S. L. Tang

Large magnetic entropy changes in the Ni45.4Mn41.5In13.1 ferromagnetic shape memory alloy

The inverse magnetocaloric effect associated with the martensitic transition in the Ni45.4Mn41.5In13.1 Heusler alloy is reported. A large positive magnetic entropy change of 8J∕kgK under a low magnetic field of 10kOe is found near the martensitic transition temperature. This change originates from the first-order transition from a low-temperature weak-magnetic martensitic phase to a high-temperature ferromagnetic austenitic phase. The large low-field magnetic entropy change indicates a great potential of Ni–Mn–In alloys as working materials for magnetic refrigeration in a wide temperature range.

The study of low-field positive and negative magnetic entropy changes in Ni43Mn46−xCuxSn11 alloys

A series of Ni43Mn46−xCuxSn11 (x=1, 2, and 3) alloys was prepared by the arc melting method. The martensitic transition shifts to a higher temperature with increasing Cu concentration. The isothermal magnetization curves around the martensitic transition temperature show a typical metamagnetic behavior. Under a low applied magnetic field of 10kOe, positive values of magnetic entropy change around the martensitic transition temperature are 14.1, 18.0, and 15.8J∕kgK for x=1, 2, and 3, respectively. While in the vicinity of the Curie temperature of the austenitic phase, these negative values are 1.1, 1.0, and 0.9J∕kgK for x=1, 2, and 3, respectively. The origin of the large entropy changes and the potential application for Ni43Mn46−xCuxSn11 alloys as a working substance for magnetic refrigeration are discussed.

Anisotropy compensation and magnetostriction in TbxNd1−xFe1.9 cubic Laves alloys

Polycrystalline TbxNd1−xFe1.9 (0⩽x⩽0.8) cubic Laves phase alloys with MgCu2-type structure were prepared by high-pressure synthesis and subsequent low-temperature annealing. The crystal structure, magnetic properties, and magnetostriction have been investigated. The change of easy magnetic direction from ⟨100⟩ to ⟨111⟩ with increasing x up to 0.1 is detected by Mossbauer spectra. In accordance with Mossbauer effect study, both magnetization and magnetostriction analyses show that TbxNd1−xFe1.9 is an anisotropy compensation system and the compensation point is close to x=0.1. The present work may open an avenue in searching magnetostrictive materials with inexpensive Nd.

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.

High-pressure synthesis of giant magnetostrictive PrxTb1−xFe1.9 alloys

PrxTb1−xFe1.9 (0⩽x⩽1) magnetostrictive alloys with cubic Laves phase have been synthesized by a high-pressure synthesis method. Crystal structure, magnetic properties, magnetocrystalline anisotropy, and the magnetostriction of PrxTb1−xFe1.9 (0⩽x⩽1) alloys are investigated. Composition anisotropy compensation is realized in Pr0.9Tb0.1Fe1.9 alloy, which shows low magnetocrystalline anisotropy and a large magnetostriction value (λ‖−λ⊥=1497ppm) at 13kOe at room temperature. These characters suggest that Pr0.9Tb0.1Fe1.9 alloy may be a promising candidate for magnetostriction application.

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≤5u2002kOe. 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.

Fabrication and magnetic properties of free-standing Ni nanotube arrays with controllable wall thickness

Free-standing Ni nanotubes were fabricated on silicon substrate using anodic aluminum oxide/polypyrrole composite template. The diameter, length, and wall thickness of the nanotubes can be precisely and independently controlled. Magnetic measurements show that the magnetic anisotropic properties are strongly dependent on the wall thickness of nanotubes. Theoretical analysis and micromagnetic simulation were performed to explain the wall thickness-dependent anisotropic behavior.

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.

Effects of annealing on the structure and magnetic properties of Fe27Co23Pb50 nanowire arrays

Ferromagnetic-nonmagnetic heterogeneous Fe27Co23Pb50 ternary metal nanowire arrays were successfully fabricated by alternating current electrodeposition into anodic alumina oxide (AAO) template. The effects of the different annealing temperatures (100, 200, 300, 400, 500, 600°C) on the structure and magnetic properties have been discussed. X-ray diffraction observations indicated that FeCo and Pb phases coexist for the as-deposited and annealed samples. Magnetic measurements indicate that the nanowire arrays have high perpendicular magnetic anisotropy with their easy axis parallel to the nanowire arrays. The coercivity and remanence ratio increases as the annealing temperature rises, reaches their maximum at 400°C, and then decreases as the annealing temperature rises further. The mechanism of the magnetic properties and magnetic variety should be attributed to the special structure of the nanowires∕AAO.

Anisotropy compensation and magnetostrictive properties in Tbx Dy1−x(Fe0.9Mn0.1)1.93 Laves compounds: Experimental and theoretical analysis

The structure, magnetic transitions, and magnetostriction of Tbxu2009Dy1−x(Fe0.9Mn0.1)1.93 polycrystalline compounds have been investigated. The Mn substitution for Fe changes the composition for the anisotropy compensation to the Dy-rich side compared with the Tbxu2009Dy1−xFe2 system, which was confirmed by the analysis of detailed scanned XRD, the temperature dependence of a.c. initial susceptibility χac(T), and the calculation of the first anisotropy constant K1. The spin configuration diagram accompanied with different crystal structures for TbxDy1−x(Fe0.9Mn0.1)1.93 was constructed. The large tetragonal distortion λ100 due to the Mn substitution for Fe could be ascribed to the change in d band structure. The largest ratio between magnetostriction and the absolute values of the first anisotropy constant λa/|K1| appears at the composition with x=0.26, which could make it potential material for magnetostrictive application. Based on our experimental results, a phenomenological approach was also proposed to theor...