Magnetic and structural studies of the alloy system REIn0.5Ag0.5

The structural and magnetic properties of the alloy system REIn_0.5Ag_0.5 [RE = Gd, Tb, Dy, Ho, Er, Tm and Yb] are reported. All these alloys (except that of Yb) crystallize in a cubic CsCl type structure at room temperature. Low temperature X-ray diffraction data does not reveal any structural phase transformation down to 8 K. On the basis of magnetic susceptibility data at a different temperature (3–300 K) and applied magnetic field (2 × 10⁵ to 8 × 10⁶ A m^-1, it has been concluded that GdIn_0.5Ag_0.5 is ferromagnetic (T_c = 118 K), TbIn_0.5Ag_0.5 and DyIn_0.5Ag_0.5 are meta magnetic (T_N = 66 and 30 K, respectively) and alloys involving Ho, Er, Tm and Yb are ferrimagnetic with Néel temperatures (T_N) equal to 24, 22, 21 and 20 K, respectively. The evaluated effective magneton number (p) is found to be slightly larger compared to theoretical values for tripositive ions of Gd, Tb and Dy and a bit smaller for Ho, Er, Tm and Yb. The results have been qualitatively explained using appropriate theories.     

Effect of isothermal treatments on the magnetic behavior of nanocrystalline Cu–Ni–Fe alloy prepared by mechanical alloying

The present study concerns magnetic behavior of nanocrystalline Cu–Ni, Cu–Fe and Cu–Ni–Fe alloys prepared by mechanical alloying. It has been found that the magnetic properties e.g. H_c, M_r and M_s of the nanocrystalline alloys were significantly influenced by the changes in microstructural constituents, grain size and evolution of phases. Microstructural changes in the alloys have been effected by carrying out isothermal treatments on the mechanically alloyed products in the temperature range of 450–650 °C. Phase evolution in the samples after the isothermal treatments were identified and characterized by X-ray diffraction (XRD) and differential scanning calorimetric (DSC) techniques and the results were correlated with the magnetic properties of the alloys.     

Synthesis,structures and magnetic properties of Pr-lean Pr2Fe14B/Fe3B nanocomposite alloys

The lean rare-earth Pr_4.5Fe_77−xTi_xB_18.5 (x=0, 1, 4, 5) nanocomposite alloys were prepared by melt spinning method and subsequent thermal annealing. The effect of Ti content and annealing temperature on the magnetic properties and the microstructure of these magnets were investigated. The enhancing coercivity H_c from 211.4 to 338.2 kA/m has been observed at the optimal annealing temperature of 700 °C by the addition of 5 at% Ti in Pr₂Fe₁₄B/Fe₃B alloys. It was also found that increasing Ti content leads to marked grain refinement in the annealed alloys, resulting in strong exchange-coupling interaction between the hard and the soft phases in these ribbons. In addition, the magnetization reversal behaviors of Pr₂Fe₁₄B/Fe₃B nanocomposites were discussed in detail.     

Magnetic properties of amorphous rare-earth—Iron alloys

The magnetic properties of various amorphous alloys of the type R_1-xFe_x (R = Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu) have been determined in the concentration range 0.3 ? x ? 0.5. With the exception of the Gd and Lu alloys pronounced thermomagnetic history effects were observed in the temperature dependence of the magnetization. These effects are due to a strong temperature dependence of the coercive force (H_c) which is found to obey an exponential law of the form H_c ∞ exp(-αT). ⁵⁷Fe Mössbauer spectra were obtained on the alloys of a composition close to 40 at% Fe. From the combined results of the Mössbauer spectroscopy and magnetic measurements it is derived that the Fe moment decreases if one passes through the rare-earth series. It is postulated that this decrease is due to small differences in the compositional short-range order in the amorphous alloys caused by the heat of mixing becoming more negative in the same sense.     

Magnetostriction, Curie temperature and microstructure of Tb0.29(Dy1−xPrx)0.71Fe1.97 oriented alloys

The Tb_0.29(Dy_1−xPr_x)_0.71Fe_1.97 (x=0, 0.1, 0.2 and 0.3) alloys were prepared by directional solidification method. The orientation, magnetostriction λ, Curie temperature T_c and microstructure of alloys were characterized by XRD, standard resistant strain gauge technique, VSM and SEM-EDS. The results reveal that the alloys have a preferred orientation of 〈1 1 0〉 and 〈1 1 3〉 direction when x>0. With the increase in Pr content, the T_c of alloys decreases gradually and the non-cubic phase appears, resulting in the decline of λ dramatically, from 1935.2×10⁻⁶ for x=0 to 695.9×10⁻⁶ for x=0.3 at a compressive stress of 6 MPa and a magnetic field of H=240 kA m⁻¹.     

