Low core loss non-oriented silicon steels

Low core loss non-oriented silicon steels are produced with high (Si+Al) content to reduce eddy current losses. However, high alloy content has detrimental effect on mechanical properties, saturation polarization and thermal conductivity. A new generation of medium and, particularly, low core loss non-oriented silicon steels was developed, with lower alloy content than the conventional grades, based on improved purity and texture. The development allowed the production of new low loss grades, with maximum core loss (W_1.5/50) of 2.30 W/kg at 0.50 mm and 1.95 W/kg at 0.35 mm, with high permeability (J₅₀ of 1.7 and 1.72 T, respectively). Texture improvement was based on hot band structure control and higher boundary mobility. Large hot band grain size and low [1 1 0]∥RD fiber fraction in the hot band texture contribute to reduce the intensity of [1 1 1]∥ND and slightly increase the intensity of [0 0 1]∥RD in the final product. Higher grain boundary mobility and/or a two-stage cold rolling process, with an intermediate annealing, increase the fraction of [0 0 1]∥RD and reduce the fraction of [1 1 1]∥ND on recrystallization and lead to favorable texture evolution on grain growth.     

Development of a new generation of high permeability non-oriented silicon steels

The paper describes a new generation of the high permeability fully processed silicon steel grades developed by Acesita, with core loss (W_1.5/60) in range of 3.10–4.20 W/kg and polarisation (J₅₀) from 1.71 to 1.75 T, respectively. The new grades have lower (Si+Al) content and a better crystallographic texture, with lower fractions of [1 1 1]||ND fibre and higher fractions of [0 0 1]||RD fibre. The new grades have better mechanical and magnetic properties than conventional grades.     

Magnetic properties and EPR spectra of [Cu(L-arginine)2](NO3)2·3H2O

Magnetic and EPR data have been collected for complex [Cu(L-Arg)₂](NO₃)₂·3H₂O (Arg=arginine). Magnetic susceptibility χ in the temperature range 2-160 K, and a magnetization isotherm at T=2.29(1) K with magnetic fields between 0 and 9 T were measured. The observed variation of χT with T indicates predominant antiferromagnetic interactions between Cu(II) ions coupled in 1D chains along the b axis. Fitting a molecular field model to the susceptibility data allows to evaluate g=2.10(1) for the average g-factor and J=−0.42(6) cm⁻¹ for the nearest neighbor exchange coupling (defined as H_ex=-∑J_ijS_i·S_j). This coupling is assigned to syn-anti equatorial-apical carboxylate bridges connecting Cu(II) ion neighbors at 5.682 Å, with a total bond length of 6.989 Å and is consistent with the magnetization isotherm results. It is discussed and compared with couplings observed in other compounds with similar exchange bridges. EPR spectra at 9.77 were obtained in powder samples and at 9.77 and at 34.1 GHz in the three orthogonal planes of single crystals. At both microwave frequencies, and for all magnetic field orientations a single signal arising from the collapse due to exchange interaction of resonances corresponding to two rotated Cu(II) sites is observed. From the EPR results the molecular g-tensors corresponding to the two copper sites in the unit cell were evaluated, allowing an estimated lower limit |J |>0.1 cm⁻¹ for the exchange interaction between Cu(II) neighbors, consistent with the magnetic measurements. The observed angular variation of the line width is attributed to dipolar coupling between Cu(II) ions in the lattice.     

Modified texture and high temperature transport properties of doubly substituted BaxAgyCa2.8Co4O9 thermoelectric oxide

Doubly substituted polycrystalline compound bulk samples of Ba_xAg_yCa_2.8Co₄O₉ were prepared via citrate acid sol-gel method followed by spark plasma sintering. The phase composition, orientation, texture and high temperature electrical properties were systematically investigated. The results showed that the orientation and the texture could be modified by altering ratio of Ba to Ag. The resistivity and the Seebeck coefficient of substituted samples were decreased by decreasing Ba/Ag ratio except for that of Ba_0.1Ag_0.1Ca_2.8Co₄O₉ sample with lowest electrical resistivity (7.2 mΩ cm at 973 K), moderately high Seebeck coefficient (172 μV/K at 973 K) and improved power factor (0.42 mW/mK² at 973 K).     

