Ferromagnetic Metallic State Research Articles

The mysterious magnetic ground state of Ba14MnBi11 is likely self-doped and altermagnetic

Magnetism in the Zintl compound Ba14MnBi11 is rather poorly understood. Experimental claims are largely inconsistent with ab initio calculations, much beyond typical errors of the latter. We revisit this old problem, assuming that the root of the problem may be in nonstoichiometry of existing samples. Our key finding is that the magnetic ground state is indeed very susceptible to charge doping (band filling). Calculations for stoichiometric Ba14MnBi11 give a rather stable ferromagnetic metallic state, in agreement with previous publications. However, by adding exactly one electron per Mn, the system becomes semiconducting as expected, and becomes weakly antiferromagnetic (AF). On the other hand, upon small amount of hole doping, the system transitions to a special type of AF state known as altermagnetism. Furthermore, hole and electron doping-induced phase transitions result from different underlying mechanisms, influencing different exchange pathways. We propose that the inconsistency between experiment and theory is not a failure of the latter, but results from a nontrivial ramification of nonstoichiometry. The possibility of doping-stabilized altermagnetism is exciting.

Metallicity and associated ferromagnetism in fluorine doped LaMnAsO

The electrical and magnetic properties of the layered oxypnictide LaMnAsO have been investigated through fluorine doping at the oxygen site. LaMnAsO is well-established as an insulator and exhibits antiferromagnetic behavior below its Neel temperature, TN = 360 K. With F-doping, the electrical and magnetic characteristics undergo a transition from insulating antiferromagnetic states to semiconducting and then to metallic ferromagnetic states. With F-doping levels ranging from approximately x=0.15 to nearly its maximum at 0.25, the resistivity experiences a remarkable reduction by five orders of magnitude, reaching values of approximately 0.04 Ω cm at room temperature. Furthermore, the temperature-dependent resistivity profile demonstrates a decidedly metallic nature for the F-doping ranges of x=0.15 to 0.25. The transition temperatures (TC) exhibit a spread of approximately 20 K around 300 K. Notably, the transverse magnetoresistance (MR) is approximately 12% in the vicinity of the room temperature transition.

A study on the kinetic arrest of magnetic phases in nanostructured Nd0.6Sr0.4MnO3 thin films

The Nd0.6Sr0.4MnO3 (NSMO) manganite system exhibits a phase transition from paramagnetic insulating (PMI) to ferromagnetic metallic (FMM) state around its Curie temperature T C = 270 K (bulk). The morphology-driven changes in the kinetically arrested magnetic phases in NSMO thin films with granular and crossed-nano-rod-type morphology are studied. The manganite thin films at low temperatures possess a magnetic glassy state arising from the coexistence of the high-temperature PMI and the low-temperature FMM phases. The extent of kinetic arrest and its relaxation was studied using the ‘cooling and heating in unequal field (CHUF)’ protocol in magnetic and magnetotransport investigations. The sample with rod morphology showed a large extent of phase coexistence compared to the granular sample. Further, with a field-cooling protocol, time-evolution studies were carried out to understand the relaxation of arrested magnetic phases across these morphologically distinct thin films. The results on the devitrification of the arrested magnetic state are interpreted from the point of view of homogeneous and heterogeneous nucleation of the ferromagnetic phase in the paramagnetic matrix with respect to temperature.

