Structural, Electronic and Magnetic Properties of Zinc-Blende Ga1−x TM x N (TM = Cr, Mn, Fe, V)

In this paper, we present a theoretical study of structural, electronic and magnetic properties for zinc-blende Ga_1?x TM _x N(TM = Cr, Fe, Mn, V) using the full-potential augmented plane wave (FP-APW) method with local-spin density approximation (LSDA). We have analysed the dependence of structural parameters values on the composition x in the range of x=0.25, x=0.50. Also, the role of p–d hybridisation is analysed by partial (PDOS) and total density of states (TDOS). The magnetic moment of Ga_1?x TM _x N has been studied by increasing the concentration of TM atom. The TM atom is the most important source of the total magnetic moment in these alloys, while the contributions from Ga and N are minor. In addition our results verify the half-metallic ferromagnetic character of TM doped GaN.     

Magnetic Properties of Mg x Mn1?x Fe2O4 Nanoferrites

We report the magnetic properties of Mg _x Mn_1?x Fe₂O₄ (0??x??1.0) nanosize compounds with particle sizes between 8?nm and 15?nm. The evolutions of the properties as a function of composition have been investigated by X-ray diffraction, M?ssbauer, and SQUID magnetometry. Pure cubic spinel could be obtained under a low reaction temperature of 200°C in all the samples. Impurity phases have been observed in compounds annealed at above 900°C. Magnetic relaxation is observed in samples with particles of about 8?nm. The spectra with particle sizes larger than 10?nm could be fitted with at least two sextets attributed to Fe³⁺ ions on tetrahedral (A) and octahedral?(B) sites. The magnetization measurement indicates superparamagnetic behavior in nanosized compounds.     

Oxidation Resistance and Magnetic Properties of SmCo7?x Si x Permanent Magnetic Alloys

The crystal structure, oxidation resistance, and magnetic properties of SmCo_7−x Si _x (x=0, 0.4, 0.6, and 0.9) permanent magnetic alloys were investigated systematically. It is found that the addition of silicon in the as-cast SmCo₇ ingot plays an important role in stabilizing TbCu₇ phase and improving inherent oxidation resistance. For the bulk nanocrystalline SmCo_7−x Si _x magnets, the oxidation resistance remarkably enhances but the corresponding Curie temperature T _c and maximum energy product (BH)_max exhibit a decreasing trend with the increase in Si content x. For the typical SmCo_6.4Si_0.6 nanocrystalline magnet, its final mass gain was about 1.71 mg/cm² after oxidation at 500 °C for 100 h, indicating the enhanced inherent oxidation resistance. Its T _c and (BH)_max were about 708 °C and 35.4 kJ/m³, respectively.     

Structural and Electrical Transport Properties of Al1−xM x B2 (M = Li, Vacancy)

AlB₂ and MgB₂ are neighboring compounds and have similar crystal structures. However, their superconducting properties are very different because the σ holes which play a key role in the superconductivity of MgB₂ do not exist in AlB₂. In this paper we reported our attempts to dope holes into AlB₂ by substituting Li and vacancy for Al, and these holes were expected to induce superconductivity in the system. However, experimental results showed that Li was hard to substitute Al in AlB₂. The variation of resistivity with temperature and x for samples with the nominal composition of Al_1?xLi _x B₂ was analyzed by considering the phase variation of the samples with x. The temperature dependence of resistivity for Al_1?xB₂ was also studied and orders of magnitude change in resistivity was observed when x was up to 0.4 and 0.5, similar to that observed in Mg_1?xB₂ system by Sharma et al. (A. Sharma, N. Hur, Y. Horibe, C. H. Chen, B. G. Kim, S. Guha, Marta Z. Cieplak, and S. W. Cheong, Phys. Rev. Lett. 89, 167003 (2002)). It is proposed that phase separation may exist in Al_1?xB₂, leading to the dramatic change of resistivity because of percolation.     

