Weak Ferromagnetism Research Articles

Pressure and temperature dependences of the canting angle and increase in the magnetic ordering temperature, Tc(P), for the weak ferromagnet Li+[TCNE]˙- (TCNE = tetracyanoethylene).

The hydrostatic pressure dependence of the magnetic ordering temperature, Tc(P), for the interpenetrating, diamondoid lattice-structured, weak ferromagnet (= canted antiferromagnet) Li+[TCNE]˙- (TCNE = tetracyanoethylene) reversibly increases from 20.9 to 23.4 K at 9.73 kbar, an increase of 12% with a rate of increase, dTc/dP, of 0.27 K kbar-1. The 5 T magnetization increased by 672% from 186 emu Oe mol-1 at ambient pressure to an average of 1440 emuOe mol-1 upon application of pressure. The remanent magnetization initially increases 30% from 10.8 to 14.0 emuOe mol-1 from ambient to 0.06 kbar, and increases further by 6% to a maximum of 14.8 emuOe mol-1 at 0.56 kbar before declining by 22% to 11.5 emuOe mol-1 at 9.73 kbar. The pressure-dependent coercive field, Hcr(P), initially decreases by 42% from 31.1 Oe at ambient pressure to 18 Oe at 0.06 kbar, then increases to 52 Oe at 9.73 kbar. The canting angle, α, increases by 28% from 0.52° to 0.66° at 0.06 kbar, then decreases by 23% to 0.51° at 9.73 kbar, as well as increases by 2% from 0.536° to 0.548° from 1.8 to 2.5 K, before decreasing by 79% to 0.117° at 19 K. The interlattice interactions are attributed to be the primary exchange mechanism. Thus, α(T) and α(P) have similar dependencies that are attributed to a competition between an increase and a decrease in the intra- and interlayer C⋯N interlattice separations as the temperature and pressure increases.

Механизмы генерации волн Лэмба доменной границей в пластине слабого ферромагнетика

The purpose of research. Study of the mechanism of Rayleigh-Lamb waves generation by the moving domain wall. Methods. The equations describing the elastic displacements generated by moving domain wall in the plate were solved by the Fourier method. Results. For yttrium orthoferrite crystal we’ve estimated the amplitudes of Lamb waves displacement for two different cases of their generation: due to bulk and surface strains arising from the movement of the domain wall. The amplitude of displacement in an unbounded crystal has the same order of magnitude as for waves excited by surface strains - 10 10 cm for the theoretical domain boundary thickness D3 = 1.1·10-6 m. The correlation between the contributions of bulk and surface mechanisms in the generation of Lamb waves by the domain wall has been determined. Conclusion. For development domain wall-based logic and memory devices it is necessary to fully investigate the factors that can affect the domain dynamics in magnetics. One of these factors is the braking of the domain wall on Rayleigh-Lamb waves. From the equations describing the elastic displacements in the orthoferrite crystal plate during the motion of the domain wall, we can conclude that there are two independent mechanisms of Rayleigh-Lamb waves generation bulk and surface. The evaluation of the contributions of these mechanisms helps to consider the effect of surfaces on the domain dynamics and can be used in the future to develop magnetic memory devices based on weak ferromagnets.

Removal of Ferrimagnetic ZnFe2O4 Impurity Phase by Li Co-Doping in Fe Doped ZnO

A simple approach is presented to remove the impurity phase of ZnFe2O4 from Fe doped ZnO. Gradual incorporation of non-magnetic Li ions reduced 5.6% phase contamination of ZnFe2O4 to negligible limit (<0.01%) from 4 at% (atomic %) Fe doped ZnO. X-ray absorption near edge spectroscopy (XANES) revealed that the most of the Fe ions were in Fe3+ state. The optical absorption spectra of Fe doped ZnO samples exhibited d-d transition between Fe ions. It also indicated the signature of ZnFe2O4 phase, which reduced gradually on Li increment. ZnFe2O4 contained samples exhibited strong magnetic ordering with spin-glass character at low temperature and weak ferromagnetism (FM) at the room temperature with disordered inverse spinel structure. However, 6 at% Li incorporated sample did not show any significant FM in the entire temperature range of 2–300 K. ZnFe2O4 is supposed to be the possible source of the observed strong magnetic ordering i.e., FM has extrinsic origin. The gradual removal of impurity phase ZnFe2O4 by increasing Li doping without damaging any intrinsic property of Fe doped ZnO is primarily due to gradual increase of tetrahedral coordination of Fe ions.