The influence of substrate orientation on the magnetic behavior of nearly-stoichiometric Mn5Ge3 thin films: DFT calculations and experimental analysis

The Mn5Ge3 exhibits a wide range of fascinating properties such as high spin polarization up to 42 %, large spin diffusion lengths, near-room Curie temperature, and possible integration with Ge, GaAs, and Si substrates. The influence of substrate orientation on magnetic behavior has been investigated. The thin films studied present an in-plane magnetic reversal which is isotropic in samples grown on GaAs(111) and anisotropic in samples grown on GaAs(001). Another difference observed is a linear trend to saturation on the out-of-plane hysteresis loop in samples grown on GaAs(111), comparatively to samples grown on GaAs(001). To better understand this scenario, Density Functional Theory (DFT) calculations were conducted. The results indicate a ferromagnetic metallic ground state with properties that are consistent with the experimental results. The projected densities of states indicate that the main responsible for the magnetic moment observed in the Mn5Ge3 is the Mn-Mn interaction. The magnetic field distribution isosurfaces obtained from the DFT calculations offer a satisfactory explanation of the magnetic reversal experimentally observed, especially the in-plane magnetic behavior in samples grown on both GaAs(111) and GaAs(001) substrates. This work provides a theoretical-experimental approach that allows a deeper understanding of the magnetic anisotropy behavior under the influence of the crystallographic orientation of the substrate observed in nearly-stoichiometric Mn5Ge3 thin films, which is a good candidate for rare-earth free magnet in spintronic applications.

A correlated ferromagnetic polar metal by design.

Polar metals have recently garnered increasing interest because of their promising functionalities. Here we report the experimental realization of an intrinsic coexisting ferromagnetism, polar distortion and metallicity in quasi-two-dimensional Ca3Co3O8. This material crystallizes with alternating stacking of oxygen tetrahedral CoO4 monolayers and octahedral CoO6 bilayers. The ferromagnetic metallic state is confined within the quasi-two-dimensional CoO6 layers, and the broken inversion symmetry arises simultaneously from the Co displacements. The breaking of both spatial-inversion and time-reversal symmetries, along with their strong coupling, gives rise to an intrinsic magnetochiral anisotropy with exotic magnetic field-free non-reciprocal electrical resistivity. An extraordinarily robust topological Hall effect persists over a broad temperature-magnetic field phase space, arising from dipole-induced Rashba spin-orbit coupling. Our work not only provides a rich platform to explore the coupling between polarity and magnetism in a metallic system, with extensive potential applications, but also defines a novel design strategy to access exotic correlated electronic states.

Perovskite-based two-dimensional ferromagnet Sr<sub>2</sub>RuO<sub>4</sub> monolayer

At present, the research on two-dimensional (2D) ferromagnets is mainly concentrated in the field of van der Waals materials, while the successful preparation of strain-free freestanding 2D perovskite films provides a great opportunity for the design of 2D ferromagnets beyond van der Waals materials. Perovskite oxide SrRuO<sub>3</sub>, as a typical perovskite itinerant ferromagnet, has broad application prospects in many fields. In this paper, the lattice dynamics, ground-state structure, electronic and magnetic properties of its perovskite monolayer with formula Sr<sub>2</sub>RuO<sub>4</sub>, as well as the effect of external electric field, are studied by combining first-principles calculation, symmetry analysis and Monte Carlo simulation. The influence of the Hubbard parameter <i>U</i> is also revealed. The results indicate that the ground-state structure under all <i>U</i> values is the structural phase (space group <inline-formula><tex-math id="M2">\begin{document}$P4/mbm$\end{document}</tex-math></inline-formula>) generated by octahedral rotation distortion. Similar to the SrRuO<sub>3</sub> bulk, the ground-state phase of the Sr<sub>2</sub>RuO<sub>4</sub> monolayer exhibits ferromagnetism, which is independent of the <i>U</i> value and thus robust. Density functional theory calculation with Hubbard parameter <i>U</i> predicts the ground-state phase of the monolayer to be a ferromagnetic half metal with out-of-plane easy-magnetization axis, while excluding the <i>U</i> parameter predicts the ground-state phase to be a ferromagnetic metallic state. The ferromagnetism mainly originates from the strong ferromagnetic exchange interaction between the nearest neighbor spin pairs. The simulated Curie temperature of the Sr<sub>2</sub>RuO<sub>4</sub> monolayer is 177 K, which is close to the value (150 K) of its bulk phase. The out-of-plane electric field does not change the ground-state structure and ferromagnetism of the Sr<sub>2</sub>RuO<sub>4</sub> monolayer, but can significantly modulate its electronic and magnetic properties. When an external electric field exceeding 0.3 V/Å is applied, the system undergoes a transition from a ferromagnetic half-metal state to a ferromagnetic metallic state. This work indicates the potential application of Sr<sub>2</sub>RuO<sub>4</sub> monolayer in low-dimensional spintrnic devices, and provides a reference for the development of perovskite-based 2D ferromagnets and the realization of controlling 2D magnetism by electric field.

