- Email: [email protected]
Magnetoimpedance effect in semiconducting La0.4Sr0.6MnO3
Materials Science and Engineering B88 (2002) 18 – 21
www.elsevier.com/locate/mseb
Magnetoimpedance effect in semiconducting La0.4Sr0.6MnO3 Jifan Hu *, Hongwei Qin Department of Physics, Shandong Uni6ersity, Jinan 250100, People’s Republic of China Received 21 May 2001; accepted 17 October 2001
Abstract In the present work, it was found that for La0.4Sr0.6MnO3, the dc resistance decreases with increasing temperature, from 77 to 280 K. Different from the case of metallic La0.65Sr0.35MnO3, the ac impedance of the semiconducting La0.4Sr0.6MnO3 at room temperature decreases with increasing frequency, from 100 kHz to 12 MHz. The magnetoimpedance effect was observed in La0.4Sr0.6MnO3 at room temperature. The value of impedance ratio (Z(0) − Z(H))/Z(0) at H = 0.8 kOe reaches 5% at a frequency of 500 kHz. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Resistance; Semiconducting manganite; Magnetoimpedance effect
1. Introduction The doped perovskite manganites La1 − x Ax MnO3 (A=Ca, Sr, Ba) have attracted much attention because of a colossal magnetoresistance effect observed near room temperature, which is potentially interesting for applications in magnetic sensors [1 – 5]. In the doping range 0.17BxB 0.5, these manganites undergo a paramagnetic PM insulator to ferromagnetic FM metal transition. It has been found that for Pr0.5Sr0.5MnO3 [6], there is a magnetic field-induced phase transition from antiferromagnetic AFM charge ordered state to the FM metal. The phase transition accompanies a large jump in resistivity and a colossal negative MR. The charge ordering phenomena appear to be the generic properties of R1 − x Ax MnO3 (x : 0.5) with a relatively narrow eg electron bandwidth. The feature seems to strongly depend on the ionic radius of (R, A) ions or equivalently on the one-electron bandwidth of the eg band [6]. In the case of La1 − x Srx MnO3, the bandwidth of which is considered to be rather wide, the doping-induced IM transition takes place at x= 0.17, but no charge-ordering phase shows up, even when the * Corresponding author. Tel.: + 86-531-856-6143; fax: + 86-531856-5167. E-mail address: [email protected] (J. Hu).
nominal hole concentration is increased up to x =0.5 [6]. Early work showed that for La0.4Sr0.6MnO3 with large x (\ 0.5), there exists a small peak in temperature dependence of the saturation magnetization at :212 K and its Curie temperature seems to be relatively high [7]. This peak corresponds to the Neel temperature of AFM, which is mainly due to the negative Mn4 + – Mn4 + interaction. Recently, the magnetoimpedance effect was observed in the metallic La0.65Sr0.35MnO3 [8]. In the present work, we report the magnetoimpedance effect in the semiconducting La0.4Sr0.6MnO3.
2. Experiments The sintered sample La0.4Sr0.6MnO3 was prepared by traditional solid state reaction method. The result of X-ray diffraction showed the sample had a perovskite structure with almost a single phase. The thermal magnetization curve was measured with a vibrating sample magnetometer VSM. The temperature dependence of the dc resistance was measured from 77 to 280 K. The magnetoimpedance measurements were carried out with an ac current through the sample in the direction parallel to the dc magnetic fields, using a HP4192A impedance analyzer and the accessory 16048 test lead at room temperature.
0921-5107/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 5 1 0 7 ( 0 1 ) 0 0 9 1 4 - X
J. Hu, H. Qin / Materials Science and Engineering B88 (2002) 18–21
19
3. Results and discussion
Fig. 1. The thermal magnetization curve of the La0.4Sr0.6MnO3 under a field of 250 Oe in the temperature range of 95 K B TB375 K.
Fig. 2. The magnetization dependence on the temperature (95 K B T B300 K) for La0.4Sr0.6MnO3 with fields H = 120 and 1120 Oe, respectively
Fig. 3. The temperature dependence of the dc resistance of the La0.4Sr0.6MnO3 at zero magnetic field.
