- Email: [email protected]
Study of giant magnetoresistance and giant electroresistance of carbon based thin film
RARE METALS
Vol .25 , Spec . Issue , Oct 2006 , p .617
Study of giant magnetoresistance and giant electroresistance of carbon based thin film ZHANG Xiaozhong’) , TIAN Peng”
, and XUE Qingzhong’”)
1 ) Laboratory of Advanced Materials, Department of Materials Science and Engineering, Tsinghua University, Beijing 100084, China 2) College of Physics Science and Technology, China University of Petroleum, Dongying 257061, China (Received 2006-06-25)
Abstract: Using pulsed laser deposition, Fe,-C1., films on Si ( 100) substrates were prepared. At T = 300 K and B = 5 T a large positive M R of 138% was found in FeO . O l 1-CO.989 film. It is also found that when T < 258 K , the M R of FeO .Ol 1-CO.989 film is negative and when 258 K < T < 340 K , the M R of the film is positive. The M R of the material is also found to be controlled by the measuring current and measuring voltage. When B = 2000 Oe , the M R is 11 . 5 % at 2.5 mA and is 35 % at about 35 V . The material has also a giant electroresistance of 500% at 8 V . Key words : magnetoresistance ; electroresistance; carbon based film
[ This work was financially supported by the Ministry of Science and Technology of China ( N o . 2002CB613500) and National Natural Science Foundation of China ( No. 50271034, No. 90401013). 1
1.
at different temperature ranges. Besides, FezCl-, film/Si thin film has an abnormal electron transport property.
Introduction The utilization of giant magnetoresistance
( M R ) effect in magnetic information storage has been attracted much attention. The negative M R materials, from artificially engineered magnetic multilayers [ 1] and granular films [ 21 to the manganite perovskites[ 31 , have been intensively studied in the last decade. Anomalous positive M R effects were discovered in nonmagnetic silver chalcogenides [ 4 ] , inhomogeneous narrow-gap semiconductors [ 51 , and ferromagnetic Fel - Co,Si [ 6 1 . Recently, we developed ( F e , Co, Ni)%-CI-% composites [ 7-91 and (Co, Fe),-C1-,/Si thin film[ 10-121, both of them have a positive giant magnetoresistance. We also find that even pure carbon can have a positive magnetoresistance [ 13,141 and C/Si film made at 27 T has a switch effect [ 151. In this paper, we report that the Fe, C, - ./Si thin film has positive and negative M R Corresponding author : ZHANG Xiaozhong
2.
Experimental
Fe,-C-, thin films with x = 1. lat.% 12.5at. % in targets were deposited on Si ( 100) substrates using pulsed laser deposition at a substrate temperature of 300 “c in 3 Pa of Argon, while pure C films were also prepared for comparison. The film thickness is 40 - 60 nm. The KrF excimer laser (Lamda Physics 205) was operated at a pulse rate of 10 Hz. The laser beam was focused through a 75 cm focal length lens onto a rotating target at a 45” angle of coincidence. The energy density of the laser beam at the target surface was maintained at 1 J*cm-*. The target-substrate distance was 4 cm. The targets were cold-pressed composite disks of 1. 8 cm in diameter and 0.5 cm in thickness with Fe atom concentration from 1.1% to 12.5%. The
E-mail: xzzhang@tsinghua .edu .cn
RARE METALS, Vol. 2 5 , Spec. Issue, Oct 2006
618
purity of the Fe and C was higher than 99.9%. The Si (100)substrates are lightly doped with P resulting in n-type materials with resistivity in the range of 0.55- 0.80SZ 'cm . Before deposition the Si substrates were ultrasonically cleaned in ethanol, then acetone, etched in diluted HF solution and rinsed in de-ionized water. The deposition chamber was initially evacuated to 1 x Torr, the substrate was then heated to 300 'T , and during the deposition Argon gas was introduced into the chamber to maintain the desired pressure.
3.
