Shaolong Tang

Influence of annealing on the magnetic entropy changes in Fe81.6Mo4Zr3.3Nb3.3B6.8Cu1 amorphous ribbons

Abstract We have prepared amorphous Fe 81.6 Mo 4 Zr 3.3 Nb 3.3 B 6.8 Cu 1 ribbon by melt-spinning. Differential thermal analysis (DTA) is used to determine the crystallization temperature of the as-quenched ribbon. As-quenched ribbons were annealed at 300 and 400xa0°C. After thermal treatment, an elevated magnetic entropy change (∣Δ S M ∣) is observed. The influence of annealing effects on the ∣Δ S M ∣ and the potential application of annealed amorphous ribbons as a working material for magnetic refrigerants have been discussed.

Magnetic properties and magnetocaloric effects in (GdxDy1−x)Co2 compounds

Abstract A series of (Gd x Dy 1− x )Co 2 ( x =0, 0.05, 0.1, 0.2, 0.3, 0.4 and 0.55) compounds have been prepared by arc-melting method. The X-ray diffraction (XRD) analysis reveals that all samples are in the MgCu 2 -type structure. The magnetization was measured by a vibrating sample magnetometer (VSM). No first-order phase transition in these compounds ( x ≠0) is observed. With the increasing Gd content, Curie temperature ( T C ) increases almost linearly. The magnetic entropy changes (| ΔS M |) as a function of the temperature in magnetic field (1xa0T) for (Gd x Dy 1− x )Co 2 have been calculated. The origin of the magnetocaloric effect and the potential application of (Gd x Dy 1− x )Co 2 as a working material for magnetic refrigerants have also been discussed.

The magnetic properties and reversal of Fe–Co nanowire arrays

20 nm diameter Fe–Co nanowire arrays with different composition were fabricated by electrodeposition. A nanoporous anodized aluminium oxide film was used as the substrate. The microstructure and magnetic properties were studied by x-ray fluorescence, transmission electron microscopy, x-ray diffraction and vibrating sample magnetometry. Both the coercivity Hc and the spontaneous magnetization Ms increase when the Co content in Fe–Co alloy increases from 0 to about 30 at.%, and then decrease with further increase in the Co content. A model called the chain of crystals is developed and solved to explain the experimental results.

The magnetocaloric effect and magnetic phase transitions in Dy(Co1−xAlx)2 compounds

Abstract Polycrystalline samples of Laves-phase compounds Dy(Co 1− x Al x ) 2 ( x =0.0, 0.02, 0.04, 0.06, 0.08, 0.1) have been prepared and their magnetic properties were investigated by means of magnetization and ac susceptibility measurements. Results on the magnetocaloric effect (MCE) of these samples have been obtained from the magnetization data, which suggest their potential as working substance of magnetic refrigerators at cryogenic temperature from 142 to 200 K. Both the ac susceptibility results and Arrott plots were used to characterize the magnetic phase transitions in these compounds. By discussing the influence of partial replacement of Co by Al on the magnetic phase transitions and magnetocaloric properties of them, we conclude that the size of the MCE and the order of the magnetic phase transition are closely related.

Large low-field magnetic entropy change in DyCo2

Abstract The magnetocaloric effect was examined for DyCo 2 , which shows a first-order transition from a ferrimagnetic to paramagnetic state at 142 K. A large magnetic entropy change Δ S M was observed in this alloy. The maximum value of Δ S M was 2.3, 4.8 and 5.8 J/kg·K for H =0.4, 0.8 and 1.0 T respectively. The origin of the large magnetocaloric effect has also been discussed. The large low-field magnetic entropy change indicates a great potential of DyCo 2 as a working material for magnetic refrigerants.

