Substitution Of Magnetic Ions Research Articles

Review on structural, magnetic, optical properties of manganese doped zinc oxide nanoparticles

Due to its distinctive features and potential applications, the ZnO nanostructure has received extensive attention in recent years. The addition of a transition metal allows ZnO optical and magnetic characteristics to be tuned, which enhances the applicability. Mn doped ZnO has received the significant attention among all transition metals due to notable improvement in ZnO magnetic behaviour at ambient temperature. The magnetism in ZnO is quite controversial and still needs a proper justification, but substitution of magnetic ions undoubtedly enhances the magnetic nature of ZnO. In this review, we have summarised the properties and applications of ZnO and explored the possible mechanism to enhance its property to make it more applicable. Overviews of the ZnO synthesis procedure, uses, and dopant impacts on the structural, magnetic, and optical characteristics of ZnO nanoparticles are provided in this work. The effect of Mn doping concentration on both magnetic and optical behaviour is assessed and justified appropriately. This work will help the novice researcher to observe the applicability of Mn doped ZnO for optoelectronic devices.

Partial magnetic ion substitution of BiFeO3 Multiferroic photocatalyst for hydrogen evolution from water splitting

BiFeO 3 as a p-type photocatalyst in BiFeO 3 –CdWO 4 p-n heterojunction was modified by partial substitution of divalent Co 2+ and Ni 2+ at Fe-site to enhance the photocatalytic performance for H 2 evolution from pure water splitting. At high impurity concentrations, XRD and Raman spectroscopy revealed a phase transition from rhombohedral to orthorhombic/tetragonal with higher crystal symmetry due to larger ionic radii of Co 2+ and Ni 2+ relative to that of Fe 3+ . The excess amount of impurities also resulted in the formation of nickel ferrite (NiFe 2 O 4 ), cobalt ferrite (CoFe 2 O 4 ), sillenite (Bi 25 FeO 40 ) and mullite (Bi 2 Fe 4 O 9 ) as secondary phases. The high resolution XPS spectra of O 1s and Fe 2p indicted that the concentration of oxygen vacancy and Fe 2+ : Fe 3+ increased with doping BiFeO 3 , which is due to the structural distortion and defection. Moreover, magnetic property of BiFeO 3 was promoted by Co and Ni doping so that the residual magnetization increased from 0.009 emu/g up to 0.061 and 0.068 emu/g by 9 mol.% doping of Ni and Co, respectively. The enhanced magnetism can be attributed to the net magnetic moment caused by different magnetic moment of Fe 3+ , Co 2+ and Ni 2+ as well as the structural defection that may be a reason for spin spiral suppression. Doping with Co and Ni led to reducing band gap energy, suppression of charge recombination, and increment of charge density and mobility. The efficiency of photocatalytic H 2 evolution increased from 268.9 μmol/h gcat by pure BFO up to 449.6 and 494.7 μmol/h gcat by 9 mol.% Ni and Co doping, respectively. • BiFeO 3 was modified by substitution of Fe 3+ with larger divalent Co 2+ and Ni 2+ . • Crystal distortion and phase transition were revealed by XRD and Raman analyses. • Magnetic property was modified as a result of crystal distortion. • Charge recombination was efficiently suppressed by Co and Ni doping. • Photocatalytic H 2 evolution was boosted by 9 mol.% Co and Ni doping.

Magnetic Ion Substitution and Peak Effect in YBCO: the Strange Case of Y1–xGdxBa2Cu3O7–δ

Magnetic Ion Substitution and Peak Effect in YBCO: the Strange Case of Y1–xGdxBa2Cu3O7–δ

Effect of magnetic ion substitution on the structure and temperature-dependent magnetic properties of strontium hexaferrite

ABSTRACT Rare earth substituted strontium hexaferrite powders were synthesised through a molten salt route at 900°C for 5 h. The influence of rare-earth magnetic ion substitution on microstructural features, morphology and temperature-dependent magnetic properties was investigated. The lattice parameter ratio of less than 3.98 proves that all the substituted samples primarily present the hexaferrite phase. Fourier transform infrared peaks also confirmed the presence of a metal-oxygen bond. A 66% increase in magnetic saturation, 38% increase in coercivity and a more than two-time increase in remanence for the samarium doped sample are seen as the highest magnetic measurements compared to pure SrFe12O19 at room temperature. There were also differences in the temperature-dependent magnetic properties of strontium ferrites. As temperature decreased from 300 K, saturation magnetisation and remanence value were found to increase. This will perhaps be a promising material for magnetic field sensor application.

