L. Zhai

Large magnetic coercive field in Bi0.9La0.1Fe0.98Nb0.02O3polycrystalline compound

Single phase Bi0.9La0.1FeO3 (BLFO) and Bi0.9La0.1Fe0.98Nb0.02O3 (BLFNO) polycrystalline ceramics were prepared by conventional solid state reaction followed immediately by the quenching process. An obvious structure transition from the rhombohedral-type to the monoclinic-type with the doping of Nb was observed. The average grain size decreased from 7??m for BLFO to 500?nm for BLFNO. The magnetic ordering temperature of BLFNO decreased in comparison with the sample free of Nb. BLFNO shows a large coercive field, 1.35?T, and a large remanent magnetization, 0.23?A?m2?kg?1, at 300?K. The possible reasons for the remarkable magnetic performance of BLFNO are discussed.

Synthesis and exchange bias effect of single-crystalline SrMn3O6−δ nanoribbons

Single-crystalline SrMn3O6−δ nanoribbons (width of 30–500 nm and lengths of up to several hundred micrometers) are synthesized by a molten-salt method. In contrast with the antiferromagnetism in bulk SrMn3O6−δ, magnetization measurements show weak ferromagnetism in these nanoribbons at low temperature. In particular, a notable exchange-bias effect, which strongly depends on the cooling field, is observed in applied magnetic field H≤5 kOe. These results suggest that the exchange bias in the SrMn3O6−δ nanoribbons can be effectively tuned by the cooling field, which is of very special interests for applications.

Composition anisotropy compensation and magnetostriction in Pr(Fe1-xCox)1.9 (0≤x≤0.5) cubic Laves alloys

Polycrystalline magnetostrictive alloys Pr(Fe1−xCox)1.9 (0⩽x⩽0.5) with cubic Laves phase were synthesized by high-pressure annealing. Measurements of Curie temperature, easy magnetic direction (EMD), and magnetostriction were made on these alloys. The EMD of the alloys rotates continuously from ⟨111⟩ for x=0.0 to ⟨110⟩ for x=0.3 and then shows a tendency to ⟨111⟩ with further increasing x. Two magnetostriction peaks at low fields are observed around x=0.2 and x=0.4 due to the lower anisotropy of these two alloys, which is consistent with the variation of EMD. This work demonstrates that the composition anisotropy compensation can be realized in Pr(Fe1−xCox)1.9 system.

Magnetostriction in high-pressure synthesized PrxNd1―xFe1.9 (0 < x< 1) alloys

Polycrystalline PrxNd1−xFe1.9 (0 ≤ x ≤ 1) magnetostrictive alloys were synthesized by high-pressure annealing. The crystal structure, Curie temperature, easy magnetic direction, and magnetostriction of the alloys were investigated. Due to the effects of high pressure, PrxNd1−xFe1.9 alloys are stabilized in a C15 cubic Laves phase with MgCu2-type structure. The Curie temperature decreases linearly with the increasing concentration of Pr. The easy magnetic direction at room-temperature of thealloys rotates continuously from 〈100〉 for x = 0 to 〈111〉 for x = 1. The magnetostriction ofPr0.5Nd0.5Fe1.9 shows a peak at low magnetic field, which indicates the possible anisotropy compensation between Pr and Nd sublattices.

Impact of postgrowth annealing on spin-glass ordering and exchange bias in SrMn3O6−δ nanoribbons

The magnetic properties of as-grown single-crystal SrMn3O6−δ nanoribbons synthesized by a simple molten-salt method can be significantly improved by a heat-treatment procedure, which enhances the ferromagnetism and spin-glass behavior. These enhanced properties might originate from a spin structure modulated by the thermodynamical equilibrium nonuniform oxygen distribution. Measurements of ac susceptibility prove the existence of a spin-glass phase in the postgrowth annealing SrMn3O6−δ nanoribbons, which differs from the only antiferromagnetic phase in the corresponding bulk material. Asymmetric magnetization hysteresis loops observed in applied magnetic fields H≤5 T are attributed to an exchange coupling between the spin-glass shell and the antiferromagnetic core of postgrowth annealing SrMn3O6−δ nanoribbons. Results suggest that the intrinsic phase inhomogeneity due to the surface effects of the nanostructural manganites may induce exchange anisotropy, which is of special interests for potential applica...

Synthesis and magnetostriction of TbxPr1−x(Fe0.8Co0.2)1.9 cubic Laves alloys

Polycrystalline magnetostrictive alloys TbxPr1−x(Fe0.8Co0.2)1.9 (0≤x≤0.4) which cannot be obtained under normal pressure were synthesized by high-pressure annealing. Measurements of crystal structure, Curie temperature, magnetization, and magnetostriction were made on TbxPr1−x(Fe0.8Co0.2)1.9 alloys. X-ray diffraction results show that the alloys exhibit C15 cubic Laves phase with MgCu2-type structure. The lattice parameter decreases with increasing Tb concentration, while the Curie temperature increases. Because of the antiparallel magnetic moment of Tb and Pr, the saturation magnetization decreases with increasing Tb concentration. The magnetostriction of Tb0.05Pr0.95(Fe0.8Co0.2)1.9 shows a peak at low magnetic fields, while that of Tb0.4Pr0.6(Fe0.8Co0.2)1.9 exhibits a minimum in the whole range of magnetic fields.

Synthesis and magnetostriction of PrxCe1−xFe1.9(0.5≤x≤1.0) alloys

High-pressure synthesis method has been used to synthesize PrxCe1−xFe1.9(0.5≤x≤1.0) magnetostrictive alloys. The x-ray diffraction results show that all the alloys exhibit cubic Laves phase with MgCu2-type structure. The lattice parameter, Curie temperature, magnetization, and magnetostriction of the alloys have been investigated. The Curie temperature, the saturation magnetostriction, and the lattice parameters increase approximately linearly with the increment of Pr concentration. The magnetostriction is mainly attributed to the Pr sublattice. The magnetostriction in the magnetic field direction (λ∥) of PrFe1.9 and Pr0.9Ce0.1Fe1.9 alloy at 5 K reaches up to 3700 and 2800 ppm at the biggest field of 50 kOe, respectively, Pr0.9Ce0.1Fe1.9 possesses lower magnetostriction than PrFe1.9 because of the quenching of the orbital 4f moment of Ce. The magnetostriction of all samples deceases as the temperature increases. The composition dependence of the ratio λ/K1 for PrxCe1−xFe1.9 alloys reaches a maximum value ...