- Email: [email protected]
Magnetic and structural characterization of the semiconductor FeIn2Se4
ARTICLE IN PRESS
Physica B 384 (2006) 100–102 www.elsevier.com/locate/physb
Magnetic and structural characterization of the semiconductor FeIn2Se4 T. Torresa,, V. Sagredoa, L.M. de Chalbauda, G. Attolinib, F. Bolzonib a
Departamento de Fı´sica, Lab. de Magnetismo, Facultad de Ciencias, Universidad de Los Andes, Me´rida, Venezuela b IMEM-CNR Institute, Parco Area delle Scienze 37 A, 43010 Fontanini, Parma, Italy
Abstract Plate-like single crystals of magnetic semiconductor FeIn2Se4 were grown with a chemical vapour transport technique. The X-ray powder diffraction analyses suggest that the compound crystallize in the hexagonal structure with space group P3m1. We have performed dc magnetization measurements at different magnetic fields on the diluted magnetic semiconductor FeIn2Se4. Low field magnetizations measurements shows irreversibility in the DC magnetization, as evidenced by field cooled and zero field cooled measurements below 17 K, suggesting a spin-glass like behaviour. The high-temperature susceptibility data follow a typical Curie–Weiss law with y ¼ 18372 K which suggest the presence of predominant antiferromagnetic interactions with high degree of frustration. The randomness and frustration necessary for spin-glass behaviour are explained in a manner compatible with the cation and charge ordering present in the material. r 2006 Elsevier B.V. All rights reserved. PACS: 74.25.Ha; 75.50.Pp; 75.10.Pq Keywords: Spin glass; Frustration; Diluted magnetic semiconductor
1. Introduction During recent years, considerable efforts have been focused in layered compounds derived from the II–III2–VI4 family, where II and III are transition metals. These compounds can be described by one of the following crystal systems: cubic spinel, tetragonal defective and hexagonal or rhombohedral structures [1]. Concerning with the last two structures the formation of different polytypes is a very interesting matter no only from the structural point of view, but also because for semimagnetic semiconductors, different polytypes means different atomic positions in the lattice, thus modifying the magnetic interactions. FeIn2Se4 is in fact a layered compound, one of the newest compound whose structural and optical properties has been reported [2,3]. Reil et al. [2] suggested that this compound crystallizes in the hexagonal structure with lattice parameters a ¼ 4.016 A˚ and c ¼ 38.975 A˚. Corresponding author. Tel.: +58 274 2401342; fax: +58 274 2401318.
E-mail addresses: [email protected] (T. Torres), [email protected] (V. Sagredo). 0921-4526/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2006.05.162
We present in this work a structural and magnetic characterization making use of X-ray powder diffraction (XRPD) and DC magnetization.
2. Experimental details Single crystals of FeIn2Se4 have been grown by chemical transport method. Starting material for the crystal growth was a polycrystalline compound prepared by firing suitable mixtures of high-purity elements in evacuated silica ampoules. The single crystals were grown in a two-zone furnace. The optimal growing conditions were 830 1C for the source temperature and 770 1C for the crystallization region over a period of 210 h. The transporting agent was iodine. Structural studies of the powdered crystals were performed by X-ray powder diffraction data. The measurements were realized with a Siemens D500—5 diffractometer, with Bragg-Brentano geometry in y/2y reflection mode and Cu Ka radiation. The data were collected in the 2y angular range 191–901, by steps of 0.051.
ARTICLE IN PRESS T. Torres et al. / Physica B 384 (2006) 100–102
Magnetization measurements were performed in a commercial superconducting quantum interference device (SQUID) magnetometer in both zero field cooling (ZFC) and field cooling (FC) modes, between 5 KpTp300 K and applied fields up to 4000 Oe. 3. Results and discussion The crystal structure at room temperature was characterized by an analysis of the diffraction patterns with the program NBS*AIDS83 and the information recently published by Ceden˜o et al. [4]. In the experimental XRPD profile shown in Fig. 1, it is possible to see peaks related to the reported phase, FeIn2Se4, and additional peaks 18000 16000
2000
14000
Intensidad
12000 1000
10000 8000 6000
0 20 25 30 35 4 0 45 50 55 60 65 70 75 80 2θ
4000 2000 0
20
30
40
50 2θ
60
70
80
Fig. 1. Observed powder diffraction pattern for FeIn2Se4. Inset shows zoom with marked peaks for the unknown phase.
