Dependence Of Magnetic Moment Research Articles

4[formula omitted] Electron Localization–Delocalization studies in CeMg[formula omitted] and PrMg[formula omitted] alloys under Pressure

The pressure dependence of magnetic moment in CeMg3 and PrMg3 has been studied through ab initio electronic structure calculations based on density functional theory (DFT). Positive as well as negative pressure conditions were simulated by different degrees of unit cell compression or expansion and a fit of the total energy to the Birch–Murnaghan equation of state. At ambient and negative pressures, the calculated magnetic moments for both the compounds reveal localized behaviour of 4f electrons. For increasing positive pressures, the magnetic moment of Ce in CeMg3 has been observed to diminish smoothly, becoming zero at a critical pressure of PC∼ 18 GPa indicative of pressure induced moment instability caused by an increase of f-conduction electron hybridization leading to delocalization of the 4f electrons. In contrast, the magnetic moment of Pr in PrMg3 does not show appreciable change with pressure, indicating strongly localized nature of the 4f electrons.

Compositional behavior of heat capacity and magnetic properties in double spinel ferrites

The purpose of the work is to identify the effects of the substitution of paramagnetic ions in ferromagnetic ferrites by diamagnetic components of zinc and aluminum. The following isomorphic spinel series are the object of review: Me(1-x)ZnxFe2O4 (Me – Ni, Co, Li, Cu, Mg) and Li0.5Fe2.5-xAlxO4 (x= 0-2.5). The single-phased samples were synthesized by ceramic procedure. Heat capacity near standard temperature Cp (298.15) was studied using calorimeter methods: drop calorimeter and DSC. Magnetic parameters – magnetic moments (M) and Curie temperatures (Tc) - were determined. All Me-Zn ferrite systems are characterized by dome-shaped correlations between heat capacity Cp(298) and composition (x), which have maximum values in the equimolecular region (x=0.4-0.6). This fact coincides with the nature of the compositional dependence of magnetic moments and indicates a significant effect of the excess magnetic contribution on the total heat capacity. A noticeable influence of the cooperative Jahn-Teller effect and the associated tetragonal distortion of the cubic lattice of Cu-Zn ferrites with a low Zn content (x<0.2) is observed, which causes overestimated values of the heat capacity of these compositions. Curie temperatures reveal the rectilinear decrease with increasing diamagnetic Zn and Al content in ferrite systems. The results are presented by graphs and tables.

Temperature dependence of magnetic moment of rare earth ions in ErFeO3 and NdFeO3 single crystals.

The interaction between rare earth and iron spins in rare earth orthoferrites leads to remarkable phenomena, such as the spin-flip process. This is despite the rare earth spins not being magnetically ordered. Instead, they are polarized by the ordered iron spins. The interaction between the two spin families is not well understood. This study reports the temperature dependence of the net magnetic moment for rare earth spins, by measuring the overall magnetization for ErFeO3 and NdFeO3 single crystals. The obtained temperature dependence can be described well using a model based on the mean field theory, giving tanh(const./T) temperature dependence. This functional dependence is not disrupted by the spin-flip transition as the crystals are cooled.

Itinerant magnetism, electronic properties and half-metallicity of Co2ZrSn and Co2HfSn Heusler alloys

Half-metallic ferromagnetic alloys are attracting considerable interest for their potential applications in spintronic devices. Co-based Heusler alloys are considered to be promising half-metallic compounds as they combine suitable magnetic, electronic and transport properties with compositional versatility and high thermal stability. In this work, Co 2 ZrSn and Co 2 HfSn Heusler alloys were studied by combining experimental and ab-initio investigations in order to accurately estimate their electronic density of states in proximity of the Fermi level and to determine their magnetic and electronic properties. Magnetization measurements, performed between 2 K and 550 K, suggest for both alloys a gradual transition from localized ferromagnetism to weak itinerant ferromagnetism with increasing temperature, well described by a simple mean field model up to the Curie temperature (454 K in Co 2 ZrSn and 432 K in Co 2 HfSn) and beyond. Ab-initio calculations were performed using two exchange-correlational functionals, PBE and PBE optimized for solids (PBEsol), in order to assess the reproducibility of theoretical results. Overall, band structures and density of states (DOS) diagrams indicated, for both compounds, the presence of a half-metallic band gap in the minority spin sub-band. The dependence of magnetic moments and band gap width on cell parameters is discussed in detail. Calculated magnetic moments and cell parameters satisfactorily match the experimental results obtained in this work and previously reported in the literature. • Itinerant weak ferromagnetic behaviour is confirmed for both alloys as they follow the Edwards-Wohlfarth model. • The mean field model indicates that the density of states profiles at the Fermi level are smooth. • Ab-initio calculation performed with PBE and PBEsol functionals show half-metallic behaviour at 0 K. • A crossover from localized magnetism to itinerant magnetism as function of temperature was found for both alloys. • The M/T crossover can be attributed to a change in spin-flip mechanism at low temperature.

