In this work, the nanostructured ZnO:Mn thin films with different Mn concentration (5, 10 and 15
mol%) have been grown on glass substrates at 500°C by the spray pyrolysis technique. The average grain
size was estimated about 25 nm using SEM micrographs. The Faraday rotations were determined in applied
magnetic fields up to 1.05 T. The highest values of Faraday rotation were observed in the sample
with 5 mol% Mn concentration. The carrier density has been calculated from the Faraday rotations and it
is observed that the sp-d exchange in magnetic semiconductor is strongly affected by carrier parameters.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3490

Ebrahimizadeh Abrishami, M.

SocioEconomic Challenges Journal (Sumy State University)

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE NANOMATERIALS: APPLICATIONS AND PROPERTIES 
Vol. 1 No 2, 02NFC29(3pp) (2012) 
 
 
2304-1862/2012/1(2)02NFC29(3) 02NFC29-1  2012 Sumy State University 
Carrier Density Dependence of sp-d Exchange in Nanostructured ZnO:Mn Thin Film 
 
M. Ebrahimizadeh Abrishami* 
 
Department of Physics, University of Neyshabur, Neyshabur, Iran 
 
(Received 28 June 2012; published online 08 August 2012) 
 
In this work, the nanostructured ZnO:Mn thin films with different Mn concentration (5, 10 and 15 
mol%) have been grown on glass substrates at 500°C by the spray pyrolysis technique. The average grain 
size was estimated about 25 nm using SEM micrographs. The Faraday rotations were determined in ap-
plied magnetic fields up to 1.05 T. The highest values of Faraday rotation were observed in the sample 
with 5 mol% Mn concentration. The carrier density has been calculated from the Faraday rotations and it 
is observed that the sp-d exchange in magnetic semiconductor is strongly affected by carrier parameters.  
 
Keywords: Faraday effect, Carrier density, ZnO, Thin film. 
 
  PACS numbers: 75.50.Pp, 81.15.Rs 
 
 
                                                          
* Ebrahimizadeh@ymail.com 
1. INTRODUCTION 
 
According search for ferromagnetism in diluted 
magnetic semiconductors (DMS) has denoted that the 
strong magnetic coupling between localized d electrons 
of the magnetic dopant and sp carriers of the semicon-
ductor depends on the carrier density in these materi-
als [1]. The optical excitation of DMS which includes 
both types of carriers leads to the strong sp-d exchange. 
This magnetic coupling leads to the interesting magne-
to-optical properties. Huge Faraday rotation observed 
in Cd1-xMnxTe [2], large magneto-optical effect reported 
in an oxide DMS Zn1-xCoxO [3] and ferromagnetic state 
in Zn1-xMnxO [4] and Zn1-xCoxO [5] are the natural re-
sult of the sp-d exchange interaction. Behan et al. [6] 
showed that the magnetic ordering and magneto-
optical properties of materials are affected by the carri-
er parameters. The carrier properties can be investi-
gated from the Faraday rotation arising from the dif-
ference between phase velocities to the of two circularly 
polarized components [7].  
In this work, we present, besides the measurement 
of the room temperature Faraday rotations observed in 
ZnO:Mn thin films, calculating the carrier densities of 
the samples are put forward.  
 
2. THEORY 
 
In this section, we present the formulation to find 
the carrier density by means of Faraday effect meas-
urements [8]. If the external magnetic field B is as-
sumed to be in the z direction as exactly applied in this 
work, then the parameters in gyrotropic media relation 
are defined by: 
 
 
2
0 2 2
1 p
c
, (2.1) 
 
                      
2
0 2 2( )
p
c
c
g ,                   (2.2) 
 
where , ωc = eB/m* and ωp = (ne2/ 0 m*)1/2 are dielectric 
constant, cyclotron frequency and plasma frequency, 
respectively. All the parameters used in this section are 
listed in Table 1. We considered the thin films as the 
slab of gyrotropic media with the thickness d and the 
wave propagated parallel to the magnetic field. Upon 
wave striking the interface, the wave will break up into 
circularly polarized waves with two different wave 
numbers, k+ and k- given by: 
 
 ( )gk , (2.3) 
 
Finally, the polarization of the electric field at z = d is 
linear but rotated by an angle F comparing to the po-
larization of incident wave will be: 
 
 
2
F
k k
d , (2.4) 
 
Because of the F dependence on k+ and k-, carrier 
density of the electrons can be measured as discussed 
above. 
 
