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Single-phase electron-doped manganite thin films with nominal composition of La0.7Ce0.3MnO3(LCeMO) have been prepared on SrTiO3(100) substrates by pulsed laser deposition. The conditions for obtaining purely single-phase LCeMO films lie within a very narrow window of substrate temperature (Ts∼720°C) and laser energy density (ED∼2J∕cm2) during deposition. In situ postdeposition annealing, mainly to relax the possible epitaxial in-plane tensile strain between the film and the substrate, leads to an increasing c-axis lattice constant accompanied by the formation of secondary CeO2 phase and higher metal-insulator transition temperature. This is indicative of a strong coupling between the electron and lattice degree of freedom.

Soft magnetic properties and high frequency characteristics of Co100-xMx (M = Ti, Zr, and Hf) thin films have been investigated. All M-doped Co100-xMx films exhibit strong induced in-plane uniaxial magnetic anisotropy. With the increase of the x, the 4 pi M-s and coercivity along the hard and easy axes (H-ch and H-ce) are decreased, while H-k reaches the maximum value for the films having the composition to become the fully amorphous. Among them, less Hf or Zr content, i.e., x = 7, are sufficient in forming the Co100-xMx amorphous, in contrast, more Ti content, i.e., x = 15, should be needed. The optimal properties of 4 pi M-s = 11.0 kG, H-ce = 5.4 Oe, H-ch = 4.0 Oe, H-k = 320 Oe and f(FMR) = 5.2 GHz for Co93Hf7 films and 4 pi M-s = 11.7 kG, H-ce = 6.1 Oe, H-ch = 1.6 Oe, H-k = 266 Oe and f(FMR) = 4.9 GHz for Co93Zr7 films can be obtained. (C) 2012 American Institute of Physics. [doi:10.1063/1.3679157]

The effects of B and C substitution for Sn on phase components, Curie temperature T-C, and magnetocaloric effect of melt-spun Mn3Sn2-xMx (M = B, C; x = 0-0.5) ribbons have been investigated. X-ray diffraction (XRD) results show that the main phase in the as-spun Mn3Sn2-xMx (M = B, C; x = 0-0.5) ribbons is Mn3Sn2 of Ni3Sn2-type (Pnma). Minor Mn2B (when x >= 0.1) or Mn5C2 (when x > 0.1) secondary phase is formed, and their amounts increase with increasing B and C concentration, respectively. The Curie temperature T-C of these ribbons varies in the temperature range of 240-250K. The peak values of the maximal magnetic entropy change, -Delta S-M(max), are about 13.6-18.3 mJ/cm(3) K for B-substituted ribbons and 13.6-17.5 mJ/cm(3) K for C-substituted ribbons, respectively, at a maximum applied field of 50 kOe. These values are about one fifth that of Gd (81.4 mJ/cm(3) K). However, the relatively broader temperature range of the half maximum of Delta S-M peak (similar to 100K), low-cost and nontoxic elements still make Mn3Sn2-based ribbons the promising candidates for magnetic refrigeration applications close to room temperature. (C) 2012 American Institute of Physics. [doi:10.1063/1.3671789]

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.

The effect of Ge on the magnetic properties and crystal structure of melt spun SmCo7–xGex (x = 0–0.8) ribbons have been investigated. SmCo7–xGex ribbons (x = 0–0.6) spun at a high wheel speed of 40 m/s crystallize in the TbCu7-type structure. The x-ray diffraction results analyzed by the Rietveld refinement method show that Ge prefers to occupy the 2e sites in the TbCu7-type structure. The grain size of the ribbons is only slightly decreased with the proper amount of Ge substitution (x

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. (C) 2011 American Institute of Physics. [doi:10.1063/1.3540666]

Gd-based Gd65−xRExFe20Al15 (x = 0–20, RE = Tb, 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(RE = Dy, 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 (RE = Dy, 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 (RE = Tb, Dy, Ho, and Er) ribbons are located in the range of 4.46–5.57 J/kg K 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...

Ab initio density functional calculations, transmission electron microscope, and x-ray diffraction (XRD) were used to study the dominant factor of increased coercivity for the doping effect in SmCo7−xZrx (x = 0 to 0.3). Simulated values of saturated magnetization are 940 emu/cm3 for SmCo7 and 799 emu/cm3 for SmCo6.7Zr0.3, which agree with experimental results within 6%. The calculated anisotropy constant (for 2e) increases from 1.151 × 107 erg/cm3 for SmCo7 to 1.934 × 107 erg/cm3 for SmCo6.7Zr0.3. The grain sizes remain almost the same by adding ∼4% (atomic percent) Zr through the analyses of XRD. The increased anisotropy is the dominated factor for enhancing the coercivity in SmCo6.7Zr0.3. In addition, both results of Rietveld refinements of XRD data and ab initio calculations show that Zr situating at 2e/3g positions are more stable than 2e/2e locations, which were suggested conventionally.