Designing switchable polarization and magnetization at room temperature in an oxide

Ferroelectric and ferromagnetic materials exhibit long-range order of atomic-scale electric or magnetic dipoles that can be switched by applying an appropriate electric or magnetic field, respectively. Both switching phenomena form the basis of non-volatile random access memory, but in the ferroelectric case, this involves destructive electrical reading and in the magnetic case, a high writing energy is required. In principle, low-power and high-density information storage that combines fast electrical writing and magnetic reading can be realized with magnetoelectric multiferroic materials. These materials not only simultaneously display ferroelectricity and ferromagnetism, but also enable magnetic moments to be induced by an external electric field, or electric polarization by a magnetic field. However, synthesizing bulk materials with both long-range orders at room temperature in a single crystalline structure is challenging because conventional ferroelectricity requires closed-shell d(0) or s(2) cations, whereas ferromagnetic order requires open-shell d(n) configurations with unpaired electrons. These opposing requirements pose considerable difficulties for atomic-scale design strategies such as magnetic ion substitution into ferroelectrics. One material that exhibits both ferroelectric and magnetic order is BiFeO3, but its cycloidal magnetic structure precludes bulk magnetization and linear magnetoelectric coupling. A solid solution of a ferroelectric and a spin-glass perovskite combines switchable polarization with glassy magnetization, although it lacks long-range magnetic order. Crystal engineering of a layered perovskite has recently resulted in room-temperature polar ferromagnets, but the electrical polarization has not been switchable. Here we combine ferroelectricity and ferromagnetism at room temperature in a bulk perovskite oxide, by constructing a percolating network of magnetic ions with strong superexchange interactions within a structural scaffold exhibiting polar lattice symmetries at a morphotropic phase boundary (the compositional boundary between two polar phases with different polarization directions, exemplified by the PbZrO3-PbTiO3 system) that both enhances polarization switching and permits canting of the ordered magnetic moments. We expect this strategy to allow the generation of a range of tunable multiferroic materials.

Structure and magnetism in hexagonal tungsten bronze metal oxides AM1/3W8/3O9 (A–K, Rb, Cs; M–Cr, Fe)

The structure and magnetic properties of hexagonal tungsten bronzes AM1/3W8/3O9 (A–K+, Rb+, Cs+; M− Cr3+, Fe3+) have been investigated. Pure ceramic samples were synthesized by solid-state reaction. The samples have been studied by X-ray powder diffraction in combination with magnetic measurements. The compounds crystallize in hexagonal space group P63/mcm. The substitution of magnetic ions into the WO6 octahedra yields dilute antiferromagnetic Cr3+-O2−-Cr3+ (or Fe3+-O2−-Fe3+) superexchange interaction causing the appearance of short-range magnetic order at low temperatures. The antiferromagnetic character of the interaction is supported by negative values of the derived Curie–Weiss temperatures, θCW. The magnitude of θCW is found to decrease with increasing ionic radius of the A cation.

Magnetism in quasibinary systems based on the valence-unstable compound CeNi

Magnetic ordering in solid solutions of Cex(Gd,Pr,Nd,La)1-xNi is studied by measuring the DC magnetization and the AC susceptibility in the temperature range of 1.8–300 K. The valence state of ceriumions in Cex(Gd,Pr,Nd,La)1-xNi quasibinary systems is studied based on X-ray absorption spectra measured at synchrotron-radiation sources in the temperature range of 5–300 K. It is shown that chemical pressure and lowering the temperature help heighten the degree of delocalization of the 4f electrons of cerium in Cex(Gd, Nd, Pr)1-xNi systems. It is found that the substitution of magnetic ions (Gd, Pr, and Nd) with cerium results in significantly weaker magnetic-ordering suppression than the substitution of these ions with lanthanum at equal concentrations. The obtained data reveal the strong influence of cerium electrons on localized magnetism in the studied compounds. This effect is most probably associated with the contribution of partially delocalized 4f electrons of cerium to the exchange interaction.

