Composition effect in ferromagnetic properties of Tb3Co3Ga

Results in Physics 15 (2019) 102591

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Composition effect in ferromagnetic properties of Tb3Co3Ga a,⁎

a

b

c

T a

Jiro Kitagawa , Hirotaka Terada , Naoki Shirakawa , Masami Tsubota , Akira Nose , Seiya Tanakaa a b c

Department of Electrical Engineering, Faculty of Engineering, Fukuoka Institute of Technology, 3-30-1 Wajiro-higashi, Higashi-ku, Fukuoka 811-0295, Japan Flexible Electronics Research Center, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8565, Japan Physonit Inc., 6-10 Minami-Horikawa, Kaita Aki, Hiroshima 736-0044, Japan

A R T I C LE I N FO

A B S T R A C T

Keywords: Rare earth alloys and compounds Crystal structure Magnetization X-ray diffraction

The magnetic properties of Tb3Co3Ga, crystallizing into the orthorhombic W3CoB3-type structure, have been investigated by focusing on a composition effect. Tb3Co3Ga has been characterized as a ferromagnet by measuring the dc and ac magnetic susceptibilities and the magnetization curve. We have found that the Curie temperature determined by the ac susceptibility is highly sensitive to the atomic composition, and ranges from 90 K to 117 K. The crystal structure parameters slightly change with the Ga concentration. The lattice parameter a correlates with the coercive field; a shrinkage of a leading to an enhanced crystalline anisotropy increases the coercive field. There are two inequivalent crystallographic sites Tb1 and Tb2 for Tb atoms. The narrowing of the Tb1-Tb2-Tb1 angle would contribute to the enhanced Curie temperature, which can be qualitatively explained by considering the 4f charge distribution of Tb3 + ion.

Introduction Several ferromagnetic compounds such as R2Co2Al and R2Co2Ga (R = heavy rare earth) with the orthorhombic W2CoB2 (or Mo2NiB2)type structure have been studied as magnetic refrigeration materials [1–4]. For example, Tb2Co2Al and Dy2Co2Al undergo ferromagnetic transitions below 100 K and 60 K, respectively [2]. The magnetic entropy change with the field changing from 0 to 50 kOe reaches 6.4 J/ kgK (10.6 J/kgK) at 97.5 K (57.5 K) for Tb2Co2Al (Dy2Co2Al). Another low-temperature remarkable feature of these compounds is huge coercive fields [2,3], attaining to approximately 60 kOe for Tb2Co2Al and 40 kOe for Dy2Co2Al, respectively. In the ternary phase diagram of R-Co-Al (R-Co-Ga), the orthorhombic W3CoB3-type R3Co3Al (R3Co3Ga) locates near R2Co2Al (R2Co2Ga). Viewing from the Schläfli symbol, the atomic network of these two structure-types are highly analogous with each other [5]. Moreover, R3Co3Al (R3Co3Ga) and R2Co2Al (R2Co2Ga) are commonly described as Rm + nCom + n Al(Ga)n with (m = 2, n = 1) and (m = 1, n = 1) for the former and latter compound, respectively. Rm + nCom + n Xn (X = Al and Ga) structure series can be regarded as mCrB-type slabs intergrown with nYAlGe-type slabs [6]. Fig. 1(a) and (b) show the crystal structure of Tb3Co3Ga to be studied in this work. In the orthorhombic structure with the space group of Cmcm (No.63), Tb atoms occupy two inequivalent crystallographic 8f (Tb1) and 4c (Tb2) sites