Reformation of La0.7Sr0.3MnO3 properties by using ZnO in La0.7Sr0.3MnO3-ZnO heterostructures grown on (001) oriented Si.

Study of the available density of states (DOS) close-to-zero bias for conduction in strongly correlated electron systems, such as half-metallic La0.7Sr0.3MnO3 (LSMO) and its heterostructures, is important for fundamental and application reasons. As the DOS is proportional to the differential conductance (dI/dV), the dI/dV of a 120 Å LSMO film and its reformation in LSMO/ZnO heterostructures was investigated for different ZnO thicknesses. Unlike in conventional metals, the dI/dV of LSMO exhibits a power-law dependent zero-bias anomaly, i.e., dI/dV ∝ Vm (m ∼ 1) near zero bias in the ferromagnetic metallic state at 10 K. The growth of ZnO on LSMO reforms the linear dI/dVvs. V of LSMO near zero bias to non-linear. The exponent 'm' becomes ∼0.5 for a higher ZnO thickness, revealing increased electron-electron interactions and suppression of Kondo-like, double and superexchange interactions, which are responsible for the depression of the DOS of LSMO near zero bias. In a magnetically disordered state, i.e., around the Curie temperature, ZnO reforms the linear V-shaped dI/dV vs. V of LSMO to parabolic U-shaped dI/dVvs.V and controls the electron concentrations in the t2g-orbitals of Mn realized from the DOS simulations. Additionally, ZnO introduces a peak in the dI/dV vs. V due to Fowler-Nordheim tunnelling, and the peak voltage can be tuned by varying the ZnO thickness or temperature from 300 K to 360 K. Such functions of ZnO yield major perspectives for novel applications in thin-film-based devices.

Field induced metamagnetic transition and mixed charge transfer Mott-Hubbard character in nanocrystalline FeCo2O4 spinel oxide: A combined study using experimental and first principles techniques

Unusual magnetic behavior of nanocrystalline FeCo2O4 (FCO) has been observed at different annealing temperatures. FCO nanoparticles have been prepared by co-precipitation method and the prepared sample annealed at different temperatures to vary its crystallite size. The powder x-ray diffraction analysis confirms the presence of pure spinel phase in the samples annealed at 900 ℃ and 1000℃. The increase in particle size with annealing temperature has been confirmed by field emission scanning electron microscopy (FESEM) analysis. High resolution x-ray photoelectron spectroscopy (HRXPS) analysis reveals the presence of mixed oxidation states of Fe+2/ Fe+3 and Co+3/Co+2 in the sample annealed at 900℃. The as-synthesized sample at 80 °C shows strong antiferromagnetic behavior due to their smaller particle size, but all the annealed samples have strong ferromagnetic behavior with large coercive field and remanence due to their larger particle size. We have observed a sharp rise in magnetization near small field values in the virgin curve and also the presence of virgin curve completely outside the main hysteresis loop in the M(H) curves measured at 5 K for the samples annealed at and above 1000 ℃ reveal the characteristic of first order nature of field induced metamagnetic transition. Structural parameters obtained after Rietveld refinement of powder x-ray diffraction pattern for sample annealed at 900 ℃ have been used for investigating the magnetic properties using first principles density functional theory. Our calculations using hybrid exchange-correlation functional, HSE06 captures the correct insulating ferromagnetic ground state and band gap for inverse spinel structure in broad agreement with our experimental results while calculations within GGA+U leads to a wrong half metallic ferromagnetic ground state. The partial density of states obtained for inverse spinel structure with HSE06 functional suggests a mixed charge transfer and Mott-Hubbard character in our system. We have explored the interplay among structural, magnetic and transport properties of FCO using experiment as well as first principles density functional theory.

