Appearance Of Ferromagnetism Research Articles

Onset of magnetic order in U2(Ni1−x Fe x )2Sn-H

We present specific heat and magnetic studies as a function of temperature and magnetic field for U2(Ni1−x Fe x )2Sn alloys (x = 0.0, 0.05, 0.1, 0.15, 0.2, 0.4, 0.6 and 0.8) and their hydrides (absorption of ≈ 2 H/f.u.). For the parent alloys, antiferromagnetic order is rapidly suppressed with increasing Fe concentration and non-Fermi-liquid behavior was found for x = 0.2. Hydrogenation of the parent alloys causes a substantial increase of T N in Fe-low hydrides (x < 0.2), while Fe-rich hydrides show an unexpected appearance of ferromagnetism in the range 0.4 ≤ x ≤ 0.8. Some of the findings are compared with similar studies in U2Co2Sn and U2Co2InH1.9.

Grain boundaries as the controlling factor for the ferromagnetic behaviour of Co-doped ZnO

The influence of the grain boundary (GB) specific area s GB on the appearance of ferromagnetism in Co-doped ZnO has been analysed based on a review of numerous research contributions from the literature on the origin of the ferromagnetic behaviour of Co-doped ZnO. An empirical correlation has been found that the value of the specific grain boundary area s GB is the main factor controlling such behaviour. The Co-doped ZnO becomes ferromagnetic only if it contains enough GBs, i.e., if s GB is higher than a certain threshold value s th = 1.5 × 106 m2/m3. It corresponds to the effective grain size of about 1 µm assuming a full dense material and equiaxial grains. The magnetic properties of Co-doped (0 to 42 at. %) ZnO dense nanograined thin films have been investigated. The films were deposited using the wet chemistry “liquid ceramics” method. The samples demonstrate ferromagnetic behaviour with J s up to 0.12 emu/g and coercivity H c ∼ 0.01 T. Saturation magnetization non-monotonically depends on the Co concentration. The dependence on Co content can be explained by the changes in the structure of a ferromagnetic “grain boundary foam” responsible for the magnetic properties of pure and doped ZnO.

Coexistence of Superconductivity and Ferromagnetism in La2-xSrxCuO4 Nanoparticles

Magnetic and superconducting properties of La2-xSrxCuO4 nanoparticles are systematically studied as a function of particle size and Sr doping. Through the magnetization and electron spin resonance measurements, it was found that the suppression of superconductivity and enhancement of ferromagnetism were observed simultaneously with decreasing particle size, which should be related to the uncompensated Cu2+ spins and oxygen defects due to the increasing role of finite size. On the other hand, although Sr doping will introduce more uncompensated spins to the La2-xSrxCuO4 nanoparticles, the low temperature ferromagnetism is reduced. The results suggest that the suppression of superconductivity and the appearance of ferromagnetism for the nanoparticles may be closely related to the destruction of antiferromagnetic correlation in CuO2 planes.

Structure and Magnetic Properties of (Al, Co) Co-Doped ZnO Thin Films

In this study, Zn0.99Co0.01Al0.015O thin film has been prepared by sol-gel method. The structural and magnetic properties of the sample were investigated. X-ray diffraction spectroscopy analyses indicate that the Co and Al codoping can not disturb the structure of ZnO. No additional peaks are observed in the Zn0.99Co0.01AlxO and Al3+ and Co2+ substitute for Zn2+ without changing the wurtzite structure. The resistance measurements confirm that Al ions increase the free carriers concentration. Based on the above experiments we think the ferromagnetic behavior of the sample could not originate from Co nanoclusters. The presence of free carriers and localized d spins is a prerequisite for the appearance of ferromagnetism. As the result, the carriers generated by Al doping is considered a main factor to induce the ferromagnetic phenomenon.

