- Email: [email protected]
Single crystal growth of manganese gallium nitride using Mn–Ga–Na melt
Journal of Alloys and Compounds 364 (2004) 280–282
Single crystal growth of manganese gallium nitride using Mn–Ga–Na melt Masato Aoki a,∗ , Hisanori Yamane b , Masahiko Shimada a , Takashi Kajiwara c a
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan b Center for Interdisciplinary Research, Tohoku University, Aramaki, Aoba-ku, Sendai 980-8578, Japan c Department of Chemistry, Graduate School of Science, Tohoku University, Aramaki, Aoba-ku, Sendai 980-8578, Japan Received 10 April 2003; accepted 6 May 2003
Abstract Manganese gallium nitride (Mn4−x Gax N) single crystals as well as Mn-doped GaN single crystals were prepared by heating a Mn–Ga–Na melt at 750 ◦ C and 5 MPa of N2 pressure. The Mn4−x Gax N crystals had the cubic anti-perovskite-type structure (space group: Pm3m) with a lattice parameter a = 3.8886(9) Å. The single crystals exhibited magnetic transitions from a ferrimagnetic phase with a spin–glass-like disorder to an antiferromagnetic phase at 107 K, and then to a paramagnetic phase at 270 K. From these magnetic transition temperatures, the composition of the Mn4−x Gax N single crystals was estimated to be Mn3.07 Ga0.93 N. © 2003 Elsevier B.V. All rights reserved. Keywords: Magnetically ordered materials; Crystal growth; X-ray diffraction; Magnetic measurements
1. Introduction Substitution of Ga for the Mn(II) site of Mn4 N (Mn(I)3 Mn(II)N) leads to solid solutions of Mn4−x Gax N with a cubic anti-perovskite-type structure [1–4]. The magnetic properties of Mn4−x Gax N were investigated in detail by Fruchart et al. [3] and Navarro et al. [4]. Although Mn4 N and Mn3 GaN is ferrimagnet and antiferromagnet, respectively, Mn4−x Gax N having the composition of 0.70 < x < 1.0 exhibits ferrimagnetism with a spin–glass-like disorder in addition to ferrimagnetism or antiferromagnetism. Therefore, there has been some interest in this peculiar magnetic behavior of Mn4−x Gax N. We have reported on single crystal growth of GaN by the Na flux method [5,6], and recently succeeded in preparing single crystals of CrN by using a Ga–Na flux [7]. In the Ga–Na flux, the role of Ga is to dissolve Cr metal in the melt and Na would play a role of a catalyst to enhance the nitriding of Cr. In this study, we applied the Ga–Na flux method to grow manganese nitride single crystals and obtained Mn4−x Gax N single crystals. Since there were no reports on Mn4−x Gax N single crystal growth, we analyzed ∗
Corresponding author. Tel./fax: +81-22-217-5160. E-mail address: [email protected] (M. Aoki).
0925-8388/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0925-8388(03)00506-1
the crystal structure by X-ray single-crystal diffraction. We also investigated the magnetic properties of the Mn4−x Gax N single crystals.