Effect of alloying on magnetic properties of Fe-Cr-12 wt% Co permanent magnet alloys

Effect of alloying additional elements (Al, Si, Ti, V, Ni, Cu, Zr, Nb and Mo) with Fe-22/30 wt% Cr-12 wt% Co permanent magnet alloys manufactured by magnetic aging has been systematically studied with magnetic measurements and transmission electron microscopy (TEM), on a laboratory scale. It is found that the alloying shifts the optimum Cr content to a lower lever. Ti and Si show the greatest enhancement on magnetic properties yet narrow the optimum magnetic aging temperature range. Mo, Nb and Cu, when used together with Si, promote magnetic properties and widen the optimum magnetic aging temperature range. Ni and Zr are simply magnetic diluents. V is good for the magnetic properties only at a large amount of addition. The origin of alloying effects explored by TEM microscopy is attributed to the degree of particle entanglement as well as elongation.     

A neutron small angle scattering study of the onset of ferromagnetism in TiBe2-xCux alloys

The onset of ferromagnetic order in TiBe_2-xCu_x alloys, with x = 0.5, 0.4, 0.3, 0.2 and 0.15, has been examined using the technique of neutron small-angle scattering. The Curie temperature, T_c, for these alloys has been determined from the temperature dependence of the magnetic critical scattering. A linear extrapolation of T_c versus copper concentration yields a critical concentration for ferromagnetic order of x_c = 0.05 ± 0.02. For the alloys with x = 0.4, 0.5 the lineshape of the magnetic critical scattering, at and above T_c, is well explained by the Ornstein-Zernicke form of the spin correlation function. For the lower concentration alloys the exact form of the spin correlation function is still unclear.     

2:17-type SmCo magnets prepared by powder injection molding using a water-based binder

2:17-type SmCo permanent magnets by powder injection molding using a water-based binder have been studied. The water-based binder is methylcellulose solution, which consists of deionized water and methylcellulose. When the solution concentration is 0.5 wt%, the carbon content of the sintered magnets is below 0.1 wt% and the magnets have better magnetic properties. The magnetic properties and density of the sintered magnets can be increased through pre-sintering in vacuum (10⁻³ Pa) at 1200 °C. However, the Sm content of the magnets loses obviously in pre-sintering for a long period. The appropriate pre-sintering duration is 20–40 min. The magnetic properties of the magnets are: Br=0.97 T, H_cj=871 kA/m, BH_max=157 kJ/m³. The structure of the magnet consists of the matrix phases (2:17 phases) and the precipitate phases (1:5 phases).     

Limits of solubility,magnetic properties and electron concentration in Fe3-xTxSi system

The role of the outer electrons on the limits of solubility and bulk magnetic properties of the system Fe_3-xT_xSi (T - Ti, V, Cr, Mn, Co, Ni) is investigated. A correlation with the magnetic and structural behavior of Fe_1-cSi_c and Fe_1-cAl_c alloys is demonstrated.     

Improvement of magnetic properties and read/write characteristics in SmCo5 perpendicular thin films

An SmCo₅ alloy is a promising candidate for ultra-high density magnetic recording media because of its strong uniaxial magnetocrystalline anisotropy, whose constant, K_u, is more than 1.1×10⁸ erg/cm³. Recently, we successfully obtained high perpendicular magnetic anisotropy for a sputter-deposited SmCo₅ thin film by introducing a Cu/Ti dual underlayer. However, it is necessary to improve magnetic properties and read/write (R/W) characteristics for applying SmCo₅ thin films to perpendicular magnetic recording media. In this study, we focused on reduction of magnetic domain size and change of a magnetization reversal process of SmCo₅ perpendicular magnetic thin films by introducing carbon (C) atoms into the constituent Cu underlayer. The magnetic domain size became small and the ratio of coercivity (H_c) against magnetic anisotropy (H_k) which is an index of the magnetization reversal process was increased by adding C atoms. We also evaluated the R/W characteristics of SmCo₅ double-layered media including C atoms. The medium noise was decreased and signal-to-noise ratio increased by introducing the C. The addition of C into the Cu underlayer is effective for changing the magnetization reversal process, reducing medium noise and increasing SNR.     

Magnetic characteristics of MgFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles obtained by glycine–nitrate synthesis

The magnetic properties of magnesium–iron spinel (MgFe₂O₄) powdered nanoparticles obtained by glycine–nitrate synthesis are investigated by X-ray phase analysis and the NMR method. According to the results of X-ray phase analysis, the average size of the crystalline part of nanoparticles of the powder under investigation is 45 ± 4 nm. Magnetization J is determined using the formula J = (B/μ0)–H, where B and H are the induction and strength of the magnetic field in the sample, which are measured by the NMR method. The magnetic characteristics of MgFe₂O₄ are as follows: specific saturation magnetization J_sat = 17.52 A m²/kg, specific residual magnetization J_r = 5.73 A m2/kg, coercive force H_c = 4600 A/m, and magnetic moment P_sat = 371 × 10^–20 A m² in the magnetic saturation state and P_r = 121 × 10^–20 A m² in the residual magnetization state.     

