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Large tunneling magnetoresistance of a ramp-edge-type junction with a SrTiO3 barrier
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 272–276 (2004) e1499–e1500
Large tunneling magnetoresistance of a ramp-edge-type junction with a SrTiO3 barrier S.S. Leea,*, K. Rhieb, D.G. Hwanga, S.W. Kimc, K.H. Leea, J.R. Rheed, K. Shine a
Department of Computer and Electronic Physics Woosan-dong, Sang-Ji University, Wonju 220-702, South Korea b Department of Physics, Korea University, Chochiwon 339-700, South Korea c Department of Physics, Dankook University, Cheonan 330-714, South Korea d Department of Physics, Sookmyung Women’s University, Seoul 140-742, South Korea e Nano Device Center, Korea Institute of Science and Technology, Seoul 136-791, South Korea
Abstract The tunneling magnetoresistance (TMR) of a ramp-edge-type junction with SrTiO3 barrier layer was studied. ( ( ( ( ( Samples with a structure of glass=NiOð600 AÞ=Coð100 AÞ=SrTiO 3 ð400 AÞ=SrTiO3 ð202100 AÞ=NiFeð100 AÞ were prepared by sputtering and etched through electron cyclotron argon ion milling. Nonlinear I–V characteristics were obtained from a ramp-type tunneling junction, with dominant difference between two external magnetic fields ( thick SrTiO3 barrier, the TMR was 52.7% at a bias ð7100 OeÞ perpendicular to the junction edge line. Given a 40-A voltage of 50 mV: The bias voltage dependence of TMR in a ramp-type tunneling junction was similar to that of the layered TMR junction. r 2003 Elsevier B.V. All rights reserved. PACS: 73.21.Hb; 71.10.Pm; 72.25.Dc Keywords: Ramp-edge-type junction; Tunneling magnetoresistance (TMR); SrTiO3 tunneling barrier; I–V characteristics
Ramp-type junctions with normal conducting interlayer were fabricated in the early 1980s to increase the density of integration in electronic circuits. Ramp-type junctions have several merits, such as solvable boundary problem at the slope interface, usage of edge domain wall effects, and easy scaling down to the sub-micron range [1]. For ramp-type tunneling magnetoresistance (TMR) junctions, however, some peculiar MR properties arising from the asymmetric tunneling processes at the junction line boundary and characteristics of the I–V response [2] have to be taken into account. In this study, ramp-type magnetic tunneling junctions with SrTiO3 tunneling barrier were fabricated and I–V curves that showed a high TMR property observed. After the depositions of NiO, Co, and SrTiO3 layers with RF and DC magnetic sputtering, the entire layers
*Corresponding author. Tel.: +82-33-730-0415; fax: +8233-730-0403. E-mail address: [email protected] (S.S. Lee).
( ( of the half region of the NiOð600 AÞ=Coð100 AÞ= ( multilayer were etched through ECR SrTiO3 ð400 AÞ argon ion milling at an angle of 15 [3]. Subsequently, a
Fig. 1. (a) Cross-section and (b) schematic view of a ramp-type structure with four electrodes for I–V and TMR measurement.
0304-8853/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.12.286
ARTICLE IN PRESS e1500
S.S. Lee et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) e1499–e1500
( thick SrTiO3 barrier: two applied magnetic fields of Fig. 2. (a) I–V characteristics of a ramp-type tunneling junction with a 20-A Ha ¼ 100 Oe (open circles) and Ha ¼ þ100 Oe (closed circles): (b) TMR curve of ramp-type tunneling junction with SrTiO3 tunneling barrier at a bias voltage of 50 mV: (c) Bias voltage dependence of TMR for the same I–V curves as shown in Fig. 2(a). The TMR was calculated using the equation fRap ð100 OeÞ Rp ðþ100 OeÞg 100=Rp ðþ100 OeÞ:
( thick and a NiFe top SrTiO3 tunneling barrier 20–100-A ( thick were deposited. The final rampelectrode 100-A type junction with a junction width of 37 mm was made after the lift-off process for the electrodes. Figs. 1(a) and (b) represent the cross-section and schematic views of a ramp-type structure, respectively. The transport properties were characterized by measuring the I–V response curves at room temperature. In these measurements, a constant voltage was applied across the junction. The current flowing from the Co to the NiFe layers was also measured. Fig. 2(a) presents the I–V characteristics of a ramp( thick SrTiO3 type tunneling junction with a 40-A tunneling barrier. The direction of an applied field and the ramp junction shape are shown in Fig. 2(a). The I–V characteristic curves under the positive ðþ100 OeÞ and negative ð100 OeÞ fields were distinctly different from each other. Both the curves were nonlinear, with the bias field significantly affecting the I–V curve. The bias voltage dependence of TMR in a ramp-type tunneling junction can be drawn from Fig. 2(a) and presented in Fig. 2(c). The TMR amplitude rose up to 52.7% at a bias voltage of 50 mV as shown in Fig. 2(b). This TMR value for a ramp-type tunneling junction was very high. The high positive TMR value was compared with earlier results of the spin inversion across the tunnel junction using the SrTiO3 barrier with a negative TMR. Spin inversion began across the tunnel junction when the tunneling SrTiO3 barrier converted the spin during the tunneling process [4]. However, these very large TMR properties for a ramp-type tunneling junction may be used as an application device. One possible reason for the higher TMR properties was the effect of asymmetric tunneling junction process between the NiFe-free layer and the wedge-pinned NiO=Co=SrTiO3 layers, with various exchange bias distributions caused by the slope angle of 15 as shown