The thermal magnetization curve of the La0.4Sr0.6MnO3, under a field of 250 Oe, in the temperature range of 95 KB TB 375 K is shown in Fig. 1. There is a small peak at 210 K, which is very similar to the previous result [7]. Such peak should correspond to the AFM ordering temperature–Neel temperature due to the negative super-exchange Mn4 + –O2 − – Mn4 + interaction [7]. The FM ordering temperature–Curie temperature is obtained as :350 K, which is attributed to the strong positive double-exchange Mn3 + –O2 − – Mn4 + interaction [9]. The magnetization dependence on temperature for La0.4Sr0.6MnO3 reflects the competition between the negative Mn4 + –O2 − –Mn4 + interaction and positive Mn3 + –O2 − –Mn4 + interaction, depending on the applied magnetic field and the temperature. We measured the magnetization dependence on the temperature (95 KBT B300 K) for the La0.4Sr0.6MnO3 with various fields. As shown in Fig. 2, an evident peak occurs in the temperature dependence of the magnetization with a lower field (such as H= 120 Oe), showing the antiferromagnetic behavior. In contrast, with a higher field (such as H= 1120 Oe), the magnetization value decreases with increasing temperature, showing the ferromagnetic behavior. Fig. 3 shows the temperature dependence of the dc resistance for La0.4Sr0.6MnO3 at zero magnetic field. It can be seen that the dc resistance of La0.4Sr0.6MnO3 decreases sharply with increasing temperature as an insulator below AFM ordering temperature. In the measured ferromagnetic temperature range 150 KB TB 300 K, the dc resistance decreases gradually with temperature as a semiconductor. The ac frequency dependence of the impedance under a magnetic field H= 0.8 kOe and zero field H=0 for La0.4Sr0.6MnO3 at room temperature are shown in Fig. 4, respectively. The impedance for both H=0 and H=0.8 kOe decrease with increasing frequency, reflecting the transport behavior of the bound carriers in a
Fig. 4. The ac frequency dependence of the impedance under a magnetic field H =0.8 kOe and zero field H = 0 for La0.4Sr0.6MnO3 at room temperature.
20
J. Hu, H. Qin / Materials Science and Engineering B88 (2002) 18–21
Fig. 5. The dc field dependence of the impedance for La0.4Sr0.6MnO3 with various ac frequencies at room temperature.
Fig. 6. The frequency dependence of change ratio of impedance (Z(0)− Z(0.8 kOe))/Z(0) for La0.4Sr0.6MnO3 at room temperature.
semiconductor. This is different from the case of metallic La0.65Sr0.35MnO3, where the impedance increases with frequency due to the skin effect [8]. It can also be seen from Fig. 4 that in the measured frequency range of 100 kHz 5f5 12 MHz, the impedance values are smaller for H= 0.8 kOe than for H= 0. Fig. 5 shows the dc field dependence of the impedance for La0.4Sr0.6MnO3 with various ac frequencies at room temperature. The negative magnetoimpedance effect can be clearly seen for 100 kHz5 f 55 MHz. For a
relative high frequency f= 12 MHz, the magnetoimpedance effect becomes very weak. The frequency dependence of the change ratio of impedance (Z(0)− Z(0.8 kOe))/Z(0) for La0.4Sr0.6MnO3 at room temperature is plotted in Fig. 6. The values of (Z(0)−Z(0.8 kOe))/Z(0) are 4, 5 and 1.5% for f= 100 and 500 kHz and 12 MHz, respectively. In conclusion, it was found that for the semiconducting La0.4Sr0.6MnO3, the dc resistance decreases with increasing temperature. Results also showed that the ac impedance of the semiconducting La0.4Sr0.6MnO3 decreases with increasing frequency. A negative magnetoimpedance effect was observed in the semiconducting La0.4Sr0.6MnO3.
References [1] R. von Helmolt, J. Wecker, B. Holzapfel, L. Schultz, K. Samwer, Phys. Rev. Lett. 71 (1993) 2331. [2] S. Jin, T.H. Tiefel, M. McCormack, R.A. Fastnacht, R. Ramesh, L.H. Chen, Science 264 (1994) 413. [3] Y. Shimakawa, Y. Kubo, T. Manako, Nature 379 (1996) 53. [4] G. Zhao, K. Conder, H. Keller, K.A. Mueller, Nature 381 (1996) 676. [5] Y. Tokura, A. Urushifara, Y. Moritomo, T. Arima, A. Asamitsu,
J. Hu, H. Qin / Materials Science and Engineering B88 (2002) 18–21 G. Kido, N. Furukawa, J. Phys. Soc. Jpn. 63 (1994) 3931. [6] Y. Tomioka, A. Asamitsu, Y. Moritomo, H. Kuwahara, Y. Tokura, Phys. Rev. Lett. 74 (1995) 5108.
[7] G.H. Jonker, J.H. van Santen, Physica 16 (1950) 337. [8] J. Hu, H. Qin, Mater. Sci. Eng. B 79 (2001) 186. [9] C. Zener, Phys. Rev. 82 (1951) 403.