Influence of pH on characteristics of BaFe12O19 powder prepared by sol–gel auto-combustion

BaFe₁₂O₁₉ powders with nanocrystalline sizes were produced by sol–gel auto-combustion. Fe³⁺ and Ba²⁺, in a molar ratio of 11.5, were chelated by citric acid ions at different pH. After dehydration, auto-combustion and calcinations, BaFe₁₂O₁₉ powders were formed. TG/DSC indicated the action to form BaFe₁₂O₁₉ first occurred at about 800. XRD patterns of the annealed powders showed that the well-crystalline powder was produced when pH=10. In addition, the data from XRD showed the lattice parameters a and c, and the unit-cell volume V had a little decrease and the density went up with the increasing pH. The data from PPMS exhibited that pH in the starting solution had an important influence on magnetic properties. In this case, BaFe₁₂O₁₉ powder, of maximum magnetization M(3 T)≈60 A m²/kg, the remanent magnetization M_r≈33 A m²/kg and the intrinsic coercive H_c≈432 kA/m, was produced under the molar ratio of citric acid to the metal nitrate of 1.5 when pH=10.     

Transport properties of n-type ferromagnetic semiconductor HgCr2−xInxSe4(x = 0.100)

Measurements of the electrical conductivity, magnetoresistance, and Hall effect were performed on a n-type ferromagnetic semiconductor HgCr_2?xIn_xSe₄(x = 0.100) single crystal from 6.3 to 296 K in magnetic fields up to 1.19×l0⁶A/m. The conductivity decreases rapidly near the Curie temperatureT_c (≈120 K) as the temperature is raised. A large peak in the magnetoresistance is observed near T_c. The Hall effect measurements indicate that the temperature dependence of the conductivity and the magnetoresistance are due mostly to a change in electron mobility. The electron mobility is 1.2 × 10^?2 m²/V · s at 6.3 K, and decreases rapidly near T_c with the rise in temperature. Then it increases slowly from 5.5 × 10^?4 m²/V · s at 160 K to 7.5 × 10^?4 m²/V · s at 241 K. This temperature dependence of the electron mobility can be explained in terms of the spin-disorder scattering which takes into account the exchange interaction between charge carriers and localized magnetic moments.     

Hard magnetic properties of sputtered Co and Co-P films

Both magnetic properties and microstructure of sputtered Co and Co-4.8 wt% P films ( ≈ 3000 Å) deposited near room temperature are studied as a function of Ar pressure P_Ar ranging from 4×10^-3 to 1.4×10^-1 Torr. The coercive force H_c of the film is a strong function of P_Ar. The coercive force of Co increases from 25 to 270 Oe with increasing P_Ar. With an addition of phosphorus in Co, H_c increases substantially. At high P_Ar ( ≈ 1×10^-1 Torr), a high H_c of 700 Oe and a low squareness of 0.58 are obtained. From observation of the microstructure, it is concluded that the structure of columns is responsible for the high H_c and the low squareness.     

Structural transformations and magnetic properties of Fe60Pt15B25 and Fe60Pt25B15 nanocomposite alloys

Structural and magnetic properties of two rapidly solidified and post-annealed Fe₆₀Pt₁₅B₂₅ and Fe₆₀Pt₂₅B₁₅ alloys are compared. The as-quenched Fe₆₀Pt₁₅B₂₅ ribbon was fully amorphous whereas in the Fe₆₀Pt₂₅B₁₅ alloy the amorphous phase coexists with an fcc FePt disordered solid solution. Differential scanning calorimetry curves of both alloys reveal a single exothermal peak with onset temperatures of 873 and 847 K for Fe₆₀Pt₁₅B₂₅ and Fe₆₀Pt₂₅B₁₅, respectively. Magnetically hard, tetragonal ordered L1₀ FePt and magnetically soft Fe₂B nanocrystalline phases were formed due to the annealing of the alloys, as indicated by X-ray diffraction and Mössbauer spectroscopy measurements. Two-phase behavior was detected in the temperature dependence of magnetization of the annealed samples. A magnetic hardening was observed for all annealed ribbons. Magnetic properties of the annealed alloys, studied by hysteresis loop measurements, were related to the differences in the relative fractions of the hard and soft magnetic phases calculated from Mössbauer spectra. The alloy with 25 at% Pt exhibits better hard magnetic properties (H_c=437 kA/m, M_r/M_s=0.74) than the alloy with smaller Pt content (H_c=270 kA/m, M_r/M_s=0.73) mainly due to the larger abundance of the ordered tetragonal FePt phase.     