Magnetic anomalies in single crystalline ErPd2Si2

Considering certain interesting features in the previously reported ¹⁶⁶Er Mössbauer effect, and neutron diffraction data on the polycrystalline form of ErPd₂Si₂ crystallizing in the ThCr₂Si₂-type tetragonal structure, we have carried out magnetic measurements (1.8–300 K) on the single crystalline form of this compound. We observe significant anisotropy in the absolute values of magnetization (indicating that the easy axis is c-axis) as well as in features due to magnetic ordering in the plot of magnetic susceptibility χ versus temperature T at low temperatures. The χ(T) data reveal that there is a pseudo-low-dimensional magnetic order setting in at 4.8 K, with a three-dimensional antiferromagnetic order setting in at a lower temperature (3.8 K). A new finding in the χ(T) data is that, for H∥〈1 1 0〉 but not for H∥〈0 0 1〉, there is a broad shoulder in the range 8–20 K, indicative of the existence of magnetic correlations above 5 K as well, which could be related to the previously reported slow-relaxation-dominated Mössbauer spectra. Interestingly, the temperature coefficient of electrical resistivity is found to be isotropic; no feature due to magnetic ordering could be detected in the electrical resistivity data at low temperatures, which is attributed to magnetic Brillioun-zone boundary gap effects. The results reveal the complex nature of magnetism of this compound.     

Effect of annealing prior to cold rolling on magnetic and mechanical properties of low carbon non-oriented electrical steels

The effects of annealing prior to cold rolling on the microstructure, magnetic and mechanical properties of low-C grain non-oriented (GNO) electrical steels have been investigated. The grain structure of hot-rolled electrical steel strips is modified by annealing at temperatures between 700 and 1050 °C. Annealing at temperatures less than the ferrite to austenite+ferrite transformation temperature on heating (Ac₁) causes a marginal effect on the grain size. However, annealing in the intercritical region at temperatures between Ac₁ and Ac₃ (the ferrite+austenite to austenite transformation temperature on heating) causes rapid decarburization and development of large columnar ferrite grains free of carbide particles. This microstructure leads, after cold rolling and a fast annealing treatment, to carbide free, large ferrite grain microstructures with magnetic and mechanical properties superior to those observed typically in the same steel in the industrially fully processed condition. These results are attributed to the increment in grain size and to the {1 0 0} fiber texture developed during the final annealing at temperatures up to 850 °C. Annealing at higher temperatures, T>Ac₃, results in a strong {1 1 1} fiber texture and an increase of the quantity of second phase particles present in the microstructure, which lead to a negative effect on the final properties. The results suggest that annealing prior to cold rolling offers an attractive alternative processing route for the manufacture of fully processed low C GNO electrical steels strips.     

Structural,magnetic and electrical properties of Co1−xZnxFe2O4 synthesized by co-precipitation method

Nanoparticles of Co_1−xZn_xFe₂O₄ with stoichiometric proportion (x) varying from 0.0 to 0.6 were prepared by the chemical co-precipitation method. The samples were sintered at 600 °C for 2 h and were characterized by X-ray diffraction (XRD), low field AC magnetic susceptibility, DC electrical resistivity and dielectric constant measurements. From the analysis of XRD patterns, the nanocrystalline ferrite had been obtained at pH=12.5–13 and reaction time of 45 min. The particle size was calculated from the most intense peak (3 1 1) using the Scherrer formula. The size of precipitated particles lies within the range 12–16 nm, obtained at reaction temperature of 70 °C. The Curie temperature was obtained from AC magnetic susceptibility measurements in the range 77–850 K. It is observed that Curie temperature decreases with the increase of Zn concentration. DC electrical resistivity measurements were carried out by two-probe method from 370 to 580 K. Temperature-dependent DC electrical resistivity decreases with increase in temperature ensuring the semiconductor nature of the samples. DC electrical resistivity results are discussed in terms of polaron hopping model. Activation energy calculated from the DC electrical resistivity versus temperature for all the samples ranges from 0.658 to 0.849 eV. The drift mobility increases by increasing temperature due to decrease in DC electrical resisitivity. The dielectric constants are studied as a function of frequency in the range 100 Hz–1 MHz at room temperature. The dielectric constant decreases with increasing frequency for all the samples and follow the Maxwell–Wagner's interfacial polarization.     