Revival of Ferromagnetic-Metallic Phase and Emergence of Griffiths Phase via Ni and Cr Substitution in Charged-Ordered Pr0.75Na0.25MnO3 Manganite

Polycrystalline samples of Pr0.75Na0.25Mn1-xAxO3 (A = Ni, Cr; x = 0, 0.03) were prepared using conventional solid-state method and their structural and magnetic properties were investigated. Monovalent-doped Pr0.75Na0.25MnO3 exhibits insulating behavior which is related to the strong localization of charge carriers due to the presence of charge ordering (CO). The substitution of different types of magnetic ions, A, which are Ni2+ and Cr3+, at a concentration of x = 0.03 at the Mn site in the CO Pr0.75Na0.25Mn1-xAxO3 manganite, has been found to dramatically modify its structural and magnetic properties. X-ray diffraction patterns showed that all samples were present in single phase and crystallized in orthorhombic structure with Pnma space group. The Rietveld refinement analysis showed that the unit cell volume increased due to Ni2+ substitution, while it decreased due to Cr3+ substitution, which may be attributed to the different ionic radii of both ions. The suppression of the CO state and the induction of the ferromagnetic-metallic state in the Ni-substituted and Cr-substituted samples are suggested to be due to the induction of double-exchange interaction involving Ni2+–O–Mn4+ and Mn3+–O–Cr3+, respectively. The variation in magnetic properties between the Ni-substituted and Cr-substituted samples is suggested to be due to the existence of different strengths of ferromagnetic interaction between Ni2+–O–Mn4+ and Mn3+–O–Cr3+. In addition, the deviation of the temperature dependence of the inverse magnetic susceptibility curves from the Curie-Weiss law suggests the existence of Griffith’s phase-like behaviour for both substitution samples. The Ni-substituted sample induced a greater GP effect than the Cr-substituted sample due to the larger difference of TC and TG value (TC-TG).

Stability of the interorbital-hopping mechanism for ferromagnetism in multi-orbital Hubbard models

The emergence of insulating ferromagnetic phase in iron oxychalcogenide chain system has been recently argued to be originated by interorbital hopping mechanism. However, the practical conditions for the stability of such mechanism still prevents the observation of ferromagnetic in many materials. Here, we study the stability range of such ferromagnetic phase under modifications in the crystal fields and electronic correlation strength, constructing a theoretical phase diagram. We find a rich emergence of phases, including a ferromagnetic Mott insulator, a ferromagnetic orbital-selective Mott phase, together with antiferromagnetic and ferromagnetic metallic states. We characterize the stability of the ferromagnetic regime in both the Mott insulator and the ferromagnetic orbital-selective Mott phase forms. We identify a large stability range in the phase diagram at both intermediate and strong electronic correlations, demonstrating the capability of the interorbital hopping mechanism in stabilizing ferromagnetic insulators. Our results may enable additional design strategies to expand the relatively small family of known ferromagnetic insulators.

Scattering-dependent transport of SrRuO3 films: From Weyl fermion transport to hump-like Hall effect anomaly