Oxygen vacancy mediated room-temperature ferromagnetism and band gap narrowing in DyFe0.5Cr0.5O3 nanoparticles.

We report on the magnetic and optical properties of DyFe0.5Cr0.5O3 nanoparticles synthesized by a sol-gel method. Rietveld refinement of a powder X-ray diffraction (XRD) pattern confirms the formation of an orthorhombic disordered phase with the Pnma space group. The formation of nano-sized particles, with an average size of 42(±12) nm, was approximated by the transmission electron microscopy (TEM) image analysis. X-ray photoelectron spectroscopy (XPS) of this compound reveals the presence of Fe2+/Fe3+ and Cr2+/Cr3+ mixed-valence states as a consequence of oxygen vacancies present at the surface of nanoparticles. The temperature-dependent magnetization (M-T) shows a finite non-zero magnetization up to 300 K and the field-dependent magnetization (M-H) curve exhibits a weak ferromagnetic (WFM) nature at 300 K with a clear hysteresis loop, which is quite appealing compared to that of the previously reported micron-sized DyFe0.5Cr0.5O3. These observations indicate that the large concentration of uncompensated surface spin of nanoparticles could be responsible for the observed room-temperature ferromagnetism. Moreover, DyFe0.5Cr0.5O3 nanoparticles show a significantly narrow band gap (Eg ∼ 2.0 eV). Meanwhile, the oxygen vacancies may generate shallow trap energy levels within the band gap as observed from photoluminescence (PL) spectroscopy. The observed band gap narrowing by Fe doping and the effect of oxygen vacancies on the band gap are consistent with the predictions of density functional theory (DFT) calculations. The evidence of room-temperature ferromagnetism in DyFe0.5Cr0.5O3 nanoparticles compared to their bulk counterparts and the significantly narrow band gap in the visible range manifest the potential of this material in spintronic and optical applications.

Structural, optical and magnetic properties of SnO2 nanoparticles synthesized via surfactant-free hydrothermal process

Tin oxide (SnO2) nanoparticles are synthesized at different molar concentrations by employing a surfactant-free hydrothermal process. The structural properties of the samples investigated using XRD analysis indicated that the synthesized SnO2 nanoparticles have pure crystalline phase with tetragonal crystal structure of P42/mnm space group. The surface morphology analyzed using SEM micrographs showed that the nanoparticles get agglomerated without any specific structure. Optical characterization using UV–visible and PL spectroscopic techniques indicated that the synthesized SnO2 nanoparticles have absorption in the ultraviolet region and emission in the visible region due to defect states. A weak room-temperature ferromagnetism (RTFM) exhibited by the nanoparticles has been observed from the analysis of magnetic parameters.

Effects of Kaplan-Shekhtman-Entin-Wohlman-Aharony interaction on quantum discord of non-markovian dynamics under different magnetic fields

Since the discovery of symmetric helical interactions in the spin-orbit coupled single-band Hubbard model by Moriya and Kaplan, Shekhtman, Entin, Aharony et al. have successfully used this non-negligible symmetric helical exchange interaction to explain the weak ferromagnetism of La&lt;sub&gt;2&lt;/sub&gt;CuO&lt;sub&gt;4&lt;/sub&gt;. By using the non-Markovian quantum state diffusion method, the quantum discord of non-Markovian dynamics in the spin chain system that has Kaplan–Shekhtman–Entin-Wohlman–Aharony interactions and Dzyaloshinskii-Moriya interactions is studied. The effects of Kaplan–Shekhtman–Entin-Wohlman–Aharony interaction on the quantum discord under different external magnetic fields at zero and finite temperatures are discussed. The results show that the quantum discord in the system can be increased via the increasing of Kaplan–Shekhtman–Entin-Wohlman–Aharony interaction in the case of zero or uniform magnetic field, while the case is opposite under the nonuniform magnetic field. More importantly, the ideal discord state can be obtained by modulating the uniform magnetic field and Kaplan–Shekhtman–Entin-Wohlman–Aharony interaction. Moreover, the Markovian case and the effect of temperature on the quantum discord are also discussed, respectively.