The role of 3d electrons in the appearance of ferromagnetism in the antiferromagnetic Ru2MnGe Heusler compound: a magnetic Compton scattering study

The antiferromagnetism in Ru2MnGe can be suppressed by the substitution of V by Mn and ferromagnetism appears. Synchrotron-based magnetic Compton scattering experiments are used in order to investigates the role of 3d electrons in the indirect/direct exchange interactions for the appearance of ferromagnetism. A small spin moment for the itinerant electron part on the magnetic Compton profile indicates that the metallic ferromagnet Ru2Mn0.5V0.5Ge has a weak indirect exchange interaction between the d-like and sp-like (itinerant) electrons. This suggests that the appearance of ferromagnetism is caused by the enhancement of the direct exchange interactions between d–d electrons in the Ru2MnGe Heusler compound. These findings indicate that the indirect exchange interaction between itinerant electrons and localized electrons is a significant key point for the appearance of ferromagnetism in this system.

Structural and magnetic properties in the powder form of Sn 1− xCr xO 2 solid solution

Structural and magnetic properties were studied in powder form of Sn 1− x Cr x O 2 with x=0.01, 0.02, 0.03, 0.04 and 0.05 in nominal composition. The structural parameters were obtained at room temperature by the Rietveld refinement of the x-ray powder diffraction profiles. Samples of x=0 to 0.04 are tetragonal phase with a space group P4 2/ mnm. The lattice parameters indicate three-step changes with increasing Cr content. The distortion of the metal-oxygen octahedral unit occurs. The substitution of Cr ions on the Sn sites shortens the lattice parameters and the octahedral unit becomes elongated with a displacement of an apical oxygen from x=0 to x=0.02. The incorporation of Cr over x=0.02 leads to the recovery of the length of lattice parameters together with a relaxation of the octahedral unit. This result indicates a possible interstitial occupation of Cr ions from x=0.03 to x=0.04. The Cr doping reaches a saturation limit at x=0.05 with a trace of the excess Cr oxides in the x-ray study. A room temperature ferromagnetism appears in the sample with x=0.01 and becomes remarkable in one with x=0.02. The magnetization decreases with increasing the Cr doping with the amount x>0.02. Thus, the appearance of ferromagnetism highly correlated with the oxygen displacements at the apical position of the octahedral in the Sn 1− x Cr x O 2 system at room temperature. The critical oxygen displacement in the elongated octahedral at around x=0.02 may encourage the vacancy of the apical oxygen and eventually leads to appearance of a ferromagnetism based on an F-center exchange with a micro- and/or nano-structural transition. The observed ferromagnetism is highly correlated with the averaged structural change appeared in the x-ray powder diffraction.

Magnetic and electronic properties of Eu0.9Ca0.1BaCo2O5.5+δ with the variation of oxygen stoichiometry

The effect of the oxygen content on the magnetic and transport properties of the ferromagnetic Eu0.9Ca0.1BaCo2O5.5+δ has been investigated. Unlike the increase in TC with calcium content, paradoxically the TC value decreases as the oxygen content increases, as observed in the undoped phase. Assuming the Kanamori-Goodenough rules apply to this very complex magnetic system, these experiments suggest that the Co3+ disproportionation into Co4+ and Co2+, plays an important role in the appearance of ferromagnetism. The magnetic phase separation scenario of ferromagnetic domains embedded in an antiferromagnetic matrix play an important role in the ferromagnetism of the calcium doped “112” cobaltites. All the samples covering a wide range of oxygen content, exhibit p-type conductivity.

Evolution of itinerant ferromagnetism in SrxPb1−xRuO3 (≤x≤1): Interplay between Jahn–Teller distortion and A-site disorder

Density functional theory with local spin density approximation is applied to study the evolution of ferromagnetism in SrxPb1−xRuO3 (0≤x≤1). Besides the enhanced Pb–O covalence and Pb–Ru hybridization, the Jahn–Teller effect, which favors the low-spin state (S=0) of Ru4+ in a stretched oxygen octahedra, is found to be the origin of the observed paramagnetism in PbRuO3. With the introduction of Sr, the Pb–Ru hybridization is weakened and an intermediate-spin state (S=1) is preferred via the opposite Jahn–Teller effect in a compressed oxygen octahedra, leading to the appearance of ferromagnetism for x&amp;gt;0.5. Our calculations provide a good explanation of recent experimental findings.