2. Experimental In an Ar filled glove box (O2 < 1 ppm, H2 O < 1 ppm), 10 mmol of Mn (Kishida Chemical, 99.99%), 15 mmol of Ga (Rasa Industries, 99.99995%) and 30 mmol of Na (Nippon Soda, 99.95%) were weighed and charged into a BN crucible (Showa Denko, 99.5%, 16 mm I.D., 12 mm depth). After the crucible was put into a stainless-steel container, the container was connected to a N2 gas feed line. The apparatus was similar to that used for the GaN single crystal growth by the Na flux method [5]. N2 gas (Nippon Sanso, >99.9999%) was introduced into the container at room temperature for a N2 pressure to be 5 MPa at a growth temperature. Then, the sample was heated to 750 ◦ C and kept at the temperature and N2 pressure for 300 h during the crystal growth. After furnace cooling of the sample to room temperature, Na metal remaining in the crucible was removed by reaction with methanol and ethanol. Products were characterized by X-ray powder diffractometry and energy dispersive X-ray spectroscopy (EDX). X-ray diffraction intensities for the powdered samples
M. Aoki et al. / Journal of Alloys and Compounds 364 (2004) 280–282
281
were collected using CuK␣ radiation with a diffractometer (Rigaku, RINT 2000). EDX spectrum was measured by an energy dispersive X-ray analyzer (Noran, Voyager) installed in a scanning electron microscope (SEM: Jeol, JSM-6320F). The magnetic susceptibility of Mn4−x Gax N single crystals was measured with a SQUID magnetometer (Quantum Design, MPMS2 ) from 5 to 350 K under the magnetic field of 0.5 T. Single-crystal X-ray diffraction intensities were measured by a diffractometer equipped with a two-dimensional CCD area detector (Bruker, SMART1000). MoK␣ radiation (λ = 0.71073 Å) and the ω scan mode were used for the intensity measurements. The lattice parameter was refined by the program SAINT [8]. An analytical X-ray absorption correction was performed using the program SADABS [9]. Crystal structure parameters were refined by the program SHELXL-97 [10].
3. Results and discussion Fig. 1 shows an SEM image of a sample prepared by using the Ga–Na flux at 750 ◦ C and 5 MPa of N2 pressure for 300 h. X-ray powder diffractometry and EDX analysis revealed that the products were cubic anti-perovskite-type Mn4−x Gax N and hexagonal wurtzite-type GaN. Black single crystals of Mn4−x Gax N had cubic habit bounded by {100} faces. The maximum size of the single crystals was about 500 m. Single crystals of GaN were also obtained and the single crystals colored in red. This coloration indicates that Mn is contained into the GaN single crystals. The Mn concentration in the GaN single crystals and the magnetic properties of Mn-doped GaN were reported in a separate paper [11]. The molar susceptibility and inverse molar susceptibility of the Mn4−x Gax N single crystals are plotted against temperature in Fig. 2. Fruchart et al. [3] and Navarro et al. [4] reported the relationship between the composition of
Fig. 1. SEM image of the sample prepared using the Mn–Ga–Na melt at 750 ◦ C and 5 MPa of N2 pressure for 300 h.
Fig. 2. Temperature dependence of molar susceptibility (a) and inverse molar susceptibility (b) of the Mn4−x Gax N single crystals.
Mn4−x Gax N and the magnetic properties. A sample with the composition of 0.85 < x < 1.0 is a ferrimagnetic phase with a spin–glass-like disorder at a ground state and exhibits two magnetic phase transitions by heating. First a second order transition from ferrimagnetism with a spin–glass-like disorder to antiferromagnetism occurs at TC which decreases with increasing x from 210 K (x = 0.85) to 37.6 K (x = 0.95). And then, the sample transforms to a paramagnetic phase at TN which increases with an increase in x from 238 K (x = 0.90) to 281 K (x = 1.0). This transition is first order and gives a lattice contraction with no change of the cubic symmetry. The stoichiometric Mn3 GaN shows only antiferromagnetism at least down to 4.2 K. In our data of the Mn4−x Gax N single crystals (Fig. 2), the magnetic phase transitions from ferrimagnetism with a spin–glass-like disorder to antiferromagnetism and then to paramagnetism were observed in increasing temperature. The transition temperatures were TC = 107 K and TN = 270 K. This suggests that the Mn4−x Gax N single crystals prepared in this study
282
M. Aoki et al. / Journal of Alloys and Compounds 364 (2004) 280–282
Table 1 Crystal data and structure refinement for Mn3.07 Ga0.93 N Empirical formula Formula weight Temperature (K) Crystal system, space group Z, Calculated density (Mg/m3 ) Crystal size (mm) Unit cell dimensions (Å) Volume (Å3 ) Absorption coefficient (mm−1 ) Theta range for data collection (◦ ) Limiting indices Reflections collected/unique Refinement method Data/restraints/parameters Goodness-of-fit on F2 Final R indices [I > 2σ(I)] R indices (all data) Extinction coefficient Largest diff. peak and hole (e Å−3 )
Mn3.07 Ga0.93 N 247.51 293(2) Cubic, Pm3m 1, 6.990 0.25 × 0.25 × 0.25 a = 3.8886(9) 58.80(2) 26.666 5.24–29.48 −5≤h≤5, −4≤k≤5, −4≤l≤5 501/32 [R(int) = 0.0404] Full-matrix least-squares on F2 32/0/6 1.601 R1 = 0.0197, wR2 = 0.0803 R1 = 0.0197, wR2 = 0.0803 5.7(11) 0.770 and −0.601
2 2 R1 = ||Fo | − |Fc ||/|Fo |, wR2 = [w Fo2 − Fc2 / wF2o ]1/2 , 2 2 2 w = 1/[σ Fo + (0.0337P) + 0.0941P], where Fo is the observed structure devistructure factor, Fc is the calculated factor, σ is the standard 2 ation of Fo 2 and P = Max Fo2 , 0 + 2Fc2 /3. S = [w Fo2 − Fc2 / 1/2 (n − p)] , where n is the number of reflections and p is the total number of parameters refined.
that the Mn3.07 Ga0.93 N single crystals prepared in this study had the cubic anti-perovskite-type structure. The refined lattice parameter was a = 3.8886(9) Å. This value is close to the lattice parameter of 3.886 Å at 294 K reported for the Ga3 MnN paramagnetic phase [2] although the difference between the compositions makes the direct comparison difficult.
4. Summary Mn4−x Gax N single crystals were prepared using the Mn–Ga–Na melt at 750 ◦ C and 5 MPa of N2 pressure. The single crystals had black color and cubic habit bounded by {100} faces. The maximum size of the single crystals was about 500 m. The crystal structure was refined with the cubic anti-perovskite-type with the lattice parameter a = 3.8886(9) Å. The crystals transformed from a ferrimagnetic phase with a spin–glass-like disorder to an antiferromagnetic phase, and then to a paramagnetic phase at 107 and 270 K, respectively. The composition of Mn3.07 Ga0.93 N was estimated from the relationship between the composition and the magnetic transition temperatures.
Acknowledgements are not stoichiometric. By comparing the magnetic transition temperatures with the values reported by Navarro et al. [4], the composition of the single crystals was estimated to be Mn3.07 Ga0.93 N. The single crystal X-ray diffraction experiment was performed for the paramagnetic phase of Mn3.07 Ga0.93 N at 293 K. The measurement conditions and the results of the structure analysis are listed in Table 1. The atomic parameters and anisotropic displacement parameters are shown in Tables 2 and 3, respectively. The crystal structure was refined with R1 = 1.97% and wR2 = 8.03% for all data. It was confirmed Table 2 Atomic coordinates and equivalent isotropic displacement parameters (Å2 ) for Mn3.07 Ga0.93 N
Mn1 Mn2 Ga N
Site
x
y
z
U(eq)
Occ.
3c 1a 1a 1a
0.0000 0.0000 0.0000 0.5000
0.5000 0.0000 0.0000 0.5000
0.5000 0.0000 0.0000 0.5000
0.011(1) 0.010(1) 0.010(1) 0.011(3)
1 0.07 0.93 1
Table 3 Anisotropic displacement parameters (Å2 ) for Mn3.07 Ga0.93 N
Mn1 Mn2 Ga N
U11
U22
U33
U23
U13
U12
0.007(1) 0.010(1) 0.010(1) 0.011(3)
0.012(1) 0.010(1) 0.010(1) 0.011(3)
0.012(1) 0.010(1) 0.010(1) 0.011(3)
0.000 0.000 0.000 0.000
0.000 0.000 0.000 0.000
0.000 0.000 0.000 0.000
We thank Y. Hayasaka for the EDX analysis. We are grateful to Nippon Soda Co. Ltd. for a gift of high-purity Na. This work was supported in part by a grant from the Ministry of Education, Culture, Sports, Science and Technology and the Japan Society for the Promotion of Science. MA is a Research Fellow of the Japan Society for the Promotion of Science.
References [1] J.P. Bouchaud, E. Fruchart, G. Lorthioir, R. Fruchart, C.R. Acad. Sci. Paris 262C (1966) 640. [2] M. Nardin, G. Lorthioir, M. Barberon, R. Madar, É. Fruchart, R. Fruchart, C.R. Acad. Sci. Paris 274C (1972) 2168. [3] D. Fruchart, Ph. L’Héritier, R. Fruchart, Mater. Res. Bull. 15 (1980) 490. [4] R. Navarro, J.A. Rojo, J. Garc´ıa, D. González, J. Bartolomé, J. Magn. Magn. Mater. 59 (1986) 221. [5] M. Aoki, H. Yamane, M. Shimada, T. Sekiguchi, T. Hanada, T. Yao, S. Sarayama, F.J. DiSalvo, J. Cryst. Growth 218 (2000) 7. [6] M. Aoki, H. Yamane, M. Shimada, S. Sarayama, F.J. DiSalvo, J. Cryst. Growth 242 (2002) 70. [7] M. Aoki, H. Yamane, M. Shimada, T. Kajiwara, J. Cryst. Growth 246 (2002) 133. [8] Bruker SAINT, Bruker AXS Inc, Madison, WI, USA, 1997. [9] Bruker SADABS, Bruker AXS Inc, Madison, WI, USA, 1997. [10] G.M. Sheldrick, SHELXL-97, University of Göttingen, Germany, 1997. [11] M. Aoki, H. Yamane. M. Shimada, S. Sarayama, H. Iwata, F.J. DiSalvo, Jpn. J. Appl. Phys. (2003) in press.
Single crystal growth of manganese gallium nitride using Mn–Ga–Na melt Masato Aoki a,∗ , Hisanori Yamane b , Masahiko Shimada a , Takashi Kajiwara c a
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan b Center for Interdisciplinary Research, Tohoku University, Aramaki, Aoba-ku, Sendai 980-8578, Japan c Department of Chemistry, Graduate School of Science, Tohoku University, Aramaki, Aoba-ku, Sendai 980-8578, Japan Received 10 April 2003; accepted 6 May 2003
Abstract Manganese gallium nitride (Mn4−x Gax N) single crystals as well as Mn-doped GaN single crystals were prepared by heating a Mn–Ga–Na melt at 750 ◦ C and 5 MPa of N2 pressure. The Mn4−x Gax N crystals had the cubic anti-perovskite-type structure (space group: Pm3m) with a lattice parameter a = 3.8886(9) Å. The single crystals exhibited magnetic transitions from a ferrimagnetic phase with a spin–glass-like disorder to an antiferromagnetic phase at 107 K, and then to a paramagnetic phase at 270 K. From these magnetic transition temperatures, the composition of the Mn4−x Gax N single crystals was estimated to be Mn3.07 Ga0.93 N. © 2003 Elsevier B.V. All rights reserved. Keywords: Magnetically ordered materials; Crystal growth; X-ray diffraction; Magnetic measurements
1. Introduction Substitution of Ga for the Mn(II) site of Mn4 N (Mn(I)3 Mn(II)N) leads to solid solutions of Mn4−x Gax N with a cubic anti-perovskite-type structure [1–4]. The magnetic properties of Mn4−x Gax N were investigated in detail by Fruchart et al. [3] and Navarro et al. [4]. Although Mn4 N and Mn3 GaN is ferrimagnet and antiferromagnet, respectively, Mn4−x Gax N having the composition of 0.70 < x < 1.0 exhibits ferrimagnetism with a spin–glass-like disorder in addition to ferrimagnetism or antiferromagnetism. Therefore, there has been some interest in this peculiar magnetic behavior of Mn4−x Gax N. We have reported on single crystal growth of GaN by the Na flux method [5,6], and recently succeeded in preparing single crystals of CrN by using a Ga–Na flux [7]. In the Ga–Na flux, the role of Ga is to dissolve Cr metal in the melt and Na would play a role of a catalyst to enhance the nitriding of Cr. In this study, we applied the Ga–Na flux method to grow manganese nitride single crystals and obtained Mn4−x Gax N single crystals. Since there were no reports on Mn4−x Gax N single crystal growth, we analyzed ∗
Corresponding author. Tel./fax: +81-22-217-5160. E-mail address: [email protected] (M. Aoki).
0925-8388/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0925-8388(03)00506-1
the crystal structure by X-ray single-crystal diffraction. We also investigated the magnetic properties of the Mn4−x Gax N single crystals.
2. Experimental In an Ar filled glove box (O2 < 1 ppm, H2 O < 1 ppm), 10 mmol of Mn (Kishida Chemical, 99.99%), 15 mmol of Ga (Rasa Industries, 99.99995%) and 30 mmol of Na (Nippon Soda, 99.95%) were weighed and charged into a BN crucible (Showa Denko, 99.5%, 16 mm I.D., 12 mm depth). After the crucible was put into a stainless-steel container, the container was connected to a N2 gas feed line. The apparatus was similar to that used for the GaN single crystal growth by the Na flux method [5]. N2 gas (Nippon Sanso, >99.9999%) was introduced into the container at room temperature for a N2 pressure to be 5 MPa at a growth temperature. Then, the sample was heated to 750 ◦ C and kept at the temperature and N2 pressure for 300 h during the crystal growth. After furnace cooling of the sample to room temperature, Na metal remaining in the crucible was removed by reaction with methanol and ethanol. Products were characterized by X-ray powder diffractometry and energy dispersive X-ray spectroscopy (EDX). X-ray diffraction intensities for the powdered samples
M. Aoki et al. / Journal of Alloys and Compounds 364 (2004) 280–282
281
were collected using CuK␣ radiation with a diffractometer (Rigaku, RINT 2000). EDX spectrum was measured by an energy dispersive X-ray analyzer (Noran, Voyager) installed in a scanning electron microscope (SEM: Jeol, JSM-6320F). The magnetic susceptibility of Mn4−x Gax N single crystals was measured with a SQUID magnetometer (Quantum Design, MPMS2 ) from 5 to 350 K under the magnetic field of 0.5 T. Single-crystal X-ray diffraction intensities were measured by a diffractometer equipped with a two-dimensional CCD area detector (Bruker, SMART1000). MoK␣ radiation (λ = 0.71073 Å) and the ω scan mode were used for the intensity measurements. The lattice parameter was refined by the program SAINT [8]. An analytical X-ray absorption correction was performed using the program SADABS [9]. Crystal structure parameters were refined by the program SHELXL-97 [10].
3. Results and discussion Fig. 1 shows an SEM image of a sample prepared by using the Ga–Na flux at 750 ◦ C and 5 MPa of N2 pressure for 300 h. X-ray powder diffractometry and EDX analysis revealed that the products were cubic anti-perovskite-type Mn4−x Gax N and hexagonal wurtzite-type GaN. Black single crystals of Mn4−x Gax N had cubic habit bounded by {100} faces. The maximum size of the single crystals was about 500 m. Single crystals of GaN were also obtained and the single crystals colored in red. This coloration indicates that Mn is contained into the GaN single crystals. The Mn concentration in the GaN single crystals and the magnetic properties of Mn-doped GaN were reported in a separate paper [11]. The molar susceptibility and inverse molar susceptibility of the Mn4−x Gax N single crystals are plotted against temperature in Fig. 2. Fruchart et al. [3] and Navarro et al. [4] reported the relationship between the composition of
Fig. 1. SEM image of the sample prepared using the Mn–Ga–Na melt at 750 ◦ C and 5 MPa of N2 pressure for 300 h.
Fig. 2. Temperature dependence of molar susceptibility (a) and inverse molar susceptibility (b) of the Mn4−x Gax N single crystals.
Mn4−x Gax N and the magnetic properties. A sample with the composition of 0.85 < x < 1.0 is a ferrimagnetic phase with a spin–glass-like disorder at a ground state and exhibits two magnetic phase transitions by heating. First a second order transition from ferrimagnetism with a spin–glass-like disorder to antiferromagnetism occurs at TC which decreases with increasing x from 210 K (x = 0.85) to 37.6 K (x = 0.95). And then, the sample transforms to a paramagnetic phase at TN which increases with an increase in x from 238 K (x = 0.90) to 281 K (x = 1.0). This transition is first order and gives a lattice contraction with no change of the cubic symmetry. The stoichiometric Mn3 GaN shows only antiferromagnetism at least down to 4.2 K. In our data of the Mn4−x Gax N single crystals (Fig. 2), the magnetic phase transitions from ferrimagnetism with a spin–glass-like disorder to antiferromagnetism and then to paramagnetism were observed in increasing temperature. The transition temperatures were TC = 107 K and TN = 270 K. This suggests that the Mn4−x Gax N single crystals prepared in this study
282
M. Aoki et al. / Journal of Alloys and Compounds 364 (2004) 280–282
Table 1 Crystal data and structure refinement for Mn3.07 Ga0.93 N Empirical formula Formula weight Temperature (K) Crystal system, space group Z, Calculated density (Mg/m3 ) Crystal size (mm) Unit cell dimensions (Å) Volume (Å3 ) Absorption coefficient (mm−1 ) Theta range for data collection (◦ ) Limiting indices Reflections collected/unique Refinement method Data/restraints/parameters Goodness-of-fit on F2 Final R indices [I > 2σ(I)] R indices (all data) Extinction coefficient Largest diff. peak and hole (e Å−3 )
Mn3.07 Ga0.93 N 247.51 293(2) Cubic, Pm3m 1, 6.990 0.25 × 0.25 × 0.25 a = 3.8886(9) 58.80(2) 26.666 5.24–29.48 −5≤h≤5, −4≤k≤5, −4≤l≤5 501/32 [R(int) = 0.0404] Full-matrix least-squares on F2 32/0/6 1.601 R1 = 0.0197, wR2 = 0.0803 R1 = 0.0197, wR2 = 0.0803 5.7(11) 0.770 and −0.601
2 2 R1 = ||Fo | − |Fc ||/|Fo |, wR2 = [w Fo2 − Fc2 / wF2o ]1/2 , 2 2 2 w = 1/[σ Fo + (0.0337P) + 0.0941P], where Fo is the observed structure devistructure factor, Fc is the calculated factor, σ is the standard 2 ation of Fo 2 and P = Max Fo2 , 0 + 2Fc2 /3. S = [w Fo2 − Fc2 / 1/2 (n − p)] , where n is the number of reflections and p is the total number of parameters refined.
that the Mn3.07 Ga0.93 N single crystals prepared in this study had the cubic anti-perovskite-type structure. The refined lattice parameter was a = 3.8886(9) Å. This value is close to the lattice parameter of 3.886 Å at 294 K reported for the Ga3 MnN paramagnetic phase [2] although the difference between the compositions makes the direct comparison difficult.
4. Summary Mn4−x Gax N single crystals were prepared using the Mn–Ga–Na melt at 750 ◦ C and 5 MPa of N2 pressure. The single crystals had black color and cubic habit bounded by {100} faces. The maximum size of the single crystals was about 500 m. The crystal structure was refined with the cubic anti-perovskite-type with the lattice parameter a = 3.8886(9) Å. The crystals transformed from a ferrimagnetic phase with a spin–glass-like disorder to an antiferromagnetic phase, and then to a paramagnetic phase at 107 and 270 K, respectively. The composition of Mn3.07 Ga0.93 N was estimated from the relationship between the composition and the magnetic transition temperatures.
Acknowledgements are not stoichiometric. By comparing the magnetic transition temperatures with the values reported by Navarro et al. [4], the composition of the single crystals was estimated to be Mn3.07 Ga0.93 N. The single crystal X-ray diffraction experiment was performed for the paramagnetic phase of Mn3.07 Ga0.93 N at 293 K. The measurement conditions and the results of the structure analysis are listed in Table 1. The atomic parameters and anisotropic displacement parameters are shown in Tables 2 and 3, respectively. The crystal structure was refined with R1 = 1.97% and wR2 = 8.03% for all data. It was confirmed Table 2 Atomic coordinates and equivalent isotropic displacement parameters (Å2 ) for Mn3.07 Ga0.93 N
Mn1 Mn2 Ga N
Site
x
y
z
U(eq)
Occ.
3c 1a 1a 1a
0.0000 0.0000 0.0000 0.5000
0.5000 0.0000 0.0000 0.5000
0.5000 0.0000 0.0000 0.5000
0.011(1) 0.010(1) 0.010(1) 0.011(3)
1 0.07 0.93 1
Table 3 Anisotropic displacement parameters (Å2 ) for Mn3.07 Ga0.93 N
Mn1 Mn2 Ga N
U11
U22
U33
U23
U13
U12
0.007(1) 0.010(1) 0.010(1) 0.011(3)
0.012(1) 0.010(1) 0.010(1) 0.011(3)
0.012(1) 0.010(1) 0.010(1) 0.011(3)
0.000 0.000 0.000 0.000
0.000 0.000 0.000 0.000
0.000 0.000 0.000 0.000
We thank Y. Hayasaka for the EDX analysis. We are grateful to Nippon Soda Co. Ltd. for a gift of high-purity Na. This work was supported in part by a grant from the Ministry of Education, Culture, Sports, Science and Technology and the Japan Society for the Promotion of Science. MA is a Research Fellow of the Japan Society for the Promotion of Science.
References [1] J.P. Bouchaud, E. Fruchart, G. Lorthioir, R. Fruchart, C.R. Acad. Sci. Paris 262C (1966) 640. [2] M. Nardin, G. Lorthioir, M. Barberon, R. Madar, É. Fruchart, R. Fruchart, C.R. Acad. Sci. Paris 274C (1972) 2168. [3] D. Fruchart, Ph. L’Héritier, R. Fruchart, Mater. Res. Bull. 15 (1980) 490. [4] R. Navarro, J.A. Rojo, J. Garc´ıa, D. González, J. Bartolomé, J. Magn. Magn. Mater. 59 (1986) 221. [5] M. Aoki, H. Yamane, M. Shimada, T. Sekiguchi, T. Hanada, T. Yao, S. Sarayama, F.J. DiSalvo, J. Cryst. Growth 218 (2000) 7. [6] M. Aoki, H. Yamane, M. Shimada, S. Sarayama, F.J. DiSalvo, J. Cryst. Growth 242 (2002) 70. [7] M. Aoki, H. Yamane, M. Shimada, T. Kajiwara, J. Cryst. Growth 246 (2002) 133. [8] Bruker SAINT, Bruker AXS Inc, Madison, WI, USA, 1997. [9] Bruker SADABS, Bruker AXS Inc, Madison, WI, USA, 1997. [10] G.M. Sheldrick, SHELXL-97, University of Göttingen, Germany, 1997. [11] M. Aoki, H. Yamane. M. Shimada, S. Sarayama, H. Iwata, F.J. DiSalvo, Jpn. J. Appl. Phys. (2003) in press.