Synthesis and magnetostriction of melt-spun Pr1−xTbx(Fe0.6Co0.4)2 alloys

Pseudobinary Pr1−xTbx(Fe0.6Co0.4)2 (0⩽x⩽0.4) cubic Laves single phases have been synthesized by melt spinning and subsequent annealing. Their structure, magnetic properties and stability have been investigated. The composition, at which the anisotropy of Pr1−xTbx(Fe0.6Co0.4)2 is compensated, is close to x=0.1. The spontaneous magnetostrictions λ111 of Pr0.9Tb0.1(Fe0.6Co0.4)2 and Pr0.8Tb0.2(Fe0.6Co0.4)2 are larger than 1500×10−6 and 1900×10−6, respectively. Pr1−xTbx(Fe0.6Co0.4)2 (0.1⩽x⩽0.4) ribbon-based materials with 3% epoxy resin combine high magnetostriction with significant magnetic coercivity. Pr0.9Tb0.1(Fe0.6Co0.4)2 is a promising magnetostrictive material.

Low-field magnetic entropy change in Dy(Co1−xSix)2

Abstract A series of Dy(Co1−xSix)2 (x=0, 0.01, 0.03, 0.05 and 0.07) compounds have been prepared by arc-melting method. The X-ray diffraction (XRD) analysis reveals that all samples are in the MgCu2-type structure. The magnetization were measured by a vibrating sample magnetometer (VSM). A first-order transition disappeared by partial substitution of Co by Si (x>0.05) in the Dy(Co1−xSix)2 alloys. The magnetic entropy changes (|ΔSM|) as a function of the temperature in magnetic field (1xa0T) for Dy(CoxSi1−x)2 have been calculated, while the maximum values of |ΔSM are 5.8, 4.1, 3.3, 3.3 and 2.6xa0J/kgxa0K for x=0, 0.01, 0.03, 0.05 and 0.07, respectively. The Curie temperature (TC) can be adjusted between 142 and 168xa0K by partial substitution of Co for Si with some reduction of the |ΔSMax|. The origin of the large magnetocaloric effect (MCE) and the potential application of Dy(Co,Si)2 as a working material for magnetic refrigerants have also been discussed.

Effect of Mo concentration on the phase composition and magnetic properties of Nd8(Fe,Mo)86B6 nanocomposite magnets

The phase composition and magnetic properties of Nd8Fe86−xMoxB6 (x=0, 1, 2, and 3) nanocomposite magnets prepared by melt spinning have been investigated by x-ray powder diffraction, transmission electron microscopy, thermomagnetic analysis, and vibrating sample magnetometer measurements. The optimal ribbons were found to be mainly composed of the α-Fe phase and the Nd2Fe14B phase. The average crystalline size of α-Fe is 14–18 nm. In the optimally quenched samples, the α-Fe phase content decreases with increasing Mo content; at the same time, an increase of coercivity and a decrease of energy products are observed. The hysteresis loops of the optimal ribbons show a single-phase hard magnetic behavior. The reduced remanence ratio is always above 0.66. The remanence enhancement is due to the exchange coupling between the soft and hard magnetic phases in these ribbons. The Curie temperature of the Nd2Fe14B phase in the samples decreases with increasing Mo content. The optimal hard magnetic properties of rema...

The study of magnetic entropy change in Dy(Co1−XMX)2 (M=Al, Si, Ga, Ge) compounds

A series of Dy(Co1−XMX)2 (M=Al Si, Ga, Ge) compounds has been prepared by arc melting method. The X-ray diffraction analysis reveals that all samples are in the MgCu2-type structure. After the substitution, the Curie temperature increases remarkably. A first-order phase transition changes into a second-order one with increasing X. The magnetic entropy changes as a function of the temperature in a magnetic field of 1 T for Dy(Co1−XMX)2 has been calculated. The origin of the large magnetic entropy change and the potential application of Dy(Co1−XMX)2 as a working material for magnetic refrigerants have been discussed.

Effect of the slight surface oxidation of ribbons on the dynamic magnetization of nanocrystalline soft magnetic ribbons

The effect of slight surface oxidation of ribbons of the optimal-annealed Nanoperm alloys on the dynamic properties of domain wall motion is studied. It is shown that the surface oxidation of ribbons may strengthen the domain wall pinning, make the number of domain walls unpinned from the initial sites decrease and the effective permeability measured smaller than the real value. Simultaneously, the existence of the surface oxidation layer may reduce the distance between the pinning sites of domain walls, which results in the relaxation frequency moving toward higher frequency. The condition of the ribbon surface is very important to the dynamic behavior of nanocrystalline soft magnetic ribbons.