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The crystal structure and magnetic properties of the GdCrxAl12−x (x = 3.5 and 4.0) intermetallics
Journal of Alloys and Compounds 438 (2007) L12–L15
Letter
The crystal structure and magnetic properties of the GdCrxAl12−x (x = 3.5 and 4.0) intermetallics Yu. Verbovytsky a,b , K. Ł˛atka b,∗ , A.W. Pacyna c , K. Tomala b a
Department of Inorganic Chemistry, Ivan Franko National University of Lviv, Kyryla and Mefodiya 6, 79005 Lviv, Ukraine b Marian Smoluchowski Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Krak´ ow, Poland c Henryk Niewodnicza´ nski Institute of Nuclear Physics, Polish Academy of Sciences, Radzikowskiego 152, 31-342 Krak´ow, Poland Received 21 July 2006; received in revised form 14 August 2006; accepted 15 August 2006 Available online 18 September 2006
Abstract The crystal structure of the GdCrx Al12−x (with x = 3.5 and 4.0) intermetallic compound was determined by X-ray powder diffraction using the Rietveld method. The investigated compound crystallizes with ThMn12 structure type (space group I4/mmm, Pearson symbol tI26). Magnetic measurements carried out for the title compound point to the antiferromagnetic–paramagnetic transition observed at TN = 6.50 and 6.75 K for compositions with x = 3.5 and 4, respectively. © 2006 Elsevier B.V. All rights reserved. Keywords: Intermetallics; Crystal structure; X-ray diffraction; Magnetic properties
1. Introduction Among the R–Cr–Al (R = Sc, Y and rare earths) ternary systems the isothermal sections were investigated in the partial or whole concentration region with R = Sc, Y, La, Ce, Gd, Dy, Yb [1–7]. Additionally, other alloys of these systems were investigated for the existence of the isostructural ternary compounds, which belong to the CeCr2 Al20 , Ho6 Mo4 Al43 and CeMn4 Al8 structure types [8–10]. Magnetic properties of some selected intermetallics of these systems were also studied [11,12]. In this paper, we report the results of crystal structure investigations of the GdCrx Al12−x (with x = 3.5 and 4.0) intermetallic compound using the Rietveld method together with the results of magnetic measurements. 2. Experimental details Samples were prepared by arc-melting of initial components under high purity argon on a water-cooled copper hearth. Starting materials were used in the form of pieces of high purity metals (>99.9 wt.%). The samples were remelted three times for a better homogeneity. Ingots were wrapped with tantalum foil and afterwards sealed in evacuated quartz tubes and annealed at 500 ◦ C for 3 months. After heat treatment, the samples were quenched by submerging the silica tubes in cold water.
∗
Corresponding author. Tel.: +48 12 663 5668; fax: +48 12 633 70 86. E-mail address: [email protected] (K. Ł˛atka).
0925-8388/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2006.08.043
The crystal structures of ternary compounds were studied by means of X-ray powder diffraction (Siemens D500 diffractometer, Cu K␣-radiation, scanning parameters: 2θ region 10–145◦ , step scan 0.05◦ , counting time per step 10 s). All the crystal structure calculations were performed by means of the Rietveld method using the FullProf programme [13]. The magnetic susceptibility and magnetization of polycrystalline samples were determined by means of SQUID (Quantum Design) magnetometer, a Cahn RG automatic electro-balance and/or ac/dc magnetic measurements with Lake Shore 7225 apparatus in the temperature range from 2 to 300 K.
