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Crystal growth, optical and magnetic properties of the Cr-doped Cu2SnGe3 semiconductor
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 272–276 (2004) e1567–e1569
Crystal growth, optical and magnetic properties of the Cr-doped Cu2SnGe3 semiconductor H. Romeroa,*, L. Nievesa, M. Chourioa, R. Echeverriab, I. Carreronc, B. Ramirezd, R. Zyslere,1 a
Grupo de Magnetismo, Department of Physics, Faculty of Science, Facultad de Ciencias, Universidad de Los Andes, M!erida 5101, Venezuela b ! Centro de Optica, Facultad de Ciencias, Universidad de Los Andes, M!erida 5101, Venezuela c Centro de Espectroscop!ıa Molecular, Facultad de Ciencias, Universidad de Los Andes, M!erida 5101, Venezuela d Centro Nacional de Cristalograf!ıa, Facultad de Ciencias, Universidad de Los Andes, M!erida 5101, Venezuela e ! Centro Atomico Bariloche, Lab. Resonancia, 8400 S.C. de Bariloche, RN, Argentina
Abstract Compound Cu2SnSe3:Crx with nominal composition x ¼ 0:08 was grown by direct fusion in a vertical oven. At 500 C was annealed during 220 h. The sample was crystallized in a monoclinic system, in the Cc space group. The temperature dependence of magnetization does not change in the (fieldcooled–zero-field-cooled) curves. At 42 K a magnetization jump is observed. The Curie temperature shifted probably due to lattice distortion. The low-temperature magnetic moment 0:37 mB was calculated. A direct band gap energy was observed at 300 K. r 2003 Elsevier B.V. All rights reserved. PACS: 81.05.Hd; 61.72.Ww; 74.25.Gz; 74.25.Ha Keywords: Ternary semiconductors; Crystal growth; Susceptibility; Optical absortion; Cu2SnSe3:Cr2+
1. Introduction The electrical and optical properties of I2–IV–VI3 semiconductors have been extensively studied [1–5]. Usually, these compounds crystallize in a monoclinic structure, or in sphalerite superstructure. For instance, for Cu2SnSe3 Marcano et al. [4] have reported a monoclinic structures and estimated a fundamental energy gap of 0.843 eV at room temperature. In the Mn-doped Cu2GeSe3, Echeverria et al. [5,7] estimated that a direct band gap energy, dependent on temperature, shifts to lower energy when is compared with undoped material. In Cu2GeSe3:Co2+ the Burstein– Moss effect, due to overlaping of the energy level of *Corresponding author. Tel.: +59-274-2401342; fax: +59274-2401286. E-mail address: [email protected] (H. Romero). 1 Also correspond to.
Co+2 and the conduction band of Cu2GeSe3:Co2+, is not observed [6]. The purpose of this work is to obtain some information about the crystal growth, crystalline structure and the magnetic and optical characteristics, when Cr ion is incorporated as a dopant in the semiconductor Cu2SnSe3 by substitution with Cr2+ ions in the sites, which are occupied by Cu2+ ions with similar value of atomic radius. According to our knowledge, no magnetic measurements have been performed in this hypothetical compound, in which is observed a weak magnetic response.
2. Experimental details The Cr-doped Cu2SnSe3:Cr0.08 was prepared by direct fusion method in a vertical oven by mixing the highpurity Cu, Sn, Se and Cr in a sealed and evacuated quartz tube, heated from room temperature up to
0304-8853/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.12.807
ARTICLE IN PRESS e1568
H. Romero et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) e1567–e1569
1150 C. Heating and cooling processes were implemented in several stages. At 500 C, the sample was annealed for 220 h and finally cooled until the room temperature. Ingots of Cu2SnSe3:Cr0.08 were chemically analyzed by atomic absorption spectrometer model AAZeeman 220 in order to determinate the Cr concentration. The compositional microanalysis of Cu2SnSe3 has been carried out by the EDX technique incorporated into the SEM Hitachi S-250. The X-ray data were recorded at room temperature by a Siemens diffractometer. The spectra of absorption coefficient were obtained by using a Fourier transform infrared spectrometer (FTIR) Perkin-Elmer model 1725X in the energy range of 0.1–1.0 eV at room temperature. Magnetic susceptibility measurements were performed by using a quantum design SQUID in the temperature range of 5– 300 K with an external applied field of 200 G.