⁎

[7]. The network of the Tb1 and Tb2 atoms is presented as a triangular prism in Fig. 1(a). The triangular prisms form a slab extending in the a-b plane. The isostructural R3Co3.25Al 0.75 (R = Gd to Ho) and R3Co2.2Si1.8 (R = Gd to Tm) have been systematically studied [8,9]. Tb3Co3.25Al 0.75 shows the Curie temperature TC of 151 K [8]. A neutron diffraction study [8] has clarified a non-collinear ferrimagnetic ordering of Tb and Co sublattices, resulting in b-axis ferromagnetic and c-axis antiferromagnetic components below TC . The magnetic moment of Tb2 atom has components along the b-axis. Tb1 atom shows the magnetic ordering with the ferromagnetic magnetic moment along the b-axis and the antiferromagnetic one along the c-axis (see also Fig. 1(b)). The magnetic moment of Co atom is relatively small compared to that of Tb atom. Below 38 K, a spin reorientation is detected by both magnetization and neutron diffraction experiments. A similar magnetic structure is reported [9] for Tb3Co2.2Si1.8 . The magnetic properties of R3Co3Ga has not been well investigated. Considering well-defined magnetic structures of Tb3Co3.25Al 0.75 and Tb3Co2.2Si1.8 , we have studied Tb3Co3Ga, which has raised an issue of composition effect. If a binary or a ternary compound possesses a certain homogeneity range in its phase diagram, magnetic ordering temperature frequently depends on the composition of the compound. For instance [10], the Néel temperature of Nd3Pd20Ge6 slightly decreases with increasing Pd atomic composition from 19.2 to 21. Another

Corresponding author. E-mail address: j-kitagawa@fit.ac.jp (J. Kitagawa).

https://doi.org/10.1016/j.rinp.2019.102591 Received 5 May 2019; Received in revised form 7 August 2019; Accepted 12 August 2019 Available online 16 August 2019 2211-3797/ © 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/BY/4.0/).

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Fig. 1. Crystal structure of Tb3Co3Ga (a) with three-dimensional view and (b) in b-c plane. There are two inequivalent crystallographic sites for Tb and Co atoms. The 4f charge distribution (elliptic closed-curve) associated with the magnetic moment of Tb3 + ion is also drawn in (b). The solid line represents the unit cell.

sample was annealed in an evacuated quartz tube at 650 °C for 4 days. A powder X-ray diffractometer (Shimadzu, XRD-7000L) with Cu-Kα radiation was employed to obtain an X-ray diffraction pattern. The metallographic structure was investigated by a field emission scanning electron microscope (FE-SEM; JEOL, JSM-7100F), and the atomic composition of sample was determined by using an energy dispersive Xray (EDX) spectrometer in the FE-SEM. The temperature dependence of ac magnetic susceptibility χac (T) between 3 K and 300 K was measured using a closed-cycle He gas cryostat. The amplitude and frequency of ac field were 5 Oe and 800 Hz, respectively. The temperature dependence of dc magnetic susceptibility χdc (T) between 1.9 K and 300 K and the magnetization curve were measured by a Quantum Design MPMS.

example is a ferromagnetic Mn1 + x Ga, showing a reduced TC with decreasing Mn concentration [11]. This study also presents an existence of homogeneity range, producing a composition effect of ferromagnetic properties depending on crystal structure parameters. In this paper, we report the composition effect of magnetic properties of polycrystalline Tb3Co3Ga by a metallographic examination and measuring the magnetic susceptibility and the magnetization curve.

Materials and methods The experiments were conducted by following the same methods as described in the previous papers of our group [12–15]. Polycrystalline samples A to G, with different starting atomic–compositions as listed in Table 1, were prepared by arc melting the constituent elements of Tb (99.9%), Co (99.9%) and Ga (99.99%) in an Ar atmosphere. The location of each sample with the starting composition is marked in the TbCo-Ga ternary phase diagram (see Fig. 2(a)), in which impurity phases except a minor one detected in this study are also added. As shown in Table 1, three Ga concentrations (11.5, 13, 14 at%) were employed for the sample A to F, because the Ga atom might play an important role for determining crystal structure parameters due to the fact that Tb3Co3Ga and Tb2Co2Ga are closely related with each other through the variation of Ga concentration. The sample G is a reference compound for assigning magnetic phase transitions due to impurity phases. Each as-cast

Results and discussion The X-ray diffraction (XRD) patterns of samples A to F are shown in Fig. 3(a), which also includes the simulated patterns of Tb3Co3Ga and Tb2Co2Ga. Although each sample contains Tb3Co3Ga as the main phase, the presence of impurity phases is confirmed as marked by arrows. For the samples E and F, the position of peaks due to impurity phases matches with those of Tb2Co2Ga. In the samples A to C, another impurity phase might be dominant in secondary phases and can be partially explained by the XRD pattern of sample G, which agrees with that