3. Results and discussion The structure of the GdCrx Al12−x (for x = 3.5 and 4.0) intermetallic compound annealed at 500 ◦ C was refined from X-ray powder diffraction data using the Rietveld method. Pseudo-Voigt profile shape function was used. The background was refined with a polynomial function. The title ternary intermetallic compound crystallizes in tetragonal space group I4/mmm (Pearson symbol tI26), with ThMn12 structure type (or CeMn4 Al8 type with x = 4.0) [14]. The results of the crystal structure determination for the GdCrx Al12−x with x = 3.5 and x = 4.0 are summarized in Table 1. Results of the Rietveld profile refinement of the GdCr4 Al8 X-ray diffraction data are presented in Fig. 1. Projections of the GdCrx Al12−x structure on the xy plane and coordination polyhedra for the atoms are given in Fig. 2. Interatomic distances and coordination numbers for atoms in the GdCrx Al12−x are presented in Table 2. These dis-
Yu. Verbovytsky et al. / Journal of Alloys and Compounds 438 (2007) L12–L15
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Table 1 Results of the crystal structure determination of the GdCrx Al12−x (x = 4.0–3.5) compound
Table 2 Interatomic distances (δ* ) and coordination numbers (CN) for atoms in the GdCrx Al12−x intermetallics
GdCrx Al12−x
x = 3.5
x = 4.0
Atoms
Lattice parameters ˚ a (A) ˚ c (A) ˚ 3) V (A
8.9900 (6) 5.1229 (4) 414.04 (5)
8.9683(7) 5.1252(5) 412.23(6)
Reliability factors RB (%) Rp (%)
GdCrx Al12−x (x = 3.5) Gd −4Al1 3.174 −8Al2 3.241 −8M 3.427
8.77 3.31
8.45 3.39
Gd in 2(a) 0 0 0 0.68(10) 0.87(3)Cr + 0.13(3)Al in 8(f) 1/4 1/4 1/4 0.67(13) Al1 in 8(i) x 0 0 x = 0.3530(8)
Gd in 2(a) 0 0 0 0.85(8) Cr in 8(f) 1/4 1/4 1/4 1.05(10) Al1 in 8(i) x 0 0 x = 0.3537(8)
0.89(18) Al2 in 8(j) x 1/2 0 x = 0.2791(8)
0.46(18) Al2 in 8(j) x 1/2 0 x = 0.2795(9)
M
˚ 2) Biso (A
˚ 2) Biso (A
Biso
˚ 2) (A
0.64(18)
0.95(20)
2.561 2.600 2.748 3.427
Al1 −Al1 −4M −2Al2 −2Al2 −4Al1 −Gd
2.642 2.748 2.824 2.836 3.170 3.174
Al2 −4M −2Al2 −2Al1 −2Al1 −2Gd
2.600 2.808 2.824 2.836 3.241
*
Fig. 1. Rietveld profile refinement of X-ray diffraction data for the GdCr4 Al8 .
CN 20
12 −2Cr −4Al2 −4Al1 −2Gd
Atom parameters ˚ 2) Biso (A
˚ δ (A)
14
12
Atoms
˚ δ (A)
GdCrx Al12−x (x = 4.0) Gd −4Al1 3.172 −8Al2 3.237 −8Cr 3.420 Cr
CN 20
12 −2Cr −4Al2 −4Al1 −2Gd
2.563 2.596 2.745 3.420
Al1 −Al1 −4Cr −2Al2 −2Al2 −4Al1 −Gd
2.624 2.745 2.827 2.829 3.164 3.172
Al2 −4Cr −2Al2 −2Al1 −2Al1 −2Gd
2.596 2.796 2.827 2.829 3.237
14
12
˚ M = 0.87(3)Cr + 0.13(3)Al. Standard deviations ≤ 0.001 A.
tances are close to the sum of the atomic radii of the respective atoms. SQUID magnetic measurements indicate that the GdCrx Al12−x with x = 3.5 orders antiferromagnetically at N´eel temperature TN = 6.50(5) K, presenting modified Curie–Weiss behaviour above TN (Fig. 3a) in the form χσ = χ0 + C/(T − Θp ), where χ0 is a temperature independent factor, C the Curie constant and Θp is the paramagnetic Curie temperature. The negative paramagnetic Θp = −5.9 K Curie temperatures obtained for this composition of GdCrx Al12−x compound points to a dominant antiferromagnetic exchange interaction among gadolinium magnetic moments. The effective magnetic moment
Fig. 2. Projections of the GdCr4 Al8 structure on the xy plane and coordination polyhedra of the atoms. Black circles indicate Gd atoms, grey filled circles are Cr atoms, and Al atoms are marked by white circles.