3. Results and discussion Cr concentration was calculated as 1.2470.03 mg/g of sample. The relative chemical composition of Cu:Sn:Se was 30.3:15.9:53.8 at%, close to the ideal value of 2:1:3. The lattice constants, obtained from the X-rays diffrac( tion peaks, are given as a ¼ 6:950ð3Þ A, ( c ¼ 6:2567ð3Þ A, ( b ¼ 108:95ð1Þ; which b ¼ 13:0613ð6Þ A, correspond to a monoclinic system Cc and z ¼ 4: The data of the low-field (H ¼ 200 G) temperature dependence of the-zero-field-cooled (ZFC) and field-cooled (FC) magnetization are shown in Fig. 1. A reversible magnetic behaviour is observed. No evidence of cooperative magnetic order could be found, in agreement with magnetic measurements a paramagnetic behaviour is observed. However, one could observe a jump of about 42 K without noticeable change of the involved magnetic moment, because at lower and higher
Fig. 2. Plot of ðahnÞ2 vs. hn for Cu2SnSe3:Cr0.08 (T=300 K).
temperatures the inverse susceptibility has a similar slope. A shift of Curie temperature could be associated with a lattice distortion. From the susceptibility data, the Curie constant C ¼ 3:47ð4Þ 105 emu K/g, the Neel temperature yN ¼ 11:6ð7Þ K and the magnetic moment m ¼ 0:37 mB were calculated. The presence of magnetic ion leads to the interactions with the electronic bands, so as exchange interactions between magnetic ions. These interactions are strongly influenced by the ground state of the magnetic ion. Magnetic ion Cr2+ can occupy the Cu2+sites. Absorption coefficient was obtained by transmittance measurements in the range of 0.1–1.0 eV at room temperature, as observed in the curve ðahnÞ2 vs. hn in Fig. 2. The band gap edge of 0.372 eV was calculated by extrapolation of the linear region when ðahnÞ2 -0 in the plot. The intrinsic absorption edge corresponds to a direct transition.
4. Conclusions The X-ray diffraction pattern shows that Cu2SnSe3:Crx crystallizes in the monoclinic structure in a Cc group space. When Cr2+ ion participates as an active doping, a decrease of band gap is observed because of a change in the density of states. The magnetic susceptibility was determined in the temperature range of 5– 300 K. It follows Curie–Weiss law and the absence of cooperative magnetic ordering is observed in the FC– ZFC magnetization curves.
Acknowledgements
Fig. 1. Inverse of magnetic susceptibility for Cu2SnSe3:Cr2+.
This work has been accomplished with a financial support under CDCHT project No C-961-99-05-A. Thanks to Mr. P. Cancines to provide support for FTIR use in optical measurements.
ARTICLE IN PRESS H. Romero et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) e1567–e1569
References [1] L.I. Berger, V.D. Prochukhan, Ternary Diamond-like Semiconductors, New York, 1969, pp. 55–63. [2] J. Rivet, Ann. Chim. 10 (1965) 247. ! D. Bracho, G. Sanchez, J. Appl. [3] G. Marcano, C. Rincon, Phys. 90 (2001) 4.
e1569
! G. Marin, R. Tovar, G. Delgado, [4] G. Marcano, C. Rincon, J. Appl. Phys. 92 (2002) 4. [5] R. Echeverr!ıa, L. Nieves, G. Marcano, Phys. Stat. Sol. (b) 220 (2000) 285. [6] J. Ju Lee, Ch. Soo Yang, Y. Sin Park, K. Ho Kim, W. Tek Kim, J. Appl. Phys. 86 (1999) 5. [7] Yang-Lae Lee, Wha-Tek Kim, Phys. Rev. B 50 (1994) 15.
