C. C. Hsieh

Magnetocaloric effect in Fe–Zr–B–M (M=Mn, Cr, and Co) amorphous systems

The magnetocaloric effect (MCE) of the amorphous Fe–Zr–B–M (M=Mn, Cr, and Co) ribbons has been investigated. The MCEs of the Fe90−xZr10Bx (x=5, 10, 15, and 20) ribbons are enhanced with small amounts of boron addition. Furthermore, the Curie temperature of the specimens can be decreased to be about room temperature with appropriate Mn and Cr substitutions, but the MCE performance of the specimens drops only slightly. It is also found that the magnetic entropy change of the Co-substitution series of Fe85−yZr10B5Coy ribbons almost remains constant although the Curie temperature is increased to be about 400K for y=5. Therefore, for the application of MCE refrigeration at above room temperature, the Fe85−yZr10B5Coy ribbons are preferred due to the constant MCE and the high refrigeration capacity of about 90J∕kg at the magnetic field change of 10kOe. Moreover, the field dependence of the magnetic entropy change exhibits power dependence for all the studied specimens. In the ferromagnetic range, the exponent is...

Alloying effect on the magnetic properties of RFeB-type bulk magnets

Composition dependence on the magnetic properties of directly casted cylindrical RFeBM-type magnets with diameters from 0.7 mm to 1.5 mm has been studied. In order to refine the microstructure for improving the magnetic properties of bulk magnets with various sizes, the following ways were adopted in the alloys: (1) changing the boron concentration, (2) substituting different kinds of refractory elements for Fe, (3) adding a slight carbon and finally, (4) adopting multi-component refractory elements. The experimental results showed that the Nd9.5Fe72.5Ti3B15 bulk magnets with a diameter of 0.7 mm demonstrated the optimal magnetic properties of Br = 6.5 kG, iHc = 10.3 kOe and (BH)max = 8.7 MG Oe, while the highest iHc of 16.2 kOe was achieved for the Pr9.5Fe71.5Nb4B15 magnet. Meanwhile, the diameter of the magnets could be increased to 0.9 mm preserving the attractive magnetic properties by the substitution of 0.5 at% Zr for Ti in the Nd9.5Fe72.5Ti3B15 magnet. Finally, the directly casted Nd9.5Fe72.5−yTi2.5Zr0.5CryB15−xCx (x = 0.25–1; y = 0–3) magnets with a larger diameter of 1.3 mm exhibited attractive magnetic properties of Br = 5.3–6.1 kG, iHc = 7.2–12.5 kOe and (BH)max = 6.5–7.2 MG Oe.

Crystal structure and magnetic properties of melt spun Sm(Co,V)7 ribbons

The crystal structure and magnetic properties of melt spun Sm(Co,V)7 ribbons have been investigated. It was found that SmCo7−xVx ribbons may crystallize in pure TbCu7-type structure for x=0.1–0.3 spun at a high wheel speed of 40 m/s. The structure refinement results show that the doping element V prefers to occupy the 2e site of TbCu7-type structure. Besides, transmission electron microscopy images show that with increasing V content, the grain size was refined from 200–400 nm for x=0.1 to 40–100 nm for x=0.3. As a result, the intrinsic coercivity enhances effectively from 1.9 kOe for SmCo7 ribbon to 11.5 kOe for SmCo6.7V0.3 ribbon. It is also verified that a slight addition of C to SmCo7−xVx could further refine the microstructure, resulting in the improvement of the magnetic properties of SmCo7−xVx ribbons. The optimal magnetic properties of σr=58.7 emu/g, Hic=13.5 kOe, and (BH)max=9.3 MG Oe can be obtained for SmCo6.9V0.1C0.1 ribbon.

Thermal stability and magnetocaloric effect of the Gd65Fe20Al15−xBx (x=0–7) glassy ribbons