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Yu. Verbovytsky et al. / Journal of Alloys and Compounds 438 (2007) L12–L15
Fig. 5. Zero field susceptibilities χ and χ recorded simultaneously as a function of temperature at internal frequency f = 120 Hz with oscillating field Hac = 5 Oe for GdCr4 Al8 .
Fig. 3. Temperature dependence of magnetic susceptibility (left, left-hand scale) and its reciprocal (top, right-hand scale) recorded in an external field of H0 = 1 kOe (a), where the solid lines are results of the fitting procedures in the paramagnetic range together with magnetization vs. external magnetic field (bottom) measured at 2 K for GdCrx Al12−x (x = 3.5) (b).
Fig. 4. Plot of the overall temperature dependencies of magnetic susceptibility (left-hand scale) and inverse susceptibility (right-hand scale), measured with a Cahn RG automatic electro-balance for GdCr4 Al8 in an external magnetic field H0 = 690 Oe. In the inset, the magnetic parameters obtained from the fit according to the modified Curie–Weiss law are presented (for details see text).
Fig. 6. Temperature dependence of the susceptibility signal registered for the real and imaginary parts of the second and third harmonics for GdCr4 Al8 , where the fundamental frequency was f = 120 Hz. Data were collected after ZFC with an oscillating field Hac = 5 Oe.
Yu. Verbovytsky et al. / Journal of Alloys and Compounds 438 (2007) L12–L15
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The magnetization measured for the highest field of 55.04 kOe (Fig. 7) attains the value σ (T = 4.25 K, 55.04 kOe) = 41.63 Oe cm3 /g per formula unit (f.u.) or 4.33 B /Gd ion which is comparable to that one obtained for the GdCr3.5 Al8.5 sample under comparable conditions as discussed above. Only small hysterisis can be registered for measurements done with rising and decreasing strength of external magnetic field (Fig. 7). Acknowledgement This work was supported by the International Visegrad Fund (IVF) (Serial Number: US-018-2005). References Fig. 7. Magnetization vs. external magnetic field (bottom) measured at 4.25 K for GdCrx Al12−x (x = 4). exp
μeff deduced from the fitted Curie constant C is equal to 7.87 being fairly well comparable the theoretical value characteristic for a free Gd3+ ion μtheor eff = 7.94 B . The value obtained for χ0 equals 1.246 × 10−6 cm3 /g. Field dependence of magnetization is also shown in Fig. 3b. The value of the magnetization σ obtained at T = 2.0 K in the field H0 = 50.14 kOe is equal to 41.79 Oe cm3 /g or to 4.25 B /Gd ion being lower than theoretical saturation moment expected for Gd ion, i.e. 7 B /Gd. Similar magnetic behaviour is presented for GdCr4 Al8 sample (Figs. 4–7). In this case modified Curie–Weiss law is obeyed (Fig. 4) above TN = 6.75(5) K giving following results: exp Θp = −12.2 K, μeff = 7.67 B , and χ0 = 5.544 × 10−6 cm3 /g. The ac temperature dependence of the magnetic susceptibility recorded in zero external field and with a small amplitude of the oscillating magnetic field strength Hac = 5 Oe reveals an antiferromagnetic phase transition at TN = 6.75(5) K (Fig. 5) for GdCrx Al12−x with x = 4.0. In Fig. 6 temperature dependencies of the real and imaginary parts of the ac magnetic susceptibility for second and third harmonics, however, no any characteristic singularities are visible for both harmonics nearby or below phase transition observed at TN = 6.75 K.