in Fig. 1(a). The influence of the spin-polarized tunnel current with a very sharp tunneling edge changed the magnetization abruptly in some of the domains of the Co layer between the pinning NiO layer and the insulating SrTiO3 layer. Another probable contributing factor for the asymmetric tunneling barrier was related to the charge accumulation at the sharp and wedged interfaces. The bias voltage dependence of TMR in a ramp-type tunneling junction was similar to those of the conventional TMR junctions, except that small sawtooth-like peaks were observed as the bias increased as shown in Fig. 2(c). In summary, a new planar tunneling structure with a ramp-type tunneling junction was fabricated and its transport properties investigated. The asymmetric bias voltage dependence of TMR was observed, indicating an asymmetric spin-dependent tunneling process through the ramp edge. It exhibited an asymmetric spindependent tunneling process, based on the unstable bias voltage dependence and large TMR of 52.7%. The origins of a large TMR for a ramp-type junction with SrTiO3 tunneling barrier may be an effect of the asymmetric tunneling junction process between the NiFe-free layer and the wedge-pinned NiO=Co=SrTiO3 layers with a local charge accumulation at the sharp and wedged interfaces. This work was supported by the Vision 21 Research Program of the Korea Institute of Science and Technology (KIST).
References [1] [2] [3] [4]
J.K. Heinshon, et al., J. Appl. Phys. 90 (2001) 4623. C.L. Platt, et al., J. Appl. Phys. 81 (1997) 5523. S.S. Lee, et al., J. Korean Phys. Soc. 41 (2002) 749. J.M.D. Teresa, et al., Phys. Rev. Lett. 82 (1999) 4288.
Journal of Magnetism and Magnetic Materials 272–276 (2004) e1499–e1500
Large tunneling magnetoresistance of a ramp-edge-type junction with a SrTiO3 barrier S.S. Leea,*, K. Rhieb, D.G. Hwanga, S.W. Kimc, K.H. Leea, J.R. Rheed, K. Shine a
Department of Computer and Electronic Physics Woosan-dong, Sang-Ji University, Wonju 220-702, South Korea b Department of Physics, Korea University, Chochiwon 339-700, South Korea c Department of Physics, Dankook University, Cheonan 330-714, South Korea d Department of Physics, Sookmyung Women’s University, Seoul 140-742, South Korea e Nano Device Center, Korea Institute of Science and Technology, Seoul 136-791, South Korea
Abstract The tunneling magnetoresistance (TMR) of a ramp-edge-type junction with SrTiO3 barrier layer was studied. ( ( ( ( ( Samples with a structure of glass=NiOð600 AÞ=Coð100 AÞ=SrTiO 3 ð400 AÞ=SrTiO3 ð202100 AÞ=NiFeð100 AÞ were prepared by sputtering and etched through electron cyclotron argon ion milling. Nonlinear I–V characteristics were obtained from a ramp-type tunneling junction, with dominant difference between two external magnetic fields ( thick SrTiO3 barrier, the TMR was 52.7% at a bias ð7100 OeÞ perpendicular to the junction edge line. Given a 40-A voltage of 50 mV: The bias voltage dependence of TMR in a ramp-type tunneling junction was similar to that of the layered TMR junction. r 2003 Elsevier B.V. All rights reserved. PACS: 73.21.Hb; 71.10.Pm; 72.25.Dc Keywords: Ramp-edge-type junction; Tunneling magnetoresistance (TMR); SrTiO3 tunneling barrier; I–V characteristics
Ramp-type junctions with normal conducting interlayer were fabricated in the early 1980s to increase the density of integration in electronic circuits. Ramp-type junctions have several merits, such as solvable boundary problem at the slope interface, usage of edge domain wall effects, and easy scaling down to the sub-micron range [1]. For ramp-type tunneling magnetoresistance (TMR) junctions, however, some peculiar MR properties arising from the asymmetric tunneling processes at the junction line boundary and characteristics of the I–V response [2] have to be taken into account. In this study, ramp-type magnetic tunneling junctions with SrTiO3 tunneling barrier were fabricated and I–V curves that showed a high TMR property observed. After the depositions of NiO, Co, and SrTiO3 layers with RF and DC magnetic sputtering, the entire layers
*Corresponding author. Tel.: +82-33-730-0415; fax: +8233-730-0403. E-mail address: [email protected] (S.S. Lee).
