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Sun et al. Microstructures 2023;3:2023028 https://dx.doi.org/10.20517/microstructures.2023.03 Page 3 of 7

RESULTS AND DISCUSSION
Tb Er Co Mn (x = 0, 0.1, 0.2, 0.4, and 0.5, y = 0, 0.1, 0.2, 0.3) were confirmed to be pure phases by XRD at
y
x
2
1-x
room temperature (except y = 0.4). For example, at 300 K, the Rietveld refinement of the SXRD data for
Tb Er Co Mn (denoted as TECM) shows the cubic structure in Supplementary Figure 1. In Tb Er Co 2
0.4
0.6
1-x
x
2
0.1
(x = 0, 0.1, 0.2, 0.4, and 0.5, Figure 1A and B: It is cubic without Er (x = 0, TbCo ) and remains cubic with
2
increasing Er content (x ≤ 0.5). Meanwhile, it was observed that the peak (220) shifted to a higher angle due
to the successful introduction of smaller radii Er atoms. In Tb Er Co Mn (x = 0, 0.1, 0.2, 0.4, and 0.5), the
1-x
x
0.1
2
peak (220) shifted to a high angle with increasing Er content, while the Mn content being fixed at y = 0.1
and still maintaining the cubic phase)[Figure 1C and D]. To investigate the effect of different Er contents on
Tb Er Co and Tb Er Co Mn , the cell parameters of which were obtained by fitting the XRD data
1-x
x
2
1-x
2
x
0.1
[Supplementary Figure 2 and Supplementary Table 1]. I n a d d i t i o n , w e s u c c e s s f u l l y s y n t h e s i z e d

Tb Er Co Mn (y = 0, 0.1, 0.2, 0.3, and 0.4) with increasing Mn content. The samples have a similar cubic
2
y
0.4
0.6
structure below y = 0.4 [Supplementary Figure 3]. The cubic structure of the RECo is shown in Figure 1F.
2
The rhombohedral structure is also presented in Figure 1E as the temperature decreases below T . The SEM
C
images and EDS elemental mappings shown in Figure 1G-K and Supplementary Table 2 illustrate the
uniform distribution of elements Tb, Er, Co, and Mn in TECM (Tb:Er:Co:Mn = 0.58:0.37:2:0.09). The
contents of Co and Mn were close to the nominal compositions, as evidenced by the ICP results shown in
Supplementary Table 3.
As shown in Figure 2, the samples Tb Er Co Mn (x = 0, 0.1, 0.2, 0.4, and 0.5, y = 0 and 0.1) exhibit a
y
2
1-x
x
significantly different linear thermal expansion behavior. The NTE behavior of TbCo occurs in a narrow
2
temperature window. Interestingly, the anomalous thermal expansion of the Tb Er Co
x
2
1-x
(x = 0, 0.1, 0.2, and 0.4) compounds ends at lower temperatures with increasing Er content. A large NTE
coefficient of Tb Er Co (denoted as TEC, α = -15.29 × 10 K , 131-167 K) was obtained [Figure 2A]. To
-6
-1
0.4
2
l
0.6
obtain LTE, the ferromagnetic (FM) exchange interactions can be enhanced by introducing Mn atoms at the
Tb/Er 8a and Co 16d sites . However, the samples Tb Er Co Mn (x = 0, 0.1, 0.2, 0.4, and 0.5)
[28]
0.1
1-x
x
2
[Figure 2B], are different from the above. As Er replaces Tb, the volume shrinkage behavior of
Tb Er Co Mn decreases, and the LTE temperature window of Tb Er Co Mn gradually appears and
0.1
1-x
2
x
0.1
1-x
x
2
-1
expands to x = 0.4. The LTE is obtained with TECM (α = 1.23 × 10 K , 125-236 K) when x = 0.4. For
-6
l
comparison, the coefficient of thermal expansion value of TECM is smaller than that of common metals
-6
-1
-1
-1
such as Fe (α = 12.2(0) × 10 K ), Al (α = 22.9(0) × 10 K ), Cu (α = 16.3(1) × 10 K ), etc. However, the
-6
-6
l
l
l
coefficient of thermal expansion trends from negative to positive with increasing Er content
[Supplementary Figure 4]. TECM has a wide temperature window of the LTE curves, which may offer
promising prospects for both basic research and applications.
The magnetic phase transition of TbCo was documented to be first-order, while that of the TbCo Mn
2
x
2
compound obtained by the addition of Mn was second-order . The addition of Mn significantly increased
[23]
the T of the compounds, for example, from 225 K for TbCo to 347 K for TbCo Mn 0.4 [29] . The macroscopic
2
2
C
FM behavior of Tb Er Co Mn (x = 0, 0.1, 0.2, 0.4, and 0.5, y = 0 and 0.1) was determined by measurements
1-x
y
x
2
of zero-field cooling (ZFC) and field cooling (FC) during heating in a 500 Oe magnetic field
[Figure 3A and B]. It is obvious that the FM transition temperature of the compound TEC is 167 K
[Figure 3C], and that of TECM is 236 K [Figure 3D]. In Tb Er Co and Tb Er Co Mn samples, the
2
1-x
1-x
x
0.1
x
2
magnetic transition temperature shifts to the low temperature with increasing Er content. The above results
can be obtained from the derivative curves of FC/ZFC. The introduction of Mn effectively increases the FM
transition temperature, as shown by the curves of T in Figure 3E, which is essential for obtaining LTE
C
materials with a wide-temperature window. To further verify the FM transition temperature, isothermal
magnetization curves M-H for selected TEC and TECM are shown in Figures 3F and