Recent observation of quantum transport phenomena of Weyl fermions has brought much attention to $4d$ ferromagnetic perovskite ${\mathrm{SrRuO}}_{3}$ as a magnetic Weyl semimetal. Additionally, the hump-like Hall effect anomaly, which might have a topological origin, has been reported for this material. Here, we show that the emergence of such phenomena is governed by the degree of scattering determined by the defect density (Ru-deficiency- and/or interface-driven-defect scattering) and measurement temperature (phonon scattering), where the former is controlled by varying the growth conditions of the ${\mathrm{SrRuO}}_{3}$ films in molecular beam epitaxy as well as the film thickness. The resulting electronic transport properties can be classified into three categories: clean, intermediate, and dirty regimes. The transport of Weyl fermions emerges in the clean regime, whereas that of topologically trivial conduction electrons in the ferromagnetic metal state prevails in the intermediate and dirty regimes. In the clean and intermediate regimes, anomalous Hall resistivity obeys a scaling law incorporating the intrinsic Karplus-Luttinger and extrinsic side-jump mechanisms. The hump-like Hall effect anomaly is observed only in the dirty regime, which is contrary to the scaling law between anomalous Hall resistivity and longitudinal resistivity. Hence, we conclude that this anomaly is not inherent to the material and does not have a topological origin. We also provide defect- and temperature-dependent transport phase diagrams of stoichiometric ${\mathrm{SrRuO}}_{3}$ and Ru-deficient ${\mathrm{SrRu}}_{0.7}{\mathrm{O}}_{3}$ where the appearance of Weyl fermions and hump-like Hall effect anomaly is mapped. These diagrams may serve as a guideline for designing $\mathrm{Sr}\phantom{\rule{0.16em}{0ex}}{\mathrm{Ru}}_{1\ensuremath{-}x}{\mathrm{O}}_{3}$-based spintronic and topological electronic devices.

Percolative transport and metamagnetic transition in phase separated La0.55Ca0.45Mn1-xAlxO3-δ

The Al3+ doping effects on the ferromagnetic metallic state of La0.55Ca0.45MnO3 have been studied by preparing the La0.55Ca0.45Mn1-xAlxO3-δ (x = 0, 0.05, 0.1, 0.15) ceramics. Various measurements such as ac susceptibility, relaxation, magnetization and resistivity were performed to study the magnetic and magnetotransport properties. The magnetic disorder produced by the Al3+ dopants and the oxygen vacancies suppress the long range ferromagnetic ordering and induce a short range charge ordered antiferromagnetic clusters, leading to a phase separated behavior in the Al3+-doped samples. A Griffith-like behavior is observed due to the occurrence of short range ferromagnetic clusters in the paramagnetic phase. The 15% Al3+ doping sample exhibits a spin-glass state. The 10% Al3+ doping system is blocked in a metastable state upon cooling at zero field, and a sharp metamagnetic transition is induced by applying a high magnetic field, in which the antiferromagnetic phase is transformed into ferromagnetic phase and the ferromagnetic clusters grow in size. The ferromagnetic domains grows rapidly when applying a high magnetic field. Once the conducting ferromagnetic domains are interconnected throughout the sample, a percolative insulating-to-metallic state transition would occur, accompanied by a sharp drop in resistivity.

Concurrent weak localization and double Schottky barrier across a grain boundary in bicrystal SrTiO3

Stoichiometric ${\mathrm{SrTiO}}_{3}$ (STO) is a wide band-gap insulator in which oxygen deficiency generates a low-temperature metallic ferromagnetic state. Here, we report weak ferromagnetic-like and metallic transport in oxygen-deficient bicrystal of $\mathrm{STO}$ with a low-temperature electron mobility and surface carrier density of $2800\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{V}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ and $3.500\ifmmode\times\else\texttimes\fi{}{10}^{16}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}2}$, respectively. Moreover, we show that magnetotransport behavior in the bulk and across the grain boundary (GB) in $\mathrm{STO}$ single crystals are significantly different. In the bulk, our magnetotransport results agree with those reported in the literature. Importantly, low-temperature magnetotransport across the GB shows a disorder-induced metal-insulator transition, and it is modeled as a quasi--two-dimensional system below 10 K that accounts for weak localization (WL), supported by electron-electron, electron-phonon, and Hikami-Larkin-Nagaoka (HLN) quantum interference models. The HLN model accounts for realistic length scales: the dephasing length ${L}_{\ensuremath{\phi}}$, and the spin-orbit (SO) scattering length ${L}_{\mathrm{SO}}$, which are comparable to the electron mean-free path, resembling the surface-conducting nature across the GB. Our experimental work shows the importance of structural defects in the interpretation of magnetotransport in ${\mathrm{SrTiO}}_{3}$ and shows that WL is concurrent with a double Schottky barrier at the GB interface.

