Narrow Results

To get some information about the interaction of two totally different kinds of superconductors in a mixture, we prepared the samples of mixture of two kinds of superconductors (YBa₂Cu₃O₇₊MgB₂), using normal annealing method at low temperature (400 °C ~ 600 °C). The variations of the transition temperature (T_c) and critical current (J_c) of the mixtures are investigated. We also prepared a series of samples of MgB₂ with small ratios of YBCO or Bi-2223 as addition. Carefully comparison shows that the J_c drops when the ratio of YBCO additions increases, but in the Bi-2223 additions the trend goes just the opposite.

The composition of Mn_0.05Si_0.95 polycrystalline films on (001) Si substrate are prepared by vacuum deposition and post-crystallization processes. X-ray diffraction studies indicate that there are two phases coexist in the film: tetragonal, Mn₄Si₇ and diamond-like Si (Mn). The content of Si(Mn) phase increases with increasing the post-annealing temperature. Temperature dependence of the magnetization shows that there are two ferromagnetic phases with Curie temperature of around 50 K and near room temperature, which is confirmed by x-ray magnetic circular dichroism (XMCD).

M-type SrFe_12-xAl_xO₁₉(0 < x < 2.5) nanoparticles have been synthesized by citrate–nitrite sol–gel technique. The experimental results have shown that Al³⁺ ions substitute Fe³⁺ ions in the sublattice, and the samples remain in the hexagonal magnetoplumbite phase. The saturation magnetization M_s and remanence M_r of M-type SrFe_12-xAl_xO₁₉(0 < x < 2.5) nanoparticles linearly decrease when x increases. x = 0, M_s = 63.5 emu/g and M_s = 23.8 emu/g at x = 2.5 when the magnets are sintered at 1100°C. Meanwhile, the coercivity H_c of the samples fluctuate as doped with Al, and reach maximum H_c = 10.59 kOe when x = 1.5. The intergranular exchange–coupling interactions between the nanoparticles, which are proved by the measurement of Henkel plots (δM), and the interactions become more intensive as the Al substitution x increases.

In this study, the (FePt)_100-xCu_x (x=0, 4.6, 6.7, 8.8, 10.9) (FePtCu) alloy films were prepared by co-sputtering. The effects of Cu addition content and heat treatment on the nanostructure and magnetic properties of the polycrystalline (FePt)_100-xCu_x films are reported. The experimental results show that the ordering temperature of the (FePt)_100-xCu_x (x=6.7) films reduced to 320°C, which is much lower than that of the FePt alloy. After heat treatment at 600°C for 1 hour, the (FePt)_100-xCu_x (x=6.7) film shows a coercive force of 15 kOe and the magnetization of 576 emu/cc. The magnetic properties of the FePtCu films can be adjusted by varying the Cu content in the films. The enhancement of the magnetic properties of the FePtCu films mainly resulted from the formation of the order L1₀ phase. DSC traces of as-deposited disorder films at different heating rates, to evaluate the crystallization of the order phase, showed that the addition of Cu atoms reduced the activation energy of ordering from 217 kJ/mol to 87 kJ/mol for the (FePt)_100-xCu_x films (x= 0 and 6.7, respectively). The reduction of the ordering temperature and corresponding activation energy might due to the solid solution of the Cu atoms in the FePt films.

Fe-Ga thin films were prepared by DC magnetron sputtering on Si (100) substrate and an alloy target consisting of Fe₈₁Ga₁₉ was used. X-ray diffraction techniques were used to quantify the strain in the Fe-Ga thin films by measuring the interplanar spacings of select crystallographic planes. The interplanar spacing, d, for the family of Fe-Ga {211} planes was measured. Using the well-established sin²ψ technique, the residual stress of the Fe-Ga thin films was calculated. It has been found that the stress for Fe-Ga thin films quickly increases with increasing the sputtering power. The residual stress of thin films is almost unchanged in the range of 220-440 nm, and then it decreases with increasing the thickness of thin films.