Thermodynamic study of the magnetic ordering of Fe3−x Mn x Si alloys

The compounds Fe_3–x Mn _x Si exhibit a complex magnetic behavior for 0.6x1.75 involving ferromagnetic ordering followed by a reordering at lower temperature. Measurements of the thermal expansion and the specific heat C _p show only a weak anomaly at the Curie temperature, T _C, whereas a large, relatively sharp peak occurs at the magnetic reordering temperature, T _R. Thermal expansion measurements for the Fe_2.2Mn_0.8Si compound made about T _R are indicative of long-range ordering that can be suppressed in an applied field of 0.4T. Magnetization measurements show that low fields, 1–2 mT, strongly influence the bulk magnetization. Irreversible magnetization behavior, similar to that in spin-glass systems, is displayed.Paper presented at the Tenth International Thermal Expansion Symposium, June 6–7, 1989, Boulder, Colorado, U.S.A.     

Magnetic and Transport Properties of Single Crystalline K 0.8Fe 2 − x Ir x Se2

A series of K_0.8Fe_2?xIr _x Se₂ single-crystal compounds with nominal compositions x = 0, 0.01, 0.03, 0.05, 0.07, and 0.1 were successfully synthesized using self-flux method. It is found that the Ir doping in the present system will induce a suppression of the c-axis lattice constants. However, the zero-resistance temperatures, \(\mathrm {T}_{\mathrm {c}}^{\text {zero}}\) , are nearly maintained around 32 K for the samples with x ≤ 0.05, and it drops to 29 K for the one with x = 0.07. The superconductivity vanishes when the doping level reaches to 0.1. The hump in resistivity which corresponds to the transition from the insulating to metallic phase shifts towards low temperatures. However, the magnitude of the normal-state resistivity above 100 K for Ir-doped samples with x ≤ 0.05 is smaller than the one of the undoped sample, indicating the doping at Fe vacancy site. An onset transition temperature of 44 K has been observed in the ρ-T curve for K_0.8Fe_1.95Ir_0.05Se_2.     

Ultrasonic, Transport, and Magnetic Properties of Nd0.5Sr0.5Mn1−x Cr x O3 Perovskites

The resistivity, magnetization and longitudinal ultrasonic velocity (V _l) have been measured in single-phase polycrystalline Nd_0.5Sr_0.5Mn_1?x Cr _x O₃ (x=0, 0.02, 0.05, 0.1) to clarify the Cr doping effect on the metal-insulator and charge ordering transitions. For x=0 sample, the V _l shows two large stiffening just below the metal-insulator transition temperature T _MI and the charge ordering temperature T _CO, respectively. It is suggested that the former ultrasonic anomaly may originate from the spin-lattice effect and the dynamic Jahn-Teller effect, and the latter is due to the electron-lattice effect arising from the static Jahn-Teller effect of Mn³⁺. With the Cr doping, the T _MI shifts to lower temperature, the maximum of magnetization becomes smaller and the resistivity remains metallic type. Furthermore, only one stiffening of ultrasonic velocity is observed below T _MI in these doping samples. The analysis suggests that the Cr doping enhances the double exchange between Mn³⁺ and Mn⁴⁺, and thoroughly destroys the charge ordering state.     

Study of Electronic and Magnetic Properties of Zn1−x M x O (M = Mn and Cr) by ab initio Calculations

The electronic structure and ferromagnetic properties of Zn_1?x M _x O (M = Mn and Cr) have been investigated by using the Korringa–Kohn–Rostoker (KKR) method combined with the coherent potential approximation (CPA). The half-metal behavior is observed for different doping concentrations. The gap energies are deduced for different dilution x values. The magnetic moment of each atom and the total magnetic moment are computed. A special attention is paid to the discussion of the mechanism of ferromagnetism in these components.     

The Influence of Vanadium on Magnetism and Magnetocaloric Properties of Fe 8 0 − x V x B12Si8 (x = 8, 10, and 13.7) Amorphous Alloys

Amorphous soft magnetic Fe_80?x V _x B₁₂Si₈ ribbons (0 ≤ x ≤ 14) have been fabricated by melt spinning technique, and their magnetic and magnetocaloric properties have been studied. The value of magnetocaloric effect has been determined from the measurements of magnetization as a function of temperature and an external magnetic field. The addition of vanadium to the ternary Fe₈₀B₁₂Si₈ alloy results in a decrease of the Curie temperature of amorphous alloys, T _C, from 473.5 to 335 K. With an increasing V content, the average magnetic moment of Fe atom and the magnetic entropy change also decrease. Fe_66.3V_13.7B₁₂Si₈ alloy exhibits the highest refrigeration capacity of 93.7 J kg^?1 and moderate peak magnetic entropy of 1.034 J kg^?1 K^?1 (T _C = 335 K) under the maximum applied field of 2 T. The results from this work showed that V containing amorphous alloy 13.7 at. % is an interesting material and potential candidate for magnetic refrigerants working near room temperature. The observed ?ΔS_M ^max values compare favorably with other amorphous Fe-based alloys.     

