Effect of Ni-substitution on Ni2MnGe Heusler alloys: Ab initio study

The effect of Ni-substitution on magnetic properties of Ni₂MnGe alloy has been investigated by first principles method FPLO, which is used in the CPA form. The theoretical lattice parameters obtained from the dependence of the total energy on the lattice parameter are comparable with experimental ones. A decreasing trend of total magnetic moment with Ni-substitution is found for Ni_2+xMn_1−xGe for studied concentrations of x. The linear pressure-magnetization behaviour is obtained for Ni_2+xMn_1−xGe for applied pressure from 0 to 9 GPa, and the pressure derivative of the total magnetic moment is calculated. The value of equilibrium bulk modulus of Ni_2+xMn_1−xGe (for x = 0.1 – 0.9) obtained from Murnaghan equation of state (EOS) shows that the studied compounds are less compressible than Ni₂MnGe.     

Controllable preparation of large-area arrays of Al-substituted CoCuNi ferrite rods with improvement of saturation magnetization and initial permeability

Co_0.5Cu_0.3Ni_0.2Al _x Fe_2?x O₄ (x = 0, 0.07, 0.14, and 0.21) rods of large-area arrays are synthesized by a solvothermal method, followed by calcination in air. The samples are characterized by powder X-ray diffraction, FT-IR spectra, scanning electron microscope, and vibrating sample magnetometer. The effect of diamagnetic Al³⁺ ion substitution and calcination temperature on the structure, morphology, and magnetic properties of Co_0.5Cu_0.3Ni_0.2Al _x Fe_2?x O₄ has been investigated. The results indicate that high-crystallized cubic Co_0.5Cu_0.3Ni_0.2Al _x Fe_2?x O₄ rods of large-area arrays are obtained when the precursors are calcined at 750 °C in air for 3 h. The crystallite size of Co_0.5Cu_0.3Ni_0.2Al _x Fe_2?x O₄ increases with the increase in Al³⁺ content, attributed to the decrease in lattice strain in Co_0.5Cu_0.3Ni_0.2Al _x Fe_2?x O₄ with the increase in Al³⁺ content. The lattice parameters of Co_0.5Cu_0.3Ni_0.2Al _x Fe_2?x O₄ slightly increase with the increase in Al³⁺ content. This is due to the transformation from cubic NiFe₂O₄ phase to cubic CoFe₂O₄ phase after doping Al³⁺ ion. Al³⁺ substitution can improve the magnetic properties of Co_0.5Cu_0.3Ni_0.2Al _x Fe_2?x O₄. Co_0.5Cu_0.3Ni_0.2Al_0.14Fe_1.86O₄, calcined at 950 °C, has the highest specific saturation magnetization (86.36 ± 2.25 emu/g) and magnetic moment (3.586 ± 0.093 μ _B ). Co_0.5Cu_0.3Ni_0.2Al_0.21Fe_1.79O₄, calcined at 950 °C, has the highest initial permeability (17.216 ± 0.448). The results are explained by Neel’s two sublattices.     

Investigations on the structure,defects, electrical and magnetic properties of Ni-substituted BiFeO<Subscript>3</Subscript> ceramics

Polycrystalline BiFe_1?x Ni _x O₃ (x = 0.00–0.30) ceramics were synthesized by solid state reaction method followed by rapid liquid phase sintering. The effect of Ni substitution on the structure, defects, electrical and magnetic properties of BiFeO₃ ceramics was investigated. X-ray diffraction measurements reveal that Ni-substituted samples exhibit distorted rhombohedral perovskite structure as that of unsubstituted BiFeO₃, and the impurity phases such as Bi₂Fe₄O₉ decrease due to Ni substitution. The changes in the phonon frequencies in Raman spectra reveal the lattice distortion in Ni-substituted samples which are in agreement with the XRD analysis. Positron annihilation lifetime measurements reveal that cation vacancy-type defects exist in all samples, the vacancy concentration increases with increasing Ni content from 0.00 to 0.30. The enhancement in leakage current and dielectric properties is observed in Ni-substituted samples due to the suppression of impurity phases and Fe²⁺. Magnetic measurements indicate that the Ni-substituted BiFeO₃ samples exhibit weak ferromagnetism. The magnetic properties are found to increase with increasing Ni concentration due to the internal structural distortion, cation vacancy, the ferromagnetic exchange between the neighboring Fe³⁺ and Ni²⁺ ions and the change in Fe–O–Fe bond angle.     