[1] B.Y. Kotur, E. Gratz, in: K.A. Gschneidner Jr., L. Eyring (Eds.), Handbook on the Physics and Chemistry of Rare Earths, vol. 27, Elsevier Science B.V, Amsterdam, 1999, pp. 339–553 (Chapter 175). [2] O.S. Zarechnyuk, R.M. Rykhal’, N.V. German, Visn. Lviv. Univ. Ser. Chem. 12 (1971) 10. [3] O.Y. Emes-Mysenko, Visn. Lviv. Univ. Ser. Chem. 12 (1971) 12. [4] O.S. Zarechnyuk, R.M. Rykhal’, Visn. Lviv. Univ. Ser. Chem. 16 (1974) 5. [5] Y. Verbovytsky, T. Mika, B. Kotur, Prace Naukowe WSP. Cz˛estochowa, Chemia i ochrona s´rodowiska, 10 (2005) 91. [6] R.M. Rykhal’, O.S. Zarechnyuk, O.P. Mats’kiv, Visn. Lviv. Univ. Ser. Chem. 21 (1979) 46. [7] T.I. Yanson, N.B. Manyako, O.I. Bodak, R. Cherny, R.E. Gladyshevskii, K. Yvon, J. Alloys Compd. 219 (1995) 219. [8] P. Villars (Ed.), Pearson’s Handbook, Desk ed. Crystallographic Data of Intermetallic Phases, vols. 1 and 2, ASM, Metals Park, OH, 1997. [9] K.H.J. Buschow, J.H.N. Van Vucht, W.W. Van der Hoogenhof, J. LessComm. Met. 50 (1976) 145. [10] V.M.T. Thiede, W. Jeitschko, S. Niemann, T. Ebel, J. Alloys Compd. 267 (1998) 23. [11] O. Moze, L.D. Tung, J.J.M. Franse, K.H.J. Buschow, J. Alloys Compd. 268 (1998) 39. [12] M.W. Wolff, S. Niemann, T. Ebel, W. Jeitschko, J. Magn. Magn. Mater. 223 (2001) 1. [13] J. Rodriguez-Carvajal, Phys. B 192 (1993) 55. [14] E. Parthe, L. Gelato, B. Chabot, M. Penzo, K. Cenzual, R. Gladyshevskii, TYPIX, Standartized Data and Crystal Chemical Characterization of Inorganic Structure Types, Springer-Verlag, Berlin, 1994.
Letter
The crystal structure and magnetic properties of the GdCrxAl12−x (x = 3.5 and 4.0) intermetallics Yu. Verbovytsky a,b , K. Ł˛atka b,∗ , A.W. Pacyna c , K. Tomala b a
Department of Inorganic Chemistry, Ivan Franko National University of Lviv, Kyryla and Mefodiya 6, 79005 Lviv, Ukraine b Marian Smoluchowski Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Krak´ ow, Poland c Henryk Niewodnicza´ nski Institute of Nuclear Physics, Polish Academy of Sciences, Radzikowskiego 152, 31-342 Krak´ow, Poland Received 21 July 2006; received in revised form 14 August 2006; accepted 15 August 2006 Available online 18 September 2006
Abstract The crystal structure of the GdCrx Al12−x (with x = 3.5 and 4.0) intermetallic compound was determined by X-ray powder diffraction using the Rietveld method. The investigated compound crystallizes with ThMn12 structure type (space group I4/mmm, Pearson symbol tI26). Magnetic measurements carried out for the title compound point to the antiferromagnetic–paramagnetic transition observed at TN = 6.50 and 6.75 K for compositions with x = 3.5 and 4, respectively. © 2006 Elsevier B.V. All rights reserved. Keywords: Intermetallics; Crystal structure; X-ray diffraction; Magnetic properties
1. Introduction Among the R–Cr–Al (R = Sc, Y and rare earths) ternary systems the isothermal sections were investigated in the partial or whole concentration region with R = Sc, Y, La, Ce, Gd, Dy, Yb [1–7]. Additionally, other alloys of these systems were investigated for the existence of the isostructural ternary compounds, which belong to the CeCr2 Al20 , Ho6 Mo4 Al43 and CeMn4 Al8 structure types [8–10]. Magnetic properties of some selected intermetallics of these systems were also studied [11,12]. In this paper, we report the results of crystal structure investigations of the GdCrx Al12−x (with x = 3.5 and 4.0) intermetallic compound using the Rietveld method together with the results of magnetic measurements. 2. Experimental details Samples were prepared by arc-melting of initial components under high purity argon on a water-cooled copper hearth. Starting materials were used in the form of pieces of high purity metals (>99.9 wt.%). The samples were remelted three times for a better homogeneity. Ingots were wrapped with tantalum foil and afterwards sealed in evacuated quartz tubes and annealed at 500 ◦ C for 3 months. After heat treatment, the samples were quenched by submerging the silica tubes in cold water.