Table 1 Starting atomic compositions of prepared samples and atomic compositions of Tb3Co3Ga phase and the other phases determined by EDX measurement. The volume fraction of each phase estimated by XRD pattern or SEM image is also shown. Sample

Starting composition

Tb3Co3Ga phase

TbCo2 − x Gax

Tb2Co2Ga phase

N phase

otherwise

A

Tb48.0Co40.5Ga11.5

C

Tb45.3Co41.6Ga13

D

Tb43.4Co43.7Ga12.8

E

Tb42.3Co43.7Ga14.1

Tb59.2(8)Co25(1)Ga16.0(3) 36 vol% (SEM) Tb56(1)Co35(1)Ga8.9(3) 10 vol% (SEM) Tb59.2(6)Co24.6(8)Ga16.1(3) 13 vol% (SEM) Tb52.6(8)Co34.2(9)Ga13.2(8) 1 vol% (SEM) –

–

Tb44.1Co44.5Ga11.5

F

Tb42.9Co42.9Ga14.2

G

Tb42.9Co50Ga7.1

Tb33.6(4)Co59.5(5)Ga7.0(8) 30 vol% (SEM) Tb36(1)Co53(1)Ga10.0(2) 33 vol% (SEM) Tb36(1)Co59(1)Ga5(1) 2 vol% (SEM) Tb39(1)Co54(1)Ga7(1) 4 vol% (SEM) Tb34.9(7)Co54.8(4)Ga10.4(4) 5 vol% (SEM) 7 vol% (XRD) Tb35.1(5)Co54.9(4)Ga 9.9(8) 3 vol% (SEM) 2 vol% (XRD) Tb36.5(8)Co56.5(9)Ga7.0(7) 63 vol% (SEM)

–

B

Tb42.6(6)Co43.6(4)Ga13.8(4) 34 vol% (SEM) Tb43.8(8)Co42.4(8)Ga13.8(8) 57 vol% (SEM) Tb42.6(2)Co42.8(6)Ga14.6(5) 83 vol% (SEM) Tb42.1(6)Co43.3(5)Ga14.6(7) 90 vol% (SEM) Tb42.8(7)Co42.3(5)Ga14.9(5) 70 vol% (SEM) 63 vol% (XRD) Tb42.3(6)Co42.6(7)Ga15.1(6) 88 vol% (SEM) 88 vol% (XRD) –

2

–

Tb40.4(8)Co41.5(2)Ga18(1) 2 vol% (SEM) Tb40.7(5)Co42.1(6)Ga17.2(1) 5 vol% (SEM) Tb39.5(6)Co41(1)Ga19.3(8) 25 vol% (SEM) 30 vol% (XRD) Tb39.8(7)Co41.2(8)Ga19.0(6) 9 vol% (SEM) 10 vol% (XRD) –

–

Tb84(1)Co12(1)Ga3.3(6) negligible – –

–

Tb91.3(3)Co9(1) negligible

Tb51.4(5)Co35.6(9)Ga13.1(8) 37 vol% (SEM)

–

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Fig. 2. (a) Ternary phase diagram of Tb-Co-Ga system for prepared samples with starting composition. The impurity phases (TbCo2 − x Gax , Tb2Co2Ga and the N phase) are also added. The area surrounded by broken lines indicates a range of the solid solution detected by EDX measurement. (b) Expanded diagram around Tb3Co3Ga phase. The area surrounded by broken lines indicates a range of the solid solution detected by EDX measurement.