Nontoxic lead-free multiferroic composites are synthesized by incorporating the dispersed 0.3CoFe₂O₄ (CFO) ferromagnetic nanoparticles into 0.7(K_0.5Na_0.5) NbO₃-LiSbO₃ (KNN-LS5.2) ferroelectric micromatrix. The multiferroicity of the composite can be verified by polarization-electric field hysteresis loop and magnetic hysteresis loop. The composite exhibits excellent magnetic properties. A dilution effect is observed in magnetic hysteresis loops. The field dependence of ME voltage coefficient is given as a function of magnetic field from -4 kOe to 4 kOe with a maximum magnetoelectric voltage coefficient of 10.7 mV⋅cm^-1⋅Oe^-1 at the frequency of 1 kHz. It is a very high value in the lead-free magnetoelectric composites system for the potential use on multifunctional devices.

Fe₈₁Zr₉B₁₀ and Fe₈₁Zr₇Nb₂B₁₀ amorphous alloys were prepared by melt-spinning. The microstructures and magnetic properties of the alloys annealed at various temperatures were investigated by X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). The crystallization progresses of Fe₈₁Zr₉B₁₀ and Fe₈₁Zr₇Nb₂B₁₀ amorphous alloys are as follows: amorphous → residual amorphous + α-Fe → α-Fe + Fe₃Zr + ZrFe₂ and amorphous → residual amorphous + α-Fe → α-Fe + Fe₂Zr, respectively. The grain size (D) of α-Fe in Fe₈₁Zr₇Nb₂B₁₀ alloy is smaller than that in Fe₈₁Zr₉B₁₀ alloy at every annealing stage. The change trend of specific saturation magnetization (M_s) of Fe₈₁Zr₇Nb₂B₁₀ alloy with increasing annealing temperature (T_a) is the same as that of Fe₈₁Zr₉B₁₀ alloy. However, the change trend of coercivity (H_c) of Fe₈₁Zr₇Nb₂B₁₀ alloy with increasing annealing temperature is different from that of Fe₈₁Zr₉B₁₀ alloy, which abruptly deteriorates at 600°C.

The electronic properties of EuS are studied by band structure calculation based on the density functional theory within LDA, LDA + U and fully relativistic schemes. When the Coulomb potential is added to the Eu 4f orbitals, the degeneracy between the different f orbitals is lifted and they are split into lower Hubbard bands and upper Hubbard bands. The fully relativistic band structure scheme shows that spin–orbit coupling splits the 4f states into two manifolds, the 4f_7/2 and the 4f_5/2 multiplet. EuS has high magnetic moments around 6.9 μ_B/f.u and its magnetic properties are determined by the occupancy of the strongly localized 4f electronic states near the Fermi level.

In this paper, the structure and magnetic properties of W_nH₂ (n = 7–12) clusters have been systematically investigated using density functional theory (DFT) within the generalized gradient approximation (GGA). The result indicates that the ground state structures of W_nH₂ clusters are generated when H₂ dissociative adsorbed on the atop site of W_n clusters. W₈H₂ and W${}_{10}$H₂ clusters are found to be more stable than other clusters. The adsorption abilities of W_n clusters are related to W–H bond length, adsorption energy and the charge transfer between H and W clusters as well as the electronic density of state.

First-principles calculations have been used to comparatively investigate electronic and magnetic properties of nitrogen-doped (N-doped) nonmagnetic semiconductor perovskite-type stannate (MSnO₃, M = Ca, Sr, Ba). A total magnetic moment of 1.0 ${\mu }_{\mathrm{\text{B}}}$ induced by N is found in MSnO₃ supercell with one N dopant. The spontaneous polarization mainly originates from spin splitting on $2p$ state of N. The medium-sized formation energy shows that the N-doped MSnO₃ can be realized experimentally under the metal-rich environments, but the clustering tendency and short-range coupling imply that the stannate matrices are unsuitable for magnetizing by substituting N for O. Our study offers a fresh sight of spontaneous spin polarization in $d^0$ magnetism. The FM coupling in N-doped MSnO₃ should be attributed to the hole-mediated $p$–$p$ coupling mechanism.