21
www.elsevier.com/locate/mseb
Magnetoimpedance effect in semiconducting La0.4Sr0.6MnO3 Jifan Hu *, Hongwei Qin Department of Physics, Shandong Uni6ersity, Jinan 250100, People’s Republic of China Received 21 May 2001; accepted 17 October 2001
Abstract In the present work, it was found that for La0.4Sr0.6MnO3, the dc resistance decreases with increasing temperature, from 77 to 280 K. Different from the case of metallic La0.65Sr0.35MnO3, the ac impedance of the semiconducting La0.4Sr0.6MnO3 at room temperature decreases with increasing frequency, from 100 kHz to 12 MHz. The magnetoimpedance effect was observed in La0.4Sr0.6MnO3 at room temperature. The value of impedance ratio (Z(0) − Z(H))/Z(0) at H = 0.8 kOe reaches 5% at a frequency of 500 kHz. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Resistance; Semiconducting manganite; Magnetoimpedance effect
1. Introduction The doped perovskite manganites La1 − x Ax MnO3 (A=Ca, Sr, Ba) have attracted much attention because of a colossal magnetoresistance effect observed near room temperature, which is potentially interesting for applications in magnetic sensors [1 – 5]. In the doping range 0.17BxB 0.5, these manganites undergo a paramagnetic PM insulator to ferromagnetic FM metal transition. It has been found that for Pr0.5Sr0.5MnO3 [6], there is a magnetic field-induced phase transition from antiferromagnetic AFM charge ordered state to the FM metal. The phase transition accompanies a large jump in resistivity and a colossal negative MR. The charge ordering phenomena appear to be the generic properties of R1 − x Ax MnO3 (x : 0.5) with a relatively narrow eg electron bandwidth. The feature seems to strongly depend on the ionic radius of (R, A) ions or equivalently on the one-electron bandwidth of the eg band [6]. In the case of La1 − x Srx MnO3, the bandwidth of which is considered to be rather wide, the doping-induced IM transition takes place at x= 0.17, but no charge-ordering phase shows up, even when the * Corresponding author. Tel.: + 86-531-856-6143; fax: + 86-531856-5167. E-mail address: [email protected] (J. Hu).
nominal hole concentration is increased up to x =0.5 [6]. Early work showed that for La0.4Sr0.6MnO3 with large x (\ 0.5), there exists a small peak in temperature dependence of the saturation magnetization at :212 K and its Curie temperature seems to be relatively high [7]. This peak corresponds to the Neel temperature of AFM, which is mainly due to the negative Mn4 + – Mn4 + interaction. Recently, the magnetoimpedance effect was observed in the metallic La0.65Sr0.35MnO3 [8]. In the present work, we report the magnetoimpedance effect in the semiconducting La0.4Sr0.6MnO3.
2. Experiments The sintered sample La0.4Sr0.6MnO3 was prepared by traditional solid state reaction method. The result of X-ray diffraction showed the sample had a perovskite structure with almost a single phase. The thermal magnetization curve was measured with a vibrating sample magnetometer VSM. The temperature dependence of the dc resistance was measured from 77 to 280 K. The magnetoimpedance measurements were carried out with an ac current through the sample in the direction parallel to the dc magnetic fields, using a HP4192A impedance analyzer and the accessory 16048 test lead at room temperature.
0921-5107/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 5 1 0 7 ( 0 1 ) 0 0 9 1 4 - X
J. Hu, H. Qin / Materials Science and Engineering B88 (2002) 18–21
19
3. Results and discussion
Fig. 1. The thermal magnetization curve of the La0.4Sr0.6MnO3 under a field of 250 Oe in the temperature range of 95 K B TB375 K.
Fig. 2. The magnetization dependence on the temperature (95 K B T B300 K) for La0.4Sr0.6MnO3 with fields H = 120 and 1120 Oe, respectively
Fig. 3. The temperature dependence of the dc resistance of the La0.4Sr0.6MnO3 at zero magnetic field.
