Magnetic Moments in SmCo5 and SmCo5?x Cu x Films

SmCo₅ is an emerging perpendicular magnetic material for super-high density magnetic recording, due to its large magnetic anisotropy energy. In this paper, the magnetic moments of SmCo_5?x Cu _x have been studied using first principles calculation based on density-functional theory (DFT). Calculations are performed using the pseudopotential plane wave DFT code Vienna ab initio simulation package (VASP) with the projector augmented wave (PAW) method. The local density approximation LDA+U method is used for the calculation of the exchange correlation energy of Sm. The calculation results show that the average Co magnetic moment of SmCo_5?x Cu _x decreases with the increase of Cu doping concentrations, and the influence of the Cu doping on the spin state of Co is greater than that of Sm. The magnetic anisotropy energy of SmCo₅ is analyzed. The electronic density of states and the differential in spin densities of atoms show that the spatial distribution of 4f electron and the 4f?C3d coupling are the controlling factors of the magnetic anisotropy energy of SmCo₅.     

Achieving Isolated Fe100−x Pt x Nanoparticles with High Magnetic Coercivity

Monodisperse Fe_100?x Pt _x (x=37, 41, 47, 54, 61, 66, 74) nanoparticles with an average size of 4.5 nm were successfully synthesized using the chemical polyol process. As-synthesized Fe_100?x Pt _x nanoparticles have the chemically disordered face-centered cubic (fcc) structure with A1 phase. To achieve an ordered structure L1₀ phase for FePt and L1₂ phase for FePt₃ particles, high-temperature annealing is required. In this work, with optimizing effective parameters of annealing and also by changing the stoichiometric of Fe_100?x Pt _x nanoparticles, we were able to achieve coercivity of 16,500 Oe for Fe₅₃Pt₄₇, which is heat treated at 650 ^°C for 60 min with 20 ^°C/min (annealing heating rate). It is obvious that the annealing procedure in this temperature leads to destruction of surfactant and sintering. In this work, chemically synthesized Fe₅₃Pt₄₇ nanoparticles were coated by a nonmagnetic CoO oxide shell to prevent them from sintering. Results show that the size of the core/shell (Fe₅₃Pt₄₇/CoO) nanoparticles after the annealing at a temperature of 650 ^°C has not changed compared to the size of the as-synthesized state. Meanwhile, the coercivity of about 5580 Oe is obtained for this nanocomposite.     

Magnetic properties of (Fe1−x M x )7Se8

The temperature dependence of the magnetization of the quenched and slowly cooled samples of Fe₇Se₈ and (Fe_1–x M _x )₇Se₈ samples with M = cobalt and nickel and x=0.02, 0.05 and 0.08 are given. All the thermomagnetic curves obtained belong to the Weiss ferrimagnetic type. Discontinuities indicating a magnetic transformation to antiferromagnetic order were obtained for some samples. The magnetic moment at 0 and 78 K (M ₀ and M₇₈) dependence on nickel and cobalt concentrations are given. The temperature dependence of the reciprocal susceptibility in the paramagnetic range was studied, and the asymptotic Curie points are given. The values of the effective magnetic moment, _eff, and the number of unpaired electrons were calculated. The thermal variation of the electrical conductivity of the host material, Fe₇Se₈, is given.     

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.     

Magnetic clusters in Cu1 ? x In1 ? x Fe2x Se2 solid solutions

We have synthesized Cu_{1 ? x} In_{1 ? x} Fe_2x Se₂ solid solutions (CuInSe₂-FeSe join). The ??-FeSe end-member of the solid-solution system is an antiferromagnet and a superconductor with a superconducting transition temperature of 8 K. The magnetic properties of the solid solutions were studied at temperatures from 5 to 300 K in magnetic fields H = 3.98 and 3184 kA/m. By fitting experimental ??(H) magnetization data with Langevin and Curie equations, we determined the magnetic moment, size, and concentration of the clusters and the concentration of noninteracting Fe²⁺ ions. The magnetic moment of the Fe²⁺ ions in the clusters is ??0.8??_B at 2x = 0.06 and 0.08, with a tendency to decrease with increasing iron content. This points to antiferromagnetic exchange interaction, which becomes stronger with increasing cluster size. The number of clusters in the materials increases with iron content up to a critical level 2x _c < 2x = 0.06. In the range 2x = 0.06 to 0.10, the cluster size increases until a limiting composition determined by the boundary of the solid-solution range is reached.     

Quantum Criticality and Scaling of the Magnetic Response in CeCu6−x Au x

The heavy-fermion system CeCu_6?x Au _x which exhibits antiferromagnetic order for Au concentrations x>0.1, can be easily tuned to a quantum phase transition, either by chemical composition, i.e., Au concentration, or by an external magnetic field. We present extensive inelastic neutron scattering measurements in order to study the momentum and energy dependence of the critical spin fluctuations for concentration- and magnetic field-tuned CeCu_6?x Au _x . The quasi-2D fluctuations, observed for x=0.1 at the magnetic instability, are already present in pure CeCu₆ and persist to x=0.2, i.e., well into the magnetically ordered regime. This is a strong hint that disorder does not play a major role in this system. The magnetic response for quantum critical CeCu_6?x Au _x exhibits critical slowing down and obeys scaling relations that depend on the tuning parameter. While the E/T scaling of the dynamic susceptibility in concentration-tuned CeCu_5.9Au_0.1 is an indication for local quantum criticality, the E/T ^3/2 scaling in field-tuned CeCu_5.8Au_0.2 points to a conventional spin-density-wave instability.     