Mechanical tuning of room temperature magnetism in flexible manganite/mica heterostructures

Flexible materials have attracted increasing attention due to their potential application in wearable or implantable circuits and systems. Here, the La0.67Sr0.33MnO3 (LSMO) thin films have been grown on single crystalline mica substrates and the impact of mechanical strain on the magnetic properties is investigated through varying external mechanical bending. The in-plane saturated magnetic moment decreases firstly with increasing radius of curvature (ROC) and then increases after attaining a minimum value of MS = 187 emu/cm3 at ROC = 3.0 mm. The nonmonotonous dependence of magnetic moment on ROC can be attributed to the mechanical bending-triggered lateral tensile strain, which can not only enhance the Jahn-Teller splitting and reduce the double-exchange interaction, but also enable the neighboring ferromagnetic domain switching in the LSMO films. Moreover, the out-of-plane magnetic anisotropy can also be reinforced by exerting mechanical tensile strain. Meanwhile, the superior mechanical antifatigue character is found in the LSMO/mica structures. These flexible LSMO thin films with highly tunable magnetism and excellent mechanical durability exhibit promising prospect in designing stable flexible spintronic devices and wearable sensors.

Single oxygen vacancy in BaCoO3: Hybrid DFT calculations and local site symmetry approach

We use the hybrid B1WC density functional calculations and the supercell model to analyze properties of BaCoO3 (BCO) in the corner-sharing CoO6 octahedra geometry. We compare the atomic and electronic structures for ideal and defective BCO containing a single oxygen vacancy (Vo). We find that the ideal BCO is better described by the triclinic space group (SG) P1 supercell than the cubic SG Pm3¯m model. The site symmetry approach allows us to derive several Vo supercell models on the basis of SGs P4mm, Pmm2 or Amm2 from the aristotype cubic SG Pm3¯m. The low symmetry Pmm2 model suggests the 0.4 eV formation energy of Vo in BCO. Furthermore, stability of this result is confirmed by the calculation of Vo in the supercell without symmetry (SG P1). The ideal and defective BCO are characterized by the intermediate spin (IS) states of Co4+ and Co4+&Co3+ ions, respectively. Additional complexity is introduced by the smooth Co magnetic moment dependence on the Co–Vo distance.

Macroeffect of magnons and thermal fluctiation on magnetization reversal

The magnetization reversal resulting from the thermal fluctuation is irreversible for overcoming the energy barrier, ant it is called the thermally assisted tunneling. In this paper the relaxation in magnetizaition reversal resulting from the thermal fluctuation is observed in Pr-Fe-B permanent magnet. The dependence of magnetic moment on the time natural logarithm is the same as that on the energy barrier in the thermally assisted tunneling. So the relaxation in magnetization reversal originates from the macroeffect of magnons which follow Bose distribution law. The critical size in the irreversible magnetization reversal obtained by the fluctuation field is on a nanometer scale and close to the theoretical domain wall size, indicating that the thermally assisted magnetization reversal undergoes the nucleation and de-pinning of domain wall. The increase of coupling volume will reduce the possibility of magnons tunneling in magnetization reversal due to the weakening effect of thermal fluctuation. The variation of fluctuation field with the field verifies the effect of exchange coupling in Pr-Fe-B magnets, and the calculated value of fluctuation field is consistent with the aftereffect of thermal activation. With the increase of temperature the thermal fluctuation energy increases, and though the aftereffect of thermal fluctuation weakens due to the exchange coupling, the ratio of thermal fluctuation aftereffect to coercivity increases in Pr-Fe-B magnet.