101
corresponding to an unknown secondary phase. The obtained results for the principal phase are reproduced in Table 1. As listed, the measured D values agree well with the calculated ones. It is found that the crystal belongs to an hexagonal structure with space group P3m1 and lattice parameters a ¼ 4.045 A˚ and c ¼ 34.587 A˚. The natural structure of this compound can be described in terms of slabs formed by anion layers, stacked in the c-axis direction and separated by a van der Waals gap [5]. For the layered compounds it is hard to get untextured powder samples; they usually presents preferred orientation which cause some strong intensities in the diffraction process like the reflexion 0 0 8. The obtained c lattice parameter present some discrepancy with the value reported by Reil et al. [2]. This can be attributed to different quality of the samples, single crystal in our case and polycrystal in the Reil work. The temperature dependence of the ZFC-FC magnetization measurements, taken at low field, are shown in Fig. 2. As can be seen from the figure both FC and ZFC magnetization increase with decreasing temperature. However the ZFC data shows a peak at Tf ¼ 17 K where the FC magnetization displays a small hump suggesting the development of some sort of a magnetic state below the peak seen in the ZFC data. The appearances of irreversibility just below the maximum of the low field ZFC suggests a spin-glass like behaviour. Similar results have been observed in others compounds belonging to the same semiconductor family: II–III2–VI4 as FeIn2S4, MnIn2Se4 and FeIn2 S2 Se2 [6–8]. Further evidence of such magnetic behaviour was found in the magnetization curves in ZFC-FC modes taken at higher magnetic fields 500; 2000; 4000 Oe, as shown in Fig. 3. The peak temperature Tf steadily shifts to lower values with increasing applied magnetic field. This
Table 1 Results obtained of the parameter refinement for NBS*AIDS93 of the FeIn2Se4
6.5
System: Hexagonal S.G: P3m1 (156) a ¼ 4.045 A˚, y c ¼ 34.587 A˚, V ¼ 490.170 A˚3
5.5
6.0
Dcal
hkl
2yobs
2ycal
D2y
4.3154 3.4582 3.2415 2.5889 2.3400 2.0071 1.9940 1.8727 1.8212 1.6983 1.6244 1.5508 1.4764 1.3240 1.3003
4.3235 3.4588 3.2469 2.5890 2.3400 2.0089 1.9922 1.8719 1.8204 1.6981 1.6235 1.5507 1.4769 1.3241 1.3005
008 0 0 10 104 109 1 0 11 112 113 117 0 0 19 205 208 1 0 20 1 1 16 210 215
20.565 25.741 27.494 34.620 38.439 45.136 45.450 48.578 50.043 53.946 56.616 59.565 62.896 71.155 72.657
20.526 25.736 27.447 34.618 38.438 45.093 45.493 48.600 50.067 53.954 56.651 59.568 62.872 71.146 72.641
0.039 0.005 0.047 0.002 0.001 0.043 0.043 0.022 0.024 0.008 0.035 0.003 0.024 0.009 0.016
M(15) ¼ 14.5, F(15) ¼ 7.4 (D2y ¼ 0.0212).
M (emu/g)10-4
5.0
Dobs
FeIn2Se4
4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0
50
100
150 T(K)
200
250
300
Fig. 2. FC–ZFC magnetization curves as a function of temperature with applied field of Hap ¼ 10 Oe.
ARTICLE IN PRESS T. Torres et al. / Physica B 384 (2006) 100–102 22 500 Oe 2000 Oe 4000 Oe
18 16 14 12
T=15K
10
4.5 χ(emu/gOe)10-5
20
M(emu/g)10-2
9
5.0
T=14K
8
FeIn2Se4
4.0
7
3.5
6
3.0 5 2.5 4
2.0
8
3
1.5
6
χ-1(g Oe/emu)104
102
2
1.0
T=19K
4
0
2 0
10
20
30 T (K)
40
50
Fig. 3. FC–ZFC magnetization curves taken at three different magnetic fields.
behaviour is in good agreement with the one observe in other spin-glasses systems [9]. The temperature dependence of the low-field DC magnetic susceptibility and its inverse in the range 5–300 K are shown in Fig. 4. In the high temperature range a Curie–Weiss (C–W) behaviour (wdc ¼ C=½T2y is displayed. The slope of w1 vs. T in the range TX100 K has been used for determining the Curie constant C and the paramagnetic Curie temperature y. The obtained value for y ¼ 18372 K indicates a strong antiferromagnetic superexchange interactions between the Fe+2 ions with an effective magnetic moment meff ¼ 5.2 mB. This value is about 6% larger than the expected for free ion. Deviations from the C–W law below 100 K arise with increase of the susceptibility. 4. Conclusions It is well known that frustration and disorder are required properties for the appearing of a spin-glass behaviour. The hexagonal crystal structure proposed for FeIn2Se4 presents an interesting fact: the presence of tetrahedral and octahedral sites in a ratio of n0/nt ¼ 1/2 per unit cell. These sites are filled by Fe and In atoms randomly distributed.
50
100
150 T(K)
200
250
300
Fig. 4. Magnetic susceptibility and its inverse as a function of temperature.
Unfortunately no complete refinement of this structure has been reported to confirm the previous assumption. Therefore we suggest that the random distribution of the magnetic atoms produces the observed spin-glass-like behaviour. The small ratio T f =y 0:1 between the transition temperature and the Curie–Weiss temperature strongly support that a large degree of frustration is indeed present in FeIn2Se4 [8]. It can be concluded that FeIn2Se4 exhibits a spin-glass behaviour with a freezing temperature Tf ¼ 17 K. Some degree of frustration in FeIn2Se4 is reflected by the small value of T f =y 0:1 Further studies are necessary to get a complete crystal structure refinement in order to get the real distribution of the Fe ions on the available lattice sites. References [1] V. Sagredo, G. Attolini, Transworld Res. Network I (2003) 441. [2] S. Reil, H. Haeuseler, J. Alloys Compounds 270 (1998) 83. [3] P.G. Rustamov, B.K. Babaeva, R.S. Gamidov, A. Alidjanov Azerb, Chem. J. 1 (1976) 120. [4] C. Ceden˜o, et al., J. Phys. Chem. Solids 66 (2005) 2049. [5] H. Haeuseler, S.K. Srivastrava, Z. Kristallogr. 215 (2000) 205. [6] V. Sagredo, et al., J. Alloys Compounds 369 (2004) 84. [7] J. Mantilla, et al., J. Magn. Magn. Mater. 272–276 (2004) 1308. [8] G. Goya, A.A. Memo, H.J. Haeuseler, Solid State Chem. 164 (2002) 326. [9] M.C. Moron, J. Campo, F. Palacio, G. Attolini, C. Pelosi, J. Magn. Magn. Mater. 196 (1999) 437.
Physica B 384 (2006) 100–102 www.elsevier.com/locate/physb
Magnetic and structural characterization of the semiconductor FeIn2Se4 T. Torresa,, V. Sagredoa, L.M. de Chalbauda, G. Attolinib, F. Bolzonib a
Departamento de Fı´sica, Lab. de Magnetismo, Facultad de Ciencias, Universidad de Los Andes, Me´rida, Venezuela b IMEM-CNR Institute, Parco Area delle Scienze 37 A, 43010 Fontanini, Parma, Italy
Abstract Plate-like single crystals of magnetic semiconductor FeIn2Se4 were grown with a chemical vapour transport technique. The X-ray powder diffraction analyses suggest that the compound crystallize in the hexagonal structure with space group P3m1. We have performed dc magnetization measurements at different magnetic fields on the diluted magnetic semiconductor FeIn2Se4. Low field magnetizations measurements shows irreversibility in the DC magnetization, as evidenced by field cooled and zero field cooled measurements below 17 K, suggesting a spin-glass like behaviour. The high-temperature susceptibility data follow a typical Curie–Weiss law with y ¼ 18372 K which suggest the presence of predominant antiferromagnetic interactions with high degree of frustration. The randomness and frustration necessary for spin-glass behaviour are explained in a manner compatible with the cation and charge ordering present in the material. r 2006 Elsevier B.V. All rights reserved. PACS: 74.25.Ha; 75.50.Pp; 75.10.Pq Keywords: Spin glass; Frustration; Diluted magnetic semiconductor
1. Introduction During recent years, considerable efforts have been focused in layered compounds derived from the II–III2–VI4 family, where II and III are transition metals. These compounds can be described by one of the following crystal systems: cubic spinel, tetragonal defective and hexagonal or rhombohedral structures [1]. Concerning with the last two structures the formation of different polytypes is a very interesting matter no only from the structural point of view, but also because for semimagnetic semiconductors, different polytypes means different atomic positions in the lattice, thus modifying the magnetic interactions. FeIn2Se4 is in fact a layered compound, one of the newest compound whose structural and optical properties has been reported [2,3]. Reil et al. [2] suggested that this compound crystallizes in the hexagonal structure with lattice parameters a ¼ 4.016 A˚ and c ¼ 38.975 A˚. Corresponding author. Tel.: +58 274 2401342; fax: +58 274 2401318.
