High Moment Fe65Co35/IrMn Exchange- Coupled Soft Underlayers for Perpendicular Media

Transcription

1 High Moment Fe65Co35/IrMn Exchange- Coupled Soft Underlayers for Perpendicular Media H. S. Jung and W. D. Doyle MINT Center The University of Alabama This project was funded by INSIC-NSF and by INSIC.

2 Historical Development of Soft Underlayers Target: 2 nm thick ferromagnetic layer and µ ~ 1 FeTaN/IrMn - G/FeTaN(2)/[IrMn(1)/FeTaN(2)]9 19 layers - High 4πM s ~ 2 kg - Thermal instability of FeTaN Increased Hk Enhanced thermal stability Fe 1 Co 9 /IrMn - G/Cu/IrMn/[FeCo(5)/IrMn(1)]4/FeCoN(2) 11 layers - Low 4πM s 15 ~ 16 kg Fe 65 Co 35 /IrMn - G/Cu/IrMn/[FeCo(5)/IrMn(1)]4/FeCo(25) 11 layers - Not enough thermal stability Increased 4πM s Improved thermal stability

3 Effect of Various Underlayers on Hc G/Underlayer(t nm)/fe65co35 (5 nm) 12 without underlayer 8 12 Ta(2.5 nm) 8 m (memu/cm 2 ) 4-4 m (memu/cm 2 ) m (memu/cm 2 ) Cu(2.5 nm) H H m (memu/cm 2 ) 12 NiFe(2.5 nm) H H 12 Ru(2.5 nm) m (memu/cm 2 ) H

4 Outstanding Hysteretic Properties G/Cu(2 nm)/irmn(1 nm)/[feco (5 nm)/irmn(1 nm)]4/feco (25 nm) 5 As-deposited 1. Annealed m (memu/cm 2 ) 25 H po = 116 Oe H -25 eb = 51 Oe H c, = 22 Oe H c, = 1.7 Oe H m / m s Top FeCo H po = 11 Oe = 62 Oe H c, = 12 Oe H c, = 2 Oe H Annealed at 225 o C for 1 min. in H = 5 Oe A single domain remanent direction, a high H po, and a high 4πM s Annealing enhanced the single domain condition of > H c.

5 Thermal Instability of FeCo/IrMn Multilayer Films Dependence of on Temperature without an orienting field G/Cu(2 nm)/irmn(1 nm)/[feco(5 nm)/irmn(1 nm)]4/feco(25 nm) As-deposited Annealed at 225 o C in H = 5 Oe H c Tmax. TB H c Tmax. TB Problems: An irreversible reduction in Heb after measurement, a low Tmax. of Heb > Hc, and a low TB

6 Thermally Stable FeCo/IrMn Multilayer Films Requirement 1. Maintenance of the single domain condition of > H c at a temperature of 12 o C Previously reported works: Either the enhanced (111) texture [1] or the increased grain size of IrMn [2] increased TB up to ~ 3 o C. 2. Ta/Cu or Ta/NiFe underlayer maintained soft properties of FeCo films [3]. In order to achieve this goal, the effect of Ta/Cu underlayers on crystallinity in IrMn and thermal stability in FeCo/IrMn systems is investigated. [1] J. van Driel et al., J. Appl. Phys. 88, 975 (2). [2] H. N. Fuke et al., Appl. Phys. Lett. 75, 368 (1999). [3] H. S. Jung and W. D. Doyle, TMRC, C4 (22).

7 Significant Enhancement of Crystallinity in IrMn Bottom Interface: G/Ta(t nm)/cu(2 nm)/irmn(1 nm)/feco(5 nm)/cu(1 nm) Intensity (CPS) t Ta (nm) β-ta (2) FeCo (11) Cu (111) IrMn (111) θ ( o ) A small lattice mismatch of.3 ~ 3.8 % between β-ta and Cu enhanced crystallinity in Cu, IrMn, and FeCo.

8 Effect of Ta Underlayer on Magnetic Properties 3 Top Interface G/Ta(t)/Cu(2)/FeCo(5)/IrMn(1) Thickness unit: nm 3 Bottom Interface G/Ta(t)/Cu(2)/IrMn(1)/FeCo(5) 2 1 H c, H c, 2 1 H c, H c, t Ta (nm) t Ta (nm) Magnetic properties in the as-deposited state were independent of the Ta thickness.

9 Thermal Stability in the Top Interface of FeCo/IrMn Dependence of on Temperature without an orienting field G/Ta(t nm)/cu(2 nm)/feco(5 nm)/irmn(1 nm)/cu(1 nm) tta = nm tta = 2 nm H c Increasing Decreasing The sample with Ta showed more irreversible reduction in than the sample without Ta but slightly higher T B.

10 Thermal Stability in the Bottom Interface of IrMn/FeCo Dependence of on Temperature without an orienting field G/Ta(t nm)/cu(2 nm)/irmn(1 nm)/feco(5 nm)/cu(1 nm) tta = nm tta = 2 nm 3 3 Increasing Decreasing H c The bottom interface enhanced after thermal cycle. T B in the sample with Ta was significantly improved to > 25 o C.

11 Outstanding Hysteretic Properties in FeCo/IrMn Multilayer with Ta G/Ta(2 nm)/cu(2 nm)/irmn(1 nm)/[feco(5 nm)/irmn(1 nm)]4/feco(25 nm) As-deposited Annealed at 225 o C in H = 5 Oe m / m s H po = 66 Oe = 38 Oe H c, = 11 Oe H c, = 1.7 Oe m / m s Top FeCo H po = 79 Oe = 49 Oe H c, = 6 Oe H c, = 1 Oe H H The Ta underlayer maintained outstanding hysteretic properties. Annealing enhanced the single domain condition of > H c.

12 Significant Improvement of Thermal Stability Dependence of on Temperature without an orienting field G/Ta(t nm)/cu(2 nm)/irmn(1 nm)/[feco(5 nm)/irmn(1 nm)]4/feco(25 nm) As-deposited samples tta = nm tta = 2 nm 6 6 Increasing Decreasing 4 2 T B 4 2 H c No irreversible reduction in Heb, an increase in Tmax. to maintain > H c from 75 to 15 o C, and an increase in TB from 175 to > 25 o C.

13 Conclusion The enhanced crystallinity in (111) IrMn by β-ta/cu underlayers significantly improved thermal stability. In the optimized structure of G/Ta(2)/Cu(2)/IrMn (1)/[FeCo(5)/IrMn(1)]4/FeCo(25), Outstanding hysteretic properties No irreversible reduction in Heb after thermal cycle An increase in Tmax. to maintain > H c from 75 to 15 o C An increase in TB from 175 to > 25 o C