Electrochemical studies of iron(II) complexeswith 4‐amino‐1,2,4‐triazole possessing spin crossover

AbstractThe electrochemical properties of a number of coordination compounds of iron(II) with 4‐amino‐1,2,4‐triazole (NH2trz), which have a sharp thermally induced spin crossover with hysteresis on the temperature curves of the effective magnetic moment dependence, were studied using method cyclic voltammetry (CV) at 298 K. The complexes were mixed with carbon powder and silicon oil and included in the paste electrode. The measurements were made in solutions of 0.10 M KNO3. It was found that the area 0.5–0.6 V and 0.3–0.4 V contains the anode and cathode current peaks of freshly prepared paste electrodes. In all cases, the redox process in the paste is quasi‐reversible. At the same molar concentration of complexes in the paste (0.1 mol kg−1), a number of current peaks depends on the nature of the anion. The peak current value correlates with the calculated fraction of the high spin form in the solid phase of the complex and the temperature of the direct spin crossover (when heated, Tc↑). The magnetic properties of Fe(NH2trz)3(NO3)2 complex, its mixture with carbon powder and the paste were measured by Faraday method in a temperature range 80–370 K. The effective magnetic moment was depended on changes in variations in the environment of the molecules of the complex in the studied samples.

Spin-lattice model for cubic crystals

We present a methodology based on the N\'{e}el model to build a classical spin-lattice Hamiltonian for cubic crystals capable of describing magnetic properties induced by the spin-orbit coupling like magnetocrystalline anisotropy and anisotropic magnetostriction, as well as exchange magnetostriction. Taking advantage of the analytical solutions of the N\'{e}el model, we derive theoretical expressions for the parameterization of the exchange integrals and N\'{e}el dipole and quadrupole terms that link them to the magnetic properties of the material. This approach allows to build accurate spin-lattice models with the desire magnetoelastic properties. We also explore a possible way to model the volume dependence of magnetic moment based on the Landau energy. This new feature can allow to consider the effects of hydrostatic pressure on the saturation magnetization. We apply this method to develop a spin-lattice model for BCC Fe and FCC Ni, and we show that it accurately reproduces the experimental elastic tensor, magnetocrystalline anisotropy under pressure, anisotropic magnetostrictive coefficients, volume magnetostriction and saturation magnetization under pressure at zero-temperature. This work could constitute a step towards large-scale modeling of magnetoelastic phenomena.

Primordial monopolium as dark matter

The existence of monopoles is a characteristic signature of Kaluza–Klein multidimensional theories. The topology of these solutions is extremely interesting. The existence of a dipole solution, which we have associated to a monopole–anti-monopole bound state, is the leitmotiv of this investigation. The dipole in its lowest energy state, which we here call also monopolium, is electromagnetically inert in free space interacting only gravitationally. Monopolium when interacting with time dependent magnetic fields acquires a time dependent induced magnetic moment and radiates. We have analyzed the most favorable astrophysical scenario for radiative monopolium and found that the amount of radiation is so small that is not detectable by conventional equipments. These findings suggest that Kaluza–Klein monopolium, if existent, would be a candidate for a primordial dark matter constituent.

The relation between X-ray magnetic circular dichroism peak and the magnetic moment for ferrimagnetic alloy Mn2VAl

To understand the relationship between the shape of X-ray magnetic circular dichroism (XMCD) and magnetic moments, we calculate V L2, 3-edge XMCD spectra for Mn2VAl while varying the magnetic moment of an absorbing atom V. We find that XMCD spectra change depending on the magnetic moment of the absorbing atom. We explain these changes based on the magnetic moment dependence of atomic terms, which are components of XMCD. When the overlaps between radial functions and photoelectron wave functions are considered, an atomic term has a value at its energy. The peak positions of the radial integral for up and down spin are different, which leads to multiple peaks of the atomic terms and determines the positive and negative direction of the peak.

Computational analysis of anomalous temperature dependence of magnetic properties in Mn4C compound

We have calculated electronic structures of Mn4C using first-principles calculations based on density functional theory (DFT) within the Perdew Burke Ernzerhof-generalized gradient approximation (PBE-GGA). The calculated band structures and density of states (DOS) indicate that stability of cubic perovskite-type crystal structured Mn4C is originated from p-d hybridization between Mnb and C and d-d hybridization between Mna and Mnb sublattices. The mean field approximation (MFA) resulted in the Néel temperature (TN) of 879 K which is in close agreement with experimental TN. The temperature dependence of magnetic moments of Mna and Mnb sublattices were also calculated using the Brillouin function to investigate the origin of unusual linearly increasing magnetization below 400 K. It was found that the increasing magnetization is originated from strong mutual interdependence of more or less linearly decreasing magnetic moment of Mna and stationary magnetic moment of Mnb below 400 K.