with in-between contrast is Tb3Co3Ga phase, the atomic composition of which is near to the starting one (see also Table 1). As displayed in Fig. 4(c), with increased starting Ga-concentration, the area of TbCo2 − x Gax and the N phase decreases. We note here that the compositions of N phase in the sample A and C are slightly different from those in the other samples (see Table 1), and the N phase might possess a homogeneity range as depicted in Fig. 2(a). In Fig. 4(c), another phase assigned as Tb2Co2Ga, characterized by shallow dips as indicated by red ellipses, appears. The main phase is Tb42.1(6)Co43.3(5)Ga14.6(7) , which is close to Tb3Co3Ga. Further increase of starting Ga-concentration as in Fig. 4(d) enlarges the area of shallow dips with Tb2Co2Ga phase. This result is consistent with the phase relation shown in Fig. 2(a). In the sample E, although TbCo2 − xGax is observed as another minority phase, the N phase disappears, which may be supported by the phase relation in Fig. 2(a), showing that the location of sample E is rather far away from that of the N phase. As can be seen from Table 1, the Ga composition in the starting material affected the determined composition of Tb3Co3Ga, even if taking into account an error of composition. To exhibit the numerically based variety of crystalline phases mentioned above, the volume fraction of each phase obtained by SEM image is listed in Table 1. For the samples E and F, the results estimated by XRD

of TbCo2 as shown in Fig. 3(b). The weak reflections in Fig. 3(b) other than the peaks of TbCo2 are ascribed to yet another phase, which was detected in EDX measurement. In the sample E or F, the crystal structures of all phases are known and the volume fraction of each phase is estimated by the Rietveld refinement program RIETAN-FP [16] as shown in Table 1. The results are cross-checked by those obtained using SEM images as mentioned below. Back-scattered electron images obtained by FE-SEM with electron beams of 15 keV are shown in Fig. 4(a) for the sample G and in Fig. 4(b)–(d) for representative samples with different starting Ga concentrations, respectively. The atomic compositions obtained by EDX measurement of all samples are listed in Table 1. The homogeneity range of Tb3Co3Ga phase deduced from Table 1 is drawn by the area surrounded by broken lines in Fig. 2(b). The sample G contains two phases; Tb36.5(8)Co56.5(9)Ga7.0(7) , which would be a pseudo binary TbCo2 − x Gax , and Tb51.4(5)Co35.6(9)Ga13.1(8) hereafter called as the N phase. The former compound is clearly confirmed in the XRD pattern and the latter one would be responsible for the weak reflections in XRD pattern other than the peaks of TbCo2 − x Gax . In the sample B, there are three areas with contrast as shown in Fig. 4(b). The darkest and the brightest areas correspond to TbCo2 − x Gax and the N phase, respectively. The region

Fig. 3. (a) XRD patterns of samples A to F. The simulated patterns of Tb3Co3Ga and Tb2Co2Ga are also shown. The origin of each pattern is shifted by an integer value for clarity. (b) XRD pattern of sample G. The simulated pattern of TbCo2 is also shown. The origin of each pattern is shifted by an integer value for clarity. 3

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Fig. 4. Back-scattered electron (15 keV) images of samples (a) G, (b) B, (c) D and (d) E, respectively.

patterns are also given and consistent with those by SEM images. The lattice parameters of samples A to F were obtained by the least squares method [16,17] using the XRD patterns in Fig. 3(a), as listed in Table 2. Focusing on the Ga-concentration dependence of refined lattice parameters, the following results would be suggested: a showing a maximum at approximately 14.6 at% Ga, b decreasing as the Ga concentration is increased above 14.6 at%, and c, on the contrary, decreasing with concertation of Ga below 14.6 at%. The inset of Fig. 5 shows χac (T) of the sample G, exhibiting two pronounced peaks at approximately 250 and 60 K. The former magnetic transition seems to occur in all the Tb3Co3Ga samples (see Fig. 5). On the other hand, the 60 K magnetic transition is not observed in the samples E and F, which do not contain the N phase (see also Table 1). Therefore the pseudo binary TbCo2 − x Gax alloy is responsible for the 250 K magnetic transition, and the 60 K one is ascribed to the N phase. TbCo2 enters into a ferromagnetic state [18] below 231 K, which is enhanced to 258 ∼ 264 K in the pseudo binary [19] TbCo2 − xGax with