Modulated magnetic structures and models of their theoretical expression

This paper is devoted to study of physical processes occurring in weak ferromagnetics iron -borate doped diamagnetic magnesium under external influence. The ideas of phase transitions are not only successfully applied in various fields of modern physics, but also in biology, chemistry, geology, and even economics and other social sciences. Thus, the article presents the results of the study of changes in the magnetic properties of iron borate when a magnesium mixture is added and the properties of this change as a result of external influences (temperature, mechanical impact, magnetic field and light).

Unusual isosymmetric order–disorder phase transition in a new perovskite-type dimethylhydrazinium manganese formate exhibiting weak ferromagnetism and photoluminescence properties

We report the synthesis, thermal, structural, dielectric, magnetic and optical properties of a novel metal–organic framework templated by the large 1,1-dimethylhydrazinium cation. We analyse the steric hindrance-related properties.

Overlayer deposition-induced control of oxide ion concentration in SrFe0.5Co0.5O2.5 oxygen sponges.

Controlling the oxide ion (O2−) concentration in oxides is essential to develop advanced ionic devices, i.e. solid oxide fuel cells, smart windows, memory devices, energy storage devices, and so on. Among many oxides several transition metal (TM)-based perovskite oxides show high oxide ion conductivity, and their physical properties show high sensitivity to the change of the oxide ion concentration. Here, the change in the oxide ion concentration is shown through the overlayer deposition on the SrFe0.5Co0.5O2.5 (SFCO) oxygen sponge film. We grew SFCO films followed by the deposition of two kinds of complex oxide films under exactly the same growth conditions, and observed the changes in the crystal structure, valence states, and magnetic ground states. As the NSMO overlayer grows, strong evidence of oxidation at the O K edge is shown. In addition, the Fe4+ feature is revealed, and the electron valence state of Co increased from 3 to 3.25. The oxide ion concentration of SFCO changes during layer growth due to oxidation or reduction due to differences in chemical potential. The present results might be useful to develop advanced ionic devices using TM-based perovskite oxides.

1D Mn(III) coordination polymers exhibiting chiral symmetry breaking and weak ferromagnetism.

Mn(iii) complexes with achiral ligands, (E)-N-(2-((2-aminobenzylidene)amino)-2-methylpropyl)-5-X-2-hydroxybenzamide (HLX, X = H, Cl, Br, and I), crystallise as chiral conglomerates containing amide oxygen-bridged one-dimensional coordination polymers that exhibit weak ferromagnetism. The bulk products exhibit symmetry breaking in that they do not contain equal amounts of enantiomers, though which is the dominant species depends on the substituent X.

A new room-temperature multiferroic material: Y2FeAlO6

In this paper, we report the finding and basic characterization of a new multiferroic material in the form of the Y2FeAlO6 (YFAO) double perovskite with orthorhombic structure. In order to study the structural and multiferroic properties in detail, we prepared the polycrystalline YFeO3 (YFO) and Y2FeAlO6 ceramic samples through traditional high temperature solid-state reaction method. XRD analysis confirmed that these two samples are single-phase and all the peaks in the pattern can be indexed with orthorhombic symmetry of the Pnma space group. Compared to YFO, YFAO is more symmetric, and has a more stable crystalline structure and smaller grain size. The Fe ion in YFO and YFAO are in the mixed oxidation state of Fe2+ and Fe3+, while the relative amount of Fe2+ in YFAO is higher than that of YFO. Al3+ with filled 2p orbital and grain refinement may be the main reasons for the greatly enhanced multiferroicity of YFAO. The magnetic properties of YFO and YFAO are mainly dominant antiferromagnetism and weak ferromagnetism, and the exchange bias effect disappears in YFAO. The coexistence of ferroelectricity and ferromagnetic orders at room temperature in YFAO promises new opportunities and improvements in next generation applications for spintronic, information storage, and sensors etc.