Multiferroic Properties of Bi4−xNdxTi3O12/CoFe2O4 Composite Films

Composite materials consisting of two or more material systems exhibits mixed physical properties of individual materials. We synthesized composite films of ferroelectric Bi4−xNdxTi3O12 and ferromagnetic CoFe2O4 to realize multiferroic properties by solution route with varying number of layers of both the materials. The alternate films of ferroelectric Bi4−xNdxTi3O12 and ferromagnetic CoFe2O4 were deposited by spin coating on Pt substrate (Pt/Ti/SiO2/Si). Structural, ferroelectric, and ferromagnetic properties were investigated using x-ray diffraction, ferroelectric probe and Vibrating Sample Magnetometer (VSM) respectively. Bi3−xNdxTi3O12/CoFe2O4 layered structures showed composite phase as revealed by x-ray diffraction patterns. The initial results show the presence of ferromagnetic and ferroelectric responses at room temperature. The appearance of ferromagnetism and ferroelectricity at room temperature indicate the possibility of existence of multiferroic phase through stress induced electric and magnetic coupling.

Appearance of Ferromagnetism in Co-Doped CeO2 Diluted Magnetic Semiconductors Prepared by Solid-State Reaction

We report on the magnetic and electronic properties of Co-doped CeO2 oxides prepared by a solid-state reaction. The as-prepared samples exhibit pure paramagnetic behavior, but postannealing at 450 °C for 1 h under H2/N2 atmosphere results in the appearance of ferromagnetism at room temperature. The electronic structure of as-prepared and postannealed Co-doped CeO2 diluted magnetic oxides is investigated using soft X-ray absorption and emission spectroscopy. Co L-edge resonant inelastic X-ray scattering (RIXS) spectra indicate that direct Co−Co bonds form due to the precipitation of Co atoms in CeO2. This is in agreement with zero-field-cooled and field-cooled thermal variations of the magnetization, which indicated the presence of Co clusters with size larger than 8 nm.

Theory of the ferromagnetism inTi1−xCrxNsolid solutions

First-principles calculations are used to investigate the magnetic properties of Ti$_{1-x}$Cr$_{x}$N solid solutions. We show that the magnetic interactions between Cr spins that favour antiferromagnetism in CrN is changed upon alloying with TiN leading to the appearance of ferromagnetism in the system at approximately $x \leq 0.50$ in agreement with experimental reports. Furthermore we suggest that this effect originates in an electron density redistribution from Ti to Cr that decreases the polarization of Cr d-states with t$_{2g}$ symmetry while it increases the polarization of Cr d-states with e$_g$ symmetry, both changes working in favour of ferromagnetism.

Ferromagnetism in transparent thin films of MgO

We show both theoretical and experimental evidences of the appearance of ferromagnetism in MgO thin films. First principles calculations allow predicting the possibility of the formation of a local moment in MgO, provided the existence of Mg vacancies which create holes on acceptor levels near the O 2p-dominated valence band. Magnetic measurements evidence of the existence of room-temperature ferromagnetism in MgO thin films. High-resolution transmission electron microscopy demonstrates the existence of cation vacancies in our samples. Finally, by applying the element specificity of the x-ray magnetic circular dichroism technique, we also demonstrate that the magnetic moments of the system arise from the spin polarization of the 2p electrons of oxygen atoms surrounding Mg vacancies.

The effect of oxygen non-stoichiometry and doping with vanadium on the nature of magnetism in titanium dioxide with the anatase structure