Results and discussion
Fig. 1 shows the positive MR measurements taken at T = 300 K by the four-probe method on the SQUID magnetometer with the magnetic field B applied parallel to the film plane and the current. The MR is defined as AR/R=(R(B,T) - R(O,T))/R(O,T), where the R ( B , T ) and R ( 0 , T ) are resistances of the sample measured at temperature T with magnetic field applied or without magnetic field applied, respectively. The MR of FezC1-, film/Si has the largest value in Feo.ollcO.989 film/Si and drops as Fe content increases ( Fig. 1( a ) ) . The MR for the applied field perpendicular to the film plane and current is much larger than the MR for the field applied parallel to the film plane and current (Fig. 1 ( b ) ) . In Fe0.011-C0.989 f i h / S i , a large positive AIR of 138% is observed at 300 K and B = 5 T
with B perpendicular to the film plane. Among granular film Feo.oll-Co.y~9 film/Si has the largest d MR/d B value of 0.005% /Oe , which is about 4 times better than the reported best dMR/dB value of 0. 0013%/0e observed in Ag,, granular film at 300 K[ 161. Fig. 2 ( a ) shows the temperature dependence of the resistance and MR of Feo.oll-Co.9ay film/Si sample. Two transitions of the resistance at 258 and 315 K were found, respectively. When T < 258 K, the resistance shows a typical behavior of amorphous carbon film. When the temperature reaches 258 K , the resistance begins to drop quickly and it decreases by more than an order of magnitudes as temperature increases to 315 K , and after that the resistance decreases slightly as temperature increases. It is found that the MR is negative when temperature T < 258 K . At 258 K the MR turns from negative to positive. The MR increases with increasing temperature before 315 K and reaches the maximum at 315 K . When 315 K < T < 340 K , the MR decreases with increasing temperature and reaches the minimum at 340 K . When T > 340 K the MR increases again with increasing temperature. Fig. 2 ( b ) shows the field dependence of the MR of Feo.olI -c0.y89 f i h / S i at different temperatures . The MR has different field dependence within the different temperature ranges. The MR at 280 and 300 K are positive and increase rapidly with increasing magnetic field before B = 1 T ,
-
-
-
-
40 35 3u
c8 -t
25 2o 15
10
5 0
BIT
Fig.1. Change in MR of Fe,-C1-, T i S i at room temperature as function of magnetic field B ( a ) ; MR of Feo.oll-Co.sssfiim/Si at room temperature for the field applied parallel and perpendicular to the f i i plane (b) (The applied measuring current is 0.005 mA)
.
Zhung X .Z . et ul . , Giant magnetoresistance and giant electroresistanceof C based thin film
619
-0.2 -0.4
0
1
2
TI K
3
4
5
Err
- C ~(a) . ~; field dependence of the Fig. 2. Temperature dependence of the resistance and MR of F Q . ~ ~ ~film/Si MR of Feo.oll-Co.sssfih/Si at merent temperatures ( b ) (The applied measuring current is 0.005 mA)
.
and then the MR increases slowly as the magnetic field increases, whereas the MR at 350 K has a B 1 . 5 of field dependence. Contrary to the above MR , the MR at 30 K is negative and decreases as the magnetic field increases. It is found that the MR of our sample is not only the function of magnetic field, but also the function of measuring electric current and measuring voltage. Fig. 3 shows the variation of the MR of a-C :Fe/Fe/Si sample with the measuring current and measuring voltage. The MRI curve is quite different from the MR-V curve. For MR-I curve, initially the MR increases sharply with increase of the measuring current. At about 2 . 5 mA, the MR reaches the maximum value of 11.5%. After that the MR decreases almost linearly with the increase of measuring current . However , for MR - V curve , CurrentImA
,
0 40
86
so 26
2
6
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the MR increases slowly with increase of the mea35 V , the MR reaches it maximum value of 35%. After that the MR starts to decrease with increase of voltage. Besides the magnetoresistance, our material also shows a giant electroresistance ( ER ) . We define the ER as:
suring voltage. At about
where R ~ is” the minimum resistance measured at a given temperature and R ( U ) is the resistance measured at the voltage U . ER-U curves of the a-C :FeIFelSi sample at room temperature is plotted in Fig.4. It is found that ER is very sensitive to the change of voltage. ER increases fast with the increase of the measuring voltage. At about 1 V , the ER is already over 100%. At 8 V , ER reaches its maximum valve of BM)
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Fig.3. MR-V curve and MR-I curve of a-C: Fe/ Fe/Si sample at room temperature.
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Fig.4. ER of a-C: Fe/Fe/Si sample at room temperature.