Journal of Magnetism and Magnetic Materials 272–276 (2004) e1567–e1569
Crystal growth, optical and magnetic properties of the Cr-doped Cu2SnGe3 semiconductor H. Romeroa,*, L. Nievesa, M. Chourioa, R. Echeverriab, I. Carreronc, B. Ramirezd, R. Zyslere,1 a
Grupo de Magnetismo, Department of Physics, Faculty of Science, Facultad de Ciencias, Universidad de Los Andes, M!erida 5101, Venezuela b ! Centro de Optica, Facultad de Ciencias, Universidad de Los Andes, M!erida 5101, Venezuela c Centro de Espectroscop!ıa Molecular, Facultad de Ciencias, Universidad de Los Andes, M!erida 5101, Venezuela d Centro Nacional de Cristalograf!ıa, Facultad de Ciencias, Universidad de Los Andes, M!erida 5101, Venezuela e ! Centro Atomico Bariloche, Lab. Resonancia, 8400 S.C. de Bariloche, RN, Argentina
Abstract Compound Cu2SnSe3:Crx with nominal composition x ¼ 0:08 was grown by direct fusion in a vertical oven. At 500 C was annealed during 220 h. The sample was crystallized in a monoclinic system, in the Cc space group. The temperature dependence of magnetization does not change in the (fieldcooled–zero-field-cooled) curves. At 42 K a magnetization jump is observed. The Curie temperature shifted probably due to lattice distortion. The low-temperature magnetic moment 0:37 mB was calculated. A direct band gap energy was observed at 300 K. r 2003 Elsevier B.V. All rights reserved. PACS: 81.05.Hd; 61.72.Ww; 74.25.Gz; 74.25.Ha Keywords: Ternary semiconductors; Crystal growth; Susceptibility; Optical absortion; Cu2SnSe3:Cr2+
1. Introduction The electrical and optical properties of I2–IV–VI3 semiconductors have been extensively studied [1–5]. Usually, these compounds crystallize in a monoclinic structure, or in sphalerite superstructure. For instance, for Cu2SnSe3 Marcano et al. [4] have reported a monoclinic structures and estimated a fundamental energy gap of 0.843 eV at room temperature. In the Mn-doped Cu2GeSe3, Echeverria et al. [5,7] estimated that a direct band gap energy, dependent on temperature, shifts to lower energy when is compared with undoped material. In Cu2GeSe3:Co2+ the Burstein– Moss effect, due to overlaping of the energy level of *Corresponding author. Tel.: +59-274-2401342; fax: +59274-2401286. E-mail address: [email protected] (H. Romero). 1 Also correspond to.
Co+2 and the conduction band of Cu2GeSe3:Co2+, is not observed [6]. The purpose of this work is to obtain some information about the crystal growth, crystalline structure and the magnetic and optical characteristics, when Cr ion is incorporated as a dopant in the semiconductor Cu2SnSe3 by substitution with Cr2+ ions in the sites, which are occupied by Cu2+ ions with similar value of atomic radius. According to our knowledge, no magnetic measurements have been performed in this hypothetical compound, in which is observed a weak magnetic response.
2. Experimental details The Cr-doped Cu2SnSe3:Cr0.08 was prepared by direct fusion method in a vertical oven by mixing the highpurity Cu, Sn, Se and Cr in a sealed and evacuated quartz tube, heated from room temperature up to
0304-8853/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.12.807
ARTICLE IN PRESS e1568
H. Romero et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) e1567–e1569
1150 C. Heating and cooling processes were implemented in several stages. At 500 C, the sample was annealed for 220 h and finally cooled until the room temperature. Ingots of Cu2SnSe3:Cr0.08 were chemically analyzed by atomic absorption spectrometer model AAZeeman 220 in order to determinate the Cr concentration. The compositional microanalysis of Cu2SnSe3 has been carried out by the EDX technique incorporated into the SEM Hitachi S-250. The X-ray data were recorded at room temperature by a Siemens diffractometer. The spectra of absorption coefficient were obtained by using a Fourier transform infrared spectrometer (FTIR) Perkin-Elmer model 1725X in the energy range of 0.1–1.0 eV at room temperature. Magnetic susceptibility measurements were performed by using a quantum design SQUID in the temperature range of 5– 300 K with an external applied field of 200 G.
