Fig. 1. (a) Rietveld refinement of XRD profiles for [(La35Ce65)x(Pr20Nd80)1-x]2.14Fe14B powders (x = 0.6, 0.7, 0.8, 0.9, 1.0) at room temperature. The black dots show the observed experimental data and the red full line represents the calculated fits. Blue line shows the difference between the fitted and observed results. Bragg positions of RE2Fe14B, α-Fe and RE-rich phases are indicated by bottom red, blue and black vertical bars. (b) Dependence of lattice parameters c, a, c/a ratio and unit cell volume V of 2:14:1 phase on the La-Ce content x. (c) XRD patterns for quenched samples after annealing for 1 h at 1273 K.

Fig. 2. Back-scattered SEM images and corresponding elemental mappings for [(La35Ce65)x(Pr20Nd80)1-x]2.14Fe14B strips with x = 0.6 (a), x = 0.8 (b), x = 1.0 (c). Red “+” symbols in the matrix phase indicate the selected positions for concentration detection.

Fig. 3. Comparison of the detected La/TRE, Ce/TRE, Pr/TRE and Nd/TRE in the 2:14:1 phase (solid symbols) and the nominal ones (unfilled symbols) for different strips. Here TRE means the total rare earth concentration.

Fig. 4. TEM characterizations for the [(La35Ce65)0.6(Pr20Nd80)0.4]2.14Fe14B strip. (a) BFI taken with the [100]T incidence of the 2:14:1 phase. (b) SAED pattern for region indicated by yellow dashed circle in (a). (c) HRTEM image taken from the red square region in (a). (d)-(i) STEM-EDS mappings of Fe, La, Ce, Pr and Nd.

Fig. 5. TEM characterizations for the[(La35Ce65)0.8(Pr20Nd80)0.2]2.14Fe14B strip. (a) BFI taken with the [100]T incidence. (b) and (c) are SAED patterns taken from the yellow dashed circle region in (a) along two different zone axes. (d) HRTEM image. (e) and (f) are Fast Fourier transformation (FFT) pattern and inversed FFT image of region indicated by red dashed square in (d), exhibiting diffraction spot splitting and local lattice mismatch features due to the spinodal-decomposition-like phase segregation. (g) Schematic illustration of such spot splitting. (h) and (i) FFT and inversed FFT images taken from another typical region indicated by blue dashed square in (d) to further demonstrate the nanoscale phase separation.

Fig. 6. TEM characterizations for the (La35Ce65)2.14Fe14B strip. (a) BFI taken with the [121]T incidence. (b) and (c) SAED patterns for two regions indicated by yellow dashed and blue dashed circles in (a), corresponding to 2:14:1 tetragonal phase and α-Fe phase, respectively. (d) HRTEM image of 2:14:1 tetragonal phase region indicated by yellow dashed circle in (a). (e) and (f) FFT and inversed FFT images of region indicated by red dashed square in (d), where no spot splitting is observed.

Fig. 7. (a) Thermomagnetic curves for the [(La35Ce65)x(Pr20Nd80)1-x]2.14Fe14B (x = 0.6, 0.7, 0.8, 0.9, 1.0) strips upon heating from 300 K to 623 K. (b) Comparison of the measured Curie temperature of the 2:14:1 phase (solid symbols) and the ones estimated from the nominal composition based on the rule of mixture (unfilled symbols) for different strips.