X-ray,electrical conductivity and infrared studies of the system Zn1−x CO x Mn1−x Fe x CrO4

The system Zn_1–x Co _x Mn_1–x Fe _x CrO₄ is tetragonal in the range 0.0x0.4 and cubic in the range 0.5x1. Electrical resistivity temperature behaviour obeys Wilson's law for all the compounds and thermoelectric coefficient values vary between 135 to 226V K^–1. All compounds exhibit P-type semiconductivity and possess low mobility values (10^–9 cm² V^–1 sec^–1). The infrared spectra show the presence of two strong absorption bands around 500 and 600 cm^–1. The probable ionic configuration for the system is suggested to be Zn _1–x ²⁺ Fe _x ^–y3+ -Co _x ²⁺ [Mn _1–x ³⁺ Fe _y ³⁺ CO _x ^–y2+ Cr³⁺]O₄.     

Magnetic Properties of Ru-rich Ru2?x Fe x CrZ (Z=Si, Ge)

The properties of Heusler compounds Ru_2?x Fe _x CrGe are investigated and compared with those of Ru_1.9Fe_0.1CrSi. Ru₂CrGe is confirmed to exhibit an antiferromagnetic transition with Ne??l temperature 13?K by magnetic susceptibility and specific heat measurements. When Fe is substituted for Ru, a peak in the magnetic susceptibility is observed, and in the lower temperature region irreversibility between temperature dependences of magnetization for zero-field-cooling and field-cooling conditions is found. Nevertheless, in specific heat of Ru_1.9Fe_0.1CrGe, there is no anomaly to indicate phase transition. The specific heat is almost identical to that for Ru_1.9Fe_0.1CrSi. The above results demonstrate that the magnetic states in the low temperature region of Fe-substituted samples are spin-glass-like states. Slight substitution of Fe for Ru destroys the long-range-order and lead to peculiar spin-glass-like states.     

Magnetically Recyclable Spinel Mn x Ni1−x Fe2 O 4 (x= 0.0–0.5) Nano-photocatalysts: Structural,Morphological and Opto-magnetic Properties

Manganese doped nickel ferrite (Mn _x Ni_1?x Fe₂ O ₄: x = 0.0–0.5) spinel nanoparticles (NPs) were successfully prepared by a facile microwave combustion method (MCM) using urea as the fuel. The prepared samples were characterized by different techniques. Powder X-ray diffraction (XRD) analysis was confirmed the formation of a single-phase NiFe₂ O ₄ spinel structure. The average crystallite sizes of the samples were in the range of 11.49 to 17.24 nm, which was confirmed by Sherrer’s formula. The morphology of the samples showed a nanoparticle-like structure with smaller agglomeration, which was confirmed by high-resolution scanning electron microscopy (HR-SEM). The particle size diameter ranges from 15 to 20 nm, which was confirmed by high-resolution transmission electron microscopy (HR-TEM). Energy dispersive X-ray (EDX) analysis confirmed the elemental composition, which was also evidence for the formation of single pure phase. Selected area electron diffraction (SAED) analysis showed well crystalline nature. UV-visible diffuse reflectance spectra (DRS) and photoluminescence (PL) spectrum analysis was used to calculate the optical band gap, and the values are slightly increased (2.02 to 2.42 eV) with increasing the Mn-dopant, due to the decreasing of particle size, which may be due to the quantum confinement effect. Magnetic properties of the samples were analyzed by vibrating sample magnetometer (VSM) technique, which showed the magnetization (M _s ) value of the samples are increased with increasing Mn content and reach a maximum value of 67.82 emu/g for Mn_0.5Ni_0.5Fe₂ O ₄ sample. Photo-catalytic activity of the samples was measured and showed the photocatalytic degradation (PCD) of methylene blue dye with good results. The catalyst was magnetically recycled and reused five consecutive cycles and showed good reproducibility without change of catalytic activity.     

Preparation and Magnetic Properties of CuCr1 – x Mn x S2 Solid Solutions

Phase relations in the CuS–CrS–MnS system (20 mol % MnS) were studied. The system was found to contain CuCr_{1 – x} Mn _x S₂ solid solutions isostructural with CuCrS₂. The solid-solution range and the oxidation states of Cr and Mn were determined.     