Structural and Magnetic Properties of Pr0.6Sr0.4Mn1−x Fe x O3 (0≤x≤0.3) Manganites Oxide Prepared by the Ball Milling Method

We present the structural and magnetic properties of Pr_0.6Sr_0.4Mn_1?x Fe _x O₃ (x=0, 0.1, 0.2, and 0.3) compounds. Samples have been prepared by the ball milling method. Rietveld refinements of the X-ray powder diffraction data show that all our synthesized samples are single phase and crystallize in the orthorhombic symmetry with the Pnma space group. The unit cell volume increases with increasing the Fe content. The infrared spectrum shows two active bands, which can be ascribed to the internal stretching and bending modes. The magnetization measurements versus temperature showed that Fe doping leads to a weakening of the ferromagnetic ordering at low temperature, the Curie temperature T _C decreases from 300 K for x=0.0 to 88 K for x=0.2. The magnetization versus applied magnetic measurements at low temperature lead to conclude that the substitution of Mn³⁺ ions by Fe³⁺ ions triggers antiferromagnetic interactions between the Fe³⁺ and Mn⁴⁺ spins, and also the magnetization versus applied magnetic measurements at room temperature shows a small hysteresis loop and a low coercive field, which indicates that the samples are superparamagnetic.     

Combined X-ray and neutron diffraction Rietveld refinement in iron-substituted nano-hydroxyapatite

Simultaneous Rietveld refinements of X-ray and neutron powder diffraction patterns were applied to study the effect of Fe substitution on the crystal structure properties of the Ca_5?x Fe _x (PO₄)₃OH system (0 ≤ x ≤ 0.3). From variations of the Ca(1) and Ca(2) site occupancies and modifications of interatomic distances with x, it is inferred that Fe substitutes at both crystallographic sites with a preference at the Ca(2) site. Such partiality is attributed to similar geometries of the sixfold coordinated Fe with the sevenfold coordinated Ca(2). The expected overall decrease of the lattice constants in the iron-substituted samples is followed by an increasing trend with x that is explained in terms of local lattice distortions. Hematite forms as a secondary phase starting at x = 0.1 up to 3.7 wt% for x = 0.3. Transmission electron microscopy reveals a nanosystem consisting of 15–65 nm rods and spheres, while hematite nanoparticles are distinguishable for x ≥ 0.1. A transition of the diamagnetic hydroxyapatite to paramagnetic Fe-hydroxyapatite was found from magnetic measurements, while the antiferromagnetic hematite develops hysteresis loops for x > 0.1.     

The Magnetic Properties of Mn x Fe1−x NiSi (x=0,0.25,0.5,0.75,1) Alloys

The magnetic properties of Mn _x Fe_1?x NiSi (x=0,0.25,0.5,0.75,1) alloys are studied using density functional theory and the WIEN2k package. The exchange correlation potential is treated by generalized gradient approximation (GGA). The total energy calculations of these alloys confirm the stability of the ferromagnetic phase as compared to a nonmagnetic phase. The total magnetic moment is not a linear function of x. By increasing x, it increases and then decreases. The peak position of the magnetic moment is near x=0.75.     

Investigation of the functional properties of Mg x Ni1−x Fe2O4 ceramics

The paper presents a complex study of the effect of Mg substitution on the functional properties of Ni-ferrite ceramics prepared by self-combustion sol–gel method. The sintered ceramics have pure cubic spinel structures with an increase of the lattice parameter and the grain size with Mg content. The electrical properties of Mg _x Ni_1?x Fe₂O₄ (x = 0; 0.17; 0.34; 0.5; 0.66; 1) ceramics have been investigated. The complex impedance spectra suggest a grain boundary contribution in the conduction process and reveal that the real part of impedance and the imaginary component (reactance) increase with increasing the Mg amount. The temperature dependence of dielectric properties shows that the hopping of charge carriers is thermally activated. The resistivity as a function of frequency for different degree of humidity was also investigated. All the investigated samples show a typical ferrimagnetic character with a strong non-linearity, small coercitive field (~50 Oe) and a saturation field of ~1kOe, typical to the investigated Mg _x Ni_1?x Fe₂O₄ ceramics. The Curie temperature determined from magnetic susceptibility versus temperature dependences presents a decrease with the addition of non-magnetic Mg²⁺ ion concentration from 603 °C (for x = 0) to 384 °C (for x = 1).     

