increasing T is explained in terms of T dependence of anisotropic chi, magnetic anisotropy, and exchange fields. The temperature dependence of magnetic specific heat and entropy shows the presence of short-range spin correlations ordering up to 140 K, a lambda-type anomaly at T-N, and a broad anomalous peak near 40 K covering the region of T-S1 and T-S2. To further explore the nature of these transitions at T-N, T-S1, and T-S2, the T dependence of various Raman modes of MTO was measured and compared with the lattice dynamics calculations from DFT + U. For T> T-N, T dependencies of the frequency and linewidth of the Raman modes are described by the three-phonon anharmonic approximation with considerable departures in these quantities observed at TN, T-S1, and T-S2, which are then related to the strong spin-phonon coupling evident in MTO.

Rational design of electrode materials with tailored structural and electronic properties is crucial for the development of high-performance supercapacitors. Here, we report a Zn/V co-doping strategy for NiMoO4 (ZV-NM), which simultaneously induces abundant oxygen vacancies and a phase transformation from the alpha to the beta phase. The synergistic effects of lattice distortion, enhanced redox activity, and improved electrical conductivity collectively endow ZV-NM3 with extraordinary charge storage capabilities, achieving a remarkable specific capacitance of 1423.1 F g-1 (316.24 mA h g-1) at a current density of 0.4 A g-1. When integrated into an asymmetric supercapacitor device (ZV-NM3/NF//GS), this optimized electrode exhibits a specific capacitance of 101 F g-1 at a current density of 0.4 A g-1. It offers a high energy density of 45.4 Wh kg-1 and a power density of 1.31 kW kg-1, while retaining 90.45% of its capacitance after 10 000 charge/discharge cycles. These results highlight the effectiveness of binary doping in engineering vacancy-rich, phase-optimized transition metal oxides for next-generation energy storage applications.

Iron oxides are one of the oldest magnetic systems in history and have been studied extensively due to their phase-tunable magnetic and electronic properties. The combination of ferrimagnetic half-metallic magnetite (Fe3O4) with antiferromagnetic insulating hematite (α-Fe2O3) forms a so-called biphase iron oxide (BPIO) system that exhibits highly tunable magnetic and spin-transport properties in terms of phase and volume fraction. In this work, we report the interfacial physics between variations of these iron oxide phases with graphene (Gr) on magnetotransport in these heterostructures. Our experiments reveal that the inclusion of graphene in these heterostructures induces an inversion in the sign of magnetoresistance at finite temperatures. We explain this observation with an effective percolative transport model. Interestingly, the switching temperature and the sharpness of the transition can be further tuned by varying the phase volume fractions of the iron oxide layer and the crystallinity. The BPIO films, which grow naturally on Si substrates, exhibit the highest switching temperature. Our observations underscore the ability to induce magnetoresistive switching in abundant iron oxide grown on cost-effective, CMOS-compatible substrates by including a single layer of Gr, which has potential applications in modern devices and neuromorphic computing.

The complex magnetic behavior of double-perovskite oxides (A2BB'O6) with rare-earth (RE) element A and transition metal (TM) elements B-B' is determined by the interactions between intra-and interatomic magnetic moments. The peculiar magnetism in these systems stems from the interplay between spin, orbit, and lattice degrees of freedom. This study comprehensively investigates the role of spin-orbit entangled J(eff) = 1/2 moments of the Kramers ion Nd3+ on the magnetic ground state of a B-site ordered ferrimagnetic (FiM) double-perovskite oxide, Nd2FeCrO6. Furthermore, employing microscopic techniques like mu SR (muon spin rotation and relaxation) and neutron diffraction, we gained insight into the origin of low-temperature anomalies in the magnetic ground state of the system. The DC magnetization data encompass the first transition at critical temperature T-N = 250 K, followed by a negative magnetization below 15 K. The temperature-dependent neutron diffraction shows a commensurate magnetic ordering below 250 K, forming a ferrimagnetic ground state, supported by theoretical calculations. In addition, a sharp drop in initial muon asymmetry confirms the transition from a disordered state to a long-range-ordered state at 250 K. Interestingly, the thermal evolution of the dynamic muon spin-relaxation rate (lambda(L)) reveals a transition at two temperatures, at 250 K and 11 K, suggesting a low-T ordering at the A site. The heat-capacity data show that Nd3+ hosts the ground-state doublet (pseudospin-1/2) at low temperatures. Our analysis of neutron diffraction, heat capacity, and mu SR results suggests that the correlation between the Nd3+ doublet and the complex interaction between Nd-TM moments gives rise to the observed low-temperature anomaly.