E-mail addresses: [email protected] (T. Torres), [email protected] (V. Sagredo). 0921-4526/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2006.05.162
We present in this work a structural and magnetic characterization making use of X-ray powder diffraction (XRPD) and DC magnetization.
2. Experimental details Single crystals of FeIn2Se4 have been grown by chemical transport method. Starting material for the crystal growth was a polycrystalline compound prepared by firing suitable mixtures of high-purity elements in evacuated silica ampoules. The single crystals were grown in a two-zone furnace. The optimal growing conditions were 830 1C for the source temperature and 770 1C for the crystallization region over a period of 210 h. The transporting agent was iodine. Structural studies of the powdered crystals were performed by X-ray powder diffraction data. The measurements were realized with a Siemens D500—5 diffractometer, with Bragg-Brentano geometry in y/2y reflection mode and Cu Ka radiation. The data were collected in the 2y angular range 191–901, by steps of 0.051.
ARTICLE IN PRESS T. Torres et al. / Physica B 384 (2006) 100–102
Magnetization measurements were performed in a commercial superconducting quantum interference device (SQUID) magnetometer in both zero field cooling (ZFC) and field cooling (FC) modes, between 5 KpTp300 K and applied fields up to 4000 Oe. 3. Results and discussion The crystal structure at room temperature was characterized by an analysis of the diffraction patterns with the program NBS*AIDS83 and the information recently published by Ceden˜o et al. [4]. In the experimental XRPD profile shown in Fig. 1, it is possible to see peaks related to the reported phase, FeIn2Se4, and additional peaks 18000 16000
2000
14000
Intensidad
12000 1000
10000 8000 6000
0 20 25 30 35 4 0 45 50 55 60 65 70 75 80 2θ
4000 2000 0
20
30
40
50 2θ
60
70
80
Fig. 1. Observed powder diffraction pattern for FeIn2Se4. Inset shows zoom with marked peaks for the unknown phase.
101
corresponding to an unknown secondary phase. The obtained results for the principal phase are reproduced in Table 1. As listed, the measured D values agree well with the calculated ones. It is found that the crystal belongs to an hexagonal structure with space group P3m1 and lattice parameters a ¼ 4.045 A˚ and c ¼ 34.587 A˚. The natural structure of this compound can be described in terms of slabs formed by anion layers, stacked in the c-axis direction and separated by a van der Waals gap [5]. For the layered compounds it is hard to get untextured powder samples; they usually presents preferred orientation which cause some strong intensities in the diffraction process like the reflexion 0 0 8. The obtained c lattice parameter present some discrepancy with the value reported by Reil et al. [2]. This can be attributed to different quality of the samples, single crystal in our case and polycrystal in the Reil work. The temperature dependence of the ZFC-FC magnetization measurements, taken at low field, are shown in Fig. 2. As can be seen from the figure both FC and ZFC magnetization increase with decreasing temperature. However the ZFC data shows a peak at Tf ¼ 17 K where the FC magnetization displays a small hump suggesting the development of some sort of a magnetic state below the peak seen in the ZFC data. The appearances of irreversibility just below the maximum of the low field ZFC suggests a spin-glass like behaviour. Similar results have been observed in others compounds belonging to the same semiconductor family: II–III2–VI4 as FeIn2S4, MnIn2Se4 and FeIn2 S2 Se2 [6–8]. Further evidence of such magnetic behaviour was found in the magnetization curves in ZFC-FC modes taken at higher magnetic fields 500; 2000; 4000 Oe, as shown in Fig. 3. The peak temperature Tf steadily shifts to lower values with increasing applied magnetic field. This
Table 1 Results obtained of the parameter refinement for NBS*AIDS93 of the FeIn2Se4
6.5
System: Hexagonal S.G: P3m1 (156) a ¼ 4.045 A˚, y c ¼ 34.587 A˚, V ¼ 490.170 A˚3
5.5
6.0
Dcal
hkl
2yobs
2ycal
D2y
4.3154 3.4582 3.2415 2.5889 2.3400 2.0071 1.9940 1.8727 1.8212 1.6983 1.6244 1.5508 1.4764 1.3240 1.3003
4.3235 3.4588 3.2469 2.5890 2.3400 2.0089 1.9922 1.8719 1.8204 1.6981 1.6235 1.5507 1.4769 1.3241 1.3005
008 0 0 10 104 109 1 0 11 112 113 117 0 0 19 205 208 1 0 20 1 1 16 210 215
20.565 25.741 27.494 34.620 38.439 45.136 45.450 48.578 50.043 53.946 56.616 59.565 62.896 71.155 72.657
20.526 25.736 27.447 34.618 38.438 45.093 45.493 48.600 50.067 53.954 56.651 59.568 62.872 71.146 72.641
0.039 0.005 0.047 0.002 0.001 0.043 0.043 0.022 0.024 0.008 0.035 0.003 0.024 0.009 0.016
M(15) ¼ 14.5, F(15) ¼ 7.4 (D2y ¼ 0.0212).