The effect of Ta addition on the structure and magnetic properties of melt-spun SmCo7−xTax (x=0–0.6) ribbons has been investigated. The intrinsic coercivity increases dramatically from 1.9 kOe for Ta-free ribbon to 9.8 kOe for SmCo6.7Ta0.3 ribbon, while further increasing Ta results in little enhancement of the coercivity. XRD patterns reveal that SmCo7−xTax ribbons crystallize in the pure TbCu7-type structure for low Ta substitution of x≤0.3 and a minor phase of TaCo3 appears when x>0.3. According to Rietveld structure refinement, the ternary alloying element Ta prefers to occupy the 2e site of TbCu7-type structure. The mechanism of the coercivity enhancement has been discussed based on crystal structure and microstructure.

Magnetic properties, phase evolution, and microstructure of melt spun Sm(Co0.97M0.03)xCy (M=Hf and Zr; x=5–9; y=0–0.15) ribbons quenched at the wheel speed of 40 m/s have been investigated. X-ray diffraction analysis show that the main phases exist in Sm(Co0.97M0.03)x ribbons are 1:5 for x=5 and 5.5, 1:5 and 1:7 for x=6 and 6.5, 1:7 for x=7 and 7.5, 1:7 and 2:17 for x=8, and 2:17 for x=8.5 and 9. The grain size of 200–500 nm for these two series of ribbons is almost unchanged when x is increased from 5 to 9. Accordingly, the magnetic properties of Sm(Co0.97M0.03)x ribbons (M=Hf and Zr) are mainly dominated by their phase constitutions. Furthermore, a slight addition of C to Sm(Co0.97M0.03)x ribbons refines the grain size down to 10–50 nm, resulting in the improvement of magnetic properties. Sm(Co0.97Hf0.03)7.5C0.1 ribbons show the optimal magnetic properties of Br=6.9 kG, Hic=9.2 kOe, and (BH)max=10.0 MGOe. For the Sm-lean Sm(Co,Hf)xCy (x=8.5–9) ribbons, higher Hf and C content are required to improve the...

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.

The crystal structure and magnetic properties of melt spun SmCo7−xMx (M=Ta, Cr, and Mo; x=0–0.6) ribbons have been investigated. Based on x-ray diffraction analysis, it is found that a pure TbCu7-type structure is formed in the melt spun SmCo7−xTax (x=0–0.3) ribbons, while minor amount of additional 2:17 phase appears for the SmCo7−xMx (M=Cr and Mo; x=0.1–0.6) ribbons, implying that the elements in VIB group (Cr and Mo) are inferior to the element in VB group (Ta) in stabilizing metastable 1:7 phase. The result, analyzed by Rietveld refinement method, shows that Ta, Cr, and Mo may occupy the 2e site of 1:7 phase, which leads to the enhancement of the magnetic anisotropy field of 1:7 phase, just like Ti, Zr, Hf, Nb, or V did. From the magnetic performance point of view, with increasing the content of doping element x from 0 to 0.6, the maximum coercivity of SmCo7−xMx ribbons is enhanced from 1.9 kOe for binary SmCo7 to 11.3 kOe for M=Ta, 6.6 kOe for M=Cr, and 7.5 kOe for M=Mo, respectively, while the reman...

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.

Effect of B content on the magnetic properties, phase evolution, magnetic after effect, and the activation energy (Ea) for the melt-spun [(Fe0.7Co0.3)0.725Pt0.275]100−xBx (x=14–18) ribbons has been investigated. Sufficient amount of boron addition effectively decreases the activation energy of ordering transformation, and also refines the grain size of the studied ribbons after thermal annealing, resulting in the improvement of Hic from 3.4 kOe for x=14 to 6.2 kOe for x=18. The highest permanent magnetic properties of Br=10.1 kG, Hic=5.4 kOe, and (BH)max=15.7 MGOe can be achieved in [(Fe0.7Co0.3)0.725Pt0.275]85B15 ribbons. Meanwhile, the magnetic after effect study evidences that the activation volume is reduced with the increase in B content from V=41.33×10−19 cm3 for x=14 to V=21.71×10−19 cm3 for x=18, arisen from the lower volume fraction of magnetically soft phases and the stronger exchange-coupling effect between magnetic grains.

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.

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...

Magnetic properties, phase constitution, and microstructure of melt spun R-lean and B-enriched Mischmetal (MM)–Fe–Co–Ti–B nanocomposites have been investigated. The thermal magnetic analysis show that only 2:14:1 and α-Fe [α-(Fe,Co)] phases appear for MM(A)9.5Fe78.5Ti2B10 and MM(A)9Fe79.5Co2.5Ti1B8 ribbons, while an additional Fe3B phase is present for R9.25Fe79.25Co2.5Ti1B8 [R=MM(A), MM(B), and MM(C)] ribbons. The magnetic properties of the above nanocomposites are determined not only by the phase constitution of MM–Fe–Co–Ti–B nanocomposites but also by the composition of MMs. Besides, fine grain size of 15–40 nm is almost unchanged for the ribbons with various MMs, giving rise to the strong exchange coupling effect between magnetic grains and the improved magnetic performance. In this study, the optimum magnetic properties of Br=9.6 kG, Hic=8.6 kOe, and (BH)max=18.2 MG Oe can be achieved for MM(B)9.25Fe79.25Co2.5Ti1B8 nanocomposites.

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.

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 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.

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.