RARE METALS, Vol . 2 5 , Spec. Issue , Oct 2006
620
about 500%. These ER values are very big and they can be regarded as giant ER ( G E R ) .
4.
Conclusions
The Fe,-C,_, films were growth on Si ( 100) substrates using pulsed laser deposition. It is found that Feo oll-Co 989 film has a large positive MR of 138% at B = 5 T and room temperature. The MR materials is dependent on the temperature. When T < 258 K , the M R of the film is negative and when 258 K < T < 340 K the MR of the film is positive. It is also found that the MR of the material is controlled by the measuring current and measuring voltage. When B =2000 Oe, the M R is 11.5% at 2 . 5 mA and is 35% at about 35 V . Besides the magnetoresistance, the material has also a giant electroresistance of 500% at 8 V . It is believed that this material can be applied in electric and magnetic devises.
Magnetoresistance from quantum interference effects in ferromagnets. Nature, 2000, 404
(6778): 581. [7] Zhang X . , and Xue Q . Z . , Room temperature positive magnetoresistance in micrometer particle size Co,CI - I Composite. Physica B , 2003, 334 ( 1 -2): 216. [ 81 Xue Q .Z . , and Zhang X. , Positive magnetoresistance in micro-sized granular Nis-CITzcomposites. P h y s . Lett. A , 2003, 313(5 - 6 ) :
461. [ 91 Xue Q .Z . , and Zhang X. , Positive linear magnetoresistance in Fe,-CI - * composites. Journal of Magnetism and Magnetic Materials, 2004, 270(3): 397. [ 101 Zhu D. D . , Zhang X . , and Xue Q . Z . , Large magnetoresistance in Co,-CI-, granular films on Si( 100) substrate prepared by pulsed laser deposition. Actu Phys . Sin. (in Chinese), 2003, 52
(12): 3181. [ l l ] Zhu D . D . , Zhang X . , and Xue Q . Z . , Anomalous positive magnetoresistance in Co,-C, granular films on Si substrates. J . Appl. Phys . ,
2004, 95(4): 1906.
References [ l ] Baibich M . N . , Broto J. M., Fert A . , el al., Giant magnetoresistance of (001 ) Fe/( 001 ) Cr magnetic superlattices. Phys . Rev . Lett . , 1988, 61(21): 2472. [2] Berkowits A. E . , Mitchell J . R . , Carey M .J . , et a1 . , Giant magnetoresistance in heterogeneous Cu-Co alloys. Phys. Rev. L e t t . , 1992, 68 (25) : 3745. 131 Jin S . , Tiefel T . H . , McCormack M . , et al., Thousandfold change in resistivity in magnetoresistive La-Ca. Science, 1994, 264(5157): 413. [4] Xu R . , Husmann A , , Rosenbaum T. F . , et a1 . , Large magnetoresistance in non-magnetic silver chalcogenides . Nature, 1997, 390
(6655): 57. [5] Solin S . A . , Thio T . , Hines D . R . , et a l . , Enhanced room-temperature geometric magnetoresistance in inhomogeneous narrow-gap semiconductors. Science, 2000, 289(5484): 1530. [6] Manyala N . , Sidis Y . , DiTusa J . F . , et a l . ,
[ 121 Xue Q. Z . , and Zhang X . , Magnetoresistance and current-controlled electric transport properties of Fe-C film on Si substrate. Muterials Science Forum, 2005, 475 - 479: 2207. [ 131 Zhang X. , and Xue Q . Z . , Positive and negative linear magnetoresistance in graphite. Phys .
Lett. A . , 2003, 320(5-6): 471. [ 141 Xue Q .Z . , and Zhang X. , Anomalous electrical transport properties of amorphous carbon films on Si substrates. Carbon , 2005, 43(4) : 760. [ 151 Xue Q . Z . , Zhang X . , Tian P . , et u l . , Anomalous current-voltage characteristics and colossal emectroresistance of amorphous carbon film on Si substrate. Appl. Phys. L e t t . , 2004, 85(19):
4397. [ 161 Takeda H . , Fujita A . , and Fukamichi K . , Application of the giant magnetoresistance effect of nanogranular Ag,,C% thin film as a sensor for brushless dc motors. J . Appl . Phys . , 2002, 91
(10): 77.