Study of Cu-doping effects on magnetic properties of Fe-doped ZnO by first principle calculations

Using ab initio calculations on Zn_{0.975? x} Fe_0.025Cu _x O (x = 0, 0.01, 0.02, 0.05), we study the variations of magnetic moments vs Cu concentration. The electronic structure is calculated by using the Korringa-Kohn-Rostoker (KKR) method combined with coherent potential approximation (CPA). We show that the total magnetic moment and magnetic moment of Fe increase on increasing Cu content. From the density of state (DOS) analysis, we show that Cu-induced impurity bands can assure, by two mechanisms, the enhancement of Fe magnetic moment in Zn_{0.975? x} Fe_0.025Cu _x O.     

First-principles investigations of structural, elastic, electronic and magnetic properties of Ga1−x Mn x P and In1−x Mn x P

We employ the full-potential linearized augmented plane wave plus local orbital (FP L/APW + lo) method based on the density functional theory (DFT) in order to investigate the structural, elastic, electronic, and magnetic properties of ordered dilute ferromagnetic semiconductors Ga_1?x Mn _x P and In_1?x Mn _x P at (x = 0.25) in the zinc blende phase, using generalized gradient approximation, GGA (PBE). To our knowledge the elastic constants of these compounds have not yet been measured or calculated, hence our results serve as a first quantitative theoretical prediction for future study. Results of calculated electronic structures and magnetic properties reveal that both Ga_0.75Mn_0.25P and In_0.75Mn_0.25P have stable ferromagnetic ground state, and they are ideal half-metallic (HM) ferromagnetic at their equilibrium lattice constants. Also we show the nature of the bonding from the charge spin-densities calculations. The calculated total magnetic moments are 4.0 μ_B per unit cell for both Ga_0.75Mn_0.25P and In_0.75Mn_0.25P, which agree with the Slater–Pauling rule quite well, and we observe that p–d hybridization reduces the local magnetic moment of Mn from its free space charge value and produces smaller local magnetic moments on the nonmagnetic Ga, In and P sites. The values of N ₀α and N ₀β exchange constants confirm the magnetic nature of these compounds. From the robust half-metallicity of Ga_0.75Mn_0.25P and In_0.75Mn_0.25P as a function of lattice constant is also investigated.     

X-ray diffraction,Mössbauer spectrometry and thermal studies of the mechanically alloyed (Fe1−xMnx)2P powders

(Fe_1?xMn_x)₂P phosphide powders in the composition range 0.15?≤?x ≤ 0.75 have been mechanically alloyed and their structural, magnetic and thermal changes with composition have been investigated by means of X-ray diffraction, ⁵⁷Fe Mössbauer spectrometry, magnetization measurements and differential scanning calorimetry. The milling process induces changes in the crystal phase diagram of the (Fe_1?xMn_x)₂P system. The XRD results reveal the coexistence of a bcc Fe(Mn)-type, hexagonal (Fe₂P and Mn₂P-type), orthorhombic (MnP-type) and tetragonal Fe₃P-type structures for all compositions. The room temperature Mössbauer spectra confirm the formation of the Fe(Mn)-type, non-stoichiometric Fe₂P-type, FeP-type and Fe₃P-type structures. Saturation magnetization exhibits a comparable behavior to that of the average hyperfine magnetic field. The DSC scans show the existence of several endothermic and exothermic peaks in the temperature range (100–700)?°C related to different phase transitions. The endothermic peak at about 582–589?°C can be related to the ferromagnetic/paramagnetic transition temperature (Curie temperature, T_C) of the Fe(Mn)-type structure.     

Effect of Zn<Superscript>2+</Superscript> doping on the structural,magnetic and dielectric properties of MnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> prepared by the sol–gel method

Mn_1?xZn_xFe₂O₄ (x?=?0.2–0.8) ferrite samples were successfully prepared by the sol–gel method. X-ray diffraction study reveals that single cubic spinel phase was formed in Mn_1?xZn_xFe₂O₄ samples. The SEM micrographs revealed that the microstructures change significantly with different Zn²⁺ doping concentration and sintering temperature while the grain size grow up to 9.48 μm for Mn_0.6Zn_0.4Fe₂O₄ sample sintered at 1100 °C. Further, the dielectric and magnetic measurements indicated that both Zn²⁺ doping and sintering temperature could affect both electrical and magnetic parameters such as dielectric constant and saturation magnetization in a great manner. The Mn_0.6Zn_0.4Fe₂O₄ sample sintered at 1100 °C for 8 h is found to show the largest M _s value (77.30 emu/g) in this work. These results indicate that Zn²⁺ doping or sintering temperature can adjust the microstructures, dielectric and magnetic properties of Mn_1?xZn_xFe₂O₄ ferrites.     