The thermal stability, magnetocaloric effect, and refrigeration capacity (RC) of Gd-based Gd(65)Fe(20)Al(15-x)B(x) (x=0-7) glassy ribbons have been investigated. A relatively wide supercooled liquid region Delta T(x)(Delta T(x)=T(x)-T(g)) (50-80 K) and large reduced glass transition temperature T(rg)(T(rg)=T(g)/T(m)) (>0.63) are found in Gd(65)Fe(20)Al(15-x)B(x) glassy ribbons. The distinctive glass transition and sharp crystalline events as well as large values of Delta T(x) and T(rg) confirm the excellent glass forming ability of these alloys. The maximal magnetic entropy changes, -Delta S(M)(max), and RC values of the specimens are about 4.80-5.21 J/kg K and 700-800 J/kg under 50 kOe, respectively. These -Delta S(M)(max) values are comparable to or even higher than that of some reported bulk metallic glasses. Moreover, the larger RC values are due to the broad Delta S(M) peak (similar to 200 K), which is caused by the glassy structure. The large Delta S(M) and RC values make the Gd-based Gd(65)Fe(20)Al(15-x)B(x) glassy ribbons attractive candidates for magnetic refrigeration materials

Magnetic properties, phase evolution, and structure of melt spun SmCo7-xNbx (x=0-0.6) ribbons

The phase evolution, microstructure, and magnetic properties of melt spun SmCo7−xNbx (x=0–0.6) ribbons have been investigated using powder x-ray diffraction, transmission electron microscopy, and vibrating sample magnetometer, respectively. SmCo7−xNbx ribbons could crystallize in TbCu7-type structure only for low Nb substitution of x=0–0.3 at high wheel speed of 30–40 m/s. According to the structure refinement, the doping element Nb prefers to occupy the 2e site. The intrinsic coercivity increases dramatically from 1.9 kOe for SmCo7 ribbon to 10.2 kOe for SmCo6.8Nb0.2 ribbon at wheel speed of 40 m/s. The mechanism of the coercivity enhancement has been discussed. The optimal magnetic properties of σr=54.4 emu/g and Hic=10.2 kOe were obtained in SmCo6.8Nb0.2 ribbon.

Magnetic properties and crystal structure of melt-spun Sm(Co, M)7 (M = Al and Si) ribbons

Effect of Si and Al contents on the magnetic properties and crystal structure of melt-spun SmCo7-xMx (M = Al and Si) ribbons have been investigated. The Rietveld refinement results show that Al and Si prefer to occupy the 3g site in the TbCu7-type structure. The changes in both the magnetocrystalline anisotropy field and the microstructure with Si or Al substitution may account for the variation of magnetic properties. The coercivity of SmCo7−xSix ribbons is enhanced from 1.9 kOe for SmCo7 to 4.7 kOe for SmCo6.5Si0.5 and 2.6 kOe for SmCo6.95Al0.05, which is mainly because of the enhancement of magnetic anisotropy field by the Si and Al substitution for Co in 3g sites. Furthermore, in melt-spun SmCo7−xMx ribbons system, with increasing x, the grain size is slightly reduced for M = Si, but increased for M = Al. In addition, with further increasing x, the enhancement of coercivity is attributed to both the third element substitution for Co in 3g sites and grain refinement.Effect of Si and Al contents on the magnetic properties and crystal structure of melt-spun SmCo7-xMx (M = Al and Si) ribbons have been investigated. The Rietveld refinement results show that Al and Si prefer to occupy the 3g site in the TbCu7-type structure. The changes in both the magnetocrystalline anisotropy field and the microstructure with Si or Al substitution may account for the variation of magnetic properties. The coercivity of SmCo7−xSix ribbons is enhanced from 1.9 kOe for SmCo7 to 4.7 kOe for SmCo6.5Si0.5 and 2.6 kOe for SmCo6.95Al0.05, which is mainly because of the enhancement of magnetic anisotropy field by the Si and Al substitution for Co in 3g sites. Furthermore, in melt-spun SmCo7−xMx ribbons system, with increasing x, the grain size is slightly reduced for M = Si, but increased for M = Al. In addition, with further increasing x, the enhancement of coercivity is attributed to both the third element substitution for Co in 3g sites and grain refinement.

Improvement of size and magnetic properties of Nd9.5Fe72.5Ti3B15 bulk magnets by Zr or Nb substitution for Ti

