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The Fe0.6Mn0.4NiSi1−xAlx (x = 0, 0.02, 0.03, 0.04, 0.05, 0.06, 0.08, and 0.12) alloys were prepared by arc melting and annealed at 1073 K for 90 h. With increasing Al contents, the structure of Fe0.6Mn0.4NiSi1−xAlx changes from TiNiSi-type to Ni2In-type at room temperature, while the Curie temperature decreases from 390 K to 136 K. Although the refrigerant capacity is relatively small, about 126 J/kg, the maximum isothermal entropy change reaches a value of −ΔSmax = 52.9 J/(kg K) under 5 T for x = 0.04. At the same time, the alloys have great corrosion resistance. From x = 0 to 0.12, samples can be tuned from a second-order to a first-order and then to a second-order phase transition. It is worth noting that there is no magnetic hysteresis for all samples although they experience structural phase transition. The structural and magnetic phase diagrams of the Fe0.6Mn0.4NiSi1−xAlx system have been figured out. The results indicate that the relatively large magnetocaloric effects with no magnetic hysteresis and good corrosion resistance make these alloys a good candidate for magnetic refrigeration near room temperature.

Direct measurements of the adiabatic temperature change (ΔTad) in Gd and Mn1.15Fe0.8P0.5Si0.5C0.05 are made using a homemade adiabatic magnetocalorimeter at 260-360 K and 0-7 T. The system uses a servo motor to drive the samples into and out of the magnetic field under a vacuum environment provided by the Physical Property Measurement System (PPMS). The peak values of ΔTad for Gd and Mn1.15Fe0.8P0.5Si0.5C0.05 at 7 T are 8.71 K and 6.41 K at ambient temperatures of 303 K and 317 K, respectively. Based on the theory model, it is found that ΔTad of Gd depends on the 2/3 exponential function of magnetic field H (ΔTad ∝ H2/3), whereas the Mn1.15Fe0.8P0.5Si0.5C0.05 compound follows the power law of ΔTad ∝ H0.66-1.04 due to the first order magnetic transitions. Furthermore, using the constructed experimental instrument, the adiabatic temperature change in different magnetic materials, including materials with first/second order magnetic transition and blocks, flakes, or powders, can be directly measured under large magnetic fields and wide temperature spans.

The high-field magnetization measurements of Zn- and Ga-doped sintered Bi-based compounds were carried out in a 40 T high-field facility. The critical current density and the flux pinning force of the Bi-series oxide superconductors were calculated using Bean’s critical state model. It is found that both the critical current density and the flux pinning force of the Zn-doped oxide compounds are decreased slightly with increasing Zn content. However, the critical current density and the flux pinning force of the Ga-doped oxide superconductors diminish significantly with enhancement of dopant content. It seems that the superconductivity of Bi-series superconductors is much more severely destroyed by a trivalent dopant than by a divalent one.

The zero-field-cooling and the field-cooling temperature dependence of magnetization for Tl-1223/Ag superconducting tape were measured by using SQUID magnetometer at fields varying from 5 Oe to 5 T in the temperature range of 5–150 K. In the field-cooling curves, some anomalous behaviors, i.e., the positive Meissner effect in the curve of 5 Oe and the diamagnetic dip effect at fields up to 5 kOe, were observed. The diamagnetic dip minimum temperature shifts to the lower temperature as increasing the external field, and the relative amplitude decreases with increasing applied field. Moreover, the dip broadens with increasing applied field. The anomalous behaviors may be attributed to the flux pinning and the flux depinning of Josephson-junction networks in the sample. The dip effect at lower fields may be ascribed to the intergrain Josephson coupling networks, and that at higher fields may be due to the intrinsic intragrain Josephson coupling networks.

The texture formation and development of Bi‐based superconducting phases during the heat‐treatment process are carefully investigated. With increasing anneal time, the (001) texture of both 2212 and 2223 phases is enhanced. The reduction of the interfacial energy due to a Bi2O2 layer in the cell is the main factor contributing to the texture formation. The texture of the parent phase and the interface parallel to the (001) plane are beneficial factors. The effects of sheathed Ag, second phases, and voids on the texture formation are studied.

Gd65Mn35−xGex (x = 0, 5, 10) alloy ribbons were prepared by melt-spinning. A fully amorphous structure was obtained for the alloys with x = 5 and 10, whereas, in melt-spun Gd65Mn35 ribbons, crystalline phases (α-Gd and GdMn2) precipitate in the amorphous matrix. The magnetic phase transition from ferromagnetic to paramagnetic is second order. The critical exponents are deduced from the Kouvel-Fisher method and scaling behavior. The obtained critical exponents are in agreement with the theoretical values of 3D Ising model. The Ising-like behavior suggests the presence of large anisotropy and short-range magnetic-coupling behavior. The maximum magnetic-entropy changes of the melt-spun alloys with x = 0, 5, and 10 for a magnetic field change from 0 to 5 T are 4.2, 4.1, and 4.5 Jkg−1 K−1, respectively. All three alloys have a broad temperature range of the magnetic-entropy peak, resulting in large refrigerant capacities.