Evolution of microstructure, defect, optoelectronic and magnetic properties of Cu1-xCaxFeO2 ceramics

Microstructures, defect characteristics, optoelectronic, and magnetic properties of polycrystalline delafossite Cu1-xCaxFeO2 (x = 0.00–0.08) samples have been systemically investigated. Our investigation results distinctly show that divalent Ca2+ ions can successfully substitute partial Cu+ ions and prompt the grain size and induce the partial Fe3+ valence variation to Fe2+. The positron annihilation lifetime spectra signifies that the cation vacancy clusters exist in all samples, the size and concentration of vacancy defects are redistributed with increasing Ca2+ ions content, while the overall defect environment of CuFeO2 system is not changed. The Hall-effect measurement results indicate the transition of semiconductor type from p-type to n-type. The UV–Visible absorption spectroscopy results indicate that the calculated band gap of the prepared samples is estimated to be 3.42–3.58 eV, indicating the series can be applied to the transparent conductive oxide materials. The magnetic measurements reveal that the transition temperature TN1 and TN2 are independent of Ca2+ content x, while the coexistence of antiferromagnetism and weak ferromagnetism for all the doped samples are observed. A moderate Ca2+ content, i.e. x = 0.02, can distinctly promote weak ferromagnetism. The above internal mechanism is probably relevant to the evolution of lattice structure and defect characteristics caused by Ca2+ ions doping.

Orthorhombic BiFeO3 : Theoretical studies on magnetoelectric effects of the multiferroic phase

The rhombohedral $\mathrm{BiFe}{\mathrm{O}}_{3}$ (BFO), as a star multiferroics, has been of particular interest, but yet it exhibits zero magnetization, which limits its practical application. Remarkably, net magnetization and magnetoelectric (ME) coupling was reported in orthorhombic BFO at room temperature in a recent experiment. However, the underlying mechanism of its ME coupling has not been fully understood. Here, we systematically investigated magnetic structures and ME coupling of the orthorhombic BFO using density functional theory and symmetry analysis. We find it can host large electric polarization and weak ferromagnetism simultaneously, the possible coupling between them is $\mathbit{\ensuremath{\omega}}\ifmmode\cdot\else\textperiodcentered\fi{}(\mathbit{L}\ifmmode\times\else\texttimes\fi{}\mathbit{M})$. More interestingly, its polarization $P$ and magnetization $M$ can be switched simultaneously under an electric field, and it shows a linear ME effect when an external magnetic field is applied. Thus, our study provides a substantially deeper understanding of the ME effect of the orthorhombic BFO and confirm it is a multiferroic with the linear ME coupling.

Reinspection of formation of BiFe1-xMnxO3 solid solutions via low temperature sol-gel synthesis route

In this study, BiFe1-xMnxO3 (BiFeMnO; x from 0 to 0.5) solid solutions were prepared by low temperature sol-gel processing. It was demonstrated that structural, magnetic and morphological properties of BiFeMnO samples are dependent on the chemical composition of the synthesized BiFe1-xMnxO3 solid solutions. The thermal behaviour of the Bi–Fe–Mn–O precursor gels was investigated by thermogravimetric and differential scanning calorimetry (TG-DSC) measurements. From X-ray diffraction (XRD) analysis it was observed that monophasic BiFe1-xMnxO3 samples have formed up to 25 mol% of substitution. The Rietveld analysis showed that the structure of BiFeMnO specimens can be indexed by rhombohedral or orthorhombic unit cell depending on Mn3+ content. Scanning electron microscopy (SEM) was used to investigate samples morphology and revealed, that smaller particles form when Mn3+ is present inside the structure. Moreover, magnetic properties of solid solutions were also investigated, and antiferromagnetism and weak ferromagnetism were observed for the samples.