The thermal magnetization curve of the La0.4Sr0.6MnO3, under a field of 250 Oe, in the temperature range of 95 KB TB 375 K is shown in Fig. 1. There is a small peak at 210 K, which is very similar to the previous result [7]. Such peak should correspond to the AFM ordering temperature–Neel temperature due to the negative super-exchange Mn4 + –O2 − – Mn4 + interaction [7]. The FM ordering temperature–Curie temperature is obtained as :350 K, which is attributed to the strong positive double-exchange Mn3 + –O2 − – Mn4 + interaction [9]. The magnetization dependence on temperature for La0.4Sr0.6MnO3 reflects the competition between the negative Mn4 + –O2 − –Mn4 + interaction and positive Mn3 + –O2 − –Mn4 + interaction, depending on the applied magnetic field and the temperature. We measured the magnetization dependence on the temperature (95 KBT B300 K) for the La0.4Sr0.6MnO3 with various fields. As shown in Fig. 2, an evident peak occurs in the temperature dependence of the magnetization with a lower field (such as H= 120 Oe), showing the antiferromagnetic behavior. In contrast, with a higher field (such as H= 1120 Oe), the magnetization value decreases with increasing temperature, showing the ferromagnetic behavior. Fig. 3 shows the temperature dependence of the dc resistance for La0.4Sr0.6MnO3 at zero magnetic field. It can be seen that the dc resistance of La0.4Sr0.6MnO3 decreases sharply with increasing temperature as an insulator below AFM ordering temperature. In the measured ferromagnetic temperature range 150 KB TB 300 K, the dc resistance decreases gradually with temperature as a semiconductor. The ac frequency dependence of the impedance under a magnetic field H= 0.8 kOe and zero field H=0 for La0.4Sr0.6MnO3 at room temperature are shown in Fig. 4, respectively. The impedance for both H=0 and H=0.8 kOe decrease with increasing frequency, reflecting the transport behavior of the bound carriers in a
Fig. 4. The ac frequency dependence of the impedance under a magnetic field H =0.8 kOe and zero field H = 0 for La0.4Sr0.6MnO3 at room temperature.
20
J. Hu, H. Qin / Materials Science and Engineering B88 (2002) 18–21
Fig. 5. The dc field dependence of the impedance for La0.4Sr0.6MnO3 with various ac frequencies at room temperature.
Fig. 6. The frequency dependence of change ratio of impedance (Z(0)− Z(0.8 kOe))/Z(0) for La0.4Sr0.6MnO3 at room temperature.
semiconductor. This is different from the case of metallic La0.65Sr0.35MnO3, where the impedance increases with frequency due to the skin effect [8]. It can also be seen from Fig. 4 that in the measured frequency range of 100 kHz 5f5 12 MHz, the impedance values are smaller for H= 0.8 kOe than for H= 0. Fig. 5 shows the dc field dependence of the impedance for La0.4Sr0.6MnO3 with various ac frequencies at room temperature. The negative magnetoimpedance effect can be clearly seen for 100 kHz5 f 55 MHz. For a
relative high frequency f= 12 MHz, the magnetoimpedance effect becomes very weak. The frequency dependence of the change ratio of impedance (Z(0)− Z(0.8 kOe))/Z(0) for La0.4Sr0.6MnO3 at room temperature is plotted in Fig. 6. The values of (Z(0)−Z(0.8 kOe))/Z(0) are 4, 5 and 1.5% for f= 100 and 500 kHz and 12 MHz, respectively. In conclusion, it was found that for the semiconducting La0.4Sr0.6MnO3, the dc resistance decreases with increasing temperature. Results also showed that the ac impedance of the semiconducting La0.4Sr0.6MnO3 decreases with increasing frequency. A negative magnetoimpedance effect was observed in the semiconducting La0.4Sr0.6MnO3.
References [1] R. von Helmolt, J. Wecker, B. Holzapfel, L. Schultz, K. Samwer, Phys. Rev. Lett. 71 (1993) 2331. [2] S. Jin, T.H. Tiefel, M. McCormack, R.A. Fastnacht, R. Ramesh, L.H. Chen, Science 264 (1994) 413. [3] Y. Shimakawa, Y. Kubo, T. Manako, Nature 379 (1996) 53. [4] G. Zhao, K. Conder, H. Keller, K.A. Mueller, Nature 381 (1996) 676. [5] Y. Tokura, A. Urushifara, Y. Moritomo, T. Arima, A. Asamitsu,
J. Hu, H. Qin / Materials Science and Engineering B88 (2002) 18–21 G. Kido, N. Furukawa, J. Phys. Soc. Jpn. 63 (1994) 3931. [6] Y. Tomioka, A. Asamitsu, Y. Moritomo, H. Kuwahara, Y. Tokura, Phys. Rev. Lett. 74 (1995) 5108.
[7] G.H. Jonker, J.H. van Santen, Physica 16 (1950) 337. [8] J. Hu, H. Qin, Mater. Sci. Eng. B 79 (2001) 186. [9] C. Zener, Phys. Rev. 82 (1951) 403.
21