On the superconductivity in in situ synthesized MgB2 tapes

Single core stainless steel (SS) sheathed MgB₂ tapes have been made by the powder-in-tube (PIT) method using commercial Mg and B powders in two series, one with nominal composition and the other with excess Mg. The electrical resistivity and susceptibility measurements have been carried out to evaluate residual resistivity ratio (RRR), the coherence length ξ(0) and critical current density J_C(T) in these tapes. Detailed structural analysis of the core material has been carried out to correlate the superconducting properties with the crystallinity. In the optimized growth condition the MgB₂ tapes exhibited an estimated J_C of ∼1.4×10⁷ A/m² at 39.45 K in zero field and the zero temperature coherence length is found to be ∼68 Å. MgB₂ tapes fabricated from starting powders having nominal Mg-composition have been shown to exhibit higher J_C than those fabricated from excess magnesium composition of the starting powders. The strained lattice together with the presence of nanosized MgO inclusion having size smaller than the coherence length, are shown to be responsible for the observed higher J_C.     

Anisotropic and large low-field magnetic entropy change in a La4/3Sr5/3Mn2O7 single crystal

We have studied the magnetocaloric effect (MCE) in a bilayered La_4/3Sr_5/3Mn₂O₇ single crystal with applied field along both ab-plane and c-direction. Due to the quasi-two-dimensional structure, the crystal exhibits a strong anisotropy in the MCE. The difference of magnetic entropy change between two crystallographic directions depends on external magnetic fields and has a maximum of 2 J/kg K. A large low-field magnetic entropy change, reaching 3.2 J/kg K for a magnetic field change of 15 kOe, is observed when the applied field is along ab-plane. This large low-field magnetic entropy change is attributed to the rapid change of magnetization in response to external magnetic fields in the easy magnetizing plane.     

Structural optimization of HfTiSiO high-k gate dielectrics by utilizing in-situ PVD-based fabrication method

We investigated the optimum structure for Ti-containing Hf-based high-k gate dielectrics to achieve EOT scaling below 1 nm. TiO₂/HfSiO/SiO₂ trilayer and HfTiSiO/SiO₂ bilayer structures were fabricated by a newly developed in-situ PVD-based method. We found that thermal diffusion of Ti atoms to SiO₂ underlayers degrades the EOT-J_g characteristics. Our results clearly demonstrated the impact of the trilayered structure with TiO₂ capping for improving EOT-J_g characteristics of the gate stack. We achieved an EOT scaling of 0.78 nm as well as reduced gate leakage of 7.2 × 10⁻² A/cm² for a TiO₂/HfSiO/SiO₂ trilayered high-k dielectric while maintaining the electrical properties at the bottom interface.     

Magnetic and electrical properties of new magnetic phase in Si1−xMnx crystals

We have investigated the magnetic and electrical transport properties of Si_1−xMn_x single crystals grown by the vertical Bridgman method. The alloys with Mn concentrations up to x=0.64 have weak ferromagnetic ordering around T_C∼30 K. However, Si_0.25Mn_0.75 alloys show weak ferromagnetic ordering at 70 K and antiferromagnetic ordering at 104 K, which is confirmed by magnetization and electrical transport studies.     

Magnetoelectric behavior in the complex CaMn7O12 perovskite

We report a magnetoelectric effect in the double perovskite CaMn₇O₁₂, that shows a complex magnetic behavior below 90 K with two magnetic phases coexisting (one ferrimagnetic and the other modulated). A second magnetic transition, associated with changes in the magnetic modulation and magnetic ordering coherence lengths of the two magnetic phases occurs at 50 K (T_N2). A detailed structural characterization of this compound, that we have carried out by means of high-resolution X-ray powder diffraction, reveals an anisotropic thermal expansion of its lattice parameters at 50 K (T_N2). In addition, our study of the complex permittivity of this sample as a function of temperature, frequency and magnetic field shows very interesting results below 90 K and specially below 50 K: the dielectric constant ε′_r that was decreasing continuously on cooling experiences an upturn, and even more, on application of a magnetic field it shows a moderate magnetoelectric response. We attribute such dielectric behavior to the formation of electric dipoles by magnetostriction in this charge and spin ordered system, that are sensible to the presence of an external magnetic field.     