Abstract The effect of oxygen non-stoichiometry and doping with vanadium on the electronic structure and magnetic properties of the titanium dioxide with the anatase structure have been studied by employing the tight-binding linear muffin-tin orbitals (TB-LMTO) method in the local spin-density approximation with the account of on-site Coulomb correlations (LSDA+U). It has been shown that the appearance of ferromagnetism in Ti1−xVxO2−y, Ti1−2xV2xO2−y compounds with 0 ≤ x ≤ 1 / 16 , 0 ≤ y ≤ 1 / 16 is favored by the oxygen non-stoichiometry and location of the exchange-coupled vanadium atoms in the ac and bc planes of the crystal structure. At the vanadium concentration of 0.125 the super-exchange mechanism of the ferromagnetism is essential, with the Curie temperature (340 K) being in good relation to experimental data. The calculations demonstrate that the probability of formation of magnetic polarons is high at the vanadium concentration of 0.0625, but low at the concentration of 0.125. The reduction of magnetic moment with the rise of vanadium concentration corresponds to the general trend revealed for dilute magnetic semiconductors. It was established that the mechanisms of the high-temperature ferromagnetism in Ti1−xVxO2−y, Ti1−2xV2xO2−y compounds are different and depend on oxygen non-stoichiometry and vanadium concentrations.

Effect of cobalt substitution on microstructure and magnetic properties in ZnO nanoparticles

Ferromagentic semiconductors have been actively pursued because of their potential as spin polarized carrier sources and easy integration into semiconductor technology. One such material, ZnO has been shown to be a potential Diluted Magnetic Semiconductor (DMS). The appearance of ferromagnetism, however, is found to be sensitive to the processing conditions. We report synthesis of ZnO nanoparticles of size ∼20 nm by a simple co-precipitation technique using metal nitrates and NaOH as precipitant. The particles are self-organised and reveal single crystalline behaviour in electron diffraction pattern. Incorporation of Co in ZnO matrix leads not only to the reduction in crystallite size but also to the modification of the structure. At 5% Co, the particles are highly textured. The particles also aggregate and the aggregated mass have nearly rectangular shape as seen through TEM. Increasing Co to 10%, results into further reduction of particle size and the particles self organize in a line, which looks like nanofibers. This alignment of particles increases by increasing the Co content further. This type of growth of nanofibers above Co ≥ 10% is well correlated with the anisotropic peak broadening observed in the XRD spectra. In addition, Co substitute Zn site up to 20% without showing any extra phase in XRD spectra as compared to 7 to 10% in case of bulk. Transport and magnetic studies indicate that conductivity increases with increasing Co content, but carrier mediated ferromagnetism is absent down to 10 K.

Frozen magnetostructural order inGd5Ge4: A calorimetric study

Temperature and magnetic field dependencies of heat capacity $C$ of ${\text{Gd}}_{5}{\text{Ge}}_{4}$ are presented. The arrest of kinetics of the first-order antiferromagnetic to ferromagnetic transition results in a broad peak in magnetic $C/T$ at $\ensuremath{\approx}15\text{ }\text{K}$. The corresponding magnetic entropy ${S}_{m}$ reduces when magnetic field is applied due to the appearance of ferromagnetism and becomes zero for the fully magnetized state. Anomalous behavior of $C$ in cycling across the antiferromagnetic to ferromagnetic transition is observed. These features are discussed in the framework of different possible mechanisms. Evidence for magnetoelastic coupling is seen from the change in entropy $\ensuremath{\Delta}{S}_{H}$ for a change in field across the magnetostructural transition.

First-Principles Study on Magnetic Properties of V-Doped ZnO Nanotubes

Electronic and magnetic properties of V-doped ZnO nanotubes in which one of Zn2+ ions is substituted by V2+ ions are studied by the first-principles calculations of plane wave ultra-soft pseudo-potential technology based on the spin-density function theory. The computational results reveal that spontaneous magnetization in V-doped (9,0) ZnO nanotubes can be induced without p-type or n-type doping treatment, and the ferromagnetism is isotropic and independent of the chirality and diameter of the nanotubes. It is found that V-doped ZnO nanotubes have large magnetic moments and are ferromagnetic half-metal materials. Moreover, the ferromagnetic coupling among V atoms is generated by O 2p electron spins and V 3p electron spins localized at the exchanging interactions between magnetic transitional metal (TM) impurities. The appearance of ferromagnetism in V-doped ZnO nanotubes gives some reference to fabrication of a transparent ferromagnet which may have a great impact on industrial applications in magneto-optical devices.