Time dependence of magnetic moment of strontium-ferrite powder measured with a biaxial vibrating sample magnetometer (VSM)

The magnetic hysteresis and viscosity of SrO(Fe2O3)6/PA-12 filaments with 5wt% and 26wt% was determined with a biaxial VSM. The hysteresis curves indicate that manufactured samples have a flow induced anisotropy with an easy plane perpendicular to the filament’s cylindrical axis. The Mx and My magnetic viscosity signals vary with field and field angle. The Mx magnetic viscosity is maximum in the easy plane and decreases to a factor of two along the macroscopic hard axis of the filament. The My magnetic viscosity is nearly zero along the hard axis and in the easy plane and is maximum for intermediate field angles.

Magnetomechanical properties of melt-spun off-stoichiometric Ni50Mn28Ga22 ribbons

A large magnetic field induced strain is indicative of an ideal ferromagnetic shape memory alloy. To achieve high strain values melt-spun ribbons of NiMnGa based Heusler alloy were prepared and annealed at different temperatures over different time periods. Thermal analysis was done to obtain the transformation temperatures of the annealed ribbons. Besides the magnetic measurements, magnetic field induced strains were measured using strain gauges and strain indicator. The dependence of magnetic moment on the angle of alignment of the sample surface with respect to the field direction has been reported. The transformation temperatures were closer to the room temperature in all the ribbons with an incremental dependence on the annealing temperature and annealing time. The martensitic transformation temperatures obtained from the thermomagnetic curves were almost similar to those obtained from thermal analysis. There was an improvement in the saturation magnetization values after annealing whereas the Curie temperature was roughly similar for all the specimens. Presence of precipitates along the grain boundaries had no significant role to play in determining the properties. The annealed ribbons showed higher magnetic field induced strain (MFIS) than the as-spun ribbons; ribbon prepared at 1300 RPM and subsequently annealed at 900 °C for 5 h showed the highest value of MFIS ~0.15%. From the texture analysis, fraction of 〈001〉 oriented grains decreased and that of 〈110〉 increased with the progression of angle of alignment from 0° to 90°. Hence, the moment was higher when the angle of alignment was 90° in the annealed specimens.

Sample Length Dependence of Magnetic Moment Detected by a SQUID Magnetometer Using Nickel Cylinders

We report here on sample length dependence measurements in a second-order gradiometer superconducting quantum interference device (SQUID) magnetometer of pure nickel (Ni) cylinders, having a diameter of 1 mm and a length of 1-7 mm. The measured magnetic moment per unit mass significantly decreases with the sample length of the Ni cylinder, when a magnetic field of 7 T was applied parallel to the long axis of the cylinder. As an example, the magnetic moment per unit mass for the 5 mm Ni cylinder is between 97% and 94% of that for the 1 mm Ni cylinder, the number depending on the specific type of magnetometer used. The magnitude of decrease also depends on the length of the second-order gradiometer superconducting coil which differs with different models of SQUID magnetometers.

Mechanical behavior, enhanced dc resistivity, energy band gap and high temperature magnetic properties of Y-substituted Mg–Zn ferrites

We report the synthesis of Y-substituted Mg–Zn [Mg0.5Zn0.5Y x Fe2−x O4 (0 ≤ x ≤ 0.05)] ferrites using conventional standard ceramic technique. The samples were characterized by x-ray diffraction (XRD) analysis, field emission scanning electron microscopy (FESEM), FTIR spectroscopy, UV–Vis spectroscopy and quantum design physical properties measurement system (PPMS). XRD patterns confirm the single phase cubic spinel structure up to x = 0.03 and appearance of a secondary phase of YFeO3 for higher Y contents. FESEM images depict the distribution of grains and EDS spectra confirmed the absence of any unwanted element. Completion of solid state reaction and formation of spinel structure has been revealed from FTIR spectra. The FTIR data along with lattice constant, bulk density and porosity were further used to calculate the stiffness constant (C ij), elastic constant and Debye temperatures. Mechanical stability of all studied compositions is confirmed from C ij using Born stability conditions. Brittleness and isotropic nature are also confirmed using Poisson’s ratio and anisotropy constants, respectively. The enhancement of dc electrical resistivity (105Ω cm to 106Ω cm) with Y content is observed. The energy band gap (increased with Y contents) is found in good agreement with dc electrical resistivity. Ferrimagnetic to paramagnetic phase change has been observed from the field dependent high temperature magnetization curves. The magnetic moments and saturation magnetization were found to be decreased with increasing temperature. The Curie temperature (Tc) has been measured from temperature dependent magnetic moment (M-T) and initial permeability (μ′i-T) measurements and found to be in good agreement with each other. Decrease in Tc with Y content is due to redistribution of cations and weakening of the exchange coupling constant. The magnetic phase transition has been analyzed by Arrott plot and found to have second order phase transition. The dc resistivity endorses the prepared ferrites are suitable for high frequency and high temperature magnetic device applications as well.

