Thermal stability of high-temperature compound La2Fe14B and magnetic properties of Nd-La-Fe-B alloys

Journal Pre-proof Thermal stability of high-temperature compound La2Fe14B and magnetic properties of Nd-La-Fe-B alloys Xiaoming Li, Zhao Lu, Qingrong Yao, Qi Wei, Jiang Wang, Yusong Du, Lin Li, Qianxin Long, Huaiying Zhou, Guanghui Rao PII:

S0925-8388(20)34144-X

DOI:

https://doi.org/10.1016/j.jallcom.2020.157780

Reference:

JALCOM 157780

To appear in:

Journal of Alloys and Compounds

Received Date: 11 August 2020 Revised Date:

21 October 2020

Accepted Date: 28 October 2020

Please cite this article as: X. Li, Z. Lu, Q. Yao, Q. Wei, J. Wang, Y. Du, L. Li, Q. Long, H. Zhou, G. Rao, Thermal stability of high-temperature compound La2Fe14B and magnetic properties of Nd-La-Fe-B alloys, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2020.157780. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier B.V.

Highlights Single-phase La2Fe14B ternary compound was successfully prepared. The La2Fe14B (space group P42/mnm) crystallizes in a tetragonal unit cell with the lattice parameters a= 0.8835(5) nm and c=1.2375(8) nm. The magnetic properties of (Nd2-xLax)Fe14B alloys decreases with increasing La substitution. Excessive addition of La (x≥0.9)could inhibit the formation of RE2Fe14B main

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phase and increase the fraction of α-Fe and other impurity phases.

Thermal stability of high-temperature compound La2Fe14B and magnetic properties of Nd-La-Fe-B alloys Xiaoming Li, Zhao Lu*, Qingrong Yao*, Qi Wei, Jiang Wang, Yusong Du, Lin Li, Qianxin Long, Huaiying Zhou, Guanghui Rao School of Materials Science and Engineering & Guangxi Key Laboratory of Information Materials, Guilin university of Electronic Technology, Guilin, 541004，

[email protected]

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address:

(Z.

Lu);

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*Corresponding author. E-mail [email protected] (Q. Yao)

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P.R. China.

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Abstract

The thermal stability and refined crystal structure of ternary La2Fe14B compound were

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investigated by integrating X-ray powder diffraction, electron probe microanalyzer

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and differential scanning calorimetry techniques. It was found that La2Fe14B is a

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high-temperature stable ternary compound, which decomposes with an eutectoid reaction: La2Fe14B→La+Fe+LaFe4B4 at 794 °C and melts via a peritectic reaction: Fe+Fe2B+Liquid→La2Fe14B at 926 °C. By investigating the effects of La substitution on the magnetic properties of Nd2-xLaxFe14B alloys, it was revealed that the Nd1.3La0.7Fe14B alloy still keeps excellent maximum energy product (113 kJ/m3), intrinsic coercivity (523 kA/m) and high remanent magnetic polarization (0.83 T). Moreover, the magnetic improvement mechanisms of Nd2-xLaxFe14B alloys were also discussed in detail. The present work is beneficial to design high-performance 2:14:1-type magnets with low-cost and abundant La addition. 1

Keywords: Thermal stability; Phase transformation; Rare earth alloys and compounds; Crystal structure; Magnetic properties 1. Introduction The substitution of Nd with price-favorable and high-abundant La/Ce/Y elements to develop the so called binary main phase (BMP) sintered magnets [1, 2], i.e., mixing the RE2Fe14B-type La/Ce/Y-rich powders, has attracted much attention in the

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permanent magnetic society. Among those low cost rare earths elements, it is well

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known that Ce and Y can be formed a stable Nd2Fe14B-type tetragonal structure [3, 4].

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However, there is large controversy on the thermal stability of the La2Fe14B

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phase in literature reports [3, 5]. According to Sagawa et al. [4], the La2Fe14B phase does not exist in both as-cast state and temperature around 1100 °C. Hadjipanayis et al.