The Ba₃V₂O₈ and Ba₃V₂O₈:Eu${}^{3+}$ microflowers were synthesized by the composite-hydroxide-mediated (CHM) method from V₂O₅, BaCl₂ and Eu(NO${}_3{)}_3$ without using any surface-capping agent. XRD, EDS and XPS spectra of the crystals indicated that Eu${}^{3+}$ ions were incorporated into the Ba₃V₂O₈ lattices. The effect of doping Eu${}^{3+}$ on the magnetic property of Ba₃V₂O₈ crystal has been investigated at room temperature. The Ba₃V₂O₈:Eu${}^{3+}$ crystals exhibited room-temperature ferromagnetic behavior with remanence magnetization (Mr) of about 5.411 × 10${}^{-3}$ emu/g and coercivity (Hc) of 28.29 Oe. The mechanism of enhanced magnetic property of Eu-doped Ba₃V₂O₈ crystals has been discussed in detail.

Graphene has vast promising applications in nanoelectronics and spintronics because of its unique magnetic and electronic properties. Making use of an ab initio spin-polarized density functional theory, implemented by the method of the Heyd–Scuseria–Ernzerhof 06 (HSE06) hybrid functional, the properties of various defect dopants in a supercell of a semi-metal monolayer graphene were investigated. We found from our calculation that introducing one defect dopant in a supercell would break the spin sublattice symmetry, and will induce a magnetic state at some appropriate doping concentrations. This paper systematically analyzes the magnetic effects of three types of defects on graphene, that is, vacancy, substitutional dopant and adatoms. Different types of defects will induce various new properties in graphene. The energies and electronic properties of these three types of defects were also calculated.

Both blue and red shifts in the absorption spectrum of Co-doped ZnO have been reported at a similar concentration range of doped Co. Moreover, the sources of magnetism of Co-doped ZnO are controversial. To solve these problems, the geometry optimization and energy of different Co-doped ZnO systems were calculated at the states of electron spin polarization and nonspin polarization by adopting plane-wave ultra-soft pseudopotential technology based on density function theory. At the state of electron nonspin polarization, the total energies increased as the concentration of Co-doped increased. The doped systems also became unstable. The formation energies increased and doping became difficult. Furthermore, the band gaps widened and the absorption spectrum exhibited a blue shift. The band gaps were corrected by local-density approximation + $U$ at the state of electron spin polarization. The magnetic moments of the doped systems weakened as the concentration of doped Co increased. The magnetic moments were derived from the coupling effects of $sp$–$d$. The band gaps narrowed and the absorption spectrum exhibited a red shift. The inconsistencies of the band gaps and absorption spectrum at the states of electron spin polarization and nonspin polarization were first discovered in this research, and the sources of Co-doped ZnO magnetism were also reinterpreted.

In this paper, Nb element was partially replaced by V element in Finemet-type Fe₇₃Cu₁Nb_3.5-xV_xSi_13.5B₉ (x = 1, 1.5, 2) alloys and the effect of annealing temperatures on the microstructure and AC magnetic properties of the samples are studied. The annealing temperatures affect the grain sizes of the bcc α-Fe phase greatly. When the annealing temperature is between 540–560°C, the samples have better AC magnetic properties than the samples annealed at other temperatures. The optimized annealing temperature of the studied samples is around 560°C. The coercivity and iron loss of the V2 sample is a little bit higher than that of V1 and V1.5 alloys while the amplitude permeability of V2 alloy is larger than that of V1 and V1.5, which indicate that the content of V element has strong influence on the magnetic properties of nanocrystalline soft magnetic alloys.

First-principle calculations have been performed to systematically investigate the electronic and magnetic properties of Mn/C-codoped GaN. The formation energy of five different configurations is studied and the ground state is demonstrated to be ferromagnetic ordering. The ferromagnetic stabilization is largely due to the strong p–d hybridization among Mn 3d, C 3d and N 2p states. Our calculations show that the GaN codoped with Mn and C has a stable FM ground state with a high Curie temperature. These results are positive to design the dilute magnetic semiconductors with codopants in spintronics applications.

Fe₇₇Co₂Zr₉B₁₀Cu₂ alloy prepared by melt-spinning was annealed at different heat treatment conditions. The thermal property, microstructure and magnetic property of alloys were investigated by differential thermal analysis (DTA), X-ray diffraction (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). Fe₇₇Co₂Zr₉B₁₀Cu₂ alloy as-quenched is a mixture of α-Fe(Co) phase, H-phase and amorphous phase. With increasing annealing temperature, the H-phase transforms to α-Fe(Co) phase. Coercivity (H_c) of Fe₇₇Co₂Zr₉B₁₀Cu₂ alloy annealed at 600°C for 40 min followed by furnace cooling reaches the minimum value, which is attributed to the small and homogeneous α-Fe(Co) grain structure.