Light-Induced Mott-Insulator-to-Metal Phase Transition in Ultrathin Intermediate-Spin Ferromagnetic Perovskite Ruthenates.

Light control of emergent quantum phenomena is a widely used external stimulus for quantum materials. Generally, perovskite strontium ruthenate SrRuO3 has an itinerant ferromagnetism with a low-spin state. However, the phase of intermediate-spin (IS) ferromagnetic metallic state has never been seen. Here, by means of UV-light irradiation, a photocarrier-doping-induced Mott-insulator-to-metal phase transition is shown in a few atomic layers of perovskite IS ferromagnetic SrRuO3- δ . This new metastable IS metallic phase can be reversibly regulated due to the convenient photocharge transfer from SrTiO3 substrates to SrRuO3- δ ultrathin films. These dynamical mean-field theory calculations further verify such photoinduced electronic phase transformation, owing to oxygen vacancies and orbital reconstruction. The optical manipulation of charge-transfer finesse is an alternative pathway toward discovering novel metastable phases in strongly correlated systems and facilitates potential light-controlled device applications in optoelectronics and spintronics.

Quasi two-dimensional electron gas generated by laser irradiation at rutile TiO2 surface

Two-dimensional electron gas exhibits abundant physical properties that can facilitate new physics and novel device applications. Herein, we report on a systematic investigation on rutile TiO2-based quasi two-dimensional electron gas generated by laser irradiation. A transition from nonmagnetic insulator to ferromagnetic metal has been demonstrated after laser irradiation. A joint X-ray photoelectron spectroscopy and Raman spectroscopy analysis allows us to associate the metallic ferromagnetic state with the surface formation of oxygen vacancies and Ti3+. The universality of laser irradiation implies wide potential applicability to the fabrication of multifunctional oxide devices.

Ferroelectricity coexisted with p-orbital ferromagnetism and metallicity in two-dimensional metal oxynitrides

Two-dimensional (2D) multiferroics have attracted increasing interests in basic science and technological fields in recent years. However, most reported 2D magnetic ferroelectrics are based on the d-electron magnetism, which makes them rather rare due to the empirical d0 rule and limits their applications for low magnetic phase transition temperature. In this work, we demonstrate that the ferroelectricity can coexist with the p-electron-induced ferromagnetism without the limitation of d0 rule and metallicity in a family of stable 2D MXene-analogous oxynitrides, X2NO2 (X = In, Tl). Remarkably, the itinerant character of p electrons can lead to the strong ferromagnetic metallic states. Furthermore, a possible magnetoelectric effect is manifested in a Tl2NO2/WTe2 heterostructure through the interface engineering. Our findings provide an alternative possible route toward 2D multiferroics and enrich the concept of ferroelectric metals.

Semiconducting spin glass to metallic ferromagnetic state phase transition in double-substituted La1−xSrxCo1−yNiyO3−γ perovskites