∗
Corresponding author. Tel.: +48 12 663 5668; fax: +48 12 633 70 86. E-mail address: [email protected] (K. Ł˛atka).
0925-8388/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2006.08.043
The crystal structures of ternary compounds were studied by means of X-ray powder diffraction (Siemens D500 diffractometer, Cu K␣-radiation, scanning parameters: 2θ region 10–145◦ , step scan 0.05◦ , counting time per step 10 s). All the crystal structure calculations were performed by means of the Rietveld method using the FullProf programme [13]. The magnetic susceptibility and magnetization of polycrystalline samples were determined by means of SQUID (Quantum Design) magnetometer, a Cahn RG automatic electro-balance and/or ac/dc magnetic measurements with Lake Shore 7225 apparatus in the temperature range from 2 to 300 K.
3. Results and discussion The structure of the GdCrx Al12−x (for x = 3.5 and 4.0) intermetallic compound annealed at 500 ◦ C was refined from X-ray powder diffraction data using the Rietveld method. Pseudo-Voigt profile shape function was used. The background was refined with a polynomial function. The title ternary intermetallic compound crystallizes in tetragonal space group I4/mmm (Pearson symbol tI26), with ThMn12 structure type (or CeMn4 Al8 type with x = 4.0) [14]. The results of the crystal structure determination for the GdCrx Al12−x with x = 3.5 and x = 4.0 are summarized in Table 1. Results of the Rietveld profile refinement of the GdCr4 Al8 X-ray diffraction data are presented in Fig. 1. Projections of the GdCrx Al12−x structure on the xy plane and coordination polyhedra for the atoms are given in Fig. 2. Interatomic distances and coordination numbers for atoms in the GdCrx Al12−x are presented in Table 2. These dis-
Yu. Verbovytsky et al. / Journal of Alloys and Compounds 438 (2007) L12–L15
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Table 1 Results of the crystal structure determination of the GdCrx Al12−x (x = 4.0–3.5) compound
Table 2 Interatomic distances (δ* ) and coordination numbers (CN) for atoms in the GdCrx Al12−x intermetallics
GdCrx Al12−x
x = 3.5
x = 4.0
Atoms
Lattice parameters ˚ a (A) ˚ c (A) ˚ 3) V (A
8.9900 (6) 5.1229 (4) 414.04 (5)
8.9683(7) 5.1252(5) 412.23(6)
Reliability factors RB (%) Rp (%)
GdCrx Al12−x (x = 3.5) Gd −4Al1 3.174 −8Al2 3.241 −8M 3.427
8.77 3.31
8.45 3.39
Gd in 2(a) 0 0 0 0.68(10) 0.87(3)Cr + 0.13(3)Al in 8(f) 1/4 1/4 1/4 0.67(13) Al1 in 8(i) x 0 0 x = 0.3530(8)
Gd in 2(a) 0 0 0 0.85(8) Cr in 8(f) 1/4 1/4 1/4 1.05(10) Al1 in 8(i) x 0 0 x = 0.3537(8)
0.89(18) Al2 in 8(j) x 1/2 0 x = 0.2791(8)
0.46(18) Al2 in 8(j) x 1/2 0 x = 0.2795(9)
M
˚ 2) Biso (A
˚ 2) Biso (A
Biso
˚ 2) (A
0.64(18)
0.95(20)
2.561 2.600 2.748 3.427
Al1 −Al1 −4M −2Al2 −2Al2 −4Al1 −Gd
2.642 2.748 2.824 2.836 3.170 3.174
Al2 −4M −2Al2 −2Al1 −2Al1 −2Gd
2.600 2.808 2.824 2.836 3.241
*
Fig. 1. Rietveld profile refinement of X-ray diffraction data for the GdCr4 Al8 .