Structural and Magnetic Characterization of the Electrodeposited Cu1?x Co x Thin Films

In this work, Cu_1?x Co _x thin films with different x values are prepared by the electrodeposition technique. The deposition is carried out in a three-electrode cell using a potentiostat/galvanostat controlled by a computer potentiostatically. Cyclic voltammetry of electrolytes is performed in order to study electroplating process of the films. The films are deposited on Cu substrates in sulfate bath. The effects of different parameters such as bath composition, working electrode??s voltage, addition of sodium saccharin to electrolyte on composition, crystal structure and surface morphology of the films are investigated. The X-ray diffraction patterns reveal that all films have single phase face-centered cubic structures with no extra reflections due to the presence of pure Co or Cu clusters. Addition of sodium saccharin affects morphology of the films by changing the grain size, grain distribution, and grain shape. Magnetic analysis indicates that the saturation magnetization increases as the cobalt percentage increases, while coercivity decreases.     

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.     

Physical and Magnetic Properties of Nd1?x Gd x Ni4B Compounds

We have produced Nd_1?x Gd _x Ni₄B (0??x??1.0) compounds by the arc-melting method. Physical properties of the produced samples have been investigated by means of the X-ray powder diffraction, zero field/field cooled magnetization between the temperature interval of 9?C70 K, and magnetic hysteresis at 9.5 K. We have observed that the substitution of Gd for Nd leads to a decrease of the unit-cell parameters a, c and the unit-cell volume V. The magnetic phase transition temperatures are found to be 12, 14, 18, 24, 29 and 35 K, for x=0.0, 0.2, 0.4, 0.6, 0.8 and 1.0, respectively.     

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.     

Structural and Magnetic Studies of Ca2?x Sm x MnO Compounds (x=0–0.4)

The Ca_2?x Sm _x MnO₄ (x=0?C0.4) compounds were synthesized by a solid?Csolid method and characterized by XRD at room temperature. The XRD profiles were indexed with a tetragonal structure (I/4mmm space group) for x??0.3 and orthorhombic one (Pnma space group) for x=0.4. The magnetic measurements were studied as a function of temperature (T=2?C300?K) and applied field (?? ₀ H=0?C10?T). When the temperature decreases, each compound has shown first a ferromagnetic?Cparamagnetic (FM?CPM) transition and then an antiferromagnetic?Cferromagnetic (AFM?CFM) one. The transition temperatures are found to be Sm-doping dependent. For all compounds, a spin-glass phenomenon is evidenced by FC/ZFC magnetization curves.     

Magnetic Properties and Metamagnetic Transition in SmCo1−x Fe x AsO (0≤x≤0.2)

Polycrystalline SmCo_1?x Fe _x AsO (x=0, 0.05, 0.1, 0.2) materials with single phase have been synthesized by solid-state reaction. According to the X-ray diffraction patterns, the a-lattice parameter shrinks, but the c-lattice parameter expends with the increased amount of Fe doping. Complicated magnetisms consist of antiferromagnetic, ferromagnetic, and paramagnetic have been observed between 5 K and 300 K in the present system. Magnetic measurement shows that with increasing Fe content, antiferromagnetic order of SmCoAsO is suppressed and ferromagnetic order is enhanced. Below their antiferromagnetic transition temperature, metamagnetic transition can be detected in samples with x<0.2, and the transition field decreases with increasing Fe content. When Fe content reaches 0.2, no metamagnetic transition is observed down to 5 K. A canting of the spins plays a crucial role in metamagnetic behavior of the present system.     

Magnetic ordering in CeCu6−x Au x single crystals: Thermodynamic and transport properties

We report on measurements of the magnetizationM, specific heatC, resistivity , and magnetoresistivity of CeCu _6–x Au _x single crystals (x=0.3 and 0.5) grown by the Czochralski method. Antiferromagnetic ordering is observed inM andC for temperatures less thanT _N=0.48 K (x=0.3) and 0.95 K (x=0.5), similar to the ordering temperatures found previously for polycrystalline samples. As a function of magnetic fieldB, M(B) andC(T, B) are strongly anisotropic, with the easy axis along the crystallographicc direction (orthorhombic notation) as for pure CeCu ₆ . For large magnetic fields where the magnetic ordering is suppressed, the specific heat can be described by the resonance-level model suggestive of a single-ion Kondo effect, similar to CeCu ₆ where for largeB the short-range magnetic correlations are suppressed. The averaged Kondo temperature as determined from a number of properties decreases with increasingx, withT _K=4.0 K forx=0.3 and 3.0 K forx=0.5, compared to 5.8 K forx=0. The magnetoresistivity shows a negative contribution arising from incoherent Kondo scattering and a positive contribution associated with the magnetic order.     