Optimizing the methods of synthesis for barium hexagonal ferrite—An experimental and theoretical study

Abstract M-type barium hexaferrite (BaM) is a hard ferrite, crystallizing in space group P6 3 /mmc possessing a hexagonal magneto-plumbite structure, which consists of alternate hexagonal and spinel blocks. The structure of BaM is thus related to those of garnet and spinel ferrite. However the material has proved difficult to synthesize. By taking into account the presence of the spinel block in barium hexagonal ferrite, highly efficient new synthetic methods were devised with routes significantly different from existing ones. These successful variations in synthetic methods have been derived by taking into account a detailed investigation of the structural features of barium hexagonal ferrite and the least change principle whereby configuration changes are kept to a minimum. Thus considering the relevant mechanisms has helped to improve the synthesis efficiencies for both hydrothermal and co-precipitation methods by choosing conditions that invoke the formation of the cubic block or the less stable Fe 3 O 4 . The role played by BaFe 2 O 4 in the synthesis is also discussed. The distribution of iron from reactants or intermediates among different sites was also successfully explained. The proposed mechanisms are based on the principle that the cubic block must be self-assembled to form the final product. Thus, it is believed that these formulated mechanisms should be helpful in designing experiments to obtain a deeper understanding of the synthesis process and to investigate the substitution of magnetic ions with doping ions.

Comparing study of magnetic-ion and nonmagnetic-ion doping effect at Mn site in La0.825 Sr0.175 MnO3 compound

Structural, magnetic, and transport properties of La0.825Sr0.175MnO3 samples doped with magnetic (Fe3+, Cr3+) and nonmagnetic (Ga3+, Al3+) ions have been studied comparatively. The structure does not change by nonmagnetic ion doping, whereas magnetic ion substitution can change the structure of the system significantly. All the doped samples show a lower Curie temperature as compared to that of the undoped sample. The change of Curie temperature TC for the magnetic-ion-doped samples is quite larger than that of the nonmagnetic-ion-doped samples. The electron configuration is suggested to play an important role in determining the change of TC for the magnetic-ion-doped samples, whereas the decrease of TC in nonmagnetic-doped samples is considered to originate mainly from the variation of local lattice. The Fe-doped sample shows semiconducting transport behavior in the whole studied temperature range besides a kink near TC. Except for two obvious M–I transitions, another inflexion-like anomaly in the ρ(T) curve at low temperatures is observed for the Ga-, Cr-, and Al-doped samples and the inflexion is suggested to be related to a two transport channel model in these samples.

Effects on superconductivity of transition-metal doping inFeSe0.5Te0.5

We investigate superconductivity in the compoundFeSe0.5Te0.5 and in its transition-metal-substituted derivativesFe1 − xTMxSe0.5Te0.5, wherex = 5% and the substituent ions studied were Mn, Co, Ni, Cu and Zn. Electronic and magneticmeasurements indicate that doping with Mn or by Co acts respectively to cause a slightenhancement or suppression of the transition temperature. However, doping with thisconcentration of Ni or Cu destroys the superconductivity completely, and leads tosemiconducting behaviour. Zn ions cannot be incorporated properly into the parentcompound. The reasons for these contrasting effects are associated with the differingmagnetic properties of the substituent ions, which determine their local impurity momentsand the net carrier concentrations in the doped 11 system. The effects of magnetic ionsubstitution on superconductivity suggest that the pairing symmetry may not be eitherpure s wave or pure d wave.

Coexistence of magnetism and superconductivity in the hole doped FeAs-based superconducting compound

Abstract The magnetic and superconducting properties of the Sm-doped FeAs-based superconducting compound were investigated under wide ranges of temperature and magnetic field. After the systematical magnetic ion substitution, the superconducting transition temperature decreases with increasing magnetic moment. The hysteresis loop of the La 0.87− x Sm x Sr 0.13 FeAsO sample shows a superconducting hysteresis and a paramagnetic background signal. The paramagnetic signal is mainly attributed to the Sm moments. The experiment demonstrates that the coexistence of magnetism and superconductivity in the hole doped FeAs-based superconducting compounds is possible. Unlike the electron doped FeAs-based superconducting compounds SmFeAsOF, the hole doped superconductivity is degraded by the substitution of La by Sm. The hole-doped and electron-doped sides are not symmetric.

