Y. K. Fang

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...

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 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.

Microstructure and magnetocaloric effect of melt-spun Y2Fe17 ribbons

The phase constitution, microstructure, and magnetocaloric effect (MCE) in low-cost iron-based binary Y2Fe17 ribbons have been investigated by using x-ray diffraction, transmission electron microscopy, and measuring their magnetic properties, respectively. It is found that the crystal structure of the as-spun ribbons is hexagonal Th2Ni17 type with the wheel speed ranging from 10to40m∕s because of the week glass-forming ability. The ribbon prepared at 20m∕s shows a magnetic entropy change of 1.89J∕kgK under magnetic field change of 10kOe. The low-cost, easy-synthesis, and considerable MCE properties make Y2Fe17 alloys in ribbon form as suitable room temperature MCE materials.

Magnetic properties, phase evolution, and microstructure of melt-spun (Sm1−xPrx)Co7−yHfyCz (x=0–1; y=0.1–0.3; z=0–0.14) ribbons

Magnetic properties, phase evolution, and microstructure of melt-spun (Sm1−xPrx)Co7−yHfyCz ribbons have been investigated. For (Sm1−xPrx)Co7−yHfy (x=0–1; y=0.1–0.3) ribbons, the magnetization increases, but coercivity decreases, with increasing Pr content. However, the phase constitution and microstructure have not been influenced by modifying Pr content x. The attractive magnetic properties of Br=6.5kG, Hci=6.1kOe, and (BH)max=7.2MGOe could be obtained for (Sm0.8Pr0.2)Co6.9Hf0.1 ribbons. A slight addition of C in (Sm0.8Pr0.2)Co6.9Hf0.1Cz (z=0.06–0.14) ribbon not only refines the microstructure, but also induces nanoscale fcc-Co precipitation in the matrix, leading to the stronger exchange-coupling effect between magnetic grains and the enhancement of remanence and magnetic energy product. As a result, the improved magnetic properties of Br=7.1kOe, Hci=8.5kOe, and (BH)max=11.2MGOe can be achieved for (Sm0.8Pr0.2)Co6.9Hf0.1C0.12 ribbons.

Structures and magnetocaloric effects of Gd65−xRExFe20Al15 (x = 0–20; RE=Tb, Dy, Ho, and Er) ribbons

Gd-based Gd65−xRExFe20Al15 (xu2009=u20090–20, REu2009=u2009Tb, Dy, Ho, and Er) alloys in ribbon form have been prepared by rapid quenching technology. It is found that the Gd65−xTbxFe20Al15 ribbons are in amorphous state. However, for the Gd65−xRExFe20Al15(REu2009=u2009Dy, Ho, and Er) ribbons, in addition to a diffuse diffraction band, peaks from hexagonal rare-earth-rich phases are present indicating a mixture of amorphous and crystalline phases. This indicates that the heavier rare-earth elements (Dy, Ho, and Er) will decrease glass formability in the Gd-based Gd65−xRExFe20Al15 (REu2009=u2009Dy, Ho, and Er) ribbons. The magnetic entropy changes of these ribbons increase with increasing the contents of the heavier rare-earth elements. The maximal magnetic entropy changes of the Gd45RE20Fe20Al15 (REu2009=u2009Tb, Dy, Ho, and Er) ribbons are located in the range of 4.46–5.57 J/kgu2005K under 50 kOe. Refrigerant capacity values are obtained to be about 580–720 J/kg under 50 kOe. These values are comparable to or even higher than those of Gd-based bul...

The influence of Si addition on the glass forming ability, magnetic and magnetocaloric properties of the Gd-Fe-Al glassy ribbons

The effects of Si substitution for Al on the glass forming ability, Curie temperature T(C), magnetocaloric effect, and refrigeration capacity (RC) of melt-spun Gd-based Gd(65)Fe(20)Al(15-x)Si(x) (x = 0-7) glassy ribbons have been investigated. The small amounts of Si substitution for Al in the Gd(65)Fe(20)Al(15-x)Si(x) glassy ribbons with high T(x)/T(m) (>0.70) and small Delta T(m) (Delta T(m) = T(m)-T(x)) promote the formation of high thermal stability of these alloys. The Si addition leads to an increase of Curie temperature T(C) of glassy ribbons from 181 K for x = 0 to 227 K for x = 7. The maximal magnetic entropy changes -Delta S(M) and RC values for magnetic field change of 50 kOe are about 4.70-5.20 J/kg K and 710-760 J/kg, respectively. The large RC values are due to the broad temperature range of the half maximum of Delta S(M) peak (similar to 200 K), which is caused by the change of the amorphous disorder structure. The moderate Delta S(M) and large RC values jointly make the Gd(65)Fe(20)Al(15-x)Si(x) glassy ribbons promising candidates for magnetic refrigeration materials working at temperature range of 100-300 K

Magnetocaloric effect of the Gd-LRE-Al-(Co, Fe) (LRE=La, Ce, Pr, Nd) glassy ribbons in the intermediate temperature

The magnetic properties and mgnetocaloric effect (MCE) of the Gd65Al15Co20−xFex(x = 0 − 20) and Gd65−yLREyAl15Fe20 (LRE = La, Ce, Pr, Nd; y = 0 − 20) glassy ribbons have been investigated. The Curie temperature (Tc) of the Gd-based Gd65Al15Co20−xFex glassy ribbons can be greatly increased by moderate Fe substitution. Furthermore, it is found that Ce atom among the other light-rare-earth elements is more prefer one for adjusting the Tc of the Gd65−yLREyAl15Fe20 glassy ribbons. The low materials cost, improved MCE properties make Gd65−yCeyAl15Fe20 glassy ribbons attractive candidates for magnetic refrigeration application in the intermediate temperatures of 80–220 K.