Magnetic properties and microstructure of directly quenched Nd9.5Fe72.5Ti3−xMxB15 (M=Nb and Zr; x=0–3) bulk magnets in rod form with a diameter of 0.9 mm have been studied. Proper Nb or Zr substitution for Ti has been found to well modify phase constitution and to refine the grain size from 200 to 50–100 nm effectively. Accordingly, the magnetic properties of the rods are enhanced remarkably from Hic=6.2 kOe and (BH)max=5.6 MG Oe for Nd9.5Fe72.5Ti3B15 to Hic=6.7–15.4 kOe and (BH)max=6.0–8.2 MG Oe for Nd9.5Fe72.5Ti3−xMxB15. The optimum magnetic properties of Br=6.6 kG, Hic=9.6 kOe, and (BH)max=8.2 MG Oe can be achieved for Nd9.5Fe72.5Ti2.5Zr0.5B15 alloy, while the highest coercivity of Hic=15.4 kOe [Br=5.9 kG and (BH)max=7.0 MG Oe] is obtained for Nd9.5Fe72.5Nb3B15. Their high permanent magnetic property arises mainly from the existence of a large volume fraction of 2:14:1 phase, finer grain size, and the existence of grain boundary phase.

Effects of C and Cr contents on the magnetic properties and microstructure of directly quenched NdFeTiZrCrBC bulk magnets

Magnetic properties and microstructure of directly quenched Nd9.5Fe72.5−yTi2.5Zr0.5CryB15−xCx (x=0–1; y=0–3) magnets with a diameter of 1.1 mm and a length of 15 mm have been investigated. The thermomagnetic analysis show that the bulk magnets with x≦0.5 and y=0–3 mainly consist of magnetically hard 2:14:1 phase. Besides, a slight substitution of C for B and Cr for Fe in Nd9.5Fe72.5Ti2.5Zr0.5B15 can effectively refine the grain size of the bulk magnet with larger diameter, resulting in the remarkable enhancement of the magnetic properties. The optimal magnetic properties of Br=5.9 kG, Hic=8.2 kOe, and (BH)max=7.2 MGOe could be attained in Nd9.5Fe71.5Ti2.5Zr0.5Cr1B14.5C0.5 magnet.

Magnetic properties and microstructure of directly quenched Nd9.5Fe75.5−xMxB15 (M=Mo, Nb, Ta, Ti, V, and Zr; x=0–4) bulk magnets

Magnetic properties and microstructure of directly quenched Nd9.5Fe75.5−xMxB15 (M=Mo, Nb, Ta, Ti, V, and Zr; x=0–4) bulk magnets in rod form with a diameter of 0.7mm have been studied. The substitution of the selected refractory elements for Fe in the Nd9.5Fe75.5MxB15 alloy can suppress the formation of the soft phases, including Nd2Fe23B3 and one unknown phase, leading to the presence of a large amount of the Nd2Fe14B phase. Besides, the grain size at the core side of the rods is refined from a micrometer scale for a ternary magnet to 50–120nm for the magnets with refractory element substitution. As a result, the magnetic properties are improved remarkably from Br=5.0kG, Hci=1.0kOe, and (BH)max=1.7MGOe for a ternary magnet to Br=5.7–6.5kG, Hci=2.0–14.6kOe, and (BH)max=3.1–8.7MGOe for refractory element substituted magnets. The optimal magnetic properties of Br=6.5kG, Hci=10.3kOe, and (BH)max=8.7MGOe can be achieved in the Nd9.5Fe72.5Ti3B15 magnet, while the highest coercivity of Hci=14.6kOe, with Br=5.9k...

Magnetic property improvement of Pt-lean FePt∕Fe–B-type nanocomposites by Co substitution

Effects of Co content on the magnetic properties and microstructure of melt-spun [(Fe1−xCox)0.675Pt0.325]84B16 (x=0–0.5) and [(Fe1−yCoy)0.725Pt0.275]85B15 (y=0 and 0.3) nanocomposite ribbons have been investigated. The substitution of Co for Fe in [(Fe1−xCox)0.675Pt0.325]84B16 ribbons enhances the coercivity (Hci) from 7.5kOe for x=0to10kOe for x=0.3, due to the formation of ordered L10-(Fe,Co)Pt phase with higher anisotropy field. The effect of Co substitution for Fe in [(Fe1−yCoy)0.725Pt0.275]85B15 series ribbons is similar to that in [(Fe1−xCox)0.675Pt0.325]84B16 system. Interestingly, larger magnetization could be obtained by decreasing the boron and Pt content simultaneously. Moreover, L10-(Fe,Co)Pt phase provides [(Fe0.7Co0.3)0.725Pt0.275]85B15 ribbons sufficient high coercivity Hci=5.4kOe, resulting in a remarkable enhancement of energy product from 10.0MGOe for Co-free ribbons to 15.7MGOe for ribbons with y=0.3.