Table 1 – List of the all parameters are used in Eqs. (2.1) and 
(2.2) 
 
 Dielectric constant 
g Dielectric constant of 
vacuum  
ω Incident light frequency 
ωp Plasma frequency  
ωc Cyclotron frequency  
e Electron charge 
n Carrier density 
m* Effective mass 
 
3. EXPERIMENTAL PROCEDURES  
 
In this work, the spray pyrolysis technique was ap-
plied to grow nanostructured ZnO thin films with dif-
ferent Mn concentration (5, 10 and 15 mol%) on glass 
substrates. ZnO:Mn thin films were prepared by depos-
iting a 0.1 M solution comprising of zinc and manga-
nese cations on glass substrates. In order to obtain the 
clear solution, we dissolved zinc acetate dehydrate and 
manganese acetate tetrahydrate in a mixture of isopro-
 M. EBRAHIMIZADEH ABRISHAMI PROC. NAP 1, 02NFC29 (2012) 
 
 
02NFC29-2 
panol and distilled water at 40 C followed by adding a 
few droplets of acetic acid. The volume ratio of isopro-
panol to distilled water was 3 to 1. The system adjust-
ing was determined as follows. The glass substrates 
were kept at 500 C during deposition. The solution was 
sprayed at a flow rate about 5 CC/min using com-
pressed air as the carrier gas. The distance of sub-
strates to the nozzle was adjusted at 30 cm. The depo-
sition process of all thin films was identically repeated 
and only the effects of Mn concentration were studied. 
The Faraday rotation was measured using a home 
designed setup which is including a He-Ne laser (λ = 
632.8 nm), an electromagnet, two polarizers and a cou-
ple of detectors. The incident light which was polarized 
by the first polarizer struck the magnetic film and the 
rotation of polarization plane was then detected. The 
magnetic field was parallel to the direction of the beam. 
In order to adjust the setup to achieve highest resolu-
tion, the axis of the polarizer and analyzer were set to 
form the angle of 45  [9]. The two spectra of the Fara-
day rotation angles, F, were obtained independently 
for the glass substrate and the substrates with the 
films at room temperature. In order to approximate the 
contribution of the film to F, these two spectra were 
subtracted.  
 
4. RESULTS 
 
Fig. 1 shows the XRD patterns of the ZnO thin film 
with different manganese concentration grown at 
500 C on glass substrates. The major peaks in these 
patterns are in close agreement with JCPDS data file 
for ZnO powder corresponding to the reflection peaks of 
the wurtzite structure which are indexed in this figure. 
All films exhibit random orientations, because glass 
substrates allowed the films to crystallize randomly.  
 
 
 
Fig. 1 – XRD patterns of ZnO:Mn thin films with different Mn 
concentration 5 mol% (a), 10 mol% (b) and 15 mol% (c)  
 
Fig. 2 shows the SEM image of 5 mol% Mn doped 
ZnO thin film. The average grain size was estimated 
about 25 nm. This image of ZnO:Mn films show that 
the grain boundaries are well defined and the grains 
distribution over the surface is uniform. Fig. 3 shows 
the measured values for Faraday rotation angles  
 