CN 20
12 −2Cr −4Al2 −4Al1 −2Gd
Atom parameters ˚ 2) Biso (A
˚ δ (A)
14
12
Atoms
˚ δ (A)
GdCrx Al12−x (x = 4.0) Gd −4Al1 3.172 −8Al2 3.237 −8Cr 3.420 Cr
CN 20
12 −2Cr −4Al2 −4Al1 −2Gd
2.563 2.596 2.745 3.420
Al1 −Al1 −4Cr −2Al2 −2Al2 −4Al1 −Gd
2.624 2.745 2.827 2.829 3.164 3.172
Al2 −4Cr −2Al2 −2Al1 −2Al1 −2Gd
2.596 2.796 2.827 2.829 3.237
14
12
˚ M = 0.87(3)Cr + 0.13(3)Al. Standard deviations ≤ 0.001 A.
tances are close to the sum of the atomic radii of the respective atoms. SQUID magnetic measurements indicate that the GdCrx Al12−x with x = 3.5 orders antiferromagnetically at N´eel temperature TN = 6.50(5) K, presenting modified Curie–Weiss behaviour above TN (Fig. 3a) in the form χσ = χ0 + C/(T − Θp ), where χ0 is a temperature independent factor, C the Curie constant and Θp is the paramagnetic Curie temperature. The negative paramagnetic Θp = −5.9 K Curie temperatures obtained for this composition of GdCrx Al12−x compound points to a dominant antiferromagnetic exchange interaction among gadolinium magnetic moments. The effective magnetic moment
Fig. 2. Projections of the GdCr4 Al8 structure on the xy plane and coordination polyhedra of the atoms. Black circles indicate Gd atoms, grey filled circles are Cr atoms, and Al atoms are marked by white circles.
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Fig. 5. Zero field susceptibilities χ and χ recorded simultaneously as a function of temperature at internal frequency f = 120 Hz with oscillating field Hac = 5 Oe for GdCr4 Al8 .
Fig. 3. Temperature dependence of magnetic susceptibility (left, left-hand scale) and its reciprocal (top, right-hand scale) recorded in an external field of H0 = 1 kOe (a), where the solid lines are results of the fitting procedures in the paramagnetic range together with magnetization vs. external magnetic field (bottom) measured at 2 K for GdCrx Al12−x (x = 3.5) (b).
Fig. 4. Plot of the overall temperature dependencies of magnetic susceptibility (left-hand scale) and inverse susceptibility (right-hand scale), measured with a Cahn RG automatic electro-balance for GdCr4 Al8 in an external magnetic field H0 = 690 Oe. In the inset, the magnetic parameters obtained from the fit according to the modified Curie–Weiss law are presented (for details see text).
Fig. 6. Temperature dependence of the susceptibility signal registered for the real and imaginary parts of the second and third harmonics for GdCr4 Al8 , where the fundamental frequency was f = 120 Hz. Data were collected after ZFC with an oscillating field Hac = 5 Oe.