Vol .25 , Spec . Issue , Oct 2006 , p .617
Study of giant magnetoresistance and giant electroresistance of carbon based thin film ZHANG Xiaozhong’) , TIAN Peng”
, and XUE Qingzhong’”)
1 ) Laboratory of Advanced Materials, Department of Materials Science and Engineering, Tsinghua University, Beijing 100084, China 2) College of Physics Science and Technology, China University of Petroleum, Dongying 257061, China (Received 2006-06-25)
Abstract: Using pulsed laser deposition, Fe,-C1., films on Si ( 100) substrates were prepared. At T = 300 K and B = 5 T a large positive M R of 138% was found in FeO . O l 1-CO.989 film. It is also found that when T < 258 K , the M R of FeO .Ol 1-CO.989 film is negative and when 258 K < T < 340 K , the M R of the film is positive. The M R of the material is also found to be controlled by the measuring current and measuring voltage. When B = 2000 Oe , the M R is 11 . 5 % at 2.5 mA and is 35 % at about 35 V . The material has also a giant electroresistance of 500% at 8 V . Key words : magnetoresistance ; electroresistance; carbon based film
[ This work was financially supported by the Ministry of Science and Technology of China ( N o . 2002CB613500) and National Natural Science Foundation of China ( No. 50271034, No. 90401013). 1
1.
at different temperature ranges. Besides, FezCl-, film/Si thin film has an abnormal electron transport property.
Introduction The utilization of giant magnetoresistance
( M R ) effect in magnetic information storage has been attracted much attention. The negative M R materials, from artificially engineered magnetic multilayers [ 1] and granular films [ 21 to the manganite perovskites[ 31 , have been intensively studied in the last decade. Anomalous positive M R effects were discovered in nonmagnetic silver chalcogenides [ 4 ] , inhomogeneous narrow-gap semiconductors [ 51 , and ferromagnetic Fel - Co,Si [ 6 1 . Recently, we developed ( F e , Co, Ni)%-CI-% composites [ 7-91 and (Co, Fe),-C1-,/Si thin film[ 10-121, both of them have a positive giant magnetoresistance. We also find that even pure carbon can have a positive magnetoresistance [ 13,141 and C/Si film made at 27 T has a switch effect [ 151. In this paper, we report that the Fe, C, - ./Si thin film has positive and negative M R Corresponding author : ZHANG Xiaozhong
2.
Experimental
Fe,-C-, thin films with x = 1. lat.% 12.5at. % in targets were deposited on Si ( 100) substrates using pulsed laser deposition at a substrate temperature of 300 “c in 3 Pa of Argon, while pure C films were also prepared for comparison. The film thickness is 40 - 60 nm. The KrF excimer laser (Lamda Physics 205) was operated at a pulse rate of 10 Hz. The laser beam was focused through a 75 cm focal length lens onto a rotating target at a 45” angle of coincidence. The energy density of the laser beam at the target surface was maintained at 1 J*cm-*. The target-substrate distance was 4 cm. The targets were cold-pressed composite disks of 1. 8 cm in diameter and 0.5 cm in thickness with Fe atom concentration from 1.1% to 12.5%. The
E-mail: xzzhang@tsinghua .edu .cn
RARE METALS, Vol. 2 5 , Spec. Issue, Oct 2006
618
purity of the Fe and C was higher than 99.9%. The Si (100)substrates are lightly doped with P resulting in n-type materials with resistivity in the range of 0.55- 0.80SZ 'cm . Before deposition the Si substrates were ultrasonically cleaned in ethanol, then acetone, etched in diluted HF solution and rinsed in de-ionized water. The deposition chamber was initially evacuated to 1 x Torr, the substrate was then heated to 300 'T , and during the deposition Argon gas was introduced into the chamber to maintain the desired pressure.
3.