Synthesis of Fe–Co alloy and cobalt–magnetite composites doped with Nd3+ by using iron disproportionation

Iron–cobalt alloy and cobalt–magnetite composites doped with Nd³⁺ (Co _x Fe_1?x /Co _y Fe_1?y Nd _z Fe_2?z O₄) in which the Fe alloy has either a bcc or a fcc structure and the oxide is a spinel phase, have been synthesized by using the disproportionation of Fe(OH)₂ and the reduction of Co(II) by Fe⁰ in a concentrated KOH solution. Powder X-ray diffraction, scanning electron microscope and vibrating sample magnetometer were employed to characterize the crystallite sizes, structure, morphology and magnetic properties of the composites. And the effect of the Co(II)/Fe(II) ratio (0 ≤ Co/Fe ≤ 1), concentration of KOH, reaction time and substitution Fe³⁺ ions by Nd³⁺ ions on structure, magnetic properties of the composites were investigated. From the perspective of thermodynamics, we explain the postulated mechanism of the disproportionation reaction.     

Effect of the Mn/Fe Ratio on the Microstructure and Magnetic Properties in the Powder Form (Fe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)<Subscript>2</Subscript>P System

The structure, morphology, and magnetic properties of the mechanically alloyed iron manganese phosphides (Fe_1?x Mn _x )₂P with 0.15 ≤ x ≤ 0.75 (Mn/Fe ratio = 0.17, 0.33, 0.66, and 3) have been studied by means of X-ray diffraction, scanning electron microscopy coupled with energy-dispersive X-ray spectrometry, and BS1 and BS2 magnetometry. The powder form (Fe_1?x Mn _x )₂P compounds exhibit multiphase structures that contain Fe(Mn)-type solid solution and Fe₂P-type, Mn₂P-type, Fe₃P-type, and MnP/FeP-type phosphides. The magnetization versus temperature reveals the existence of multiple magnetic phase transitions. The saturation magnetization, coercivity, and squarness M _r/M _s ratio values are discussed as a function of both the Mn content and the temperature. From the approach to saturation magnetization studies, several fundamental magnetic parameters were extracted. The local magnetic anisotropy constant K ₁ was determined.     

Anisotropic ferromagnetism in Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Sn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> nanostructure arrays

Periodic arrays of Fe _x Sn_1?x O₂ nanostructures were fabricated by glancing angle sputter deposition onto self-assembled close-packed arrays of 200-nm-diameter polystyrene microspheres. After annealing at 873 K for 3 h, all the films were crystallized to rutile SnO₂ and maintained good thermal stability in the morphology. Compared with Fe _x Sn_1?x O₂ flat films, arrays of Fe _x Sn_1?x O₂ nanostructures possessed larger saturation magnetic moment and exhibited both perpendicular and in-plane magnetic anisotropy, resulting from the anisotropic morphology of Fe _x Sn_1?x O₂ nanostructures. The EPR signal originating from the oxygen vacancies significantly varied with the Fe concentration and reached the strongest at x = 0.059, which is consistent with the saturation magnetization. It demonstrates that the oxygen vacancies are an important factor for the ferromagnetism of Fe _x Sn_1?x O₂ films.     

Glass Forming Ability and Magnetic Properties of Fe36Ni36B19.2Si4.8Nb4−x M x (M=Cu, Zr, Ti, Y, Pt) Bulk Glassy Alloys Fabricated by Suction Casting

In this study, the effects of Cu, Zr, Ti, Y, Pt substitution for Nb additions on the stability and magnetic properties of Fe-Ni-based bulk metallic glass (BMG) alloys fabricated by the suction casting method are investigated. The saturation magnetization (J _s) and coercivity (H _c) for as-cast Fe₃₆Ni₃₆B_19.2Si_4.8Nb_4?x M _x (M=Cu, Ti) BMG alloys were in the range of 0.51 T–0.55 T and 76–779 A/m, respectively. Differential scanning calorimetry curves show that the Fe₃₆Ni₃₆B_19.2Si_4.8Nb_4?x M _x (M=Cu, Ti) bulk metallic glasses have a supercooled liquid region for Cu at 44 K and for Ti at 39 K.     

New transition metal substituted cadmium tellurides

While crystal growth and physical phenomena in the Mn_xCd_−xTe system have been extensively investigated, little is known about the substitution of other transition metals in cadmium telluride. We have examined the substitution of Fe, Co, and Ni for Cd in CdTe. We find that Co and Ni have very low solubilities in CdTe less than a percent while Fe can be substituted to ≈ 10%. Magnetic susceptibility shows that the iron sites couple antiferromagnetically and gives evidence for clustering at higher Fe concentrations. The lattice constant is observed to decrease with increasing iron concentration, behavior similar to that observed in Mn_xCd_1−xTe. Manganese cadmium tellurides have shown interesting magneto-optical properties. Investigations of this newly formed analog. Fe_xCd_1−xTe, may reveal interesting behavior in this system as well.     