 
Fig. 2 – SEM image of 5 mol% Mn doped ZnO thin film 
 
versus applied magnetic field. Faraday rotation origi-
nates in anisotropy of refractive index and arises from 
differences between the phase velocities of two circular-
ly polarized components. The observed Faraday rota-
tion can be attributed to the sp-d interaction between 
the carriers and the localized magnetic moments of Mn 
ions. As shown in Fig. 3, it is observed that the rotation 
angles of the thin film with 5 mol% Mn concentration is 
stronger than the other films with higher Mn content.  
According to the carrier-mediated model [1], the 
magnetic properties of a material are strongly affected 
by free electron concentration. So, it can be concluded 
that decreasing the oxygen vacancies in ZnO structure 
with the increase in Mn content, leads to the reduction 
in the Faraday rotation angle. Neal et al. [10] have 
been also reported that the carrier density is reduced 
with the increase in Mn concentration. The validity of 
this approximation was checked by the calculation of 
carrier density using Eq. (2.4).  
The Faraday rotations were recorded for the mag-
netic fields from 0 to 1.05 T and the carrier densities 
can be calculated using the Eq. (2.4). Because the cyclo-
tron frequency is depended on the magnetic field, it 
may be expected that the carrier density in DMS is also 
affected by magnetic field. The values of carrier density 
obtained for all films in two typical magnetic fields (0.3 
 
 
 
Fig. 3 – Room temperature Faraday rotation spectra versus 
magnetic field at λ = 632.8 nm 
 CARRIER DENSITY DEPENDENCE OF SP-D EXCHANGE… PROC. NAP 1, 02NFC29 (2012) 
 
 
02NFC29-3 
 
 
 
Fig. 4 – Dependence of the carrier density on amount of Mn 
concentration in the samples 
 
T and 0.6 T) are given in Fig. 4. As shown in this figure, 
the carrier density decreases with the increase in Mn 
concentration. Mn atoms tend to accumulate in the grain 
boundaries and play a significant role in grain bounda-
ries oxidation. So, weakening the magnetic ordering with 
increase in Mn content originates in decreasing the oxy-
gen deficiencies and hence carrier density in specimens. 
Also, the carrier densities increase with the 
increase in magnetic field from 0.3 T to 0.6 T. As 
discussed by Ohno [11] and Awschalom et al. [12], in 
magnetic semiconductor quantum structure, the 
carriers interactions via exchange with magnetic ions 
(such as Mn in this paper) resulting spin dependent 
transport and carrier induced ferromagnetism which 
are in good agreement with our results in Figs. 3 and 4. 
 
5. CONCLUSIONS 
 
In this paper, the transparent thin films of ZnO:Mn 
were grown by spray pyrolysis. The Faraday effect stud-
ies revealed that the rotation angle decreased with the 
increase in Mn concentration. The similar changes have 
been also observed between carrier density and Mn con-
tent. So, it may be generally accepted that in ZnO based 
ferromagnetic semiconductors, the carrier density 
strongly affects the sp-d exchange. Also, it is found that 
the carrier densities increased with increase in magnetic 
filed which relates to spin dependent transport. 
 
 
REFERENCES 
 
1. D.P. Nortona, S.J. Pearton, A.F. Hebard, N. Theodoropou-
lou, L.A. Boatner, R.G. Wilson, Appl. Phys. Lett. 82, 239 
(2003). 
2. M. Prakasam, O. Viraphong, L.T.-Gay, R. Decourt, P. 
Veber, E.G. Víllora, K. Shimamura, J. Crys. Growth.  318, 
533 (2011). 
3. A. J. Behan, A. Mokhtari, H. J. Blythe, D. Score, X-H. Xu, 
J. R. Neal, A. M. Fox, G. A. Gehring, Phys. Rev. Lett. 100, 
047206 (2008). 
4. T. Fukumura, Z. Jin, A. Ohtomo, H. Koinuma, M. Kawa-
saki, Appl. Phys. Lett. 75, 3366 (1999). 
5. F. Wen, Mod. Phys. Lett. B 23, 1799 (2009).  
6. A.J. Behan, J.R. Neal, R.M. Ibrahim, A. Mokhtari, M. 
Ziese, H. J. Blythe, A.M. Fox, G. A. Gehring, J. Magn. 
Magn. Mater. 310, 2158 (2007). 
7. L. Ogawa, K. Yamada, T. Idehara, A. Tsushima, S. Yama-
guchi, Int. J. Infrared Milli. Waves 24, 651 (2003). 
8. S. L. Chaung, Physics of photonic devices (Wiley & sons, 
2009). 
9. F. Oliveira, M.F. Cerqueira, M.I. Vasilevskiy, T. Viseu,  
J. Ayres de Campos, A.G. Rolo, J.S. Martins, N.A. Sobolev, 
E. Alves, Thin Solid Films 518, 4612 (2010). 
10. J.R. Neal, A. J.Behan, R.M. Ibrahim, H.J. Blythe, M. 
Ziese, A.M. Fox, G.A. Gehring, Phys. Rev. Lett. 96, 197208 
(2006). 
11. H. Ohno, Science 281, 951 (1998). 
12. D.D. Awschalom, N. Samarth, J. Magn. Magn. Mater. 200, 
130 (1999). 
 