Electric‐Potential‐Induced Complete Control of Magnetization in MnZnSb Metallic Ferromagnets

AbstractMagnetoelectric coupling refers to electric‐field control of magnetism, which may offer low‐power memory and beyond‐CMOS electronics. However, contenders of magnetic phase change materials, such as the dilute magnetic semiconductors (DMS), show weak ferromagnetism whereas the ultra‐small screening lengths of robust metallic magnets in artificially stacked thin film heterostructures reduce the extent of controllable magnetization to sub‐atomic distances, thereby diminishing the sheer magnitude of the tunable magnetization. In contrast, an electrochemical control of magnetization has recently been proposed where reversible electrochemistry/ion‐exchange is used to control magnetism in bulk ferromagnets. However, so far, ionic control of magnetism is limited to spinel ferrites and highly correlated oxide systems. Here, it is reported that the ionic control of magnetism can be extended to metallic ferromagnets; complete and reversible switching of ferromagnetism is demonstrated in bulk MnZnSb intermetallic compounds at room temperature. An electrochemically controlled reversible tuning of magnetization across the magnetic phase transition temperature is demonstrated. The observed phenomenon can be explained by the distortion of the crystal lattice, upon Li‐ion insertion into the MnZnSb interstitial sites, accompanied by a change in the magnetic moment of the manganese ions; acting together, both these effects lead to the collapse of the ferromagnetic order in MnZnSb.

Syntheses and Properties of (Nitronyl nitroxide)-substituted Tri-phenylamine ortho-Bridged by Two Oxygen and Sulfur Atoms.

A nitronyl nitroxide unit (NN) was linked with a triphenylamine-based condensed polycyclic skeleton DOTT to form a radical substituted donor NN-DOTT. X-ray crystal structure analysis demonstrated a flat bowl shape of the DOTT unit. EPR spectra showed the localization of electron spin on the NN unit. Chemical oxidation of the DOTT unit produced radical-substituted radical cation salts NN-DOTT+ ⋅ SbF6 - and NN-DOTT+ ⋅ FeBr4 - that are stable under ambient conditions. The magnetic behavior of NN-DOTT+ ⋅ SbF6 - is characterized by the strong intramolecular ferromagnetic interaction between NN and DOTT+ . The X-ray structural analysis of NN-DOTT+ ⋅ FeBr4 - shows planar structure of DOTT and 1D mixed-stack column of NN-DOTT+ and FeBr4 - . Magnetic measurements established that NN-DOTT+ ⋅ FeBr4 - undergoes magnetic phase transition into a weak ferromagnet at 7 K.

π-electron weak ferromagnetism in potassium-intercalated 9-phenylanthracene

Intercalation of alkali metal is an effective way to tune the physicochemical property of polyaromatic hydrocarbons. Herein, we show for the first time that the weak ferromagnetism with a Curie temperature of 5.2 K can be realized in an all-carbon π-electron compound – potassium-intercalated 9-phenylanthracene. The magnetic measurements reveal that there exists an antiferromagnetic transition around 35 K before transition to the weak ferromagnetic phase. An in-depth theoretical investigation indicates that the weak ferromagnetism is produced by the intramolecular ferromagnetic and intermolecular antiferromagnetic spin couplings in the crystal unit cell. Our finding enriches the physical functionality of anthracene derivatives and adds a new member of organic magnetic materials.