A comprehensive study of the structural, magnetic, and transport properties of double-substituted ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{Co}}_{1\ensuremath{-}y}{\mathrm{Ni}}_{y}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\gamma}}$ ($0.1\ensuremath{\le}x\ensuremath{\le}0.5, 0.05\ensuremath{\le}y\ensuremath{\le}0.25$) perovskite systems was carried out. The average oxidation number of Co ions was found to be $3+$ for the most subsystems. The existence of several characteristic concentration regions for various degrees of substitution in the A (La, Sr) and B (Co, Ni) sublattices is shown. Low levels of Sr and Ni ion substitution subsystems demonstrate cluster spin-glass behavior with a semiconducting character of the conductivity and a diamagnetic low-spin (LS) ${\mathrm{Co}}^{3+}$ matrix. An increase of Ni substitution leads to the stabilization of intermediate-spin (IS) ${\mathrm{Co}}^{3+}$ ions in ${\mathrm{CoO}}_{6}$ octahedra, approaching the percolation threshold of ferromagnetic clusters. For strongly Sr-substituted subsystems an effect of stabilization of IS ${\mathrm{Co}}^{3+}$ is not observed, since the contribution of this effect is smaller than the effect of the dilution by antiferromagnetically interacting Ni ions. In this case, an increase of Ni content leads to a decrease in the magnetic ordering temperature ${T}_{\text{mo}}$ and magnetization values. For weakly Sr-substituted systems, on the contrary, it leads to their growth. Anomalies in the conductivity dependences for several subsystems are due to the thermally induced spin crossover of the part of ${\mathrm{Co}}^{3+}$ ions, first from the LS to the IS state, and then to the mixed IS/high-spin (HS) state, similar to the parent ${\mathrm{LaCoO}}_{3}$.

Manipulating magnetic and magnetoresistive properties by oxygen vacancy complexes in GCMO thin films

The effect of in situ annealing is investigated in Gd0.1Ca0.9MnO3 (GCMO) thin films in oxygen and vacuum atmospheres. We show that the reduction of oxygen content in GCMO lattice by vacuum annealing induced more oxygen complex vacancies in both subsurface and interface regions and larger grain domains when compared with the pristine one. Consequently, the double exchange interaction is suppressed and the metallic-ferromagnetic state below Curie temperature turned into spin-glass insulating state. In contrast, the magnetic and resistivity measurements show that the oxygen treatment increases ferromagnetic phase volume, resulting in greater magnetization (M S) and improved magnetoresistivity properties below Curie temperature by improving the double exchange interaction. The threshold field to observe the training effect is decreased in oxygen treated film. In addition, the positron annihilation spectroscopy analysis exhibits fewer open volume defects in the subsurface region for oxygen treated film when compared with the pristine sample. These results unambiguously demonstrate that the oxygen treated film with significant spin memory and greater magnetoresistance can be a potential candidate for the future memristor applications.

Ферромагнетизм нанопорошков графита с примесью оксида кобальта и его эволюция при умеренном отжиге

In the paper, the influence of a small impurity of the cobalt oxide CoO on the magnetic properties of the graphite nanopowder is studied. It is shown that such an impurity causes a weak ferromagnetism of the as-prepared and annealed in the air at 670 K samples which significantly increases after an annealing in vacuum. Exchange bias effect is observed that originates from the partial reduction of the antiferromagnetic CoO particles to the ferromagnetic metallic state.

Lattice Parameters, Electronic, and Magnetic Properties of Cubic Perovskite Oxides ARuO3 (A=Sr, Rb): A First‑Principles Study

Trioxides of rubidium, strontium, and ruthenium belong to the family of alkali and alkaline earth ruthenates. SrRuO3 crystallizes in various symmetry classes—orthorhombic, tetragonal, or cubic—whereas RbRuO3 is perovskite (cubic) structured and crystallizes only in the cubic space group Pm3¯¯¯m(No. 221). In this study, we investigated the structural stability as well as the electronic and magnetic properties of two cubic perovskites SrRuO3 and RbRuO3. We established the corresponding lattice parameters, magnetic moments, density of states (DOS), and band structures using ab‑initio density‑functional theory (DFT). Both compounds exhibited a metallic ferromagnetic ground state with lattice parameter values between 3.83 and 3.96 Å; RbRuO3 had magnetic moments between 0.29 and 0.34 µBwhereas SrRuO3 had magnetic moments between 1.33 and 1.66 µB. This study paves way for further RbRuO3 research.