Influence of Stripe Height on Critical Current Density of Spin-Torque Noise in Tunneling Magnetoresistive Read Heads

Effect of stripe height on the critical current density of spin-torque noise in a tunneling magnetoresistive read head with a low resistance area product below 1.0 Ω μm2

“…6,7 The value for the heads with h ¼ 15 nm is much higher than those for previously reported TMR heads with a large resistance-area product and size (þ5.00 6 2.30 Â 10 11 A/m 2 ). 12 To verify j c as a function of h, Fig. 4 plots the j c values of select TMR heads as a function of h. As h decreases, j c increases markedly and the maximum value is approximately þ1.5 Â 10 12 A/m 2 , which is much higher than the value for a TMR head with a MgO barrier (j c ¼ þ1.1 Â 10 11 A/m 2 ) 7 and our previous report.…”

“…4 plots the j c values of select TMR heads as a function of h. As h decreases, j c increases markedly and the maximum value is approximately þ1.5 Â 10 12 A/m 2 , which is much higher than the value for a TMR head with a MgO barrier (j c ¼ þ1.1 Â 10 11 A/m 2 ) 7 and our previous report. 12 This difference originates from the smaller head dimension and the stronger shape anisotropy. The non-thermal fluctuation noise originating from spintorque in the TMR head disappears for j < 10 12 A/m 2 , as h decreases and the shape anisotropy is strengthened in smaller sized TMR heads.…”

“…For the area density in hard disk drives to exceed 5 Tbit/in 2 , 1 the read head dimensions must be less than 20 nm, which increases the current density to read data 2 and leads to magnetic instability due to thermally excited magnetization fluctuation noise (thermal mag-noise) 3 and non-thermal fluctuation noise originating from the spin-torque. [4][5][6][7][8][9][10][11][12] In particular, non-thermal fluctuation noise due to spin-torque in a read head [e.g., a tunneling magnetoresistive read head (TMR head)] has received much attention because spin-torque influences the 1/f noise and generates several noise peaks in the GHz range when the current density exceeds the threshold value, which is called the critical current density (j c ). Exceeding j c leads to serious issues for TMR heads with a small size and a resistancearea product less than 1.0 X lm 2 .…”

“…10 Additionally, we demonstrated that j c above which steady state precession occurs in a TMR head with a physical track width (w) of 60 nm, and resistance-area product of 1.7 X lm 2 is independent of the stripe height, and estimated j c ¼ 4.7 Â 10 11 A/m 2 . 12 For TMR heads with a resistance-area product less than 1.0 X lm 2 , it is unclear whether the spin-torque effect enhances the thermal mag-noise. Herein, we investigate the dependence of noise spectra on j in TMR heads with w ¼ 36 nm and a varying stripe height (h) between 15 and 45 nm and a resistance-area product below 1.0 X lm 2 .…”