Cobalt disulfide (CoS2) nanoparticles were combined with varying amounts of MXene (Ti3C2Tx) sheets via a hydrothermal method for microwave absorption applications. X-ray diffraction confirmed the coexistence of crystalline CoS2, Ti3C2Tx, and TiO2 phases, revealing the partial surface oxidation of Ti3C2Tx sheets. Scanning electron microscope images demonstrated that CoS2 nanoparticles were uniformly anchored on the MXene sheets, and X-ray photoelectron spectra showed the presence of Co-S, Ti-C, and Ti-O bonds, indicating strong interfacial interactions. The CoS2-35 wt % Ti3C2Tx composite exhibited a minimum reflection loss of -15.23 dB at a matching thickness of 2.4 mm and a broad effective absorption bandwidth of 7.3 GHz (from 10.7 to 18 GHz) at 3.2 mm, which was mainly attributed to impedance matching. Synergistically, the presence of multiple interlayer interactions and the extension of the wave-propagation path within the layered microstructure of the CoS2-35 wt % Ti3C2Tx composite mutually contribute to wave attenuation.

The nature of magnetism in the cubic spinel Cr0.1Mn0.9Fe0.2Co1.8O4 is reported based on systematic investigations by means of magnetization (M), ac susceptibility (chi) and heat capacity (C-P) measurements, as well as by neutron diffraction. Structural characterization of the sample was done using x-ray absorption spectroscopy, neutron and synchrotron diffraction. The M vs. T variation in different magnetic fields indicate ferrimagnetic ordering below T-C = 230 K, followed by a magnetic field and anisotropy induced spin reorientation at T-SR similar to 150 K. With increasing T starting from 2 K, the coercivity H-C and anisotropy field H-K decrease and become negligible for T>T-SR. A model to explain the H(C )vs. T data shows that T-SR is due to reorientation of M along H when H>H-K. The C-P vs. T data shows a weak lambda -type anomaly at T(C)with changes in magnetic entropy smaller than those observed below T-SR suggesting that long-range magnetic ordering is completed below T-SR. For T-SR T-C. This analysis also shows the low-spin S = 0 state of Co3+ ions on the B sites which along with negligible H-K for T-SR

Realizing next-generation intelligent applications requires novel resistive switching devices that can operate with low power, high stability, and desired neuromorphic performance. La0.8Ba0.2MnO3 (LBMO), a functional complex oxide exhibiting a room-temperature metal-insulator transition, shows promise in this context. In this work, we demonstrate interface-engineered resistive switching in the LBMO thin film junction by introducing an ultrathin CeO2 insertion layer. Compared to bare LBMO film, which requires higher forming voltages and suffers from limited stability and large cycle-to-cycle variability, the CeO2/LBMO (LBC) device exhibits stable, low-power bipolar resistive switching. The LBC device achieves a low forming voltage of 2.2 V, an ON/OFF ratio of ∼102, endurance of 600 switching cycles, and data retention of 103 seconds. The improved performance is attributed to controlled oxygen vacancy migration and redistribution facilitated by the CeO2 interlayer. Furthermore, the LBC device displays, for the first time, bioinspired synaptic behaviors, such as gradual potentiation and depression under pulsed stimuli, and exhibits linear plasticity under nonidentical pulse schemes, effectively emulating synaptic weight modulation. Our results demonstrate an interface-induced resistive switching device as a compelling candidate for next-generation neuromorphic components.