Magnetic clusters in Fe3−x V x Al alloys with DO3 type structure forx≤1.1

Polycrystalline Fe_3?x V _x Al alloys with the DO₃ type structure were investigated by magnetostatic and Mössbauer methods. In alloys with 0.2<x<0.5 the ferro- and superpara-magnetic phases coexist. For alloys withx≥0.5 these investigations showed that in spite of the lack of magnetic order, they are characterized by strong nonlinear variations of the magnetization in a magnetic field over a wide temperature range. This indicates the presence of magnetic clusters of Fe atoms with very large magnetic moments. Analysis of the magnetization isotherms indicates that in these alloys a distribution of magnetic moments of clusters (μ_c) from 10 μ_B to 10⁴ μ_B exists.     

Magnetic and electrical transport properties in the self-doped manganite La0.9Mn0.9M0.1O3 (M=Mn,Zn and Ti)

The magnetic and electrical transport properties of La_0.9Mn_0.9M_0.1O₃ (M=Mn, Zn and Ti) were investigated. The temperature and magnetic field dependence of electrical resistivity (ρ) and dc magnetization were studied. All the compounds are found in rhombohedral structure. The excess oxygen in all three compounds was detected through iodometric titration. A modification in resistivity is observed when M=Mn is replaced by M=Zn and Ti. The high temperature resistivity above T_C follow variable range hopping model for both Zn and Ti compounds. For Zn doping, the observation of large field-cool effect and decrease in resistivity at room temperature and is assumed to be due to the implant of Mn⁴⁺ in Mn³⁺ matrix, which favor Mn³⁺/Mn⁴⁺ double exchange. The ferromagnetic behavior below T_C for the compound with M=Ti is correlated to the excess oxygen in it, which implants Mn⁴⁺ and thus incorporates ferromagnetic interactions. The substitutions lead to a reduction of T_c and magnetization.     

MAGNETIC PROPERTIES AND CRYSTALLIZATION OF THE RAPIDLY QUENCHED (Fe1-xNdx) 81.5B18.5 ALLOYS

Magnetic properties and crystallization behaviors of amorphous (Fe_1-xNd_x) _81.5B_18.5 alloys were studied. The crystallization temperature is found to rise at first and then drop monotonically with x, having a maximum value of 976K at x=0.11 (9at% Nd). The (Fe_1-xNd_x) _81.5B_18.5 alloys prepared at a quenching rate of v_s = 6.6m /s are amorphous, and exhibit good glass formability. Both the coercive field H_c and energy product (BH)_max depend strongly on Nd concentration. Amorphous (Fe_1-xNd_x) _81.5B_18.5 alloys with higher Nd concentration have a high coercive field at low temperature, due to the large random uniaxial anisotropy of Nd. The room-temperature H_c and (BH)_max obtained on optimal annealing con-ditions show two maxima as a function of Nd concentration x. The highest room-temperature coercive field H_c =22 kOe within the Nd concentrations around x=0.368 and the maximum energy product(RH)_max= 13.3 MG·Oe at x =0.055 are observed. The hard magnetic properties of these crystallized samples are related to the presence of the bard magnetic Nd₂Fe₁₄B phase.     

Quantum transitions of relativistic electrons in a superstrong magnetic field

The probability of emission of a hard γ-quantum in relativistic electron transitions to the ground (or near it) level in a magnetic field H ～ H₀ = m²c³/e₀? = 4.41 × 10¹³G is obtained. For the inverse transitions from these levels the cross-section of electron photoexitation is calculated.     

Microstructure and soft magnetic properties of Finemet-type ribbons obtained by twin-roller melt-spinning

Soft magnetic ribbons of Finemet-type (Fe_73.5Cu₁Nb₃Si_13.5B₉) alloys are synthesized by the twin-roller melt-spinning technique directly from the melt, at tangential wheel speeds of 15, 18, 19 and 20 m/s. The microstructure and the magnetic properties are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), differential thermal analysis (DTA), thermo-gravimetric analysis (TGA) and hysteresis loops measurements. Samples cooled at 20 m/s are amorphous, while those quenched at lower wheel speeds are partially crystalline. All samples studied present saturation magnetization values (150-160 A m²/kg) higher than the commercial Finemet alloys (∼135 A m²/kg), obtained by controlled crystallization of amorphous single-roller melt-spun alloys. Optimal soft magnetic properties - σ_S=(154±8) A m²/kg and H_C=(6.9±0.9) A/m - are found in samples quenched at 19 m/s, consisting of size-distributed bcc Fe-Si nanograins (∼18 nm in average) embedded in an amorphous residual matrix. A minority nanocrystalline magnetic phase (≤10 nm) is also detected.