Possible Ferromagnetism in YCuO System

polycrystalline CuxYyOz are made through solid state reaction. Ferromagnetism is found in this YCuO system at room temperature. The ferromagnetism quite probably originates from Cu2Y2O5 , the Copper Yttrium Oxide. The average magnetic moment per Cu2+ is estimated to be 0.04μB. Itinerant electron magnetism is a rational explaination for the observed ferromagnetism. The experiment shows that the excessive amount of Cu may lead more defects and further distortion in the lattice and decrease the exchange interaction. This reminds us that the Copper Yttrium Oxide is a substance not only should be avoided in fabricating YBCO superconductors but also should be considered as a potential substance of magnetic semiconductor.

Effect of Mn content in Fe(1−x)MnxB (x = 0, 0.25, 0.5, 0.75 and 1) on physical properties - ab initio calculations

Structural, electronic, intrinsic magnetic, anisotropic elastic properties, sound velocities and Debye temperature of Fe1−xMnx B (x = 0, 0.25, 0.5, 0.75, 1) transition metal monoborides have been studied by first-principles calculations within the method of virtual crystal approximation (VCA) based on density-functional theory (DFT) through generalized gradient approximation (GGA). The average magnetic moment per cell increased with increasing of Mn content, which could be associated with the relationship between the composition and magnetic properties. The observed magnetic behavior of Fe1−xMnx B compounds can be explained by Stoner model. Lattice parameters and Debye temperature agree well with the experimental values. Furthermore, we have plotted three-dimensional (3D) surfaces and planar contours of the directional dependent Young and bulk moduli of the compounds on several crystallographic planes, to reveal their elastic anisotropy versus Mn content (x) in Fe1−xMnx B.

Stochastic proton heating by kinetic-Alfvén-wave turbulence in moderately high- plasmas

Stochastic heating refers to an increase in the average magnetic moment of charged particles interacting with electromagnetic fluctuations whose frequencies are smaller than the particles’ cyclotron frequencies. This type of heating arises when the amplitude of the gyroscale fluctuations exceeds a certain threshold, causing particle orbits in the plane perpendicular to the magnetic field to become stochastic rather than nearly periodic. We consider the stochastic heating of protons by Alfvén-wave (AW) and kinetic-Alfvén-wave (KAW) turbulence, which may make an important contribution to the heating of the solar wind. Using phenomenological arguments, we derive the stochastic-proton-heating rate in plasmas in which $\unicode[STIX]{x1D6FD}_{\text{p}}\sim 1$–30, where $\unicode[STIX]{x1D6FD}_{\text{p}}$ is the ratio of the proton pressure to the magnetic pressure. (We do not consider the $\unicode[STIX]{x1D6FD}_{\text{p}}\gtrsim 30$ regime, in which KAWs at the proton gyroscale become non-propagating.) We test our formula for the stochastic-heating rate by numerically tracking test-particle protons interacting with a spectrum of randomly phased AWs and KAWs. Previous studies have demonstrated that at $\unicode[STIX]{x1D6FD}_{\text{p}}\lesssim 1$, particles are energized primarily by time variations in the electrostatic potential and thermal-proton gyro-orbits are stochasticized primarily by gyroscale fluctuations in the electrostatic potential. In contrast, at $\unicode[STIX]{x1D6FD}_{\text{p}}\gtrsim 1$, particles are energized primarily by the solenoidal component of the electric field and thermal-proton gyro-orbits are stochasticized primarily by gyroscale fluctuations in the magnetic field.

About oxide dispersion particles chemical compatibility with areas coherent dissipation/sub-grains of bcc-alloys in Fe - (Cr, V, Mo, W) systems

A concept of partial magnetic moments (PMM) of the iron atoms located in the first ? four coordination spheres (1?4 CS) for bcc lattice have been introduced based on analysis of results obtained by quantum-mechanical calculations (QMC) for volume dependence of the average magnetic moment ferromagnetic (FM) Fe. The values of these moments have been calculated for pure bcc Fe and bcc - Fe-Cr alloys. This concept has been used to formulate a three sub-lattice model for binary FM alloys of the Fe-M systems (M is an alloying paramagnetic element). Physical reason for sign change dependence of the short-range order and mixing enthalpy obtained by QMCs for Fe-(Cr, V) bcc phases has been found. Using this model it has been predicted that static displacements of Fe - atoms in alloy matrix increase with increasing the of CS number and result in reducing of the area of coherent dissipation (ACD) size with growth of the dimension factor (DF) in the Fe-(Cr, V, Mo, W) systems in agreement with the X-ray experiments. It has been shown theoretically that anisotropy of spin- density in bcc lattice Fe and DF in binary Fe - (Cr, V, Mo, W) systems is main factor for origins of segregations on small angle boundaries of ACD and sub-grains boundaries To prevent the coagulation of both ACD and sub-grains, and to increase the strength of alloys, it is advisable to add oxide dispersion particles into ferrite steel taking into account their chemical compatibility and coherent interfacing with the crystalline lattice of a ferrite matrix. Application of phase diagrams for binary and ternary the Fe-(Y, Zr)-O systems to verify chemical compatibility of oxide dispersion particles with ferrite matrix have been discussed

Magnetic Properties and AC Losses in AFe2O4(A = Mn, Co, Ni, Zn) Nanoparticles Synthesized from Nonaqueous Solution

Nanosized particles of AFe2O4(A = Mn, Co, Ni, or Zn) spinel ferrites were synthesized by coprecipitation from nonaqueous solutions using nitrate salts as starting reagents. The particles were characterized by X-ray diffraction, transmission electron microscopy, and magnetic measurements. Quasistatic magnetic measurements show superparamagnetic behavior with blocking temperature below room temperature for cobalt, nickel, and zinc spinel ferrite nanoparticles. Characteristic magnetic parameters of the particles including average magnetic moment of an individual nanoparticle and blocking temperature have been determined. The specific loss power which is released on the exposure of an ensemble of synthesized particles to a magnetic field is calculated and measured experimentally. It is shown that among all nanoferrites under study, the ZnFe2O4nanoparticles demonstrate the highest heating efficiency in AC magnetic fields. The key parameters responsible for the heating efficiency in AC magnetic field have been determined. The directions to enhance the SLP value have been outlined.

