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GaAs films processed by focused ion beam
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 272–276 (2004) e1385–e1386
Room temperature magnetoresistance effect observed in Au/GaAs films processed by focused ion beam Masaki Mizuguchi*, Takashi Manago, Hiro Akinaga Research Consortium for Synthetic Nano-Function Materials Project, Nanotechnology Research Institute, National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8562, Japan
Abstract Huge magnetoresistance (MR) effect was observed in Au/GaAs films with a nano-size trench fabricated by a focused ion beam process. Positive MR effect with the ratio of 32,000% was obtained in the magnetic field of 15,000 Oe at room temperature. This huge MR effect is promising for the application to spintronic devices such as magnetic sensors. r 2003 Elsevier B.V. All rights reserved. PACS: 73.61.At; 73.61.Ey; 75.47.De Keywords: Metal and metallic alloys; Semiconductors; Giant magnetoresistance
1. Introduction
2. Experimental
High-performance magnetoresistance (MR) devices are required with an increase of recording density in storage media. We have already reported a roomtemperature huge MR effect, which is termed magnetoresistive switch (MRS) effect, in Sb/MnSb clusters/GaAs (0 0 1) granular systems [1,2]. MnSb clusters were grown on a sulfur-passivated GaAs substrate [3]. This effect occurs because transport properties of the granular film change according to the increase of the magnetic field [4]. These films show the huge MR effect, but they also need a high voltage of about 80 V to generate the MRS effect. The voltage required for the operation was not low enough for spintronic devices. In this report, the magnetotransport properties of Au thin films with a nano-meter size trench fabricated by focused ion beam (FIB) are described. Substantial improvements in the required voltage has been achieved for the films.
The growths of Au films were performed in a molecular-beam epitaxy chamber under ultra high vacuum. Subsequent to the removal of a surface oxide layer of a GaAs (1 1 1)B substrate, a GaAs buffer layer with the thickness of 10 nm was grown at 580 C for flattering the surface. Next, a Au layer with the thickness of 10 nm was grown at room temperature. A trench with the width of 100 nm was fabricated in the Au layer by an FIB process. Two wires were bonded at the surface of the Au layer. Schematic illustration in section of a structure of the sample is shown in Fig. 1. The current between two contacts was measured with applying a constant voltage in the magnetic field. The magnetic field up to 15,000 Oe was applied to samples in plane. All the measurements of magnetotransport properties were performed in the air at room temperature.
3. Results and discussion *Corresponding author. Tel.: +81-298-61-5080; fax: +8129-861-2777. E-mail address: [email protected] (M. Mizuguchi).
Fig. 2 shows current versus voltage (I2V ) relation curves of the processed film measured in several magnetic fields. A clear jump was observed at around
0304-8853/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.12.285
ARTICLE IN PRESS e1386
M. Mizuguchi et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) e1385–e1386
Fig. 1. Schematic illustration in section of a Au film processed by focused ion beam grown on a GaAs substrate.
Fig. 3. An MR curve of the Au/GaAs film with the trench when a constant voltage of 30 V is applied.
effect. Pursuit of the mechanism of the MRS effect is now in progress.
4. Conclusions
Fig. 2. I2V curves of the Au/GaAs film with the trench in several magnetic fields.
14 V in zero magnetic field. This voltage where the jump occurs shifted toward higher voltage, which is just same as that in MnSb granular films [4]. Moreover, this voltage to generate MRS effect is much smaller than that of MnSb granular films. The reason why the required voltage decreased drastically is attributed to the decrease in a number of junctions in the trench structures. An MR curve of this film is shown in Fig. 3. Huge positive MR effect was observed by applying the electric field of only 30 V at room temperature. MR ratio at each magnetic field is estimated as follows: 120% at 3000 Oe, 25,000% at 5000 Oe, 32,000% at 15,000 Oe. Magnetotransport properties of this film is very similar to that of MnSb granular films fundamentally, therefore the MR effect is thought to be driven by MRS
We have discovered the huge MR effect in Au/GaAs films with the trench fabricated by an FIB process. The MR ratio reached up to 32,000% at room temperature. The operating voltage to generate MRS effect decreased to 14 V in these films which is much lower than that of MnSb granular films.
Acknowledgements This work was partly supported by NEDO under the Nanotechnology Materials Program.
References [1] H. Akinaga, M. Mizuguchi, K. Ono, M. Oshima, Appl. Phys. Lett. 76 (2000) 357. [2] H. Akinaga, M. Mizuguchi, K. Ono, M. Oshima, Appl. Phys. Lett. 76 (2000) 2600. [3] M. Mizuguchi, H. Akinaga, K. Ono, M. Oshima, Appl. Phys. Lett. 76 (2000) 1743. [4] M. Mizuguchi, H. Akinaga, K. Ono, M. Oshima, J. Magn. Magn. Mater. 226–230 (2001) 1838.