3. Results and discussion Cr concentration was calculated as 1.2470.03 mg/g of sample. The relative chemical composition of Cu:Sn:Se was 30.3:15.9:53.8 at%, close to the ideal value of 2:1:3. The lattice constants, obtained from the X-rays diffrac( tion peaks, are given as a ¼ 6:950ð3Þ A, ( c ¼ 6:2567ð3Þ A, ( b ¼ 108:95ð1Þ; which b ¼ 13:0613ð6Þ A, correspond to a monoclinic system Cc and z ¼ 4: The data of the low-field (H ¼ 200 G) temperature dependence of the-zero-field-cooled (ZFC) and field-cooled (FC) magnetization are shown in Fig. 1. A reversible magnetic behaviour is observed. No evidence of cooperative magnetic order could be found, in agreement with magnetic measurements a paramagnetic behaviour is observed. However, one could observe a jump of about 42 K without noticeable change of the involved magnetic moment, because at lower and higher
Fig. 2. Plot of ðahnÞ2 vs. hn for Cu2SnSe3:Cr0.08 (T=300 K).
temperatures the inverse susceptibility has a similar slope. A shift of Curie temperature could be associated with a lattice distortion. From the susceptibility data, the Curie constant C ¼ 3:47ð4Þ 105 emu K/g, the Neel temperature yN ¼ 11:6ð7Þ K and the magnetic moment m ¼ 0:37 mB were calculated. The presence of magnetic ion leads to the interactions with the electronic bands, so as exchange interactions between magnetic ions. These interactions are strongly influenced by the ground state of the magnetic ion. Magnetic ion Cr2+ can occupy the Cu2+sites. Absorption coefficient was obtained by transmittance measurements in the range of 0.1–1.0 eV at room temperature, as observed in the curve ðahnÞ2 vs. hn in Fig. 2. The band gap edge of 0.372 eV was calculated by extrapolation of the linear region when ðahnÞ2 -0 in the plot. The intrinsic absorption edge corresponds to a direct transition.
4. Conclusions The X-ray diffraction pattern shows that Cu2SnSe3:Crx crystallizes in the monoclinic structure in a Cc group space. When Cr2+ ion participates as an active doping, a decrease of band gap is observed because of a change in the density of states. The magnetic susceptibility was determined in the temperature range of 5– 300 K. It follows Curie–Weiss law and the absence of cooperative magnetic ordering is observed in the FC– ZFC magnetization curves.
Acknowledgements
Fig. 1. Inverse of magnetic susceptibility for Cu2SnSe3:Cr2+.
This work has been accomplished with a financial support under CDCHT project No C-961-99-05-A. Thanks to Mr. P. Cancines to provide support for FTIR use in optical measurements.
ARTICLE IN PRESS H. Romero et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) e1567–e1569
References [1] L.I. Berger, V.D. Prochukhan, Ternary Diamond-like Semiconductors, New York, 1969, pp. 55–63. [2] J. Rivet, Ann. Chim. 10 (1965) 247. ! D. Bracho, G. Sanchez, J. Appl. [3] G. Marcano, C. Rincon, Phys. 90 (2001) 4.
e1569
! G. Marin, R. Tovar, G. Delgado, [4] G. Marcano, C. Rincon, J. Appl. Phys. 92 (2002) 4. [5] R. Echeverr!ıa, L. Nieves, G. Marcano, Phys. Stat. Sol. (b) 220 (2000) 285. [6] J. Ju Lee, Ch. Soo Yang, Y. Sin Park, K. Ho Kim, W. Tek Kim, J. Appl. Phys. 86 (1999) 5. [7] Yang-Lae Lee, Wha-Tek Kim, Phys. Rev. B 50 (1994) 15.