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[5] reported that this compound occurs in as-cast La16Fe76B8 alloys and the alloy

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annealed at 800°C, but it is unstable and transformed to α-Fe plus La-B intermettallics

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at temperature higher 900 °C. Zhang et al. [6] reported that La2Fe14B phase is not present in the melt spun ribbons even though the as-spun ribbon was annealed at 800 °C. Thus the temperature range for thermal stability and the types of reaction of La2Fe14B are still ambiguous. Moreover, the refined crystal structure of the compound has not been established up to now. That is because it is difficult to prepare a single stoichiometric phase. In order to better understanding of metallurgical behavior of the BMP sintered magnets, such as elemental segregation, phase formation of the rare earth elements, optimization of the fabrication processes, the thermal stabilities and detailed crystal structures of the main phases in the BMP magnets are indispensable. 2

Theoretically, La-Fe-B type magnets or La-added Nd-Fe-B magnets have potential to achieve good properties since La2Fe14B phase exhibits intrinsic magnetic properties with the saturation magnetic polarization Js= 1.38 T, the magnetocrystalline anisotropy field HA = 2.0 T, and the Curie temperature Tc = 516 K. Liao [7] found that the magnetic properties was well improved by over 30% Nd substitution in La-based permanent magnets, due to partially substituting La by Nd can effectively enhance the

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formation of the hard magnetic (2:14:1) phase. Chang [8] found that La can

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effectively reduce the grain size of the Nd2Fe14B-based melt spun ribbons.

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Unfortunately, although much work have been done on La-Nd-Fe-B, the phase

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precipitation process of La2Fe14B is still not clear, due to the hard magnetic La2Fe14B phase is difficult to obtain. Hence, to make full use of La-rich RE-Fe-B magnets, it is

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necessary to investigate the effect of La on magnetic properties of Nd-La-Fe-B alloys .

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Consequently, the main objects of present work are: 1) determine the thermal

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stability and refined crystal structure of the La2Fe14B ternary compound; 2) investigate the effects of increasing La substitution on the phase evolution and magnetic properties of Nd-La-Fe-B magnets. This study will be valuable to explore metallurgical behavior of La-rich Nd-La-Fe-B magnets and optimization of the fabrication processes. 2. Experimental procedure High-purity elements, i.e., La (purity: 99.99 wt.%), Fe (purity:99.99 wt.%) and B (purity: 99.99 wt.%) purchased from Alfa Aesar (China) Chemicals Co., Ltd., were used as starting components. The samples of (Nd2-xLax)Fe14B (x= 0.7, 0.9, 1.0, 1.1, 3

1.3, 2.0) were melted by an electric arc furnace under high pure argon gas atmosphere, each ingot was re-melted five times to make the ingots homogeneous. All the ingots was divided into two parts. The melt-spun ribbons of (Nd2-xLax)Fe14B were prepared by induction melting the drop-cast ingots in a quartz crucible under 253 Torr of high purity argon atmosphere, and then ejected at 125 torr overpressure onto a copper wheel rotating at a tangential speed of 25 m/s. The smaples of Nd1.0La1.0Fe14B and

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La2Fe14B were enclosed in Al2O3 crucible, sealed in the evaluated quartz tubes and

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filled with 0.8 atm pure argon. Subsequently, the ingots were annealed in the

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annealing furnaces at different temperature for 40 days. Finally, all the samples were

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quenched into liquid nitrogen to retain their high-temperature phases. Magnetic hysteresis (M-H) loops of the ribbons were obtained from a vibrating

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sample magnetometer (VSM, 7400-S, Lake Shore Cryotronics) with a magnetic field

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cycling between −20 and +20 kÖe at 300 K. All the annealed samples were polished

