Transport Properties of Magnetic Nanowires with Multiple Constrictions Formed by FIB
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M11.37.1
Transport Properties of Magnetic Nanowires with Multiple Constrictions Formed by FIB Tie Liu and Yihong Wu* Data Storage Institute, DSI Building, 5 Engineering Drive 1, Singapore 117608, REPUBLIC OF SINGAPORE and Department of Electrical and Computer Engineering, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260 ABSTRACT Ni nanowires were fabricated by electrochemical deposition in the pores of alumina filtration membranes, with the diameter around 200nm. To study the magnetic and electrical properties of Ni nanowires, individual nanowire was selected and connected with metal electrodes. Single and multiple constrictions were formed on the nanowires by focused ion beam (FIB). The wires were further thinned using oxygen plasma oxidation. Magnetoresistance curves were studied and compared before and after FIB trimming and oxidization. INTRODUCTION Ferromagnetic metal nanowires were studied intensively during recent years because of their possible potential use in high-density magnetic recording. Electroplating through porous Alumina and polycarbonate is widely used due to the simple process and easy to control [1]. Magnetic and electronic properties of magnetic nanowire arrays and individual nanowire were studied through M-H measurement by vibrating sample magnetometer (VSM) [2-3] and Superconducting Quantum Interference Device (SQUID) [4-7], and magnetoresistance (MR) measurement [4, 8-13]. Theoretical explanation and modeling were done by several groups [12, 14]. Studies on nanowires of different physical aspects have been conducted, such as zigzag ferromagnetic wires [18-19], bent ferromagnetic wires [9], individual straight nanowires [8, 11, 13] and constricted structures [15- 16]. In our work, Ni nanowires with high aspect ratio were fabricated by electrodeposition in the pores of alumina, with the diameter around 200 nm. The maximum length of nanowires is dependant on the thickness of membranes, which are 50 µm. To study the transport properties of Ni nanowires, individual nanowires were selected and connected with metal electrodes. The advantage of this method is that single nanowires can be investigated without the need to take magnetic interactions between neighboring wires into account. The magnetization reversal of the nanowires was studied by AMR at room temperature. The switching field was measured on individual nanowires as a function of the angle between the applied magnetic field and the wire axis. The results were quantitatively simulated and analyzed using classical magnetization reversal theories. To further study the shape dependence of magnetic properties of magnetic nanowires, we use FIB to form single and multiple constrictions. The wires were further thinned using oxygen plasma oxidation. The magnetoresistance was measured with the nanowires parallel and perpendicular to the applied magnetic field. The results were compared before and after FIB trimming and oxidation.
M11.37.2
Experiment Commercially available porous alumina filtration membranes (WhatmanTM)
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