Results and discussion
Fig. 1 shows the positive MR measurements taken at T = 300 K by the four-probe method on the SQUID magnetometer with the magnetic field B applied parallel to the film plane and the current. The MR is defined as AR/R=(R(B,T) - R(O,T))/R(O,T), where the R ( B , T ) and R ( 0 , T ) are resistances of the sample measured at temperature T with magnetic field applied or without magnetic field applied, respectively. The MR of FezC1-, film/Si has the largest value in Feo.ollcO.989 film/Si and drops as Fe content increases ( Fig. 1( a ) ) . The MR for the applied field perpendicular to the film plane and current is much larger than the MR for the field applied parallel to the film plane and current (Fig. 1 ( b ) ) . In Fe0.011-C0.989 f i h / S i , a large positive AIR of 138% is observed at 300 K and B = 5 T
with B perpendicular to the film plane. Among granular film Feo.oll-Co.y~9 film/Si has the largest d MR/d B value of 0.005% /Oe , which is about 4 times better than the reported best dMR/dB value of 0. 0013%/0e observed in Ag,, granular film at 300 K[ 161. Fig. 2 ( a ) shows the temperature dependence of the resistance and MR of Feo.oll-Co.9ay film/Si sample. Two transitions of the resistance at 258 and 315 K were found, respectively. When T < 258 K, the resistance shows a typical behavior of amorphous carbon film. When the temperature reaches 258 K , the resistance begins to drop quickly and it decreases by more than an order of magnitudes as temperature increases to 315 K , and after that the resistance decreases slightly as temperature increases. It is found that the MR is negative when temperature T < 258 K . At 258 K the MR turns from negative to positive. The MR increases with increasing temperature before 315 K and reaches the maximum at 315 K . When 315 K < T < 340 K , the MR decreases with increasing temperature and reaches the minimum at 340 K . When T > 340 K the MR increases again with increasing temperature. Fig. 2 ( b ) shows the field dependence of the MR of Feo.olI -c0.y89 f i h / S i at different temperatures . The MR has different field dependence within the different temperature ranges. The MR at 280 and 300 K are positive and increase rapidly with increasing magnetic field before B = 1 T ,
-
-
-
-
40 35 3u
c8 -t
25 2o 15
10
5 0
BIT
Fig.1. Change in MR of Fe,-C1-, T i S i at room temperature as function of magnetic field B ( a ) ; MR of Feo.oll-Co.sssfiim/Si at room temperature for the field applied parallel and perpendicular to the f i i plane (b) (The applied measuring current is 0.005 mA)
.
Zhung X .Z . et ul . , Giant magnetoresistance and giant electroresistanceof C based thin film
619
-0.2 -0.4
0
1
2
TI K
3
4
5
Err
- C ~(a) . ~; field dependence of the Fig. 2. Temperature dependence of the resistance and MR of F Q . ~ ~ ~film/Si MR of Feo.oll-Co.sssfih/Si at merent temperatures ( b ) (The applied measuring current is 0.005 mA)
.
and then the MR increases slowly as the magnetic field increases, whereas the MR at 350 K has a B 1 . 5 of field dependence. Contrary to the above MR , the MR at 30 K is negative and decreases as the magnetic field increases. It is found that the MR of our sample is not only the function of magnetic field, but also the function of measuring electric current and measuring voltage. Fig. 3 shows the variation of the MR of a-C :Fe/Fe/Si sample with the measuring current and measuring voltage. The MRI curve is quite different from the MR-V curve. For MR-I curve, initially the MR increases sharply with increase of the measuring current. At about 2 . 5 mA, the MR reaches the maximum value of 11.5%. After that the MR decreases almost linearly with the increase of measuring current . However , for MR - V curve , CurrentImA
,
0 40
86
so 26
2
6
4
the MR increases slowly with increase of the mea35 V , the MR reaches it maximum value of 35%. After that the MR starts to decrease with increase of voltage. Besides the magnetoresistance, our material also shows a giant electroresistance ( ER ) . We define the ER as:
suring voltage. At about
where R ~ is” the minimum resistance measured at a given temperature and R ( U ) is the resistance measured at the voltage U . ER-U curves of the a-C :FeIFelSi sample at room temperature is plotted in Fig.4. It is found that ER is very sensitive to the change of voltage. ER increases fast with the increase of the measuring voltage. At about 1 V , the ER is already over 100%. At 8 V , ER reaches its maximum valve of BM)
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.
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.
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0 1,
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-
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’5
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MR- c’ a-C: Fe/Fe/Si 0 MR-I 8=2000 Oe
m
E
s
4
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-10
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Fig.3. MR-V curve and MR-I curve of a-C: Fe/ Fe/Si sample at room temperature.
-5
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5
10
VoltageN
Fig.4. ER of a-C: Fe/Fe/Si sample at room temperature.