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with automatic polishing equipment using an oxide polishing suspension (OP-S) at a rotation speed of 250 rpm for 1 min. After that, the polished samples were examined and analyzed by back-scattered electron (BSE) mode equipped with an EPMA (JXA-8530, JEOL). To determine the phase transformation temperatures, DSC (SDT-Q600, TA) measurement was performed on the La2Fe14B alloys annealed at 600 °C between room temperature to 1200 °C with the heating rate of 10 K/min under argon atmosphere. A Pt-Pt/Rh thermocouple was used, and the accuracy for temperature measurement was estimated to be ± 1.0 °C. The sample annealed at 850 °C was ground into powders less than 38 μm. The 4

high-quality XRD data of sample was collected on a Bruker D8 Advance (D8AA25X) powder diffractometer using Cu Kα radiation (λ= 1.5406 Å). The diffractometer was operated at 40 kV and 40 mA, the 2θ scan ranges from 15 to 80° with a step size of 0.02 degrees and a counting time of 5 s per step. 3. Results and discussion

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3.1. Thermal stability of La2Fe14B

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Fig. 1(a) ~ 1(d) shows BSE images of the La2Fe14B alloy annealed at 600, 850,

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1000 and 1200 °C for 40 days, respectively. The phase formation of the annealed

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alloys could be clearly observed. As shown in Fig. 1(a), the microstructure was

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dominated by equiaxial Fe phase (with composition La0.10Fe99.67B0.23). Besides the

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dominating dark-black Fe phase, there are two phases with distinct contrast. The

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composition of irregular gray phase was determined by EPMA to be

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La11.15Fe43.27B45.23 while the bright phase to be La99.60Fe0.25B0.15, which correspond to the stoichiometry phases LaFe4B4 and La, respectively. In Fig. 1(b), a single phase with composition of La11.98Fe82.27B5.75 (La2Fe14B) was successfully obtained. However, when the alloy was annealed at 1000 °C, the La2Fe14B phase totally disappears, as shown in Fig. 1c. Besides Fe and Fe2B (La0.64Fe65.14B34.22) phases in Fig. 1(c), it was found that many La-rich regions (La85.70Fe1.06B13.24) with eutectic structure occurred at the grain boundaries of Fe and Fe2B phases, suggesting that those La-rich regions are not an equilibrium structure, but rather are a solidified structure from the liquid phase. Thus, the alloy annealed at 1000 °C should be equilibrium at the Fe+Fe2B+Liquid three-phase field. There are three distinct contrasts in Fig. 1(d). The dark grains are Fe 5

phase. The gray and bright regions refer to un-equilibrium eutectic structure Fe+Fe2B and La-rich phase. These two regions were solidified from the liquid phase after quenching the annealed alloy into the liquid nitrogen. Thus, the alloy annealed at 1200 °C should be equilibrium at the Fe+Liquid two-phase field. These observations indicated that the La2Fe14B phase is a high-temperature stable compound.

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The heating and cooling curves of La2Fe14B alloy (annealed at 600 °C) measured

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by DSC are shown in Fig. 2 to accurately determine the forming and decomposing

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temperature of the La2Fe14B phase. Three distinct endothermic peaks are observed at

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794, 926 and 1115 °C on the heating curve, and three corresponding exothermal peaks

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can be also detected at 786, 880, 1098 °C on the cooling curve. Lower temperature of

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the exothermal peak compared to that of the corresponding endothermic peak could be attributed to undercooling required for solidification reaction. Therefore, we did

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not take exothermal signals on the cooling curve as equilibrium reaction due to

