Correlation of tunnel magnetoresistance with the magnetic properties in perpendicular CoFeB-based junctions with exchange bias

Abstract

We investigate the dependence of magnetic properties on the post-annealing temperature/time, the thickness of soft ferromagnetic electrode and Ta dusting layer in the pinned electrode as well as their correlation with the tunnel magnetoresistance ratio, in a series of perpendicular magnetic tunnel junctions of materials sequence Ta/Pd/IrMn/CoFe/Ta(x)/CoFeB/MgO(y)/CoFeB(z)/Ta/Pd. We obtain a large perpendicular exchange bias of 79.6 kA/m for x = 0.3 nm. For stacks with z = 1.05 nm, the magnetic properties of the soft electrode resemble the characteristics of superparamagnetism. For stacks with x = 0.4 nm, y = 2 nm, and z = 1.20 nm, the exchange bias presents a significant decrease at post annealing temperature Tann = 330 • C for 60 min, while the interlayer exchange coupling and the saturation magnetization per unit area sharply decay at Tann = 340 • C for 60 min. Simultaneously, the tunnel magnetoresistance ratio shows a peak of 65.5% after being annealed at Tann = 300 • C for 60 min, with a significant reduction down to 10% for higher annealing temperatures (Tann ≥ 330 • C) and down to 14% for longer annealing times (Tann = 300 • C for 90 min). We attribute the large decrease of tunnel magnetoresistance ratio to the loss of exchange bias in the pinned electrode.

Polycrystalline exchange-biased bilayers: magnetically effective vs. structural antiferromagnetic grain volume distribution

“…An antiferromagnet (AF) and a ferromagnet (F) sharing an interface in a thin bilayer system commonly results in a horizontal shift of the ferromagnetic hysteresis loop accompanied by an additional modification of its coercivity as compared to loops of a pure F [1][2][3]. With the effect arising from exchange interaction across the common interface, the phenomenon has been named exchange bias (EB) and is a key effect for of the development of data storage and magnetic sensor technology [4][5][6][7]. Further, domain engineering of polycrystalline EB thin films [8][9][10][11][12][13] has proven to be an important ingredient of lab-ona-chip devices [14] enabling the actuation of magnetic particles in liquid media [15][16][17].…”

Effects of Annealing and Thickness of Co60Fe20Yb20 Nanofilms on Their Structure, Magnetic Properties, Electrical Efficiency, and Nanomechanical Characteristics

“…Due to its excellent characteristics, the Co-Fe system has received extensive attention. At present, Co-Fe alloys are often used in magnetic devices, sensors, actuators, and magnetic storage [ 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 ]. Magnetic properties are affected by thickness, crystallinity, and interfacial interactions.…”

Impact of Annealing on Magnetic Properties and Structure of Co40Fe40W20 Thin Films on Si(100) Substrate

“…Ever since the discovery of Co 50 Fe 50 by Ellis in 1927 and Elmen in 1929, it has been shown that it has good soft magnetic properties [1]. The soft magnetic material of the Co-Fe system has been extensively applied in read heads of hard disks and magnetoresistive random access memories (MRAMs) because of their good mechanical properties, high spin polarization, high Curie temperature (T c ), high saturation magnetization (M s ), low coercivity (H c ), and high spin polarization [2][3][4][5][6][7][8]. The CoFeB layer was utilized to combine with the MgO layer to form magnetic tunnel junctions (MTJs).…”