0.1 ≦ x ≦ 0.3. In our case, x of TbCo2 − x Gax is estimated to be 0.16 ∼ 0.32, and therefore, the observed magnetic transition temperatures are consistent with the reported ones. The 60 K magnetic transition of χac grows on going from the sample D to A, which corresponds to the successive increase of the area of N phase, observed in metallographic studies. For the samples C to F, an additional anomaly is observed at approximately 155 K. In these samples, the EDX measurement has revealed the existence of Tb2Co2Ga phase, the area of which is depressed with decreasing Ga concentration. Thus the additional anomaly can be assigned as a magnetic transition of Tb2Co2Ga phase, which is supported by our preliminary composition effect study of Tb2Co2Ga, suggesting that TC of Tb2Co2Ga in the vicinity of Tb3Co3Ga in the ternary phase diagram is approximately 150 K. The magnetic transitions of Tb3Co3Ga are then assigned to χac peaks between 90 and 117 K. The MH (M:magnetization, H:external field) curve as mentioned below evidences that the ordering type is ferromagnetic. As in other ferromagnetic compounds [19,20], the peak position of χac (T) is employed as

Table 2 Lattice parameters and TC determined by χac of prepared Tb3Co3Ga samples. Sample

Composition of Tb3Co3Ga

a (Å)

b (Å)

c (Å)

TC (K)

A

Tb42.6(6)Co43.6(4)Ga13.8(4)

4.10046(85)

10.06851(257)

12.88666(296)

117

B

Tb43.8(8)Co42.4(8)Ga13.8(8)

4.10655(62)

10.07320(170)

12.92130(218)

117

C

Tb42.6(2)Co42.8(6)Ga14.6(5)

4.11559(52)

10.07376(144)

12.94423(183)

99

D

Tb42.1(6)Co43.3(5)Ga14.6(7)

4.10743(88)

10.05452(265)

12.93617(301)

98

E

Tb42.8(7)Co42.3(5)Ga14.9(5)

4.09744(101)

9.99452(329)

12.93870(344)

92

F

Tb42.3(6)Co42.6(7)Ga15.1(6)

4.10350(84)

10.01880(250)

12.93900(295)

90

4

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examinations. For the sample D or F, χdc shows an additional anomaly caused by magnetic transition of Tb2Co2Ga phase at approximately 150 K. Fig. 7(a)–(c) exhibit the M-H curves measured at several temperatures denoted in the figures for the samples B, D and F, respectively. In each sample, below TC of Tb3Co3Ga phase, an obvious hysteresis grows, which is characteristic of ferromagnetism. M at 10 kOe for the sample B or D (for the sample F) decreases below 50 (80) K. An external field higher than 10 kOe is required to obtain an entire magnetization process at lower temperature. It should be noted that TbCo2, which is the end member of TbCo2 − x Gax , does not show a noticeable hysteresis in MH curve down to 4.2 K [21]. In our preliminary M-H measurement of Tb2Co2Ga sample with TC ∼ 150 K, a hysteresis similar to those of Tb3Co3Ga samples is observed at approximately 80 K. Absence of Tb2Co2Ga in the sample B and the very small amount of it in the sample D indicate that the obvious hysteresis in Fig. 7(a) or (b) is intrinsic for Tb3Co3Ga phase. Although, in the sample F, the rather large amount of Tb2Co2Ga might partially contribute to the hysteresis of M-H curve, it is assumed that Tb3Co3Ga dominates the hysteresis observed in Fig. 7(c). The assumption would be supported by the χac (T) data as discussed below. The isothermal curves at 80 K of three samples are compared in Fig. 7(d). M at 10 kOe and the coercive field Hc range from 8.0 to 9.3 μB /f.u. and 0.58 to 1.1 kOe, respectively. They negatively correlate with each other; a decreased M at 10 kOe leads to an enhanced Hc . Fig. 8(a) is the Hc vs a plot, demonstrating the decreasing Hc with increasing a. Hc generally reflects a crystalline anisotropy, and an enhanced anisotropy results in a larger Hc . Assuming that the magnetic moment of Tb ion stays in the b-c plane as in the isostructural compounds Tb3Co3.25Al 0.75 and Tb3Co2.2Si1.8 , the shrunk a would enhance the crystalline anisotropy and make a magnetization process along the aaxis more difficult, which causes the increased Hc . It should be noted that χac peak at TC is in particularly broad for the sample D with the smallest Hc (see Fig. 5). χac is correlated with the reversible initial magnetization process. Broadness of the χac peak at TC suggests easiness of reverse process, which is consistent with the small Hc determined by M-H curve. We note here that χac peak of the sample F with the largest Hc is the sharpest, supporting that the magnitude of Hc is determined autonomously in Tb3Co3Ga, irrespective of the presence of Tb2Co2Ga. Shown in Fig. 8(b) is the TC vs θ Tb plot, in which θ Tb is the Tb1-Tb2Tb1 angle (see Fig. 1(b)). TC tends to be enhanced as θ Tb is decreased, the origin of which is qualitatively discussed below. The magnetic ordering temperatures of R3Co2.2Si1.8 well follow the de Gennes scaling [9], which suggests that an energy-level splitting of the J-multiplet due to the crystalline-electric-field effect is negligible [22,23] at TC . The present isostructural compound Tb3Co3Ga might also show a negligible splitting of J-multiplet at TC . Under such a circumstance, the 4f electron distribution of single Tb3 + ion is oblate [24], and the direction of magnetic moment is perpendicular to the equatorially expanded 4felectron charge cloud [25]. Following the reported magnetic structure of Tb sublattice in Tb3Co3.25Al 0.75 [8], a simple schematic arrangement of Tb magnetic moment accompanying the 4f-electron charge cloud is given in Fig. 1(b). The magnetic moment of Tb1 atom cants slightly to the c-axis and that of Tb2 atom aligns along the b-axis near below TC . The electrostatic interaction of the 4f charge cloud with ligand atoms determines the direction of magnetic moment of Tb ion. In Tb3Co3Ga, neighboring atoms for Tb1 (Tb2) atom are 4 Co1 atoms and 2 Co2 atoms (4 Co1 atoms and 1 Co2 atom), and the arrangement of polyhedron, formed by these Co atoms is given in Fig. 9. Superimposing the 4f charge cloud illustrated in Fig. 1(b) on the Tb atoms in polyhedrons, it is understood that the 4f charge cloud and Co atom is repulsive. When the angle θp is defined as in Fig. 9, a narrowing θ Tb means a decreasing θp , which gives rise to the magnetic moment of Tb1 atom more aligned along the b-axis to reduce the electrostatic interaction. Therefore, a ferromagnetic exchange energy gain would increase and TC increases with narrowing θ Tb .