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occurrence of undercooling. It is noted that the first and second endothermic peaks in Fig. 2 are very small, suggesting that they referred to a solid state reaction. Based on the present BSE images and EPMA results, one could confirm that the signal at 794 °C reflects a eutectoid decomposition of La2Fe14B phase, while the signal at 926 °C corresponds to the melting of La2Fe14B via a peritectic reaction. This suggests that the La2Fe14B compound only stable at very narrow temperature range (794~926 °C). According to Fe-B binary phase diagram, there is a eutectic reaction Liquid→Fe+Fe2B at 1171 °C [9]. This invariant eutectic reaction becomes monovariant transition in the La-Fe-B ternary system, and thus reaction temperature 6

decreases to 1115 °C, which is in good agreement with BSE observation and EPMA results. Therefore, the exact reaction sequence of the La2Fe14B alloy during equilibrium solidification process should be: Liquid→Fe (at temperature higher 1200 °C); Liquid→Fe+Fe2B (at 1115 °C), Fe+Fe2B+Liquid→La2Fe14B (at 926 °C) and La2Fe14B→LaFe4B4+Fe+La (occurs at 794 °C). It is important to mention that about 46 °C undercooling is needed to form La2Fe14B phase, while decomposition of

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this phase only requires 8 °C undercooling, indicating that the La2Fe14B compound is

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difficult to crystallize but easy to decompose. This discovery is of importance for

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design of MMP sintered magnets with La addition.

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3.2. Refined crystal structure of La2Fe14B compound

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Through BSE observation, EPMA and phase analysis of XRD pattern of the sample annealed at 850 °C, we found that the sample was single phase. So the XRD

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pattern can be used for structure refinement analysis. The X-ray diffraction data and

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indices of La2Fe14B summarized in Supplementary materials Table S1 indicate that all the reflections of the La2Fe14B phase were well indexed using Jade 6.0 program [10] in a tetragonal structure with lattice parameters a= 0.8825 nm, c= 1.2355 nm. The structure refinement was performed on the Topas V5.0 program [11] using Rietveld method [12]. The Pseudo-Voigt function was used to simulate the peak shapes and background was estimated by the Chebyshev Polynomial. Because the X-ray powder diffraction patterns of La2Fe14B are similar with that of Nd2Fe14B (space group P42/mnm, No. 136) [13, 14], the starting atomic positions of the unit cell were taken from the data by J. H. Herbst et al. [14]. The indexing results were adopted as the 7

starting lattice parameters. The refined crystal-structure parameters of the La2Fe14B compound are shown in the Table 1. The refined results show that the La2Fe14B compound has lattice parameters a= 0.8835(5) nm, c= 1.2375(8) nm, which are larger than that of Nd2Fe14B compound (a= 0.8803(1) nm, c= 1.2196(1) nm) [14] due to a little bit larger atomic radius of La (2.74 Å) compared to that of Nd (2.64 Å). The observed and calculated values as well as residuals of the powder diffraction patterns

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3.3 Solubility of La in Nd for (Nd2-xLax)Fe14B

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of the alloy are shown in Fig. 3.

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Based on the thermal stability of the La2Fe14B compound, it is interesting to get

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insight into the inter solubility of the La2Fe14B and Nd2Fe14B compounds at high

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temperature. Fig. 4 shows the BSE image, EPMA linear scanning and elemental

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mapping of the Nd1.0La1.0Fe14B alloy annealed at 850°C for 30 days. Fig. 4(b) show the

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line scan along the red solid line in Fig. 4(a). As can be seen in Fig. 4(b), the content of Nd decreases with the increase of La content, and vice versa. However, the content of Fe almost does not change across the scanning line. The EDS mapping (Fig. 4(c) ~ (e)) of the red square area marked in Fig. 4(a) show the concentration distribution of the La, Nd and Fe elements. It can be seen that the distribution of Fe is homogeneous, while the Nd- and La-rich grains (2:14:1 phase) are clearly observed, the grain boundaries of the Nd- and La-rich grains are not clear and a composition gradient is observed, which indicate that the La2Fe14B and Nd2Fe14B main phases possess limited inter solid solubility. This observation shows that it is possible to develop high performance of the binary-main-phases Nd1.0La1.0Fe14B sintered magnets with 8

appropriate heat treatment (794 °C to 926 °C) processes. 3.4. Magnetic properties of quenching Nd2-xLaxFe14B alloys Fig. 5(a) shows the demagnetization curves of the melt-spun Nd2-xLaxFe14B (x= 0.7, 0.9, 1.0, 1.1, 1.3, 2.0) alloys. For x= 2.0 (La2Fe14B), the alloy shows soft magnetism. However, the alloy exhibits relatively good loop squareness when x = 0.7.