The role of the Nd-rich phase in developing microstructure and properties of isotropic and anisotropic NdFeB magnets has been investigated. Melt spun Nd-rich Nd13.5Fe73.5Co6.7Ga0.5B5.6 and Fe-rich Nd7.7Pr2.6Fe84.1B5.5 alloy powders were mechanically mixed with different ratios. The mixed powders were consolidated into isotropic magnets and anisotropic magnets by spark plasma sintering (SPS) and SPS followed by hot deformation, respectively. The composition and microstructure of diffusion area between Nd-rich and Fe-rich compositions for isotropic and anisotropic magnets were investigated. The gradient distribution of Nd content from Nd-rich to Fe-rich area due to the diffusion of liquid Nd-rich phase in the SPS and hot deformation was observed, which leads to gradually changes in grain structure. The remanent polarization of 1.29 T, coercivity of 995 kA/m, and maximum energy product of 293 kJ/m3 are obtained for an anisotropic magnet. The role of the Nd-rich phase has to be carefully considered in order to achieve deformation anisotropy and fine grains in the NdFeB magnets.

Crystal structure and magnetic properties of R5Sn4 alloys with R = Tb, Dy, Ho, and Er have been studied. R5Sn4, R11Sn10, and R5Sn3 phases coexist in the annealed alloys and the content of 11:10 and 5:3 phases varies between 9 and 17 wt.%. The R5Sn4 major phase has Sm5Ge4-type orthorhombic structure with space group Pnma. Tb5Sn4 has a complex magnetic structure, spin re-orientation and ferrimagnetic-paramagnetic phase transitions occur at ∼54 and ∼84 K, respectively. For Dy5Sn4, Ho5Sn4, and Er5Sn4, the antiferromagnetic-paramagnetic phase transitions occur at about 22, 15, and 8 K, respectively. The magnetic entropy changes (−ΔSM) of all alloys are negative at low temperature and changes to positive at higher temperatures, which could be attributed to the change of magnetic states.

The electronic structures and magnetic properties of spinel Co1-x Zn (Cd)xFe2O4 (x = 0.0, 0.25, 0.5, 0.75, and 1.0) have been studied systematically by the first-principles calculation. The optimized structures show that with increasing Zn (Cd) content the crystal lattice parameter increases by 1.47% (5.13%) when the Co ions are completely replaced by Zn (Cd) ions. The results also indicate that the magnetic moment of Co/Fe ion increases and the total spin magnetic moment linearly increases with the Zn (Cd) doping from 3.00 μB for x = 0.0 up to 10.00 μB for x = 1.0 per formula unit. The electronic distribution in the Co spin-down subband is highly localized for the crystal field splitting between t2g and eg levels in the Zn (Cd) doped CoFe2O4 compounds and the energy band moves downwards while doped with Zn (Cd). Meanwhile, the bandgap decreases with the increase of Zn (Cd) except where x = 1 and the spinel structure is half-metal at some degree of doping.

NdFeB based permanent magnetic nanocomposites were prepared by depositing soft magnetic Fe, Co, or Fe65Co 35 nanoparticles on the melt spun NdFeB powders with near single phase composition by a chemical reduction method. The effects of the reduction process, the composition, and the concentrations of metal ions on the magnetic properties of nanocomposites were investigated. Introducing and increasing soft nanoparticle content improved the remanence and maximum energy product of the nanocomposites at the expense of coercivity. Fe65Co35 coated NdFeB powders had higher remanence and energy product than Co or Fe coated powders. The inter-grain exchange coupling between hard and soft magnetic grains was demonstrated by the smooth demagnetization curve with high remanent polarization.Remanence enhanced bulk magnets were also fabricated by consolidating the nanocompositepowders using spark plasma sintering (SPS) technique.

The structure and magnetocaloric properties of polycrystalline (Gd12-xTbx)Co7 (x=0, 4, and 8) alloys with Ho12Co7-type monoclinic structure have been investigated. A spin reorientation transition occurs at about 123 K for the alloy with x=0. The peak values of magnetic entropy change −ΔSM under a magnetic field change ΔH of 5 T is 8.8 J·kg−1·K−1 at 160.8 K (Tc), 8.2 J·kg−1·K−1 at 140.8 K (Tc), and 7.1 J·kg−1·K−1 at 118.9 K (Tc) for the alloys with x=0, 4 and 8, respectively. The refrigerant capacities reach 478, 327, and 160 J·kg−1 for x=0, 4, and 8, respectively. The relatively large magnetic entropy change and reversible magnetization behavior make these alloys a good choice for magnetic refrigeration applications in the temperature range of 118–160 K.

Magnetostriction and its inverse effect (also referred to as a magnetomechanical effect) in the Tb0.3Dy0.7Fe2 alloy have been investigated based on the three dimensional Stoner–Wohlfarth model in this paper. The solutions of direction cosines of magnetization under a compressive stress and a field both applied along the [112] axis have been obtained by following a conventional minimization procedure in which the nonlinear equations for equilibrium conditions have been solved numerically. With a more accurate computation presented here, some new theoretical results have been achieved. These results are in good agreement with experimental observations reported previously. In the demagnetized state the resultant anisotropy for the alloy is determined by the combination of the magnetocrystalline and stress-induced anisotropy energies, and degenerates from cubic into uniaxial at a critical stress. When a field is applied to the alloy along the [112] axis, the alloy under the compressive stress is more difficult to magnetize and can attain a maximum change in bulk magnetostriction at the critical stress. The main reason for the large bulk magnetostriction is that the fractional occupancy of the [1¯1¯1] or [111¯]-oriented domains increases from 1/8 to 1/2 with the stress. This more accurate computation has been proposed for similar investigations and the results will also be helpful for a better understanding of the magnetostriction in materials such as the FeGa alloys.