First-principles study based on density functional theory has been employed to investigate width-dependent structural stability and magnetic properties of monolayer zigzag MoS₂ nanoribbons (ZZ-MoS₂ NRs). The width N = 4–6 (the numbers of zigzag Mo–S chains along the ribbon length) are considered. The results show that all studied ZZ-MoS₂ NRs are less stable than two-dimensional MoS₂ monolayer, exhibiting that a broader width ribbon behaves better structural stability and an inversely proportional relationship between the structural stability (or the ribbon with) and boundary S–Mo interaction. Electronic states imply that all ZZ-MoS₂ NRs exhibit magnetic properties, regardless of their widths. Total magnetic moment increases with the increasing width N, which is mainly ascribed to the decreasing S–Mo interaction of the two zigzag edges. In order to confirm this reason, a uniaxial tension strain is applied to ZZ-MoS₂ NRs. It has been found that, with the increasing tension strain, the bond length of boundary S–Mo increases, at the same time, the magnetic moment increases also. Our results suggest the rational applications of ZZ-MoS₂ NRs in nanoelectronics and spintronics.

Microstructures, electrical transport and magnetic properties of Sr${}_2$Ti${}_{1-x}$Co${}_x$O${}_4(0\le x\le 0.3)$ ceramics are investigated. With Co doping, the Sr${}_2$Ti${}_{1-x}$Co${}_x$O${}_4$ ceramics remain tetragonal structure while the grain size is decreased with doping. Magnetic moment is enhanced with Co doping and ferromagnetism is observed at low temperatures for Co-doped Sr${}_2$TiO${}_4$. The Sr${}_2$Ti${}_{0.9}$Co${}_{0.1}$O${}_4$ and Sr${}_2$Ti${}_{0.7}$Co${}_{0.3}$O${}_4$ show semiconductor-like transport properties, which can be well fitted by Mott variable range hopping model. The results will provide an effective route to synthesize Sr${}_2$Ti${}_{1-x}$Co${}_x$O${}_4$ ceramics as well as to investigate the physical properties.

Nd–Fe–B permanent magnets possess excellent properties. However, they are highly sensitive to the attack of corrosive environment. The aim of this work is to improve the corrosion resistance of the magnets by phosphatization, silanization, and electrostatic spraying with organic resin composite coatings. Field emission scanning electron microscope (FE-SEM) and energy dispersive spectrometer (EDS) tests showed that uniform phosphate conversion coatings and spray layers were formed on the surface of the Nd–Fe–B magnets. Neutral salt spray tests exhibited that, after treated by either phosphating, silanization or electrostatic spraying, the protectiveness of Nd–Fe–B alloys was apparently increased. And corrosion performance of magnets treated with silane only was slightly inferior to those of phosphatized ones. However, significant improvement in corrosion protection was achieved after two-step treatments, i.e. by top-coating spray layer with phosphate or silane films underneath. Grid test indicated that the phosphate and silane coating were strongly attached to the substrate while silane film was slightly weaker than the phosphate-treated ones. Magnetic property analysis revealed phosphatization, silanization, and electrostatic spraying caused decrease in magnetism, but silanization had the relatively smaller effect.

The alloy 50Ag−50Mn (wt.%) was prepared using ball milling. After 50 h of milling, the samples were isothermally annealed for 1 h at a time at three different temperatures ranging from 350^∘C to 550^∘C. By analyzing the X-ray diffraction data, Rietveld refinement structure analysis was used to measure the lattice strain and crystallite size. The introduction of lattice strain and the decrease in crystallite size as a function of milling time may both contribute to the increase in coercivity. The analysis of superconducting quantum interference devices demonstrates the soft ferromagnetic behavior of as-milled and annealed Ag−Mn alloy. After being annealed at 350^∘C for 1 h, the 50Ag−50Mn alloy’s maximum coercivity was discovered to be 253 Oe.