Fig. 5. Temperature dependences of χac for samples A–F. The origin of each χac is shifted by a value for clarity. The inset is χac (T) of the sample G.

the magnetic transition temperature, which might be governed by the Ga concentration (see Table 2). The broad peak around 20 K in each sample would suggest a spin reorientation. The position of the broad peak is positively correlated with that of the magnetic transition of Tb3Co3Ga. Fig. 6 shows χdc (T) under the external field of 10 Oe of the samples B, D and F, respectively. In each sample, χdc steeply increases below approximately TC of Tb3Co3Ga phase. As in Tb3Co3.25Al 0.75 and Tb3Co2.2 Si1.8 , each χdc at low temperature shows a small hump indicated by a closed circle in the inset of Fig. 6. The anomaly, which would be ascribed to a spin reorientation, is already detected as the χac broad peak in the corresponding temperature range. In all samples, magnetic transitions due to TbCo2 − x Gax are observed at approximately 260 K. The height of χdc jump progressively develops with decreasing Ga concentration, which is consistent with χac (T) results and metallographic

Fig. 6. Temperature dependences of χdc for samples B, D and F. The external field is 10 Oe. The inset is the low temperature part of χdc (T) of respective sample. 5

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J. Kitagawa, et al.

Fig. 7. M-H curves measured at several temperatures as denoted in figure for samples (a) B (b) D and (c) F, respectively. (d) Comparison of isothermal M-H curves at 80 K of three samples.