Room Temperature Ferromagnetism in Powder Form of Sn1-xCrxO2 (x = 0.01, 0.02, 0.03, 0.04 and 0.05) Solid Solution

AbstractStructural and magnetic properties were investigated in the mixed powders of Sn1-xCrxO2 (x = 0.01, 0.02, 0.03, 0.04 and 0.05) in nominal composition. The lattice parameter observed in (110) x-ray diffraction indicates two step changes with increasing Cr content. The occupation of Cr ion at the interstitial position leads to elongation of the lattice parameter for x = 0.01 to x =0.03. Then, the Cr3+ ions are remarkably substituted into the Sn4+ ion site for x = 0.04 to x = 0.05, which results in shortening of the lattice. The lattice parameters for x = 0.01 and 0.02 are larger than x = 0.03 to 0.05. The room temperature ferromagnetism appeared in the sample with x = 0.01 and reaches maximum at the doping rate of x = 0.02; while the magnetization decreases for x &gt; 0.02 was observed. Present study clearly shows the existence of correlation between appearance of ferromagnetism and the structural change.

Ferromagnetism induced by strains in Pd nanoparticles

The origin of the ferromagnetism that appears in the core region of Pd nanoparticles is discussed. According to many previous theoretical calculations, the onset of this ferromagnetism is closely related to the crystal structure and defects. In order to consider the contribution of crystal structure to the appearance of ferromagnetism in the Pd nanoparticles, we performed x-ray diffraction experiments and Warren-Averbach analysis. The results revealed that the standard deviation of strain $\ensuremath{\Delta}\ensuremath{\epsilon}$ showed a positive correlation with the saturation magnetization, with the ferromagnetism appearing when $\ensuremath{\Delta}\ensuremath{\epsilon}$ became larger than about 0.5%. This suggests that the strains induce internal ferromagnetism in the Pd nanoparticle. Compared to the critical magnitude of the strain at which ferromagnetism is predicted by the theoretical calculations, however, the estimated $\ensuremath{\Delta}\ensuremath{\epsilon}$ is too small to explain the origin of ferromagnetism. Therefore, the strains smaller than the theoretical predictions should also give rise to the ferromagnetism or the strains should contribute to the magnetism not only through lattice expansion but also through changes in the crystal symmetry.

High temperature ferromagnetism of the vacuum-annealed (In1−xFex)2O3 powders

(In1−xFex)2O3 (x=0.02, 0.05, 0.2) powders were prepared by a solid state reaction method and a vacuum annealing process. A systematic study was done on the structural and magnetic properties of (In1−xFex)2O3 powders as a function of Fe concentration and annealing temperature. The X-ray diffraction and high-resolution transmission electron microscopy results confirmed that there were not any Fe or Fe oxide secondary phases in vacuum-annealed (In1−xFex)2O3 samples and the Fe element was incorporated into the indium oxide lattice by substituting the position of indium atoms. The X-ray photoelectron spectroscopy revealed that both Fe2+ and Fe3+ ions existed in the samples. Magnetic measurements indicated that all samples were ferromagnetic with the magnetic moment of 0.49–1.73μB/Fe and the Curie temperature around 783K. The appearance of ferromagnetism was attributed to the ferromagnetic coupling of Fe2+ and Fe3+ ions via an electron trapped in a bridging oxygen vacancy.

X-ray magnetic circular dichroism study on ferromagnetic Pd nanoparticles

An x-ray magnetic circular dichroism (XMCD) experiment was performed for freestanding Pd nanoparticles which were prepared in a high purity atmosphere and showed ferromagnetism. We observed the XMCD signal at Pd M2,3 absorption edges of nanoparticles. This is clear experimental evidence of ferromagnetic moment in pure Pd. Using the sum rules, the ratio of orbital to spin magnetic moments mL/mS of ∼0.1 was obtained. In the x-ray absorption spectrum, the intensities of white lines increased in Pd nanoparticles relative to the bulk. This shows the increase in the number of unoccupied 4d states nh which can contribute to the appearance of ferromagnetism in Pd.