Yu. Verbovytsky et al. / Journal of Alloys and Compounds 438 (2007) L12–L15
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The magnetization measured for the highest field of 55.04 kOe (Fig. 7) attains the value σ (T = 4.25 K, 55.04 kOe) = 41.63 Oe cm3 /g per formula unit (f.u.) or 4.33 B /Gd ion which is comparable to that one obtained for the GdCr3.5 Al8.5 sample under comparable conditions as discussed above. Only small hysterisis can be registered for measurements done with rising and decreasing strength of external magnetic field (Fig. 7). Acknowledgement This work was supported by the International Visegrad Fund (IVF) (Serial Number: US-018-2005). References Fig. 7. Magnetization vs. external magnetic field (bottom) measured at 4.25 K for GdCrx Al12−x (x = 4). exp
μeff deduced from the fitted Curie constant C is equal to 7.87 being fairly well comparable the theoretical value characteristic for a free Gd3+ ion μtheor eff = 7.94 B . The value obtained for χ0 equals 1.246 × 10−6 cm3 /g. Field dependence of magnetization is also shown in Fig. 3b. The value of the magnetization σ obtained at T = 2.0 K in the field H0 = 50.14 kOe is equal to 41.79 Oe cm3 /g or to 4.25 B /Gd ion being lower than theoretical saturation moment expected for Gd ion, i.e. 7 B /Gd. Similar magnetic behaviour is presented for GdCr4 Al8 sample (Figs. 4–7). In this case modified Curie–Weiss law is obeyed (Fig. 4) above TN = 6.75(5) K giving following results: exp Θp = −12.2 K, μeff = 7.67 B , and χ0 = 5.544 × 10−6 cm3 /g. The ac temperature dependence of the magnetic susceptibility recorded in zero external field and with a small amplitude of the oscillating magnetic field strength Hac = 5 Oe reveals an antiferromagnetic phase transition at TN = 6.75(5) K (Fig. 5) for GdCrx Al12−x with x = 4.0. In Fig. 6 temperature dependencies of the real and imaginary parts of the ac magnetic susceptibility for second and third harmonics, however, no any characteristic singularities are visible for both harmonics nearby or below phase transition observed at TN = 6.75 K.
[1] B.Y. Kotur, E. Gratz, in: K.A. Gschneidner Jr., L. Eyring (Eds.), Handbook on the Physics and Chemistry of Rare Earths, vol. 27, Elsevier Science B.V, Amsterdam, 1999, pp. 339–553 (Chapter 175). [2] O.S. Zarechnyuk, R.M. Rykhal’, N.V. German, Visn. Lviv. Univ. Ser. Chem. 12 (1971) 10. [3] O.Y. Emes-Mysenko, Visn. Lviv. Univ. Ser. Chem. 12 (1971) 12. [4] O.S. Zarechnyuk, R.M. Rykhal’, Visn. Lviv. Univ. Ser. Chem. 16 (1974) 5. [5] Y. Verbovytsky, T. Mika, B. Kotur, Prace Naukowe WSP. Cz˛estochowa, Chemia i ochrona s´rodowiska, 10 (2005) 91. [6] R.M. Rykhal’, O.S. Zarechnyuk, O.P. Mats’kiv, Visn. Lviv. Univ. Ser. Chem. 21 (1979) 46. [7] T.I. Yanson, N.B. Manyako, O.I. Bodak, R. Cherny, R.E. Gladyshevskii, K. Yvon, J. Alloys Compd. 219 (1995) 219. [8] P. Villars (Ed.), Pearson’s Handbook, Desk ed. Crystallographic Data of Intermetallic Phases, vols. 1 and 2, ASM, Metals Park, OH, 1997. [9] K.H.J. Buschow, J.H.N. Van Vucht, W.W. Van der Hoogenhof, J. LessComm. Met. 50 (1976) 145. [10] V.M.T. Thiede, W. Jeitschko, S. Niemann, T. Ebel, J. Alloys Compd. 267 (1998) 23. [11] O. Moze, L.D. Tung, J.J.M. Franse, K.H.J. Buschow, J. Alloys Compd. 268 (1998) 39. [12] M.W. Wolff, S. Niemann, T. Ebel, W. Jeitschko, J. Magn. Magn. Mater. 223 (2001) 1. [13] J. Rodriguez-Carvajal, Phys. B 192 (1993) 55. [14] E. Parthe, L. Gelato, B. Chabot, M. Penzo, K. Cenzual, R. Gladyshevskii, TYPIX, Standartized Data and Crystal Chemical Characterization of Inorganic Structure Types, Springer-Verlag, Berlin, 1994.