 


English

Carrier Density Dependence of sp-d Exchange in Nanostructured ZnO:Mn Thin Film

Electronic Sumy State University Institutional Repository

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE NANOMATERIALS: APPLICATIONS AND PROPERTIES Vol. 1 No 2, 02NFC29(3pp) (2012)   2304-1862/2012/1(2)02NFC29(3) 02NFC29-1  2012 Sumy State University Carrier Density Dependence of sp-d Exchange in Nanostructured ZnO:Mn Thin Film  M. Ebrahimizadeh Abrishami*  Department of Physics, University of Neyshabur, Neyshabur, Iran  (Received 28 June 2012; published online 08 August 2012)  In this work, the nanostructured ZnO:Mn thin films with different Mn concentration (5, 10 and 15 mol%) have been grown on glass substrates at 500°C by the spray pyrolysis technique. The average grain size was estimated about 25 nm using SEM micrographs. The Faraday rotations were determined in ap-plied magnetic fields up to 1.05 T. The highest values of Faraday rotation were observed in the sample with 5 mol% Mn concentration. The carrier density has been calculated from the Faraday rotations and it is observed that the sp-d exchange in magnetic semiconductor is strongly affected by carrier parameters.   Keywords: Faraday effect, Carrier density, ZnO, Thin film.    PACS numbers: 75.50.Pp, 81.15.Rs                                                             * Ebrahimizadeh@ymail.com 1. INTRODUCTION  According search for ferromagnetism in diluted magnetic semiconductors (DMS) has denoted that the strong magnetic coupling between localized d electrons of the magnetic dopant and sp carriers of the semicon-ductor depends on the carrier density in these materi-als [1]. The optical excitation of DMS which includes both types of carriers leads to the strong sp-d exchange. This magnetic coupling leads to the interesting magne-to-optical properties. Huge Faraday rotation observed in Cd1-xMnxTe [2], large magneto-optical effect reported in an oxide DMS Zn1-xCoxO [3] and ferromagnetic state in Zn1-xMnxO [4] and Zn1-xCoxO [5] are the natural re-sult of the sp-d exchange interaction. Behan et al. [6] showed that the magnetic ordering and magneto-optical properties of materials are affected by the carri-er parameters. The carrier properties can be investi-gated from the Faraday rotation arising from the dif-ference between phase velocities to the of two circularly polarized components [7].  In this work, we present, besides the measurement of the room temperature Faraday rotations observed in ZnO:Mn thin films, calculating the carrier densities of the samples are put forward.   2. THEORY  In this section, we present the formulation to find the carrier density by means of Faraday effect meas-urements [8]. If the external magnetic field B is as-sumed to be in the z direction as exactly applied in this work, then the parameters in gyrotropic media relation are defined by:   20 2 21 pc, (2.1)                        20 2 2( )pccg ,                   (2.2)  where , ωc = eB/m* and ωp = (ne2/ 0 m*)1/2 are dielectric constant, cyclotron frequency and plasma frequency, respectively. All the parameters used in this section are listed in Table 1. We considered the thin films as the slab of gyrotropic media with the thickness d and the wave propagated parallel to the magnetic field. Upon wave striking the interface, the wave will break up into circularly polarized waves with two different wave numbers, k+ and k- given by:   ( )gk , (2.3)  Finally, the polarization of the electric field at z = d is linear but rotated by an angle F comparing to the po-larization of incident wave will be:   2Fk kd , (2.4)  Because of the F dependence on k+ and k-, carrier density of the electrons can be measured as discussed above.  