Magnetic and Magnetocaloric Properties of Laves Phase Dy1−x Gd x (Co1−x Ni x )2 Solid Solutions

We report magnetic and magnetocaloric properties of the polycrystalline series of Dy_1?x Gd _x (Co_1?x Ni _x )₂ (x=0.1, 0.2, 0.3, 0.4 and 0.5) solid solutions. The samples were characterized by powder X-ray diffraction patterns taken at room temperature and revealed that all the Dy_1?x Gd _x (Co_1?x Ni _x )₂ solid solutions consist of the C15 cubic Laves phase MgCu₂ type structure and a small amount of DyCo₃ and Dy₂O₃ impurity phases. Magnetic measurements showed that the samples undergoes a second-order type phase transition at T _C<130 K, from paramagnetic to ferromagnetic state. Heat capacity measurements have been performed for all solid solutions and allowed us to determine the Debye temperature. The magnetocaloric effect has been studied by means of specific heat measurements in magnetic field 0.42, 1 and 2 T. The GdNi₂ substitution effect on magnetic and magnetocaloric properties will be discussed.     

Study of Magnetic Properties in Spinels Co x Zn1?x Cr2O4 systems

The exchange interactions J _AA(x) and J _AB(x) are calculated by using a probability law for the Co _x Zn_1?x Cr₂O₄. The magnetic properties of a diluted ferromagnetic spinels Co _x Zn_1?x Cr₂O₄ system are investigated by using the high-temperature series expansions combined with the Padé approximants. The magnetic phase diagram, i.e., T _N versus?x, and the critical exponent associated with the magnetic susceptibility (??) are deduced.     

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.     

Magnetic and Mössbauer investigation of PbFe12−x Ga x O19 hexagonal ferrites

Magnetic and Mö ssbauer measurements have been performed on polycrystalline samples of Ga substituted M-type hexagonal ferrites having compositions PbFe_12–x Ga _x O₁₉ (0 < x < 11). The saturation magnetisation (_S) at 0 K falls with increasing x, from 20 _B for x = 0 to 4.32 _B for x = 6. The Curie temperature tends to zero at x 9, indicating that the compounds with x > 9 are paramagnetic at all temperatures. The magnetic moments of the non substituted Fe³⁺ ions in the spin-up predominant sublattice do not have the same temperature dependence, because of the presence of non magnetic Ga³⁺ ions in the neighbouring lattice sites. For x < 3, the Mössbauer data show that there is no significant deviation from collinear magnetic order. The decrease of _S(0) for x < 3 agrees with the collinear model and the distribution of gallium in all the five available sublattices. At x > 3, the faster decline of the saturation magnetisation can be attributed to the onset of non collinear magnetic order.     

Magnetic characterization of Zr(Cr1−x Cu x )2 alloys and their hydrides

Magnetization measurements were carried out on the alloys Zr(Cr_1–x Cu _x )₂ (x=0, 0.1, 0.3, 0.5) before and after hydrogenation. All the binary and the ternary alloys, as well as their hydrides, exhibit a temperature-independent or nearly temperature-independent Pauli type of paramagnetism. Beside the Pauli paramagnetism, a ferromagnetic contribution to the total magnetization was observed for most of the alloys and their hydrides. It was also observed that hydrogen absorption enhances the Pauli paramagnetism as well as the ferromagnetism of the alloys. The rather unusual magnetic behaviour of these systems is briefly discussed in terms of 3d band filling of the transition metal, and is compared with some related systems.     

Magnetic Transport Properties in GdBa2Cu3?x Ru x O7?δ Superconducting Phase

Bulk superconducting samples of type GdBa₂Cu_3?x Ru _x O_7?δ phase, Gd-123, with?x ranging from 0.0 to 0.15 were prepared by the conventional solid-state reaction technique. X-ray powder diffraction (XRD) and the electrical resistivity measurements were performed in order to investigate the effect of Ru⁴⁺ ions substitution on Gd-123 phase. Enhancement of the phase formation and the superconducting transition temperature T _c for GdBa₂Cu_3?x Ru _x O_7?δ phase up to x=0.05 was observed. The effect of magnetic field up to 4.4?kG on the electrical resistivity behavior of the prepared samples was studied to investigate the flux motion of this phase. The derived flux pinning energy?U, based on the thermally activated flux creep TAFC model, decreased with increasing the magnetic field?B. The flux pinning energy followed the exponent behavior as U(B)～B ^?β . The superconducting transition width ΔT increased as the magnetic field increased, showing the scaling relation as ΔT～B ⁿ . Using Ambegaokar and Halperin AH theory, the magnetic field and temperature dependence of U was found to be U(B,T)～ΔTB ^?η , η=β+n. The critical current density J _c (0) enhanced up to x=0.05, beyond which it decreased with further increase in Ru-content.