( ( of the half region of the NiOð600 AÞ=Coð100 AÞ= ( multilayer were etched through ECR SrTiO3 ð400 AÞ argon ion milling at an angle of 15 [3]. Subsequently, a
Fig. 1. (a) Cross-section and (b) schematic view of a ramp-type structure with four electrodes for I–V and TMR measurement.
0304-8853/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.12.286
ARTICLE IN PRESS e1500
S.S. Lee et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) e1499–e1500
( thick SrTiO3 barrier: two applied magnetic fields of Fig. 2. (a) I–V characteristics of a ramp-type tunneling junction with a 20-A Ha ¼ 100 Oe (open circles) and Ha ¼ þ100 Oe (closed circles): (b) TMR curve of ramp-type tunneling junction with SrTiO3 tunneling barrier at a bias voltage of 50 mV: (c) Bias voltage dependence of TMR for the same I–V curves as shown in Fig. 2(a). The TMR was calculated using the equation fRap ð100 OeÞ Rp ðþ100 OeÞg 100=Rp ðþ100 OeÞ:
( thick and a NiFe top SrTiO3 tunneling barrier 20–100-A ( thick were deposited. The final rampelectrode 100-A type junction with a junction width of 37 mm was made after the lift-off process for the electrodes. Figs. 1(a) and (b) represent the cross-section and schematic views of a ramp-type structure, respectively. The transport properties were characterized by measuring the I–V response curves at room temperature. In these measurements, a constant voltage was applied across the junction. The current flowing from the Co to the NiFe layers was also measured. Fig. 2(a) presents the I–V characteristics of a ramp( thick SrTiO3 type tunneling junction with a 40-A tunneling barrier. The direction of an applied field and the ramp junction shape are shown in Fig. 2(a). The I–V characteristic curves under the positive ðþ100 OeÞ and negative ð100 OeÞ fields were distinctly different from each other. Both the curves were nonlinear, with the bias field significantly affecting the I–V curve. The bias voltage dependence of TMR in a ramp-type tunneling junction can be drawn from Fig. 2(a) and presented in Fig. 2(c). The TMR amplitude rose up to 52.7% at a bias voltage of 50 mV as shown in Fig. 2(b). This TMR value for a ramp-type tunneling junction was very high. The high positive TMR value was compared with earlier results of the spin inversion across the tunnel junction using the SrTiO3 barrier with a negative TMR. Spin inversion began across the tunnel junction when the tunneling SrTiO3 barrier converted the spin during the tunneling process [4]. However, these very large TMR properties for a ramp-type tunneling junction may be used as an application device. One possible reason for the higher TMR properties was the effect of asymmetric tunneling junction process between the NiFe-free layer and the wedge-pinned NiO=Co=SrTiO3 layers, with various exchange bias distributions caused by the slope angle of 15 as shown
in Fig. 1(a). The influence of the spin-polarized tunnel current with a very sharp tunneling edge changed the magnetization abruptly in some of the domains of the Co layer between the pinning NiO layer and the insulating SrTiO3 layer. Another probable contributing factor for the asymmetric tunneling barrier was related to the charge accumulation at the sharp and wedged interfaces. The bias voltage dependence of TMR in a ramp-type tunneling junction was similar to those of the conventional TMR junctions, except that small sawtooth-like peaks were observed as the bias increased as shown in Fig. 2(c). In summary, a new planar tunneling structure with a ramp-type tunneling junction was fabricated and its transport properties investigated. The asymmetric bias voltage dependence of TMR was observed, indicating an asymmetric spin-dependent tunneling process through the ramp edge. It exhibited an asymmetric spindependent tunneling process, based on the unstable bias voltage dependence and large TMR of 52.7%. The origins of a large TMR for a ramp-type junction with SrTiO3 tunneling barrier may be an effect of the asymmetric tunneling junction process between the NiFe-free layer and the wedge-pinned NiO=Co=SrTiO3 layers with a local charge accumulation at the sharp and wedged interfaces. This work was supported by the Vision 21 Research Program of the Korea Institute of Science and Technology (KIST).
References [1] [2] [3] [4]
J.K. Heinshon, et al., J. Appl. Phys. 90 (2001) 4623. C.L. Platt, et al., J. Appl. Phys. 81 (1997) 5523. S.S. Lee, et al., J. Korean Phys. Soc. 41 (2002) 749. J.M.D. Teresa, et al., Phys. Rev. Lett. 82 (1999) 4288.