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The values of intrinsic coercivity (Hcj) and remanent magnetic polarization (Jr)

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decrease with increase of the La content. Fig. 5(b) shows dependence of Hcj, Jr and

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(BH)max on La content for the melt-spun Nd2-xLaxFe14B (x= 0.7, 0.9, 1, 1.1, 1.3, 2.0)

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alloys. It can be found that the increase of La substitution decreases the magnetic

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properties (Hcj, Jr and (BH)max) of the alloys. The highest (BH)max (113 kJ/m3) was

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obtained in Nd1.3La0.7Fe14B alloy, and the Jr and Hcj of the alloy reach 0.83 T and 523

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kA/m, respectively. Obviously, the alloy is still applicable to specific magnetic device,

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but possesses favorable price.

To reveal the reasons for the reduction of Hcj and Jr, the phase constitutions of the Nd2-xLaxFe14B alloys were investigated. Fig. 6(a) shows the XRD patterns for the as-spun Nd2-xLaxFe14B (x= 0.7, 1.0, 1.3) alloys. Besides Nd2-xLaxFe14B main phase, the diffraction peaks corresponding to α-Fe were detected at the x= 1.0 and 1.3 alloys. When La substitution increases to x = 1.3, the diffraction peaks for Nd2-xLaxFe14B phase became weaker, while diffraction peaks for the α-Fe phase became stronger compared to the alloys with smaller La addition. Moreover, the α-La and β-La phases were detected. Moreover, the grain sizes of melt-spun ribbons with different La content were calculated by XRD patterns and Scherrer equation. The calculated result 9

shows that the grain size of the melt-spun ribbons was about 20 nm, which is not significantly affected by La content. The enlarged XRD patterns in Fig. 6(b) show that the increase of the La content not only weakens the intensity of main diffraction peak (410) of Nd2Fe14B phase, but also shifts the diffraction peaks toward the lower angle. These observations could be attributed to: 1) a small amount of La can be dissolved in the main Nd2Fe14B phase, which makes the Nd1.3La0.7Fe14B alloy still keep good

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magnetic properties; 2) too much amount of La addition results in the appearance of

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α-Fe and other impurity phases because the solid solubility between La2Fe14B and

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Nd2Fe14B is limited; 3) the La2Fe14B phase is difficult to crystallize but easy to

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decompose, which decrease the fraction of the 2:14:1 main phases in the alloy and deteriorate the magnetic performance of the alloy. This suggests that low cost

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Nd2-xLaxFe14B magnets with high performance may be obtained by combining

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appropriate heat treatment.

4. Conclusion

Single-phase La2Fe14B ternary compound was successfully prepared. It was found to melt at 926 °C via a peritectic reaction: Fe+Fe2B+Liquid→La2Fe14B. This ternary compound is not stable at low temperature and decomposes into La, Fe and LaFe4B4 at 794 °C via a eutectoid reaction: La2Fe14B→La+Fe+LaFe4B4, The crystal structure of La2Fe14B was refined by the Rietveld method. It crystallizes in a tetragonal unit cell, space group P42/mnm (No. 136) with the

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structure type of Nd2Fe14B. The lattice parameters of La2Fe14B are a= 0.8835(5) nm and c= 1.2375(8) nm. The Nd1.3La0.7Fe14B alloy showed magnetic parameters of (BH)max= 113 kJ/m3, Jr= 0.83 T and Hcj= 523 kA/m, suggesting that partially substitute Nd with La, the alloy still remains a good magnetic properties. Excessive addition of La (x≥0.9) could inhibit the formation of RE2Fe14B main

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phase and increase the fraction of α-Fe phase, which is attributed to easy

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decomposition of the La2Fe14B main phase at low temperature.