RARE METALS, Vol . 2 5 , Spec. Issue , Oct 2006
620
about 500%. These ER values are very big and they can be regarded as giant ER ( G E R ) .
4.
Conclusions
The Fe,-C,_, films were growth on Si ( 100) substrates using pulsed laser deposition. It is found that Feo oll-Co 989 film has a large positive MR of 138% at B = 5 T and room temperature. The MR materials is dependent on the temperature. When T < 258 K , the M R of the film is negative and when 258 K < T < 340 K the MR of the film is positive. It is also found that the MR of the material is controlled by the measuring current and measuring voltage. When B =2000 Oe, the M R is 11.5% at 2 . 5 mA and is 35% at about 35 V . Besides the magnetoresistance, the material has also a giant electroresistance of 500% at 8 V . It is believed that this material can be applied in electric and magnetic devises.
Magnetoresistance from quantum interference effects in ferromagnets. Nature, 2000, 404
(6778): 581. [7] Zhang X . , and Xue Q . Z . , Room temperature positive magnetoresistance in micrometer particle size Co,CI - I Composite. Physica B , 2003, 334 ( 1 -2): 216. [ 81 Xue Q .Z . , and Zhang X. , Positive magnetoresistance in micro-sized granular Nis-CITzcomposites. P h y s . Lett. A , 2003, 313(5 - 6 ) :
461. [ 91 Xue Q .Z . , and Zhang X. , Positive linear magnetoresistance in Fe,-CI - * composites. Journal of Magnetism and Magnetic Materials, 2004, 270(3): 397. [ 101 Zhu D. D . , Zhang X . , and Xue Q . Z . , Large magnetoresistance in Co,-CI-, granular films on Si( 100) substrate prepared by pulsed laser deposition. Actu Phys . Sin. (in Chinese), 2003, 52
(12): 3181. [ l l ] Zhu D . D . , Zhang X . , and Xue Q . Z . , Anomalous positive magnetoresistance in Co,-C, granular films on Si substrates. J . Appl. Phys . ,
2004, 95(4): 1906.
References [ l ] Baibich M . N . , Broto J. M., Fert A . , el al., Giant magnetoresistance of (001 ) Fe/( 001 ) Cr magnetic superlattices. Phys . Rev . Lett . , 1988, 61(21): 2472. [2] Berkowits A. E . , Mitchell J . R . , Carey M .J . , et a1 . , Giant magnetoresistance in heterogeneous Cu-Co alloys. Phys. Rev. L e t t . , 1992, 68 (25) : 3745. 131 Jin S . , Tiefel T . H . , McCormack M . , et al., Thousandfold change in resistivity in magnetoresistive La-Ca. Science, 1994, 264(5157): 413. [4] Xu R . , Husmann A , , Rosenbaum T. F . , et a1 . , Large magnetoresistance in non-magnetic silver chalcogenides . Nature, 1997, 390
(6655): 57. [5] Solin S . A . , Thio T . , Hines D . R . , et a l . , Enhanced room-temperature geometric magnetoresistance in inhomogeneous narrow-gap semiconductors. Science, 2000, 289(5484): 1530. [6] Manyala N . , Sidis Y . , DiTusa J . F . , et a l . ,
[ 121 Xue Q. Z . , and Zhang X . , Magnetoresistance and current-controlled electric transport properties of Fe-C film on Si substrate. Muterials Science Forum, 2005, 475 - 479: 2207. [ 131 Zhang X. , and Xue Q . Z . , Positive and negative linear magnetoresistance in graphite. Phys .
Lett. A . , 2003, 320(5-6): 471. [ 141 Xue Q .Z . , and Zhang X. , Anomalous electrical transport properties of amorphous carbon films on Si substrates. Carbon , 2005, 43(4) : 760. [ 151 Xue Q . Z . , Zhang X . , Tian P . , et u l . , Anomalous current-voltage characteristics and colossal emectroresistance of amorphous carbon film on Si substrate. Appl. Phys. L e t t . , 2004, 85(19):
4397. [ 161 Takeda H . , Fujita A . , and Fukamichi K . , Application of the giant magnetoresistance effect of nanogranular Ag,,C% thin film as a sensor for brushless dc motors. J . Appl . Phys . , 2002, 91
(10): 77.