Local magnetic study for cluster-layered Fe/Cr nanostructures

Local magnetic structures of cluster-layered Fe/Cr thin films are studied by X-ray magnetic circular dichroism (XMCD) and extended X-ray absorption fine structure (EXAFS). The magnetic moment of Fe atoms evaluated from XMCD for Al2O3/Cr(70Å)/[Fe(1.2Å )/Cr(10.5Å)]30/Cr(12Å), which shows the minimum point in the resistivity, decreases as the temperature increases and disappears around the temperature of the minimum resistivity. EXAFS shows the local structure of this film around Fe atoms is rather disordered and it can be related the fluctuation of magnetic structure estimated from the theoretical analysis of the temperature dependence of magnetic moments.

Oscillatory dynamics of the magnetic moment of a Pt/Co/Ir/Co/Pt synthetic antiferromagnet

In this paper, we present a detailed study of the oscillating magnetic relaxation in the synthetic antiferromagnet (SAF) with two ferromagnetic Co layers of different thicknesses separated by an Ir spacer. The four stable magnetic states of the SAF are determined by the mutual alignment of magnetic moments in the layers and are controlled by both the magnetic interlayer exchange interaction and the Zeeman energy. The specific variations in the thicknesses of the layers and/or temperature allow the existence of a ``triple point,'' which corresponds to a coincidence of the critical switching fields for two or three interstate transitions. In this case, two or even three different types of magnetization reversals occur simultaneously and competitively. A nonmonotonic dependence of the domain-wall speed ${v}_{\mathrm{DW}}$ on magnetic field $H$ and an oscillating time dependence of magnetic moment $M$ in a constant magnetic field were observed in a Pt/Co/Ir/Co/Pt synthetic antiferromagnet with perpendicular anisotropy due to interplay between the magnetic nuclei produced by Dzyaloshinskii-Moriya interaction. The proximity of two or three (triple-point) critical fields of SAF switching is the necessary condition for both a nonmonotonic magnetic relaxation and the oscillating time variations of the magnetic moment. The dynamical model describing the interaction and subsequent evolution of the magnetic nuclei demonstrates that this nontrivial magnetic relaxation obeys a simple Schr\odinger equation.

Fabrication and characterization of YIG nanotubes

Abstract We have successfully synthesized Y3Fe5O12 (yttrium iron garnet, YIG) nanotubes (NTs) of different diameters using a conventional sol-gel method in anodized aluminum oxide (AAO) templates. An annealing process at 800 °C is performed to get a pure phase of YIG. The room-temperature magnetization measurements show that the coercivity decreases significantly as the diameter of nanotubes increases. The temperature dependence of magnetic moments in field-cooled (FC) and zero-field-cooled (ZFC) modes indicates that YIG NTs transform from ferromagnetic-like (FM-like) state to superparamagnetic (SPM) state when temperature decreases (in the region of 310 K–400 K). The Blocking temperature dramatically decreases as the size of YIG NTs reduces. In the FM-like state, the temperature-dependent coercivity in three different samples yields a 1/2 power law of the temperature. The temperature dependence of saturation magnetization in three different samples can be well fitted to Bloch’s T3/2 law. Characterization of ferromagnetic resonance (FMR) is conducted, which indicates the Gilbert damping parameter of YIG NTs is around 7–9 × 10−3.

Research of magnetic properties of spolic technosols (alcalic/hyperartefactic) on the landfill of industrial waste from nickel production

Abstract The article presents the results of measurements of magnetic properties of samples spolic technosols (alcalic/hyperartefactic) form the landfill of black nickel mud at Sered’, Slovakia. We measured the dependence of magnetic moment as a function of temperatures (240-340 K) and applied magnetic fields up to 7.2 MA/m (90 kOe). We observed at room temperature the tendency to saturation of magnetic moment. The temperature dependences showed possible ferromagnetic behaviour.