X-ray diffraction and57Fe Mössbauer spectra of the system Fe2O3−Ga2O3

The influence of gallium substitution on the chemical and structural properties of haematite, α-Fe₂O₃, has been studied using X-ray diffraction and⁵⁷Fe Mössbauer spectroscopy. The presence of only α-(Ga _x Fe_1?x )₂O₃ phase is detected for the compositions withx between 0.01 and 0.90. A gradual decrease of the unit-cell parameters of α-(Ga _x Fe_1?x )₂O₃ with the increase of gallium substitution is measured.⁵⁷Fe Mössbauer spectra showed that the value of the magnetic hyperfine field of pure α-Fe₂O₃ decreases with increasing gallium for iron substitution. The hyperfine magnetic structure, which is observed for α-(Ga _x Fe_1?x )₂O₃ at room temperature, collapsed for the composition withx?0.50. The changes in the⁵⁷Fe Mössbauer spectra of the α-(Ga _x Fe_1?x )₂O₃ phase are discussed in the sense of the electronic relaxation and the superparamagnetic effects.     

GGA and GGA+U Description of Structural, Magnetic, and Elastic Properties of Rh2MnZ (Z=Ge, Sn, and Pb)

Structural, magnetic, electronic, and elastic properties of Rh₂MnGe, Rh₂MnSn, and Rh₂MnPb Heusler compounds have been calculated using full potential linearized augmented-plane wave plus local orbitals (FP-L/APW+lo) method based on the spin density functional theory, within the generalized gradient approximation (GGA) and (GGA+U) (U is the Hubbard correction). Results are given for the lattice parameters, bulk moduli, spin magnetic moments and elastic constants. We have derived the bulk and the shear moduli, Young’s and Poisson’s ratio for Rh₂MnZ (Z=Ge, Sn, and Pb). The elastic modulus of Rh₂MnGe is predicted to be the highest. Also, we have estimated the Debye temperatures from the average sound velocity. We discuss the electronic structures, total and partial densities of states and local moments and we investigate the pressure effect on the elastic properties by calculating the elastic constants at various volumes.     

Physical Properties of Sn1−x Fe x O2 Powders Using Solid State Reaction

Iron-doped SnO₂ diluted magnetic semiconducting powders (Sn_1?x Fe _x O₂, x=0.00, 0.03, 0.05, 0.07, 0.10, and 0.15) were synthesized by a simple solid state reaction followed by vacuum annealing and studied the effect of Fe dopant concentrations on structural, optical, and magnetic properties of the synthesized samples. From the X-ray diffraction, it was confirmed that the samples prepared at lower dopant concentrations were tetragonal in structure whereas the samples prepared at higher dopant concentration exhibited orthorhombic SnO and Fe₂O₃ phases along with tetragonal SnO₂ structure. FT-IR spectrum has been used to confirm the formation of Sn–O bond. The optical band gap of the Sn_1?x Fe _x O₂ powders was increased from 3.6 eV to 3.7 eV with increase of dopant concentration. Raman spectroscopy measurement revealed that the broadening of the most intense Raman peak observed at 630 cm^?1 with Fe doping, conforming that the Fe ions are substituted at the Sn sites in the SnO₂ lattice. Vibrating sample magnetometer measurements confirmed that the Sn_1?x Fe _x O₂ powders were ferromagnetic at room temperature.     

Invar like properties of transition metal monoborides Mn1−xCrxB and Mn1−xFexB

Lattice parameters of the pseudo-binary monoborides Mn_1?xCr_xB and Mn_1?xFe_xB were studied in the temperature range from 298 to 1000 K. Expansion of the a- and c-axes and contraction of the b- axis are brought about by the ferromagnetic ordering in the composition range near to MnB. The lattice-parameter-composition curve at 973 K shows that the lattice is affected by the local magnetic moment even at higher temperature than the Curie temperature. Paramagnetic susceptibility in these systems was studied and the number of magnetic carriers per atom q_c, deduced from the Curie-Weiss constant, does not always coincide with the number of carriers q_s, deduced from the saturation moment. In the system Mn_1?xCr_xB, the magnetic properties are strongly affected by local fluctuations of the composition.