M (emu/g)10-4
5.0
Dobs
FeIn2Se4
4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0
50
100
150 T(K)
200
250
300
Fig. 2. FC–ZFC magnetization curves as a function of temperature with applied field of Hap ¼ 10 Oe.
ARTICLE IN PRESS T. Torres et al. / Physica B 384 (2006) 100–102 22 500 Oe 2000 Oe 4000 Oe
18 16 14 12
T=15K
10
4.5 χ(emu/gOe)10-5
20
M(emu/g)10-2
9
5.0
T=14K
8
FeIn2Se4
4.0
7
3.5
6
3.0 5 2.5 4
2.0
8
3
1.5
6
χ-1(g Oe/emu)104
102
2
1.0
T=19K
4
0
2 0
10
20
30 T (K)
40
50
Fig. 3. FC–ZFC magnetization curves taken at three different magnetic fields.
behaviour is in good agreement with the one observe in other spin-glasses systems [9]. The temperature dependence of the low-field DC magnetic susceptibility and its inverse in the range 5–300 K are shown in Fig. 4. In the high temperature range a Curie–Weiss (C–W) behaviour (wdc ¼ C=½T2y is displayed. The slope of w1 vs. T in the range TX100 K has been used for determining the Curie constant C and the paramagnetic Curie temperature y. The obtained value for y ¼ 18372 K indicates a strong antiferromagnetic superexchange interactions between the Fe+2 ions with an effective magnetic moment meff ¼ 5.2 mB. This value is about 6% larger than the expected for free ion. Deviations from the C–W law below 100 K arise with increase of the susceptibility. 4. Conclusions It is well known that frustration and disorder are required properties for the appearing of a spin-glass behaviour. The hexagonal crystal structure proposed for FeIn2Se4 presents an interesting fact: the presence of tetrahedral and octahedral sites in a ratio of n0/nt ¼ 1/2 per unit cell. These sites are filled by Fe and In atoms randomly distributed.
50
100
150 T(K)
200
250
300
Fig. 4. Magnetic susceptibility and its inverse as a function of temperature.
Unfortunately no complete refinement of this structure has been reported to confirm the previous assumption. Therefore we suggest that the random distribution of the magnetic atoms produces the observed spin-glass-like behaviour. The small ratio T f =y 0:1 between the transition temperature and the Curie–Weiss temperature strongly support that a large degree of frustration is indeed present in FeIn2Se4 [8]. It can be concluded that FeIn2Se4 exhibits a spin-glass behaviour with a freezing temperature Tf ¼ 17 K. Some degree of frustration in FeIn2Se4 is reflected by the small value of T f =y 0:1 Further studies are necessary to get a complete crystal structure refinement in order to get the real distribution of the Fe ions on the available lattice sites. References [1] V. Sagredo, G. Attolini, Transworld Res. Network I (2003) 441. [2] S. Reil, H. Haeuseler, J. Alloys Compounds 270 (1998) 83. [3] P.G. Rustamov, B.K. Babaeva, R.S. Gamidov, A. Alidjanov Azerb, Chem. J. 1 (1976) 120. [4] C. Ceden˜o, et al., J. Phys. Chem. Solids 66 (2005) 2049. [5] H. Haeuseler, S.K. Srivastrava, Z. Kristallogr. 215 (2000) 205. [6] V. Sagredo, et al., J. Alloys Compounds 369 (2004) 84. [7] J. Mantilla, et al., J. Magn. Magn. Mater. 272–276 (2004) 1308. [8] G. Goya, A.A. Memo, H.J. Haeuseler, Solid State Chem. 164 (2002) 326. [9] M.C. Moron, J. Campo, F. Palacio, G. Attolini, C. Pelosi, J. Magn. Magn. Mater. 196 (1999) 437.