Fig. 8. (a) Hc vs a plot. (b) Tb1-Tb2-Tb1 angle dependence of TC . 6

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axis, which contributes to an increase of ferromagnetic exchange energy gain. Acknowledgment J.K. is grateful for the support provided by Comprehensive Research Organization of Fukuoka Institute of Technology. References [1] Sengupta K, Iyer KK, Sampathkumaran EV. Phys Rev B 2005;72:054422 . [2] Fu H, Zou M, Guo MS, Zheng Q, Zu XT. Mater Charact 2011;62:451. [3] Morozkin AV, Genchel VK, Garchev AV, Yapaskurt VO, Isnard O, Yao J, Nirmala R, Quezado S, Malik SK. J Magn Magn Mater 2017;442:36. [4] Morozkin AV, Garchev AV, Yapaskurt VO, Yao J, Nirmala R, Quezado S, Malik SK. J Solid State Chem 2018;260:95. [5] Solokha P, De Negri S, Pavlyuk V, Saccone A, Marciniak B. J Solid State Chem 2007;180:3066. [6] Parthé E, Gelato L, Chabot B, Penzo M, Cenzual K, Gladyshevskii R. TYPIX standardized data and crystal chemical characterization of inorganic structure types. Berlin: Springer-Verlag; 1994. p. 159. [7] Yarmolyuk YP, Grin Y, Gladyshevskii EI. Dopov Akad Nauk Ukr RSR Ser A 1978;9:855. [8] Morozkin AV, Garshev AV, Knotko AV, Yapaskurt VO, Isnard O, Yao J, Nirmala R, Quezado S, Malik SK. J Solid State Chem 2017;251:33. [9] Morozkin AV, Yao J, Mozharivsky Y. J Solid State Chem 2012;192:371. [10] Kitagawa J, Takeda N, Sakai F, Ishikawa M. J Phys Soc Jpn 1999;68:3413. [11] Lu QM, Yue M, Zhang HG, Wang ML, Yu F, Huang QZ, Ryan DH, Altounian Z. Sci Rep 2015;5:17086. [12] Ishizu N, Kitagawa J. Res Phys 2019;13:102275 . [13] Kitagawa J, Sakaguchi K. J Magn Magn Mater 2018;468:115. [14] Hamamoto S, Kitagawa J. Mater Res Express 2018;5:106001 . [15] Abe T, Uenishi K, Orita K, Tsubota M, Shimada Y, Onimaru T, Takabatake T, Kitagawa J. Res Phys 2014;4:137. [16] Izumi F, Momma K. Solid State Phenom 2007;130:15. [17] Tsubota M, Kitagawa J. Sci Rep 2017;7:15381. [18] Halder M, Yusuf SM, Mukadam MD. Phys Rev B 2010;81:174402 . [19] De¸biec I, Chełkowska G. J Magn Magn Mater 2003;261:73. [20] Miyahara J, Shirakawa N, Setoguchi Y, Tsubota M, Kuroiwa K, Kitagawa J. J Supercond Nov Magn 2018;31:3559. [21] Jun-Ding Z, Bao-Gen S, Ji-Rong S. Chin Phys 2007;16:3843. [22] Bucher E, Maita JP, Hull GW, Fulton RC, Cooper AS. Phys Rev B 1975;11:440. [23] Kitagawa J, Takeda N, Ishikawa M. J Alloys Compd 1997;256:48. [24] Coey JMD. Magnetism and magnetic materials. Cambridge: Cambridge University Press; 2010. p. 123. [25] Rinehart JD, Long JR. Chem Sci 2011;2:2078.

Fig. 9. Crystal structure of Tb3Co3Ga tilted from b-c plane. The solid line represents a polyhedron surrounding Tb1 or Tb2 atom.

Summary The ferromagnetic properties of Tb3Co3Ga, crystallizing into the orthorhombic W3CoB3-type structure, were investigated by examining the composition effect of magnetic susceptibility and the magnetization curve. The atomic composition studied by EDX measurement has revealed the existence of homogeneity range especially along the Ga concentration. The prepared samples show TC ranging from 90 K to 117 K. We have found that Hc determined by M-H curve and TC depend on the crystallographic parameters. The increasing Hc obtained at 80 K with decreasing a-axis length can be explained by speculating that an enhanced crystalline anisotropy due to the shrinkage of a-axis causes a larger energy difference of magnetic moment in the b-c plane from that along the a-axis. The TC enhancement with narrowing Tb1-Tb2-Tb1 angle can be qualitatively understood by considering the 4f charge distribution of single Tb3 + ion. The narrowing Tb1-Tb2-Tb1 angle makes the magnetic moment of Tb1 atom to more align along the b-

7