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Acknowledgements

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This work was supported by the National Key R&D Program of China (Grant

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No.2016YFB0700901), Natural Science Foundation of China (Grant Nos.52061007, 51761008,

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51761007), Guangxi Natural Science Foundation (Grant Nos. 2019GXNSFAA245003,

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2018GXNSFAA294069), the Guangxi Project of Science and Technology (Grant No. AD19110078),

Guangxi

Key

Laboratory

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Infor-mation

Materials

(191012-Z),

Science and Technology Program of Fujian Province (Grant No. 2018Ⅰ1010). The authors thank the support from the foundation for Guangxi Bagui scholars.

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References [1] J.Y. Jin, Z. Wang, G.H. Bai, B.X. Peng, Y.S. Liu, M. Yan, Coercivity enhancement for Nd-La-Ce-Fe-B sintered magnets by tailoring La and Ce distributions, J. Alloys Compd. 749 (2018) 580-585. [2] J.Y. Jin, M. Yan, Y.S. Liu, B.X. Peng, G.H. Bai, Attaining high magnetic performance in as-sintered multi-main-phase Nd-La-Ce-Fe-B magnets: Toward skipping the post-sinter annealing treatment, Acta Mater. 69 (2019) 248-259. [3] S. Sinnema, R.J. Radwanski, J.J.M. Franse, Magnetic properties of ternary rare-earth compounds of the type R2Fe14B, J. Magn. Magn. Mater. 44 (1984) 333-341. [4] M. Sagawa, S. Fujimura, H. Yamamoto, Y. Mastsuura, Permanent magnet materials based on the rare earth-iron-boron teragonal compounds (invited), IEEE Tran. Magn. Mag. 20 (1984) 1584-1589.

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[5] G.C. Hadjipanayis, Y.F. Tao, K. Gudimetta, Formation of Fe14La2B phase in as-cast and melt-spun samples, Appl. Phys. Lett 1985 (1985) 757-758.

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[6] Z.Y. Zhang, L.Z. Zhao, J.S. Zhang, X.C. Zhong, W.Q. Qiu, D.L. Jiao, Z.W. Liu, Phase precipitation behavior of rapidly quenched ternary La-Fe-B alloy and the efects of Nd substitution, J. MATER. Res.

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Express 4 (2017)

[7] X.F. Liao, L.Z. Zhao, J.S. Zhang, D.L. Jiao, Z.W. Liu, Enhanced formation of 2:14:1 phase in

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La-based rare earth-iron-boron permanent magnetic alloys by Nd substitution, J. Magn. Magn. Mater. 464 (2018) 31-35.

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[8] W.C. Chang, S.H. Wu, B.M. Ma, C.O. Bounds, The effects of La-substitution on the microstructure and magnetic properties of nanocomposite NdFeB melt spun ribbons, J. Magn. Magn. Mater. 167 (1997)

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65-70.

[9] M.-A.V. Ende, I.-H. Jung, Critical thermodynamic evaluation and optimization of the Fe-B, Fe-Nd,

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B-Nd and Nd-Fe-B systems, J. Alloys Compd. 548 (2013) 133-154. [10] J. 0, XRD Pattern Processing, Materials Data Inc. (1999)

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[11] T. V5.0, Diffraction Suite Bruker AXS Gmbh., (2014) [12] H.M. Rietveld, A profile refinement method for nuclear and magnetic structures, J. Appl. Cryst. 2 (1969) 65-71.