Cation distribution, structure and magnetic properties of lithium manganese iron oxide spinel solid solutions

Single phase cubic spinel compounds Li x Mn 1+ x Fe 2−2 x O 4 ( x = 0, …, 1) were obtained by thermal decomposition of freeze-dried formate solutions of appropriate composition. The samples were characterized by X-ray powder diffraction and Rietveld refinement, XANES, 57Fe Mössbauer spectroscopy and magnetization measurements. The combination of these methods provides useful conclusions concerning the structure, cation distribution and properties of the spinel solid solutions. The Li x Mn 1+ x Fe 2−2 x O 4 samples contain Mn(II) and Mn(III) or Mn(III) and Mn(IV) for x < 0.5 or x > 0.5, respectively. With the increase of x the portion of Li ions occupying tetrahedral sites increases and becomes 100% at about x = 4/7. In spite of the preferred occupation of octahedral sites by manganese(III), the experimental results can only be explained by a partial occupation also of tetrahedral sites by Mn(III). An increase of M S with the increase of x (expected for a preferred substitution of magnetic ions in tetrahedral sites by non-magnetic Li ions) is not observed. It should be prevented by the decreasing cooperative coupling effects due to the reduction of the iron content.

Rare earth ion size effect in the rates of suppression of the Tc's of the `RE-123' high-temperature superconductors due to magnetic ion substitution into the Cu(2) sites

The observed dependences of the rates of suppression of the T c's due to the substitution of magnetic transition metal (TM 2+) ions into the Cu(2) sites of the `RE-123' high-temperature superconductors (HTSCs) on the size of the rare earth ions are studied within the framework of a ( d+ s)-wave symmetry description of the order parameters in these superconductors. It is assumed that the orthorhombic distortions which occur in these HTSCs induce a modification in the pairing potential responsible for superconductivity (the exchange of spin fluctuations) in the originally tetragonal HTSC. It is found that the rate of suppression of T c due to magnetic ion substitution into the Cu(2) sites depends on the orthorhombicity D=( b− a)/ a of these HTSCs, the orthorhombicity being in turn dependent on the rare earth ion size.

Valence Band Crystal Field Splitting of Hexagonal Diluted Magnetic Semiconductors

AbstractThe valence band crystal field and spin‐orbit splitting in hexagonal diluted magnetic semiconductors based on CdSe and CdS is studied. It is found that the crystal field splitting is practically magnetic ion independent for CdSe based crystals, whereas in the case of CdS based samples a strong influence of magnetic ion substitution on crystal field splitting is observed.

Local density of states in the vicinity of a Kondo hole

The substitution of magnetic ions by nonmagnetic impurities in a Kondo lattice gradually destroys the coherence of the heavy fermion groundstate. These nonmagnetic impurities are frequently referred to as Kondo holes. We consider a simple cubic Anderson lattice without orbital degeneracy and study the effects of the scattering off the Kondo hole in the local density of f states in the neighborhood of the nonmagnetic impurity. The correlations within the f band are introduced via a self-energy, evaluated to second order perturbation in U. We use the 1/d expansion method of Schweitzer and Czycholl to leading order (d=∞) in which the k integrations are properly carried out, but the k dependence of the self-energy is neglected. For a Kondo insulator we find a δ-function-like boundstate in the gap. The spectral weight of the boundstate decreases rapidly with increasing distance from the impurity. In the metallic case we obtain a resonance of finite width in the pseudogap of the lattice, which again is localized in the neighborhood of the Kondo hole. These states only appear in the coherent phase and disappear in the continuum at higher temperatures.

Magnetic properties of stage-1 CoCl2-graphite intercalation compounds diluted with MgCl2.

We report a detailed study of the dilution of the magnetic properties of stage-1 ${\mathrm{CoCl}}_{2}$-graphite intercalation compounds (GIC's) with nonmagnetic ${\mathrm{MgCl}}_{2}$. The substitution of magnetic ions by nonmagnetic ions reduces the three-dimensional antiferromagnetic ordering temperature ${\mathit{T}}_{\mathit{N}}$, and reduces the low-temperature transition field ${\mathit{H}}_{\mathit{t}}$ that is a measure of the antiferromagnetic interlayer coupling. The intercalate layer in the stage-1 ${\mathrm{Co}}_{\mathit{x}}$${\mathrm{Mg}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Cl}}_{2}$-GIC's fills only 85% of the available volume of the intercalate gallery. The extrapolated value of the Co concentration, ${\mathit{x}}_{\mathit{p}}$=0.65, at which ${\mathit{H}}_{\mathit{t}}$ and ${\mathit{T}}_{\mathit{N}}$ go to zero, suggests that the 15% concentration of voids is distributed randomly throughout the intercalate layer. It is proposed that for x\ensuremath{\ge}0.65 there is a connected magnetic two-dimensional triangular lattice. Our indirect measurement of the in-plane intercalate distribution is in agreement with recent transmission-electron-microscopy studies that show there is a connected network of intercalate with a structural coherence length as large as 1 \ensuremath{\mu}m.