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.     

Effect of Ni Doping on Structural,Morphological, Optical and Magnetic Properties of Zn1−x Ni x O Dilute Magnetic Semiconductors

Ni²⁺-doped ZnO diluted magnetic semiconducting materials (Zn_1?x Ni _x O with x=0.01,0.02,0.03,0.04,0.05) were synthesised by the co-precipitation method. All synthesised samples were sintered at 600 °C for 6 hours. The effects of Ni²⁺ ion-doping on the structural, morphological, optical and magnetic properties of ZnO were investigated using powder X-ray diffraction, field emission SEM, UV–DRS spectroscopy, photoluminescence and vibrating sample magnetometry. The XRD patterns of pure and Ni-doped ZnO samples revealed single phase hexagonal wurtzite structure. The SEM analysis revealed the morphology of prepared samples, and the chemical compositions of all samples were analysed using exhibit energy density X-ray analysis (EDAX) characterisation. The absorption and emission properties revealed the effect of Ni²⁺ doping in ZnO samples. All Ni²⁺ ion-doped samples showed ferromagnetism at room temperature. The observed results are here analysed and reported.     

Electrical and Magnetic Properties of Zr4+ and Ni2+ Ions Substituted Mn–Cu Spinel Ferrites

The Mn–Cu nanoferrites of composition Mn_0.5Cu_0.5Fe_2−2x Ni _x Zr _x O₄ (0.00≤x≤0.80) were synthesized by incorporating dopant Zr⁴⁺ and Ni²⁺ cations via a chemical coprecipitation technique. The single phase of the prepared spinel nanoferrites with particle sizes 15–31 nm was confirmed by XRD. Both electrical and magnetic properties are found to depend on the x contents and explained by considering the Zr⁴⁺ and Ni²⁺ cations distribution, displacement of the Fe³⁺ ions by dopants, changes in magnetic moment at tetrahedral A site and octahedral B site, Fe³⁺(A)–O₂–Fe³⁺ [B] linkages and extent of the primary superexchange interactions (A)–O–[B] of the Fe³⁺ ions on the A and B-sites. DC resistivity, saturation magnetization (M _s), remanence (M _r) and Bohr magneton (n _B) are observed to increase up to x≤0.40, while these parameters fall at relatively higher value of x≥0.60.     

Diamagnetic and Electrical Properties of Si x Mo2S3−x (x=0.1, 0.2, 0.33, 0.5) and A0.1Mo2S3−x (A=C, B, and Ru)

Mo₂S₃ doped with Si, C, B, and Ru, is identified to bear the same crystalline structure P2₁/m as that of Mo₂S₃ through XRD analysis. Diamagnetic transitions with χ _m ～10^?4 emu/g?Oe at temperature ranging from 2 K to 6 K were observed in the doped samples of Si _x Mo₂S_3?x (x=0.1, 0.2, 0.33, 0.5). And both of the x=0.2 and 0.5 samples were found to have double diamagnetic transitions with higher T _c at the same temperature of 6.01 K, while Si _x Mo₂S_3?x of x=0.33 displayed an extra ferromagnetic-like response at 63 K. The corresponding transition in resistivity of Si _x Mo₂S_3?x with x=0.1 was noticed to show a mild drop with less than 10 % of its original transition values as measured down to 2 K. But a superconducting-like magnetic field dependence on the phase transition of resistivity was also noted. Its diamagnetic signals were greatly reduced when the applied magnetic fields were raised to 10³ Oes. In the doped samples of A_0.1Mo₂S_2.9 (A=C, B, and Ru), the phase transition in resistivity at 4.08 K, 4.62 K, and 4.35 K, respectively, exhibited similar fashion as that in the case of Si_0.1Mo₂S_2.9.     

Physicochemical Properties of Amorphous and Crystalline Fe–P–Mn and Fe–P–Mn–V Alloys

Annealing Fe–P–Mn and Fe–P–Mn–V soft-magnetic amorphous alloys prepared from ferrophosphorus waste leads to the formation of fine-particle crystalline phases. The associated structural hardening is more pronounced in alloys with stronger interatomic interactions. The dissolution of Mn and V inhibits the growth of Fe₃P particles, which become smaller than the -Fe particles.