[13] C.B. Shoemaker, D.P. Shoemaker, The structure of a new magnetic phase related to the sigma phase: iron neodymium boride Nd2Fe14B, Acta. Cryst. C40 (1984) 1665-1668. [14] J.F. Herbst, J.J. Croat, W.B. Yelon, Structural and magnetic properties of Nd2Fe14B, J. Appl. Phys. 57 (1985) 4086-4090. [15] H.H. Stadelmaier, N.C. Liu, N.A. Elmasry, Conditions of formation and magnetic properties of tetragonal Fe14La2B, Mater. Lett. 3 (1985) 130-132.

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Table 1. Rietveld refinement data of the La2Fe14B (i.e., La11.76Fe82.35B5.89, in at.%) alloy annealed at 850 ºC Formula

La2Fe14B

Space group

P42/mnm (No.136)

Lattices parameters/nm

a= 0.8835(5),

3

Volume of unit cell/nm

Site

x

y

z

Occ.

Beq (Å 2)

La1

4f

0.2637(5)

0.2637(5)

0.0

1

2.1

La2

4g

0.1542(9)

-0.1233(2)

0.0

1

2.1

Fe1

4c

0.0

0.5

0.0

1

0.6

Fe2

4e

0.5

0.5

0.1102(4)

1

0.6

Fe3

8j2

0.0952(2)

0.0952(2)

0.2078(5)

1

0.6

Fe4

8j1

0.3255(7)

0.3255(7)

0.2071(3)

1

0.6

Fe5

16k1

0.0342(6)

0.3552(4)

0.1686(8)

1

0.6

Fe6

16k2

0.2307(0)

0.5676(9)

0.1384(3)

1

0.6

B

4g

0.4980(4)

-0.4995(6)

0.0

1

1.3

Rwp=2.04

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Atoms

Rp=1.33

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Figures captions

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Residual values

0.9661(2)

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Atomic parameters

c= 1.2375(8)

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Figure 1. BSE images of the La2Fe14B alloy annealed at different temperatures for 40

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days : (a) 600 °C; (b) 850 °C; (c) 1000 °C and (d) 1200 °C. Figure 2. Heating and cooling DSC curves of the La2Fe14B alloy annealed at 600 °C for 40 days. Figure 3. Observed (black one) and calculated (red one) XRD patterns as well as their residuals of the La2Fe14B alloy annealed at 850 °C for 40 days. The pattern factor Rp and

weighted

pattern

factor

Rwp

were

inserted

in

the

figure,

Rp = ∑{  yi ( obs )  −  yi ( cal )  }/ ∑ [ yi (obs)] , Rwp = ∑{wi [ yi (obs)] − yi (cal))2 }/ ∑wi yi (obs)2 }1 2 ,

where yi(obs) is observe intensity, yi(cal) is calculate intensity and wi is weight factor. Figure 4. EPMA analysis Images of the NdLaFe14B alloy: (a) BSE image; (b) the line 13

scan along the red solid line in Fig. 4(a); (c) , (d) and (e) are element mapping for La, Nd, and Fe of region marked by the red square in Fig. 4(a), respectively. Figure 5. The demagnetization curves (a) and magnetic properties (b) for the melt-spun Nd2-xLaxFe14B (x= 0.7, 0.9, 1.0, 1.1, 1.3, 2.0) alloys. Figure 6. (a) XRD patterns for the (Nd2-xLax)Fe14B (x=0.7, 1, 1.3) alloys; (b) The

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enlarged view for 2θ between 41.5° ~ 42.5°.

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Supplementary materials

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Table S1. The X-ray powder diffraction data and indices of La2Fe14B compound

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Credit Author Statement Xiaoming Li, Qi Weiand Qingrong Yao are responsible for the study, full-text writing and EPMA measurements and analysis. Zhao Lu and Jiang Wang are responsibl the literature search and revised the manuscript. Lin Li and Yusong Du are responsibl the VSM measurements and analysis. Qianxin Long are responsibl the DSC measurements and analysis.Huaiying Zhou and Guanghui Rao

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are responsible for the review of the full text.

Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: