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Mn1−xFexIn2Se4: a new layered semiconductor system
Journal of Physics and Chemistry of Solids 66 (2005) 2027–2029 www.elsevier.com/locate/jpcs
Mn1KxFexIn2Se4: a new layered semiconductor system V. Sagredo a,*, T. Torres a, G. Attolini b, F. Bolzoni b a
Lab de Magnetismo, Physics Department, Faculty of Science, Universidad de los Andes, Me´rida, Venezuela b IMEM-CNR Institute, Parco Area delle Scienze 37 A, 43010 Fontanini, Parma, Italy
Abstract Mn1KxFexIn2Se4 compounds (xZ0.1; xZ0.7) were grown by the chemical vapor transport method. X-ray diffraction analysis data show that these compositions crystallize as different polytypes that belong to the hexagonal structure. The crystal symmetry of the sample with xZ0.1 and for the sample with xZ0.7 the space group is P63mc. belongs to the space group R3m The magnetic behavior of both samples has been investigated in the temperature range between 5 and 300 K. Spin-glass-like behavior below the freezing temperature TfZ9 K has been found for the sample with xZ0.7. The sample with Fe content xZ0.1 behaves as a paramagnet down to the lowest experimental measured temperature. High-temperature susceptibility data follow the Curie–Weiss law with a negative paramagnetic temperature indicating predominant antiferromagnetic interactions. Optical studies reveal that both samples (xZ0.1; 0.7) are direct band gap semiconductors. The temperature dependence of the energy gap fits Varshni relation quite well. q 2005 Elsevier Ltd. All rights reserved. Keywords: Semiconductors; Crystal growth; X-ray diffraction; Magnetic properties
1. Introduction Diluted magnetic semiconductors (DMS) are of great current interest because of their peculiar magnetic and magneto-optical properties that arise from the presence of magnetic ions in the lattice. DMS derived from the II–III2–VI4 are interesting because they exhibit wide transparency intervals, high photosensitivity and strong luminescence [1]. They mainly crystallize in the following three structures: the cubic spinel structure, a tetragonal defect structure and a layered structure. An interesting fact in these structures is the different number of tetrahedral and octahedral sites per unit cell. Thus in the layered structure there are (noC2nt) sites. Layered compounds, as H. Haeuseler et al. have reported, form a very interesting group because of their particular structural characteristics [2]. MnIn2Se4 exhibits rhombohedral structure whose unit cell consists of three van der with space group R3m, Waals bonded layers, each of which consists of four Se layers. Between these layers there are octahedral and tetrahedral sites, which are filled by Mn and In atoms [3]. For FeIn2Se4, which
* Corresponding author. Fax: C58 0274 2401318. E-mail address: [email protected] (V. Sagredo).
0022-3697/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.jpcs.2005.09.085
has been less studied, S. Reil et al. [4] proposed an hexagonal ˚ , cZ38.975 A ˚. unit cell with lattice parameters aZ4.016 A In this paper, we report on the growth of single crystals of Mn1KxFexIn2Se4 compounds (xZ0.1; xZ0.7) and their structural, optical and magnetic characterization. 2. Experimental details Mn1KxFexIn2Se4 single crystals with nominal Fe concentrations 0%x%1.0 were grown by the chemical vapor transport method using iodine as a transporting agent. About 2 g of the reactants were introduced into a quartz ampoule. The ampoule was placed in a two-zone furnace with the reactants at the lower temperature end, at 800 8C. This facilitated the formation of the multinary compounds used as a starting material for crystal growth. After three days the temperature gradient was inverted, leaving the temperature in the deposition zone at 750 8C when the Fe concentration is x!0.5 and 770 8C when xR0.5. After 10 days the resulting crystals appear as black plates with dimensions of about 20–30 mm2. X-ray powder diffraction (XRPD) patterns of the powdered samples were recorded using a Siemens D6000 powder diffractometer which makes use of Ni-filtered CuKa radiation in scanning mode with a step time of 0.05 8/s. The optical absorption spectra were obtained using an Acton Research Spectra Pro500 spectrometer, in the range of
2028
V. Sagredo et al. / Journal of Physics and Chemistry of Solids 66 (2005) 2027–2029
Mn 0 . 9 F e 0 . 1 I n 2 S e 4
14
H = 10 Oe
6
12
5
10
4
8
3
6 2
χ – 1 10 4 ( g O e/ emu)
χ 10 – 5 ( em u/ g O e)
7 16
4 1
2 0
0.7–1.6 eV. The samples were mounted on a cold finger of a Janis closed cycle refrigerator to record spectra at different temperature. Low field magnetization measurements (10 Oe) were performed in the temperature range 5 K%T%300 K with a Quantum Design SQUID magnetometer.
3. Results and discussion Figure 1 shows the experimental XRPD profiles for samples with x value between 0.1 and 0.9. It is possible to note a distinct behavior that depends on the Fe concentration. Replacing Mn, Fe up to 40% does not destroy the rhombohedral phase of MnIn2Se4. When xO0.7, the system becomes hexagonal with a space group P63mc, possible a polytype of the ZnIn2S4 structure, the powder diffraction data could be totally indexed based on a rhombohedral cell unit for samples with x%0.5 and a hexagonal unit cell for x%0.5, using the NBS*AIDS program.
1.26
χ (emu/g*Oers)10–4
4
1.24 1.23
3
1.22 1.21
2
1.20
0
50
100
150
200
250
T = 295K T = 240K T = 175K T = 125K T = 70K T = 50K T = 30 T = 10K
300
T(K)
1 0 0.6
0.8
1.0
1.2
1.4
200
250
3 00
0
2.0
2.0
Mn0.3Fe0.7In2Se4.
1.8
1.8
H = 10 Gauss.
1.6
1.25
Eg (eV)
(ahn)2 *105(cm–2eV2)
5
150 T(K)
For samples with xZ0.1 and 0.7, the obtained lattice ˚ ; cZ39.514 A ˚; parameters and space group were aZ4.062 A ˚ ˚ R3m and aZ4.058 A cZ34.750 A; P63mc, respectively. The absorption edge of Mn0.9Fe0.1In2Se4 recorded at different temperatures is shown in Fig. 2, where (ahn)2 is plotted as a function of the incident photon energy. An extrapolation of the linear portion of the plots as (ahn)2 tends to 0, indicates that the energy of the direct transition is 1.2 eV at room temperature. The inset shows calculation of the thermal shift of the energy gap, determined by fitting the data to the Varshni relation [5], from which we obtained the values aZ 3.9!10K4 eV/K and bZ344.8 K. The temperature dependence of the magnetic susceptibility, c, and its inverse in the range 5–300 K are shown in Fig. 3, for the sample with xZ0.1. No magnetic order was observed down to 5 K. However, below about 90 K, the 1/c plot deviates from the straight line, showing a down turn towards the temperature axis, which suggests an increase in the magnetic interactions between the magnetic ions. Zero-field cooling (ZFC) and field-cooling (FC) magnetization cycles as a function of temperature for sample with xZ0.7
Mn0.1Fe0.9In2Se4. t = 200mm
Mn0.9Fe0.1In2Se4
100
Fig. 3. Temperature dependence of the magnetic susceptibility and its inverse for Mn0.9Fe0.1In2Se4.
6 1.27
50
χ 10–4(emu/g Oe)
Fig. 1. X-ray diffraction pattern of Mn1KxFexIn2Se4 with x values taken from xZ0.1 to xZ0.9.
0
1.4 1.2
1.6 1.4 1.2
ZFC FC
1.0
1.0
0.8
0.8
0.6 0
10
20
30 40 T(K)
100
150 T(K)
0.6
50
60
0.4 0.2 1.6
E(eV) Fig. 2. Optical absorption spectrum of Mn0.9Fe0.1In2Se4 single crystal. The inset shows the temperature dependence of the energy gap.
0.0
0
50
200
250
300
Fig. 4. ZFC and FC dc magnetization as a function of temperature for Mn0.3Fe0.7In2Se4 in a field of 10 Oe.
V. Sagredo et al. / Journal of Physics and Chemistry of Solids 66 (2005) 2027–2029
are shown in Fig. 4. As one can see from the figure, the ZFC magnetization shows a peak at 9 K where as the FC magnetization displays a small hump. This indicates the development of some irreversible behavior similar to that of iron-containing thiospinels [6]. The appearance of that irreversibility just below the maximum in the ZFC curve has been assumed indicative of spin-glass-like behavior. At higher temperature (TR100 K), a Curie–Weiss behavior (cZC/(TK q)) is displayed for xZ0.1 and 0.7 samples, with qZK8k and K131 K, respectively, which suggests predominant antiferromagnetic interactions. These results suggest that in sample with xZ0.7 some degree of frustration and structural disorder is present in the lattice [7]. The small ratio Tf/qz0.1 indicates that a large degree of frustration is indeed present in Mn0.3Fe0.7In2Se4. In summary, new quaternary selenide Mn1KxFexIn2Se4 (xZ0.1; 0.7) single crystals have been grown in different polytypes of the hexagonal structure. Magnetic susceptibility studies reveal that both compounds present antiferromagnetic interactions between the magnetic ions. The sample having the higher Fe concentration, Mn0.3Fe0.7In2Se4 exhibits spin-glass-like behavior below 9 K. Optical absorption studies show that this compound is a direct band gap semiconductor.
2029
Acknowledgements The authors (V.S and T.T.) gratefully appreciate the support of this research by grants from CDCHT-ULA. References [1] V. Sagredo, G. Attolini, Structural and magnetic properties of II–III2–VI4 semimagnetic semiconductors, Recent Research Development in Magnetism and Magnetic Meterial Transwold Research Network, vol. I, 2003, pp. 441–463. [2] H. Haeuseler, S.K. Srevastava, Phase equilibria and layered phases in the systems A2X3–M2X3–M 0 X (AZ Ga,In; MZ trivalent metal; M 0 Z divalent metal; XZS,Se), Z. Kristallogr. 215 (2000) 205–221. [3] K.J. Range, U. Klement, G. Doll, E. Buscher, J. Baumann, The crystal structure of MnIn2Se4 a ternary layered semiconductor, Z. Naturforsch. 46b (1991) 1122–11234. [4] S. Reil, H. Haeuseler, Materials with layered structures X1: subsolidus phase diagram of the FeIn2Se4–FeIn2S4, J. Alloys. Comp. 270 (1998) 83–87. [5] Y.P. Varshni, Temperature dependence of the energy gap in semiconductors, Physica 34 (1967) 149–154. [6] G.F. Goya, H.R. Rechenberg, V. Sagredo, Study of the spin-glass transition in FeCr2x In2–2x S4 thiospinel, J. Magn. Magn. Mater. 226–230 (2001) 1298–1299. [7] G.F. Goya, A. Memo, H. Haeuseler, Magnetic and Mossbauer study of the novel FeIn2S2Se2 layered compound, J. Solid State Chem. 164 (2002) 326– 331.
Mn1KxFexIn2Se4: a new layered semiconductor system V. Sagredo a,*, T. Torres a, G. Attolini b, F. Bolzoni b a
Lab de Magnetismo, Physics Department, Faculty of Science, Universidad de los Andes, Me´rida, Venezuela b IMEM-CNR Institute, Parco Area delle Scienze 37 A, 43010 Fontanini, Parma, Italy
Abstract Mn1KxFexIn2Se4 compounds (xZ0.1; xZ0.7) were grown by the chemical vapor transport method. X-ray diffraction analysis data show that these compositions crystallize as different polytypes that belong to the hexagonal structure. The crystal symmetry of the sample with xZ0.1 and for the sample with xZ0.7 the space group is P63mc. belongs to the space group R3m The magnetic behavior of both samples has been investigated in the temperature range between 5 and 300 K. Spin-glass-like behavior below the freezing temperature TfZ9 K has been found for the sample with xZ0.7. The sample with Fe content xZ0.1 behaves as a paramagnet down to the lowest experimental measured temperature. High-temperature susceptibility data follow the Curie–Weiss law with a negative paramagnetic temperature indicating predominant antiferromagnetic interactions. Optical studies reveal that both samples (xZ0.1; 0.7) are direct band gap semiconductors. The temperature dependence of the energy gap fits Varshni relation quite well. q 2005 Elsevier Ltd. All rights reserved. Keywords: Semiconductors; Crystal growth; X-ray diffraction; Magnetic properties
1. Introduction Diluted magnetic semiconductors (DMS) are of great current interest because of their peculiar magnetic and magneto-optical properties that arise from the presence of magnetic ions in the lattice. DMS derived from the II–III2–VI4 are interesting because they exhibit wide transparency intervals, high photosensitivity and strong luminescence [1]. They mainly crystallize in the following three structures: the cubic spinel structure, a tetragonal defect structure and a layered structure. An interesting fact in these structures is the different number of tetrahedral and octahedral sites per unit cell. Thus in the layered structure there are (noC2nt) sites. Layered compounds, as H. Haeuseler et al. have reported, form a very interesting group because of their particular structural characteristics [2]. MnIn2Se4 exhibits rhombohedral structure whose unit cell consists of three van der with space group R3m, Waals bonded layers, each of which consists of four Se layers. Between these layers there are octahedral and tetrahedral sites, which are filled by Mn and In atoms [3]. For FeIn2Se4, which
* Corresponding author. Fax: C58 0274 2401318. E-mail address: [email protected] (V. Sagredo).
0022-3697/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.jpcs.2005.09.085
has been less studied, S. Reil et al. [4] proposed an hexagonal ˚ , cZ38.975 A ˚. unit cell with lattice parameters aZ4.016 A In this paper, we report on the growth of single crystals of Mn1KxFexIn2Se4 compounds (xZ0.1; xZ0.7) and their structural, optical and magnetic characterization. 2. Experimental details Mn1KxFexIn2Se4 single crystals with nominal Fe concentrations 0%x%1.0 were grown by the chemical vapor transport method using iodine as a transporting agent. About 2 g of the reactants were introduced into a quartz ampoule. The ampoule was placed in a two-zone furnace with the reactants at the lower temperature end, at 800 8C. This facilitated the formation of the multinary compounds used as a starting material for crystal growth. After three days the temperature gradient was inverted, leaving the temperature in the deposition zone at 750 8C when the Fe concentration is x!0.5 and 770 8C when xR0.5. After 10 days the resulting crystals appear as black plates with dimensions of about 20–30 mm2. X-ray powder diffraction (XRPD) patterns of the powdered samples were recorded using a Siemens D6000 powder diffractometer which makes use of Ni-filtered CuKa radiation in scanning mode with a step time of 0.05 8/s. The optical absorption spectra were obtained using an Acton Research Spectra Pro500 spectrometer, in the range of
2028
V. Sagredo et al. / Journal of Physics and Chemistry of Solids 66 (2005) 2027–2029
Mn 0 . 9 F e 0 . 1 I n 2 S e 4
14
H = 10 Oe
6
12
5
10
4
8
3
6 2
χ – 1 10 4 ( g O e/ emu)
χ 10 – 5 ( em u/ g O e)
7 16
4 1
2 0
0.7–1.6 eV. The samples were mounted on a cold finger of a Janis closed cycle refrigerator to record spectra at different temperature. Low field magnetization measurements (10 Oe) were performed in the temperature range 5 K%T%300 K with a Quantum Design SQUID magnetometer.
3. Results and discussion Figure 1 shows the experimental XRPD profiles for samples with x value between 0.1 and 0.9. It is possible to note a distinct behavior that depends on the Fe concentration. Replacing Mn, Fe up to 40% does not destroy the rhombohedral phase of MnIn2Se4. When xO0.7, the system becomes hexagonal with a space group P63mc, possible a polytype of the ZnIn2S4 structure, the powder diffraction data could be totally indexed based on a rhombohedral cell unit for samples with x%0.5 and a hexagonal unit cell for x%0.5, using the NBS*AIDS program.
1.26
χ (emu/g*Oers)10–4
4
1.24 1.23
3
1.22 1.21
2
1.20
0
50
100
150
200
250
T = 295K T = 240K T = 175K T = 125K T = 70K T = 50K T = 30 T = 10K
300
T(K)
1 0 0.6
0.8
1.0
1.2
1.4
200
250
3 00
0
2.0
2.0
Mn0.3Fe0.7In2Se4.
1.8
1.8
H = 10 Gauss.
1.6
1.25
Eg (eV)
(ahn)2 *105(cm–2eV2)
5
150 T(K)
For samples with xZ0.1 and 0.7, the obtained lattice ˚ ; cZ39.514 A ˚; parameters and space group were aZ4.062 A ˚ ˚ R3m and aZ4.058 A cZ34.750 A; P63mc, respectively. The absorption edge of Mn0.9Fe0.1In2Se4 recorded at different temperatures is shown in Fig. 2, where (ahn)2 is plotted as a function of the incident photon energy. An extrapolation of the linear portion of the plots as (ahn)2 tends to 0, indicates that the energy of the direct transition is 1.2 eV at room temperature. The inset shows calculation of the thermal shift of the energy gap, determined by fitting the data to the Varshni relation [5], from which we obtained the values aZ 3.9!10K4 eV/K and bZ344.8 K. The temperature dependence of the magnetic susceptibility, c, and its inverse in the range 5–300 K are shown in Fig. 3, for the sample with xZ0.1. No magnetic order was observed down to 5 K. However, below about 90 K, the 1/c plot deviates from the straight line, showing a down turn towards the temperature axis, which suggests an increase in the magnetic interactions between the magnetic ions. Zero-field cooling (ZFC) and field-cooling (FC) magnetization cycles as a function of temperature for sample with xZ0.7
Mn0.1Fe0.9In2Se4. t = 200mm
Mn0.9Fe0.1In2Se4
100
Fig. 3. Temperature dependence of the magnetic susceptibility and its inverse for Mn0.9Fe0.1In2Se4.
6 1.27
50
χ 10–4(emu/g Oe)
Fig. 1. X-ray diffraction pattern of Mn1KxFexIn2Se4 with x values taken from xZ0.1 to xZ0.9.
0
1.4 1.2
1.6 1.4 1.2
ZFC FC
1.0
1.0
0.8
0.8
0.6 0
10
20
30 40 T(K)
100
150 T(K)
0.6
50
60
0.4 0.2 1.6
E(eV) Fig. 2. Optical absorption spectrum of Mn0.9Fe0.1In2Se4 single crystal. The inset shows the temperature dependence of the energy gap.
0.0
0
50
200
250
300
Fig. 4. ZFC and FC dc magnetization as a function of temperature for Mn0.3Fe0.7In2Se4 in a field of 10 Oe.
V. Sagredo et al. / Journal of Physics and Chemistry of Solids 66 (2005) 2027–2029
are shown in Fig. 4. As one can see from the figure, the ZFC magnetization shows a peak at 9 K where as the FC magnetization displays a small hump. This indicates the development of some irreversible behavior similar to that of iron-containing thiospinels [6]. The appearance of that irreversibility just below the maximum in the ZFC curve has been assumed indicative of spin-glass-like behavior. At higher temperature (TR100 K), a Curie–Weiss behavior (cZC/(TK q)) is displayed for xZ0.1 and 0.7 samples, with qZK8k and K131 K, respectively, which suggests predominant antiferromagnetic interactions. These results suggest that in sample with xZ0.7 some degree of frustration and structural disorder is present in the lattice [7]. The small ratio Tf/qz0.1 indicates that a large degree of frustration is indeed present in Mn0.3Fe0.7In2Se4. In summary, new quaternary selenide Mn1KxFexIn2Se4 (xZ0.1; 0.7) single crystals have been grown in different polytypes of the hexagonal structure. Magnetic susceptibility studies reveal that both compounds present antiferromagnetic interactions between the magnetic ions. The sample having the higher Fe concentration, Mn0.3Fe0.7In2Se4 exhibits spin-glass-like behavior below 9 K. Optical absorption studies show that this compound is a direct band gap semiconductor.
2029
Acknowledgements The authors (V.S and T.T.) gratefully appreciate the support of this research by grants from CDCHT-ULA. References [1] V. Sagredo, G. Attolini, Structural and magnetic properties of II–III2–VI4 semimagnetic semiconductors, Recent Research Development in Magnetism and Magnetic Meterial Transwold Research Network, vol. I, 2003, pp. 441–463. [2] H. Haeuseler, S.K. Srevastava, Phase equilibria and layered phases in the systems A2X3–M2X3–M 0 X (AZ Ga,In; MZ trivalent metal; M 0 Z divalent metal; XZS,Se), Z. Kristallogr. 215 (2000) 205–221. [3] K.J. Range, U. Klement, G. Doll, E. Buscher, J. Baumann, The crystal structure of MnIn2Se4 a ternary layered semiconductor, Z. Naturforsch. 46b (1991) 1122–11234. [4] S. Reil, H. Haeuseler, Materials with layered structures X1: subsolidus phase diagram of the FeIn2Se4–FeIn2S4, J. Alloys. Comp. 270 (1998) 83–87. [5] Y.P. Varshni, Temperature dependence of the energy gap in semiconductors, Physica 34 (1967) 149–154. [6] G.F. Goya, H.R. Rechenberg, V. Sagredo, Study of the spin-glass transition in FeCr2x In2–2x S4 thiospinel, J. Magn. Magn. Mater. 226–230 (2001) 1298–1299. [7] G.F. Goya, A. Memo, H. Haeuseler, Magnetic and Mossbauer study of the novel FeIn2S2Se2 layered compound, J. Solid State Chem. 164 (2002) 326– 331.