The role of iron in the formation of the magnetic structure and related properties of La0.8Sr0.2Co1−xFexO3 (x=0.15, 0.2, 0.3)

La_0.8Sr_0.2Co_1−xFe_xO₃ (x=0.15, 0.2, 0.3) samples were studied by means of AC magnetic susceptibility, magnetization, magnetoresistance and ⁵⁷Fe Mössbauer spectrometry. Iron was found to take on a high spin 3d^5−α electronic state in each of the samples, where α refers to a partly delocalized 3d electron. The compounds were found to exhibit a spin-cluster glass transition with a common transition temperature of ∼53 K. The spin-cluster glass transition is visualized in the ⁵⁷Fe Mössbauer spectra as the slowing down of magnetic relaxation below ∼70 K, thereby showing that iron takes part in the formation of the glassy magnetic phase. The paramagnetic-like phase found at higher temperatures is identified below T_c≈195 K as being composed of weakly interacting, magnetically ordered nanosized clusters of magnetic ions in part with a magnetic moment oriented opposite to the net magnetic moment of the cluster. For each of the samples a considerable low-temperature negative magnetoresistance was found, whose magnitude in the studied range decreases with increasing iron concentration. The observed results obtained on the present compounds are qualitatively explained assuming that the absolute strengths of magnetic exchange interactions are subject to the relation ∣J_Co–Co∣<∣J_Fe–Co∣<∣J_Fe–Fe∣.     

Valence fluctuation in Ce2Co3Ge5 and crystal field effect in Pr2Co3Ge5

Polycrystalline samples of ternary rare-earth germanides R₂Co₃Ge₅ (R=La, Ce and Pr) have been prepared and investigated by means of magnetic susceptibility, isothermal magnetization, electrical resistivity and specific heat measurements. All these compounds crystallize in orthorhombic U₂Co₃Si₅ structure (space group Ibam). No evidence of magnetic or superconducting transition is observed in any of these compounds down to 2 K. The unit cell volume of Ce₂Co₃Ge₅ deviates from the expected lanthanide contraction, indicating non trivalent state of Ce ions in this compound. The reduced value of effective moment (μ_eff≈0.95 μ_B) compared to that expected for trivalent Ce ions further supports valence-fluctuating nature of Ce in Ce₂Co₃Ge₅. The observed temperature dependence of magnetic susceptibility is consistent with the ionic interconfiguration fluctuation (ICF) model. Although no sharp anomaly due to a phase transition is seen, a broad Schottky-type anomaly is observed in the magnetic part of specific heat of Pr₂Co₃Ge₅. An analysis of C_mag data suggests a singlet ground state in Pr₂Co₃Ge₅ separated from the singlet first excited state by 22 K and a doublet second excited state at 73 K.     

The evolution of magnetic,electrical and structural properties of nanogranular [FeCoBN/SiN]×n thin films

Some results concerning the magnetic, electrical and microstructural properties of multilayer [FeCoBN/Si₃N₄]×n films in view of their utilization for manufacturing thin film magnetic inductors are presented. A comparison between the magnetic, electrical and structural properties of FeCoBN and [FeCoBN/Si₃N₄]×n thin films is also reported. The [FeCoBN/Si₃N₄]×n thin films with the thickness of the FeCoBN layers varied from 10 to 30 nm, exhibit good soft magnetic characteristics and high values for electrical resistivity such as Ms of 172–185 A m²/kg, Hc of 318–1433 A/m and ρ of 82–48×10⁻⁷ Ω m, respectively. These physical properties of the samples are discussed in relation with the microstructure of the multilayer system.     

Investigation on the magnetocaloric effect in DyNi2, DyAl2 and Tb1−nGdnAl2 (n=0, 0.4, 0.6) compounds

The magnetocaloric effect (MCE) in the DyNi₂, DyAl₂ and Tb_1−nGd_nAl₂ (n=0, 0.4, 0.6) was theoretically investigated in this work. The DyNi₂ and DyAl₂ compounds are described considering a model Hamiltonian which includes the crystalline electrical field anisotropy. The anisotropic MCE was calculated changing the magnetic field direction from 〈1 1 1〉 to 〈0 0 1〉 in DyNi₂ and from 〈1 0 0〉 to 〈0 1 1〉 in DyAl₂. The influence of the second- and first-order spin-reorientation phase transitions on the MCE that occurs in these systems is discussed. For the calculations of the MCE thermodynamic quantities in the Tb_1−nGd_nAl₂ systems we take into account a two sites magnetic model, and good agreement with the available experimental data was obtained.     