Realizing next-generation intelligent applications requires novel resistive switching devices that can operate with low power, high stability, and desired neuromorphic performance. La0.8Ba0.2MnO3 (LBMO), a functional complex oxide exhibiting a room-temperature metal-insulator transition, shows promise in this context. In this work, we demonstrate interface-engineered resistive switching in the LBMO thin film junction by introducing an ultrathin CeO2 insertion layer. Compared to bare LBMO film, which requires higher forming voltages and suffers from limited stability and large cycle-to-cycle variability, the CeO2/LBMO (LBC) device exhibits stable, low-power bipolar resistive switching. The LBC device achieves a low forming voltage of 2.2 V, an ON/OFF ratio of ∼102, endurance of 600 switching cycles, and data retention of 103 seconds. The improved performance is attributed to controlled oxygen vacancy migration and redistribution facilitated by the CeO2 interlayer. Furthermore, the LBC device displays, for the first time, bioinspired synaptic behaviors, such as gradual potentiation and depression under pulsed stimuli, and exhibits linear plasticity under nonidentical pulse schemes, effectively emulating synaptic weight modulation. Our results demonstrate an interface-induced resistive switching device as a compelling candidate for next-generation neuromorphic components.

Efficient control of the structural, magnetic and electrical properties of Rare-earth (RE) based perovskites (ABO3) is crucial for advanced spintronic applications and can be achieved by means of site-specific substitution. In this comprehensive study, we explore the role of (Nd)A-site and (Mn)B-site co-substitution on the physical properties of pristine LaCoO3 perovskite. The resulting compound La0.5Nd0.5Co0.5Mn0.5O3 (LNCMO) with an orthorhombic (Pbnm) crystal structure (a =5.4811(4) & Aring;, b = 5.5074(4) & Aring; and c =7.7491(5) & Aring;) exhibits a significantly reduced Jahn-Teller distortion (JT) compared to pristine LaCoO3 with a monoclinic (I2/a) structure. The ac-magnetic susceptibility chi(T, f, Hdc) measurements and wait time dependence of the isothermal magnetization M(t) provide clear evidence for the re-entrant spin-glass-like behavior with freezing temperature TSG =133 K below the ferrimagnetic Curie temperature (TFiM similar to 137.4 K). Additionally, the asymmetric response of magnetic relaxation in the system to positive and negative temperature cycling well below the freezing temperature has been explained by means of the hierarchical model. Furthermore, a giant coercivity (HC similar to 14 kOe) and remanence (MR similar to 6440 emu mol-1 ) with weak loop-asymmetry indicates the presence of large magnetic anisotropy in LNCMO, evidenced by a high magneto-crystalline anisotropy field (HK similar to 80 kOe) and anisotropy constant (K1 similar to 1.45 x 107 erg cm-3). The unique electronic structure of trivalent Nd (5f 3) and mixed valent Mn (3d4/3d3) with spin-orbit coupling energies 4 eV and 11.43 eV/10.51 eV, respectively and competing exchange interaction (similar to 0.67 meV) between Mn and Co cations in different pathways results in enhanced magnetic-order parameters. Moreover, the co-substitution results to a pseudo-first order like state close to the spin-state transition H* of Co (S = 0 -> 2) which has been verified by the modified Arrott plot analysis yielding critical exponents beta = 0.67, gamma = 1.44 and delta = 3.13. A field-induced metamagnetic transition HT emerges in the range 30 K <= T <= 130 K which has been mapped along with other parameters resulting in a H-T phase diagram which clearly distinguishes various magnetic phases and sharp crossover between the different states providing a clear and vivid picture of the overall magnetic structure of LNCMO.

We report a detailed study on the composition (x) dependence of structural, electronic, magnetic, and optical studies of nickel chromate spinel (NiCr2O4) at various levels of Mn substitution at B sites. No significant structural distortion from cubic symmetry Fd-3m was noticed for all the compositions in the range 0 <= x <= 1 of Ni(Cr1-xMnx)(2)O-4. However, there is significant alteration in the bond angles angle B-O-B (90.51 degrees-93.86 degrees) and angle A-O-B (122.48 degrees-124.90 degrees) (both of which follow completely opposite trend with increasing x) and bond lengths A-O (1.82-1.94 angstrom) and B-O (2.02-2.08 angstrom). The corresponding lattice parameter (a) follows Vegard's law (8.32 +/- 0.001 angstrom <= a <= 8.45 +/- 0.001 angstrom). The electronic structure determined from the x-ray photoelectron spectroscopy reveals the divalent nature of Ni (with spin-orbit splitting energy Delta similar to 17.62 eV). While the Cr and Mn are stable with trivalent electronic states having Delta = 8 and 11.7 eV, respectively. These results are in consonance with the cationic distribution (Ni)(A)[(Cr1-xMnx)(2)](B)O-4 obtained from the Rietveld refinement analysis. Interestingly, the current series shows a direct bandgap (E-G) semiconducting nature in which E-G varies from 1.16 to 2.40 eV within the range of x = 0.85-0. Such variation of E-G (x) is consistent with the compositional variation of the crystal structure data with anomalous change between x = 0.25 and 0.6. Beyond this range, the E-g mode (140 cm(-1)) in Raman spectra arising from Mn-O octahedral decreases continuously and vanishes at higher Mn concentrations. Our analysis shows that all the investigated compounds show long-range ferrimagnetic ordering below the Neel temperature, T-FN due to the unequal magnetic moments of the cations. However, both the ordering temperature T-FN and saturation magnetization (M-S) increases progressively from 73.3 K (1500 emu mol(-1)) to 116 K (3600 emu mol(-1)) with increasing the Mn content from 0 to 1, yet the maximum anisotropy (H-K similar to 4.5 kOe, K-1 similar to 2.5 x 10(4) erg cc(-1)) shows an opposite trend with x. Such variation is ascribed to the altered magnetic superexchange interactions between the cations located at A and B sites following the trend J(BB) > J(AB) > J(AA), (J(BB)/k(B) =13.36 K).

Micro‐grained high surface‐to‐volume ratio thin ribbons of magnetic shape memory Ni 42 Co 8 Mn 39 Sn 11‐ x Ge x ( x = 1, 2, 3) alloys are prepared, and their martensitic transformation (MT) behavior, magnetic and magnetocaloric properties are investigated. X‐ray diffraction reveals that the incorporation of Ge consistently decreases the lattice parameters and the transformation volume change, thereby improving geometric compatibility between martensitic and austenitic crystal lattices. This improvement facilitated a reduction of the thermal hysteresis of MT to a minimum of ≈12.1 K at the Ge concentration of x = 2. Direct measurements of adiabatic temperature changes show that the x = 2 alloy (SnGe2 ribbon) exhibited the highest peak value (≈2 K) at a moderate magnetic field change of 1.96 T. In addition, SnGe2 ribbon demonstrates exceptional isothermal entropy changes of ΔS iso = 35.5 J kg −1 K −1 K at 7 T and 22.8 J kg −1 K −1 K at 2 T, which are competitive with those of bulk alloys and surpassing previously reported melt‐spun ribbons of the Heusler‐type magnetocaloric materials. The significance of intricate microstructure in boosting the magnetocaloric effect is emphasized. These results highlight the substantial potential of Ni–Co–Mn–Sn–Ge thin ribbons as highly effective, micro‐sized magnetocaloric materials for cutting‐edge solid‐state refrigeration systems.

We have investigated the bottom-up sol-gel synthesis of nanocomposite powders comprising two magnetic phases (hexagonal Sr ferrite and spinel Co ferrite) in order to outline a strategy to obtain permanent magnets with large coercivities via low-cost and scalable syntheses. The correlation between morphological, structural and macroscopic magnetic properties of Al-substituted SrFe12O19 and SrFe12O19/CoFe2O4 nanocomposites was analyzed in detail. The hysteretic behavior can be tuned by cation substitution and/or modulation of the super-exchange coupling at the interface of the constituting phases. The magnetic data, supported by Monte Carlo simulations, indicates enhanced magnetic coupling within the composite: this observation underscores the significance of soft crystallite size and epitaxial growth quality at the interface as key factors influencing super-exchange coupling strength, ranging from fully coupled to essentially decoupled composites. Bulk magnets with high density were manufactured by compacting these nanostructured phases using spark plasma sintering, without an applied magnetic field. Consolidation of powders significantly impacted magnetic properties, by increasing remanent magnetization and decreasing coercivity due to enhanced super-exchange coupling. The presence of two phases hindered reciprocal growth, influencing coercivity differently in various compositions. Overall, the compaction enhanced magnet performance through improved particle alignment and super-exchange coupling, offering the potential for optimized magnet design.

Short-range spin correlations, memory and rejuvenation effects have been reported in the trication oxispinel ZnMnCoO4 whose low-temperature spin dynamics, triggered by magnetic frustration ( f(r)similar to 6), could be better explained by the 'phenomenological' hierarchical free-energy model than the short-range droplet theory. Accordingly, the aging mechanism of the system had an asymmetric memory response to the positive and negative thermal cycles within the cluster-glass state ( T< 32.6 K) and demonstrated a hierarchical organization of the phase space where its metastable energy states undergo continuous splitting with decreasing temperature. An attempt to reproduce the time evolution of the isothermal remanent magnetization in the system led to an investigation of various relaxation models featuring semi-logarithmic, algebraic, fractional or stretched-exponential tails. Nevertheless, Weron's probabilistic relaxation model (here, the fractal character beta similar to 0.4, the hierarchical constraint k> 0, and the order parameter q(T similar to 0.12T(SG)) = 1.88) based on a purely stochastic approach, was best suited for understanding the slow spin dynamics of the cluster-glass phase in the entire temporal range. A comprehensive picture of the magnetic phase map was developed for the system, aided by magnetometry techniques and heat-capacity studies.

The widespread use of wireless devices and telecommunication networks has given rise to electromagnetic interference (EMI) pollution that can cause data corruption, critical device failure, and detrimental effects on wildlife and human health. Developing EMI shielding materials can block these harmful electromagnetic waves. This study explores inter-dimensional composite systems composed of dielectric and magnetic phases (WS2/biphasic lithium iron oxide) for EMI shielding applications. WS2 is a 2D material with unique dielectric properties and flake-like morphology that enhances surface effects. In contrast, biphasic magnetic lithium iron oxide nanocomposites have grain-like morphology with greater magnetic losses. The formation of interfaces between these two phases with different morphologies and dimensionalities leads to enhanced interfacial polarization loss. This work demonstrates that by carefully controlling the weight percentage of the two phases, and thereby the interfaces, the EMI shielding properties can be significantly enhanced. An optimum phase composition is determined that exhibits maximum shielding efficiency (SET approximate to 55.6 dB at 12.4 GHz) with high absorption shielding (SEA approximate to 48.8 dB at 12.4 GHz), and an absorption coefficient more than 100% higher than either end member. The studied nanocomposites, with their tunable absorption and reflection capabilities, are suitable for a wide range of EMI shielding applications.

There is a great demand for efficient electromagnetic interference (EMI) shielding materials due to exponential growth in wireless telecommunication devices. These devices emit electromagnetic radiation that can disrupt electronic devices, and cause health hazards. Therefore, it is crucial to develop materials that can shield devices and humans from exposure to electromagnetic radiation. In this context, nanocomposite materials offer huge advantages due to the dual possibility of tailoring the interfaces as well as using the complementary properties of magnetic and dielectric components in the nanocomposite to enhance the EMI shielding performance. This work shows that by a careful tuning of the synthesis parameters, we can grow biphasic lithium iron oxide (ferrimagnetic alpha-LiFe5O8 and paramagnetic alpha-LiFeO2) nanocomposite with different relative fractions of the two phases. The variation of the phase fraction and the simultaneous growth of the two phases allow us to control the interfaces between the two phases as well as the physical properties of the nanocomposite, which have a direct effect on the EMI shielding performance. Detailed structural (X-ray diffraction), compositional (Raman spectroscopy), and morphological (high-resolution transmission electron microscopy) characterization is presented to understand the effect of the synthesis conditions on the EMI shielding parameters. Improved dielectric and magnetic properties together with an increased number of interfaces in the sample with nearly equal amounts of the two phases results in the best performance. This work demonstrates the significant potential of using biphasic magnetic oxide nanocomposites with controllable interfaces and physical properties for EMI shielding, which can form the base for more complex triphasic systems in the future.