Crystal chemistry and physicochemical investigation of aliovalent substituted SnO2 nanoparticles

This paper investigates the physicochemical properties of rare earth metal Dysprosium (Dy) doped SnO2 dilute magnetic semiconducting nanoparticles. Sol-gel method was adopted to synthesize Sn(1-x)DyxO2 (x = 0, 0.05 and 0.10) compositional series. Structural analysis revealed that all the compositions exhibit pure rutile type tetragonal crystal structure with space group P42/mnm as manifested by Rietveld refinement without any secondary phases and impurities. FTIR spectra of all the compositions showed a band at 592 cm−1 belonging to Sn–O symmetric vibration. Pure and Dy3+ modified SnO2 nanoparticles exhibited pseudo-spherical morphology with an average particle size of 16 nm, 19 nm, and 22.8 nm for x = 0, 0.05, and 0.10, respectively as calculated from the statistical bar graph distribution of particles. The particle size increased with increasing Dy3+ concentration. The enhancement in cell volume with increasing Dy3+ concentration as calculated from Rietveld refinement studies also complimented TEM results. HRTEM fringe pattern and ring pattern of SAED plot endorsed the formation of tetragonal structure of Sn(1-x)DyxO2 (x = 0, 0.05 and 0.10) nanoparticles. Photoluminescence spectra of all the compositions displayed a strong emission peak of ~407 nm, which may be ascribed due to oxygen vacancies in the samples. MH hysteresis loop of pure SnO2 showed weak ferromagnetism at low fields and diamagnetic nature at the higher field but Dy3+ doped SnO2 nanoparticles displayed paramagnetism at x = 0.05 and ferromagnetism at x = 0.10, which might be due to increase in oxygen vacancies upon increasing aliovalent Dy3+ in the host SnO2.

Magnetic Properties and Magnetodielectric Effect in (C6H5CH2NH3)2[CuCl4] with Organic-Inorganic Hybrid Layered Structure

Metal Organic Frameworks (MOFs) are a group of multiferroic candidates that exhibit various optical, electrical, magnetic, and structural properties depending on the type of organic cations, transition metals and halogen elements, and their molar ratio. (C6H5CH2NH3)2[CuCl4] (BZACC), one of the MOF materials, has a special hybrid layered structure of organic and inorganic layers. Magnetic property measurement showed that BZACC exhibits weak in-plane ferromagnetism below the Curie point (TC) of 10.25 K and the saturated magnetic moment of 1 µB per formula unit at 2 K. When the magnetic field is less than 0.1 T along the c axis, it exhibits weak antiferromagnetism below 8 K. From the measurement of the dielectric constant with external magnetic field, we observed a maximum magnetodielectric (MD) effect of 0.4% at 2 K. Furthermore, it was found that the magnetic-field dependence of the MD effect is similar to that of the second derivative of magnetization with respect to magnetic field. We suggest that the observed MD effect is the consequence of the magnetic-field-induced spin structure change in the inorganic layer, which induces the change in the interlayer magnetic coupling and, as a result, induces the change in the dielectric constant by the applied magnetic field.

Exploring weak ferromagnetism and conduction mechanism in the layered oxide BiPbSr2MnO6

Layered oxide BiPbSr2MnO6 (BPSMO), isostructural to 10 K Bi-based cuprates, is prepared by employing solid-state route in nitrogen atmosphere. Phase purity of the compound is determined from the room temperature Rietveld refined X-ray diffraction (XRD) data. BPSMO crystallizes in an orthorhombic crystal structure, thereby confirming its space group as ‘A2aa’. Presence of weak ferromagnetism in BPSMO below magnetic transition temperature (TN) is validated from isothermal magnetization data accompanied by the Arrott plot at 2.8 K, in contrast to its antiferromagnetic behavior at 290 K. The coexistence of Mn2+ and Mn3+ is confirmed from X-ray photoelectron spectroscopy study. The conduction mechanism in BPSMO is studied following two different hopping models, i.e., Arrhenius model for T > 250 K and Mott's variable range hopping (MVRH) model for T < 250 K. The relaxation in BPSMO is found to be polaronic in nature and may have originated due to the mixed valence structure of the sample. Lastly, the frequency domain analysis of dielectric spectra reveals the presence of two distinct relaxations. Moreover, it is determined that the low-frequency and high-frequency relaxation have activation energy 0.35 eV and 0.48 eV, respectively.