Specific heat and magnetic susceptibility of single-crystalline ZnCr2−xAlxSe4 (x=0.15, 0.23)

A correlation between the second critical field H_c2 of the helix to paramagnetic transition and the magnetic specific heat C-peak was found in ZnCr_2−xAl_xSe₄ spinel single crystals with x=0.15, 0.23. The specific heat peak is anomalously sharp for all finite magnetic fields used here and this points to a first order magneto-structural transition (from cubic to tetragonal symmetry). The C(T)-peak is increasingly suppressed as the external field increases. Approaching the Neel temperature T_N, a broad ac-magnetic susceptibility peak is observed for zero dc-magnetic field. That peak does not show an energy loss and thus points towards a return to a second order type of transition. The magnetic contribution to the specific heat displays a sharp peak at T_N and is maximal at the spin fluctuation temperature T_sf=34 K. T_sf is related to the maximum of the magnetic susceptibility at T_m=40 K (at 50 kOe) in the spin fluctuation region, as evidenced by the entropy exceeding 90% of the entropy calculated classically for the complete alignment of the Cr spins, (2−x)R ln(2S+1). The X-ray photoelectron spectroscopy (XPS) data indicate that Al-substitution does not affect Cr³⁺ 3d³ electronic configuration.     

Tunneling magnetoresistance in exchange-biased CoFeB/AlOx/Co/IrMn junctions

A series of exchange-biased magnetic tunneling junctions (MTJs) were made in an in-plane deposition field (h) = 500 Oe. The deposition sequence was Si(1 0 0)/Ta(30 Å)/CoFeB(75 Å)/AlO_x(d Å)/Co(75 Å)/IrMn(90 Å)/Ta(100 Å), where d was varied from 12 Å to 30 Å. The MTJ was formed by the cross-strip method with a junction area of 0.0225 mm². The tunneling magnetoresistance (ΔR/R) of each MTJ was measured. The high-resolution cross-sectional transmission electron microscopic (HR X-TEM) image shows the very smooth interface and clear microstructure. X-ray diffraction (XRD) demonstrates that the IrMn layer of the MTJ exhibits a (1 1 1) texture. From the results (ΔR/R) increases from 17% to 50%, as d increases from 12 Å to 30 Å. The tunneling resistance (R_o) of these junctions ranges from 150 Ω to 250 Ω. The exchange-biasing field (H_ex) of the MTJ is 50-95 Oe. Finally, the saturation resistance (R_s) was measured as a function of the angle (α) of rotation, where α is the angle between h and the in-plane saturation field (H_s) = 1.1 kOe. The following figure presents the dependence of R_s on α, instead of originally expected independence, the curve actually varies with a period of π.     

Asymmetric angular dependence of Jc in coated conductors prior to and after fast neutron irradiation

Angular dependent measurements of J_c were performed on a commercial coated conductor (SuperPower) consisting of a 1 μm thick YBCO layer grown on a MgO IBAD buffer layer. An asymmetric behavior of the angular dependence of J_c (J_c(Ф)) was found with a changing distance between the two peaks at different temperatures and applied magnetic fields. One peak always occurs when the field is oriented parallel to the tape surface, the other smaller peak is located in the perpendicular orientation at high fields, but slightly shifted (by up to 10°) at 77 K and low magnetic fields. This peak shift, the overall J_c(Ф) asymmetry and the influence of fast neutron irradiation on J_c(Ф) are discussed. The spherical defects, introduced by collisions of fast neutrons with the lattice atoms, are randomly distributed, add to the as-grown defect structure and change the critical current anisotropy by altering both peaks.     

Effects of assisting and sputtering ion current on ion beam assisted deposition textured yttria stabilized zirconia buffer layers of coated conductors

Biaxially textured yttria stabilized zirconia (0 0 1) thin films were fabricated on untextured hastelloy substrates by ion beam assisted deposition method. The effects of assisting beam current density J_a and sputtering beam current density J_s on the textures of the films were studied. The results indicate that as J_a or J_s increase, both the out-of-plane and the in-plane textures are improved initially, and then degrade. The results can be attributed to anisotropic damage and selective sputtering effect of assisting ions. At the same ion-to-atom arrival ratio r, which is reflected with J_a/J_s value, lower deposition rate can enhance the biaxial texture.