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New method for detecting domain wall...

Zambano, Antonio Javier.

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New method for detecting domain wall trapping and motion at a constriction in narrow ferromagnetic wires using perpendicular-current giant magnetoresistance.

Record Type:	Electronic resources : Monograph/item
Title/Author:	New method for detecting domain wall trapping and motion at a constriction in narrow ferromagnetic wires using perpendicular-current giant magnetoresistance./
Author:	Zambano, Antonio Javier.
Description:	112 p.
Notes:	Source: Dissertation Abstracts International, Volume: 65-09, Section: B, page: 4635.
Contained By:	Dissertation Abstracts International65-09B.
Subject:	Physics, Condensed Matter. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3146135
ISBN:	0496052020

New method for detecting domain wall trapping and motion at a constriction in narrow ferromagnetic wires using perpendicular-current giant magnetoresistance.
Zambano, Antonio Javier.

New method for detecting domain wall trapping and motion at a constriction in narrow ferromagnetic wires using perpendicular-current giant magnetoresistance. - 112 p.

Source: Dissertation Abstracts International, Volume: 65-09, Section: B, page: 4635.

Thesis (Ph.D.)--Michigan State University, 2004.

We present a versatile, new method for detecting the presence and small motions of a trapped domain wall in a narrow ferromagnetic wire using current-perpendicular-to-plane, CPP, giant magnetoresistance, GMR. We have adapted the Ono et al.1-2 method for trapping domain walls to CPP GMR measurements. We shaped a spin valve multilayer Cu(10nm)/Py(20nm)/Cu(10nm)/Py(5nm)/Cu(5nm)/Au(15nm), where Py = Ni84 Fe16, into a long &sim;500-nm-wide wire with a U-shaped or V-shaped constriction (notch) near its middle that acts as a trapping site for a head-to-head (or tail-to-tail) domain wall. A sweeping external magnetic field, H, is applied along the wire axis. The magnetization is restricted to be parallel to the wire axis due to the shape anisotropy. Magnetization reversal in the wire takes place by propagation of a magnetic domain wall, which initially nucleates in a diamond-shaped reservoir and is injected from there into the nanowire at a particular value of H. As a wall in either Py layer moves past the measuring contact, the CPP GMR detects the change of the relative magnetizations of the two Py layers, from parallel to antiparallel. The CPP GMR response to small motions of the trapped domain wall is enhanced because the CPP current is restricted to the region of wall trapping; but in addition, the CPP current can be also localized to a measuring region outside the constriction. Superconducting 150-nm-thick (top) and 100-nm-thick (bottom) Nb contacts are used to obtain a uniform CPP current density in the wall trapping region at 4.2 K; but measurements at 295K, including 200-nm-Au top contacts, have also been successful with non-uniform CPP currents. Data for the two different types of constrictions show that for U-shape notches, several pinning sites were seen as the wall in the thinner Py layer remained trapped in the constriction, while in V-shaped notches one trapping site occurred. Successful pinning of a wall at the constriction in the thicker Py layer was more improbable. With this technique, the position of the wall inside the notch region can be precisely determined. While H is swept, a wall trapped in a constriction moves between different points in the notch seeking a lower energy state, and it does not have to leave the constriction when the system is relaxed by sweeping the field to 0 Oe. When H is kept fixed, time dependence of wall position inside a U-shaped constriction in the thinner Py layer appears to be thermally activated at 4.2 K. No wall motion was observed in a V-shaped notch under the same circumstances. Along with these results, data from other studies, such as domain wall stability and effects of a high-density CPP current, are presented in this thesis to confirm the success and effectiveness of our technique.

ISBN: 0496052020Subjects--Topical Terms:

1018743
Physics, Condensed Matter.

New method for detecting domain wall trapping and motion at a constriction in narrow ferromagnetic wires using perpendicular-current giant magnetoresistance.
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100 1 $a Zambano, Antonio Javier. $3 1940323
245 1 0 $a New method for detecting domain wall trapping and motion at a constriction in narrow ferromagnetic wires using perpendicular-current giant magnetoresistance.
300 $a 112 p.
500 $a Source: Dissertation Abstracts International, Volume: 65-09, Section: B, page: 4635.
500 $a Adviser: William P. Pratt, Jr.
502 $a Thesis (Ph.D.)--Michigan State University, 2004.
520 $a We present a versatile, new method for detecting the presence and small motions of a trapped domain wall in a narrow ferromagnetic wire using current-perpendicular-to-plane, CPP, giant magnetoresistance, GMR. We have adapted the Ono et al.1-2 method for trapping domain walls to CPP GMR measurements. We shaped a spin valve multilayer Cu(10nm)/Py(20nm)/Cu(10nm)/Py(5nm)/Cu(5nm)/Au(15nm), where Py = Ni84 Fe16, into a long &sim;500-nm-wide wire with a U-shaped or V-shaped constriction (notch) near its middle that acts as a trapping site for a head-to-head (or tail-to-tail) domain wall. A sweeping external magnetic field, H, is applied along the wire axis. The magnetization is restricted to be parallel to the wire axis due to the shape anisotropy. Magnetization reversal in the wire takes place by propagation of a magnetic domain wall, which initially nucleates in a diamond-shaped reservoir and is injected from there into the nanowire at a particular value of H. As a wall in either Py layer moves past the measuring contact, the CPP GMR detects the change of the relative magnetizations of the two Py layers, from parallel to antiparallel. The CPP GMR response to small motions of the trapped domain wall is enhanced because the CPP current is restricted to the region of wall trapping; but in addition, the CPP current can be also localized to a measuring region outside the constriction. Superconducting 150-nm-thick (top) and 100-nm-thick (bottom) Nb contacts are used to obtain a uniform CPP current density in the wall trapping region at 4.2 K; but measurements at 295K, including 200-nm-Au top contacts, have also been successful with non-uniform CPP currents. Data for the two different types of constrictions show that for U-shape notches, several pinning sites were seen as the wall in the thinner Py layer remained trapped in the constriction, while in V-shaped notches one trapping site occurred. Successful pinning of a wall at the constriction in the thicker Py layer was more improbable. With this technique, the position of the wall inside the notch region can be precisely determined. While H is swept, a wall trapped in a constriction moves between different points in the notch seeking a lower energy state, and it does not have to leave the constriction when the system is relaxed by sweeping the field to 0 Oe. When H is kept fixed, time dependence of wall position inside a U-shaped constriction in the thinner Py layer appears to be thermally activated at 4.2 K. No wall motion was observed in a V-shaped notch under the same circumstances. Along with these results, data from other studies, such as domain wall stability and effects of a high-density CPP current, are presented in this thesis to confirm the success and effectiveness of our technique.
520 $a 1T. Ono, H. Miyajima, K. Shigeto and T. Shinjo, Appl. Phy. Lett. 72, 1116 (1998). 2T. Ono, Y. Ooka, S. Kasai, H. Miyajima, N. Nakatani, N. Hayashi, K. Shigeto, K. Mibu and T. Shinjo, Mater. Sci. Eng. B 84, 126 (2001).
590 $a School code: 0128.
650 4 $a Physics, Condensed Matter. $3 1018743
650 4 $a Physics, Electricity and Magnetism. $3 1019535
690 $a 0611
690 $a 0607
710 2 0 $a Michigan State University. $3 676168
773 0 $t Dissertation Abstracts International $g 65-09B.
790 1 0 $a Pratt, William P., Jr., $e advisor
790 $a 0128
791 $a Ph.D.
792 $a 2004
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3146135