Diamagnetic Magnetization Strength as a Consequence of Electromagnetic Induction Law’s Effect

A qualitative proof of diamagnetic non-zero magnetization based on the electromagnetic induction law is presented in this paper. Modeling diamagnetic phenomena as a result of Larmor precession or effect of the electromagnetic induction’s law in scale of one hydrogen-like atom performed in classical physics contributes to formation of obviously incorrect idea of the diamagnetic magnetization process in students. It is well-known that the average magnetic moment of a diamagnetic calculated with the help of classical statistics laws is zero which can be explained by quantum character of magnetic phenomena. On the contrary, electromagnetic induction’s law is effective both in classical and quantum physics. Applying it to the diamagnetism problem will allow to solve it for the diamagnetic in whole and to avoid averaging which is proved in the present paper.

THE EFFECT OF HYDROGEN ON THE MAGNETIC PROPERTIES OF FeV SUPERLATTICE

The electronic and magnetic structures of a hydrogenated and hydrogen free superlattice of three iron monolayers and nine vanadium monolayers are studied using the first principle full-potential augmented-plane-wave method as implemented in WIEN2k package. The average and the local magnetic moments of the system are studied versus the hydrogen positions at the octahedral sites within the superlattice and also versus the filling of the vanadium octahedral location by hydrogen atoms. The local Fe magnetic moment and the average magnetic moment per iron atom are found to increase as the H position moves towards the Fe – V interface. On the other hand, the average magnetic moment per Fe atom is found to initially decrease up to filling by three H atoms and then increases afterwards. To our knowledge, this is the first reporting on the increase in the computed magnetic moment with hydrogenation. These trends of magnetic moments are attributed to the volume changes resulting from hydrogenation and not to electronic hydrogen–metal interaction.

FIRST-PRINCIPLES INVESTIGATION INTO FERROMAGNETISM IN C-DOPED ZINC OXIDE CLUSTERS (ZnO)n; N = 1 – 12

We report the first-principle calculations of ferromagnetism in C -doped ZnO clusters. The carbon impurities in ZnO clusters are doped at substitutional O or Zn sites and at interstitial sites and the total energy calculations suggest C at O site is more stable than that at Zn site. The substitutional C impurity is found more favorable than interstitial C impurity in these clusters. The ZnC region is mainly responsible for the observed ferromagnetism in ZnO:C systems. The average magnetic moment of Zn n O n–m C m clusters is found to be 2 μB/ C for n, m < 7. For n, m > 6 the magnetic moment decreases below 2 μB/ C . The magnetic moment in ( ZnO )n C i; i = 1 – 2 is found to be 0.1–2.0 μB/ C . The combination of substitutional and interstitial C impurities in ZnO clusters leads to magnetic moment of 0.4–1.0 μB/ C .

Ultrafine metallic Fe nanoparticles: synthesis, structure and magnetism

The results of the investigation of the structural and magnetic (static and dynamic) properties of an assembly of metallic Fe nanoparticles synthesized by an organometallic chemical method are described. These nanoparticles are embedded in a polymer, monodisperse, with a diameter below 2 nm, which corresponds to a number of around 200 atoms. The X-ray absorption near-edge structure and Mössbauer spectrum are characteristic of metallic Fe. The structural studies by wide angle X-ray scattering indicate an original polytetrahedral atomic arrangement similar to that of β-Mn, characterized by a short-range order. The average magnetic moment per Fe atom is raised to 2.59 µB (for comparison, bulk value of metallic Fe: 2.2 µB). Even if the spontaneous magnetization decreases rapidly as compared to bulk materials, it remains enhanced even up to room temperature. The gyromagnetic ratio measured by ferromagnetic resonance is of the same order as that of bulk Fe, which allows us to conclude that the orbital and spin contributions increase at the same rate. A large magnetic anisotropy for metallic Fe has been measured up to (3.7 ± 1.0)·105 J/m3. Precise analysis of the low temperature Mössbauer spectra, show a broad distribution of large hyperfine fields. The largest hyperfine fields display the largest isomer shifts. This indicates a progressive increase of the magnetic moment inside the particle from the core to the outer shell. The components corresponding to the large hyperfine fields with large isomer shifts are indeed characteristic of surface atoms.

Effect of Organic Capping on the Magnetic Properties of Au Nanoparticles

The magnetic and optical properties of regioregular poly(3-hexylthiophene)-capped Au nanoparticles (NPs) have been investigated in order to clarify the effectiveness of polythiophene capping on the induction of ferromagnetism in Au. The room-temperature magnetization curve of the polythiophene-capped Au NPs exhibits a clear hysteresis behavior with a spontaneous magnetization of 8.5 x 10-3 emu/g. The average magnetic moment of the surface Au atoms is estimated to be 2.6 x 10-3 B. The ultraviolet-visible spectrum shows a clear sign of the surface plasmon absorbance of metallic Au which reflects the week character of the chemical bond between the Au and S atoms on capping surface. Our results show clearly that Au NPs capped with polythiophene can be ferromagnetic.