Journal of Magnetism and Magnetic Materials 272–276 (2004) e1385–e1386
Room temperature magnetoresistance effect observed in Au/GaAs films processed by focused ion beam Masaki Mizuguchi*, Takashi Manago, Hiro Akinaga Research Consortium for Synthetic Nano-Function Materials Project, Nanotechnology Research Institute, National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8562, Japan
Abstract Huge magnetoresistance (MR) effect was observed in Au/GaAs films with a nano-size trench fabricated by a focused ion beam process. Positive MR effect with the ratio of 32,000% was obtained in the magnetic field of 15,000 Oe at room temperature. This huge MR effect is promising for the application to spintronic devices such as magnetic sensors. r 2003 Elsevier B.V. All rights reserved. PACS: 73.61.At; 73.61.Ey; 75.47.De Keywords: Metal and metallic alloys; Semiconductors; Giant magnetoresistance
1. Introduction
2. Experimental
High-performance magnetoresistance (MR) devices are required with an increase of recording density in storage media. We have already reported a roomtemperature huge MR effect, which is termed magnetoresistive switch (MRS) effect, in Sb/MnSb clusters/GaAs (0 0 1) granular systems [1,2]. MnSb clusters were grown on a sulfur-passivated GaAs substrate [3]. This effect occurs because transport properties of the granular film change according to the increase of the magnetic field [4]. These films show the huge MR effect, but they also need a high voltage of about 80 V to generate the MRS effect. The voltage required for the operation was not low enough for spintronic devices. In this report, the magnetotransport properties of Au thin films with a nano-meter size trench fabricated by focused ion beam (FIB) are described. Substantial improvements in the required voltage has been achieved for the films.
The growths of Au films were performed in a molecular-beam epitaxy chamber under ultra high vacuum. Subsequent to the removal of a surface oxide layer of a GaAs (1 1 1)B substrate, a GaAs buffer layer with the thickness of 10 nm was grown at 580 C for flattering the surface. Next, a Au layer with the thickness of 10 nm was grown at room temperature. A trench with the width of 100 nm was fabricated in the Au layer by an FIB process. Two wires were bonded at the surface of the Au layer. Schematic illustration in section of a structure of the sample is shown in Fig. 1. The current between two contacts was measured with applying a constant voltage in the magnetic field. The magnetic field up to 15,000 Oe was applied to samples in plane. All the measurements of magnetotransport properties were performed in the air at room temperature.
3. Results and discussion *Corresponding author. Tel.: +81-298-61-5080; fax: +8129-861-2777. E-mail address: [email protected] (M. Mizuguchi).
Fig. 2 shows current versus voltage (I2V ) relation curves of the processed film measured in several magnetic fields. A clear jump was observed at around
0304-8853/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.12.285
ARTICLE IN PRESS e1386
M. Mizuguchi et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) e1385–e1386
Fig. 1. Schematic illustration in section of a Au film processed by focused ion beam grown on a GaAs substrate.
Fig. 3. An MR curve of the Au/GaAs film with the trench when a constant voltage of 30 V is applied.
effect. Pursuit of the mechanism of the MRS effect is now in progress.
4. Conclusions
Fig. 2. I2V curves of the Au/GaAs film with the trench in several magnetic fields.
14 V in zero magnetic field. This voltage where the jump occurs shifted toward higher voltage, which is just same as that in MnSb granular films [4]. Moreover, this voltage to generate MRS effect is much smaller than that of MnSb granular films. The reason why the required voltage decreased drastically is attributed to the decrease in a number of junctions in the trench structures. An MR curve of this film is shown in Fig. 3. Huge positive MR effect was observed by applying the electric field of only 30 V at room temperature. MR ratio at each magnetic field is estimated as follows: 120% at 3000 Oe, 25,000% at 5000 Oe, 32,000% at 15,000 Oe. Magnetotransport properties of this film is very similar to that of MnSb granular films fundamentally, therefore the MR effect is thought to be driven by MRS
We have discovered the huge MR effect in Au/GaAs films with the trench fabricated by an FIB process. The MR ratio reached up to 32,000% at room temperature. The operating voltage to generate MRS effect decreased to 14 V in these films which is much lower than that of MnSb granular films.
Acknowledgements This work was partly supported by NEDO under the Nanotechnology Materials Program.
References [1] H. Akinaga, M. Mizuguchi, K. Ono, M. Oshima, Appl. Phys. Lett. 76 (2000) 357. [2] H. Akinaga, M. Mizuguchi, K. Ono, M. Oshima, Appl. Phys. Lett. 76 (2000) 2600. [3] M. Mizuguchi, H. Akinaga, K. Ono, M. Oshima, Appl. Phys. Lett. 76 (2000) 1743. [4] M. Mizuguchi, H. Akinaga, K. Ono, M. Oshima, J. Magn. Magn. Mater. 226–230 (2001) 1838.