Table 1 – List of the all parameters are used in Eqs. (2.1) and (2.2)   Dielectric constant g Dielectric constant of vacuum  ω Incident light frequency ωp Plasma frequency  ωc Cyclotron frequency  e Electron charge n Carrier density m* Effective mass  3. EXPERIMENTAL PROCEDURES   In this work, the spray pyrolysis technique was ap-plied to grow nanostructured ZnO thin films with dif-ferent Mn concentration (5, 10 and 15 mol%) on glass substrates. ZnO:Mn thin films were prepared by depos-iting a 0.1 M solution comprising of zinc and manga-nese cations on glass substrates. In order to obtain the clear solution, we dissolved zinc acetate dehydrate and manganese acetate tetrahydrate in a mixture of isopro- M. EBRAHIMIZADEH ABRISHAMI PROC. NAP 1, 02NFC29 (2012)   02NFC29-2 panol and distilled water at 40 C followed by adding a few droplets of acetic acid. The volume ratio of isopro-panol to distilled water was 3 to 1. The system adjust-ing was determined as follows. The glass substrates were kept at 500 C during deposition. The solution was sprayed at a flow rate about 5 CC/min using com-pressed air as the carrier gas. The distance of sub-strates to the nozzle was adjusted at 30 cm. The depo-sition process of all thin films was identically repeated and only the effects of Mn concentration were studied. The Faraday rotation was measured using a home designed setup which is including a He-Ne laser (λ = 632.8 nm), an electromagnet, two polarizers and a cou-ple of detectors. The incident light which was polarized by the first polarizer struck the magnetic film and the rotation of polarization plane was then detected. The magnetic field was parallel to the direction of the beam. In order to adjust the setup to achieve highest resolu-tion, the axis of the polarizer and analyzer were set to form the angle of 45  [9]. The two spectra of the Fara-day rotation angles, F, were obtained independently for the glass substrate and the substrates with the films at room temperature. In order to approximate the contribution of the film to F, these two spectra were subtracted.   4. RESULTS  Fig. 1 shows the XRD patterns of the ZnO thin film with different manganese concentration grown at 500 C on glass substrates. The major peaks in these patterns are in close agreement with JCPDS data file for ZnO powder corresponding to the reflection peaks of the wurtzite structure which are indexed in this figure. All films exhibit random orientations, because glass substrates allowed the films to crystallize randomly.     Fig. 1 – XRD patterns of ZnO:Mn thin films with different Mn concentration 5 mol% (a), 10 mol% (b) and 15 mol% (c)   Fig. 2 shows the SEM image of 5 mol% Mn doped ZnO thin film. The average grain size was estimated about 25 nm. This image of ZnO:Mn films show that the grain boundaries are well defined and the grains distribution over the surface is uniform. Fig. 3 shows the measured values for Faraday rotation angles    Fig. 2 – SEM image of 5 mol% Mn doped ZnO thin film  versus applied magnetic field. Faraday rotation origi-nates in anisotropy of refractive index and arises from differences between the phase velocities of two circular-ly polarized components. The observed Faraday rota-tion can be attributed to the sp-d interaction between the carriers and the localized magnetic moments of Mn ions. As shown in Fig. 3, it is observed that the rotation angles of the thin film with 5 mol% Mn concentration is stronger than the other films with higher Mn content.  