ZnO-based sensors often suffer from low response rates and long response and recovery times. To address this issue, Ag-incorporated ZnO-based gas sensors with Ag contents of 2, 4, 6, and 8% were synthesized using a simple, fast, and cost-effective method, making them promising candidates for future industrial applications. Structural analysis confirmed the presence of Zn–O bonding and the incorporation of silver as a secondary metallic phase, well integrated with the ZnO nanoparticles. Gas sensing tests were performed under different conditions, and the sample with 2% Ag content exhibited an extraordinary response of 4357%, approximately 29 times higher than that of pure ZnO nanoparticles. The sample with 8% Ag content showed the lowest response and recovery times. Additionally, the response rates of the samples were positively correlated with both concentration and temperature. The increase in response rate was attributed to the spill-over effect in the samples, which enhanced hydrogen mobility. The results demonstrated that Ag-doped ZnO nanoparticles exhibited higher porosity compared to the pure ZnO sample. This suggests that tuning the porosity or structure can further enhance the performance of ZnO-based sensors. Moreover, the fabricated sensor showed high sensitivity and an exceptionally low detection limit, indicating strong potential for the continued development of ZnO nanostructure-based gas sensors.

Innovations in resistive switching devices constitute a core objective for the development of ultralow-power computing devices. Forming-free resistive switching is a type of resistive switching that eliminates the need for an initial high voltage for the formation of conductive filaments and offers promising opportunities to overcome the limitations of traditional resistive switching devices. Here, we demonstrate mixed charge state oxygen vacancy-engineered electroforming-free resistive switching in NiFe2O4 (NFO) thin films, fabricated as asymmetric Ti/NFO/Pt heterostructures, for the first time. Using pulsed laser deposition in a controlled oxygen atmosphere, we tune the oxygen vacancies together with the cationic valence state in the nickel ferrite phase, with the latter directly affecting the charge state of the oxygen vacancies. The structural integrity and chemical composition of the films are confirmed by X-ray diffraction and hard X-ray photoelectron spectroscopy, respectively. Electrical transport studies reveal that resistive switching characteristics in the films can be significantly altered by tuning the amount and charge state of the oxygen vacancy concentration during the deposition of the films. The resistive switching mechanism is seen to depend upon the migration of both singly and doubly charged oxygen vacancies formed as a result of changes in the nickel valence state and the consequent formation/rupture of conducting filaments in the switching layer. This is supported by the existence of an optimum oxygen vacancy concentration for efficient low-voltage resistive switching, below or above which the switching process is inhibited. Along with the filamentary switching mechanism, the Ti top electrode also enhances the resistive switching performance due to interfacial effects. Time-resolved measurements on the devices display both long- and short-term potentiation in the optimized vacancy-engineered NFO resistive switches, ideal for solid-state synapses achieved in a single system. Our work on correlated oxide forming-free resistive switches holds significant potential for CMOS-compatible low-power, nonvolatile resistive memory and neuromorphic circuits.

In this work, CoFe2O4 powders were combined with various amounts of MXene (Ti3C2Tx) through the solution combustion method for microwave absorption applications. Despite the absence of MXene reflections in X-ray diffraction patterns, the MXene sheets were observed in electron microscopy images. The CoFe2O4 nanoparticles were uniformly dispersed on the MXene nanosheets. The specific surface area increased from 57 to 83 m2 g-1 by adding 20 wt% MXene. The saturation magnetization and coercivity decreased from 44 to 35 emu g-1 and from 834 to 775 Oe, respectively. By adding the MXene, the minimum reflection loss and effective absorption bandwidth increased up to -38 dB and 5.6 GHz at a matching thickness of 1.8 mm, respectively, which was attributed to the enhancement of impedance matching by the decrease of permittivity.