Nanowire and memory device using it as a medium for current-induced domain wall displacement
Disclosed herein are a nanowire and a current-induced domain wall displacement-type memory device using the same. The nanowire has perpendicular magnetic anisotropy and is configured in a manner that when a parameter Q, calculated by a saturation magnetization per unit area, a domain wall thickness and a spin polarizability of a ferromagnet that is a constituent material of the nanowire, has a value of (formula 1 should be inserted here) a domain wall thickness, a width “*′” and a thickness −* of the nanowire satisfy the relationship of (formula 2 should be inserted here) The present invention can be designed such that a current density capable of driving a memory device utilizing the current-driven domain wall displacement has a value of less than (formula 3 should be inserted here), through the determination of the optimal nanowire width and thickness satisfying a value of a critical current density, Jc for the domain wall displacement below a certain value required for commercialization, for a given material in the nanowire with perpendicular anisotropy. According to such a configuration of the present invention, the current density required for the domain wall displacement can be at least 10 times or further lowered than the current density in currently available nano wires. Therefore, the present invention is capable of solving the problems associated with high power consumption and malfunction of the device due to generation of Joule heat and is also capable of achieving low-cost production of memory devices. 3 × 10 8 A / cm 2 ≤ Q ≤ 10 9 A / cm 2 , ( 1 ) 1.39 T / λ + 4.51 ≤ W λ ≤ 1.53 T / λ + 4.44 ( 2 ) 10 7 A / cm 2 , ( 3 )
1. A nanowire with perpendicular magnetic anisotropy, wherein when a parameter Q, calculated by a saturation magnetization per unit area, a domain wall thickness and a spin polarizability of a ferromagnet that is a constituent material of the nanowire, has a value of 3×10 8 A/cm 2 ≦Q≦10 9 A/cm 2 , a domain wall thickness λ, a width W and a thickness T of the nanowire satisfy the relationship of Equation 10, (wherein, 0</λ≧4), the parameter Q and a domain wall demagnetizing factor N d meets the requirement |N d |×J c in /Q≦ 10 7 /Q (J c in is a critical current density for the magnetic field-free current-induced domain wall displacement has a value of less than 10 7 A/cm 2 ), the N d is a physical quantity that is determined upon the determination of a nanowire width W, and nanowire thickness T and a domain wall thickness λ,
1.39
T
/
λ
+
4.51
≤
W
λ
≤
1.53
T
/
λ
+
4.44
.
(
Equation
10
)
2. The nanowire according to claim 1 , wherein the nanowire is formed of any one selected from the group consisting of Fe, Co, Ni and any combination thereof.
3. The nanowire according to claim 1 , wherein the nanowire is formed of a rare-earth metal.
4. A memory device comprising the nanowire of any one of claims 1 to 3 and utilizing the current-induced domain wall displacement.