According to the carrier-mediated model [1], the magnetic properties of a material are strongly affected by free electron concentration. So, it can be concluded that decreasing the oxygen vacancies in ZnO structure with the increase in Mn content, leads to the reduction in the Faraday rotation angle. Neal et al. [10] have been also reported that the carrier density is reduced with the increase in Mn concentration. The validity of this approximation was checked by the calculation of carrier density using Eq. (2.4).  The Faraday rotations were recorded for the mag-netic fields from 0 to 1.05 T and the carrier densities can be calculated using the Eq. (2.4). Because the cyclo-tron frequency is depended on the magnetic field, it may be expected that the carrier density in DMS is also affected by magnetic field. The values of carrier density obtained for all films in two typical magnetic fields (0.3    Fig. 3 – Room temperature Faraday rotation spectra versus magnetic field at λ = 632.8 nm  CARRIER DENSITY DEPENDENCE OF SP-D EXCHANGE… PROC. NAP 1, 02NFC29 (2012)   02NFC29-3    Fig. 4 – Dependence of the carrier density on amount of Mn concentration in the samples  T and 0.6 T) are given in Fig. 4. As shown in this figure, the carrier density decreases with the increase in Mn concentration. Mn atoms tend to accumulate in the grain boundaries and play a significant role in grain bounda-ries oxidation. So, weakening the magnetic ordering with increase in Mn content originates in decreasing the oxy-gen deficiencies and hence carrier density in specimens. Also, the carrier densities increase with the increase in magnetic field from 0.3 T to 0.6 T. As discussed by Ohno [11] and Awschalom et al. [12], in magnetic semiconductor quantum structure, the carriers interactions via exchange with magnetic ions (such as Mn in this paper) resulting spin dependent transport and carrier induced ferromagnetism which are in good agreement with our results in Figs. 3 and 4.  5. CONCLUSIONS  In this paper, the transparent thin films of ZnO:Mn were grown by spray pyrolysis. The Faraday effect stud-ies revealed that the rotation angle decreased with the increase in Mn concentration. The similar changes have been also observed between carrier density and Mn con-tent. So, it may be generally accepted that in ZnO based ferromagnetic semiconductors, the carrier density strongly affects the sp-d exchange. Also, it is found that the carrier densities increased with increase in magnetic filed which relates to spin dependent transport.   REFERENCES  1. D.P. Nortona, S.J. Pearton, A.F. Hebard, N. Theodoropou-lou, L.A. Boatner, R.G. Wilson, Appl. Phys. Lett. 82, 239 (2003). 2. M. Prakasam, O. Viraphong, L.T.-Gay, R. Decourt, P. Veber, E.G. Víllora, K. Shimamura, J. Crys. Growth.  318, 533 (2011). 3. A. J. Behan, A. Mokhtari, H. J. Blythe, D. Score, X-H. Xu, J. R. Neal, A. M. Fox, G. A. Gehring, Phys. Rev. Lett. 100, 047206 (2008). 4. T. Fukumura, Z. Jin, A. Ohtomo, H. Koinuma, M. Kawa-saki, Appl. Phys. Lett. 75, 3366 (1999). 5. F. Wen, Mod. Phys. Lett. B 23, 1799 (2009).  6. A.J. Behan, J.R. Neal, R.M. Ibrahim, A. Mokhtari, M. Ziese, H. J. Blythe, A.M. Fox, G. A. Gehring, J. Magn. Magn. Mater. 310, 2158 (2007). 7. L. Ogawa, K. Yamada, T. Idehara, A. Tsushima, S. Yama-guchi, Int. J. Infrared Milli. Waves 24, 651 (2003). 8. S. L. Chaung, Physics of photonic devices (Wiley & sons, 2009). 9. F. Oliveira, M.F. Cerqueira, M.I. Vasilevskiy, T. Viseu,  J. Ayres de Campos, A.G. Rolo, J.S. Martins, N.A. Sobolev, E. Alves, Thin Solid Films 518, 4612 (2010). 10. J.R. Neal, A. J.Behan, R.M. Ibrahim, H.J. Blythe, M. Ziese, A.M. Fox, G.A. Gehring, Phys. Rev. Lett. 96, 197208 (2006). 11. H. Ohno, Science 281, 951 (1998). 12. D.D. Awschalom, N. Samarth, J. Magn. Magn. Mater. 200, 130 (1999).   

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Carrier Density Dependence of sp-d Exchange in Nanostructured ZnO:Mn Thin Film

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