Dependence of domain wall structures on repetition n in [Pt(0.5 nm)/Co(0.4 nm)] _n/NiO(1.1 nm)/[Co(0.4 nm)/Pt(0.5 nm)] _n multilayers

Abstract

The magnetic force microscopy and a sample vibrating magnetometer have been used to investigate the domain structure in two antiferromagnetically coupled Co/Pt multilayers. In the antiferromagnetic coupled [Pt(0.5 nm)/Co(0.4 nm)] _n/NiO(1.1 nm)/[Co(0.4 nm)/Pt(0.5 nm)] _n multilayers with perpendicular anisotropy, the antiferromagnetic interlayer coupling strength increases linearly with the repetition number n in Co/Pt multilayers. In demagnetized states, relatively shifted domain walls in the two Co/Pt multilayers are observed, with net ferromagnetic stripes formed between them for the repetition number n less than 5, and the stripe width decreases with the increase of n. The occurrence of these features can be attributed to the competition between the interlayer coupling and magnetostatic energies.

Keywords

perpendicular anisotropy / antiferromagnets / interlayer coupling / domain walls / magnetostatic energy

References

[1] Nishimura N., Hirai T., Koganei A., et al. Magnetic tunnel junction device with perpendicular magnetization films for high-density magnetic random access memory. J. Appl. Phys., 2002, 91(8): 5246.

[2] Hellwig O., Kirk T.L., Kortright J.B., et al. A new phase diagram for layered antiferromagnetic films. Nat. Mater., 2003, 2(2): 112.

[3] Wolf S.A., Treger D., Chtchelkanova A. Spintronics: The future of data storage. MRS Bull., 2006, 31(5): 400.

[4] O. Hellwig, A. Berger, and E.E. Fullerton, Domain walls in antiferromagnetically coupled multilayer films, Phys. Rev. Lett., 91(2003), No.19, art. No.197203.

[5] De Teresa J.M., Serrate D., Blasco J., et al. Large magnetoresistance in (AA′)₂FeReO₆ double perovskites. J. Magn. Magn. Mater., 2005, 290–291(2): 1043.

[6] Z.Y. Liu and S. Adenwalla, Oscillatory interlayer exchange coupling and its temperature dependence in [Pt/Co]₃/NiO/ [Pt/Co]₃ multilayers with perpendicular anisotropy, Phys. Rev. Lett., 91(2003), No.3, art. No.037207.

[7] J.E. Davies, O. Hellwig, E.E. Fullerton, et al., Magnetization reversal of Co/Pt multilayers: Microscopic origin of high-field magnetic irreversibility, Phys. Rev. B, 70(2004), No.22, art. No.224434.

[8] Z.Y. Liu, L. Yue, D.J. Keavney, et al., Oscillatory interlayer exchange coupling in [Pt/Co]_n/NiO/[Pt/Co]_n multilayers with perpendicular anisotropy: dependence on NiO and Pt layer thicknesses, Phys. Rev. B, 70(2004), No.22, art. No.224423.

[9] Moritz J., Garcia F., Toussaint J.C., et al. Orange peel coupling in multilayers with perpendicular magnetic anisotropy: application to (Co/Pt)-based exchange-biased spin-valves. Europhys. Lett., 2004, 65(1): 23.

[10] Z.Y. Liu, G.H. Yu, and Z.C. Wang, Magnetic reversal and temperature dependence of coupling strength in two antiferromagnetically coupled Co/Pt multilayers, Phys. Rev. B, 72(2005), No.6, art. No.064451.

[11] Hellwig O., Berger A., Kortright J.B., et al. Domain structure and magnetization reversal of antiferromagnetically coupled perpendicular anisotropy films. J. Magn. Magn. Mater, 2007, 319(1–2): 13.

[12] Z.Y. Liu, J.L. He, D.L. Yu, et al., Magnetic reversal in two antiferromagnetically coupled Co/Pt multilayers with perpendicular anisotropy: Effect of competing interlayer coupling and interfacial biasing, Phys. Rev. B, 74(2006), No.9, art. No.094405.

[13] Liu Z.Y., Adenwalla S. Variation of domain formation in a 15 nm NiFe layer exchange coupled with NiO layers of different thicknesses. Appl. Phys. Lett., 2006, 82(13): 2106.

[14] Liu Z.Y., He J.L., Yu D.L., et al. Noncollinear interlayer coupling and its effect on exchange bias in Co(32 &0A)/NiO(tNiO Å)/[Co(4 Å)/Pt(6 Å)]4/Pt(50 Å) multilayers. J. Magn. Magn. Mater., 2007, 309(2): 176.

[15] O. Hellwig, A. Berger, and E.E. Fullerton, Magnetic phase separation in artificial A-type antiferromagnetic films, Phys. Rev. B, 75(2007), No.13, art. No.134416.

[16] A. Baruth, L. Yuan, J.D. Burton, et al., Domain overlap in antiferromagnetically coupled [Co/Pt]/NiO/[Co/Pt] multilayers, Appl. Phys. Lett., 89(2006), No.20, art. No.202505.

[17] Liu Z.Y., Yu G.H., Han G., et al. Oscillatory ferromagnetic interlayer coupling in [Pt(0.5 nm)/Co(0.4 nm)]₃/Cr(x nm)/ [Co(0.4 nm)/Pt(1.2 nm)]₃ multilayers with perpendicular anisotropy. J. Magn. Magn. Mater., 2006, 302(1): 29.

[18] Liu Z.Y., Yu G.H., Han G., et al. Investigation of ferromagnetic coupling between Co layers in a Co/Pt multilayer with perpendicular anisotropy. J. Magn. Magn. Mater., 2006, 299(1): 120.

[19] K. Janicka, J.D. Burton, and E.Y. Tsymbal, Effects of magnetostatic coupling on stripe domain structures in magnetic multilayers with perpendicular anisotropy, J. Appl. Phys., 101(2007), No.11, art. No.113921.

[20] N.S. Kiselev, I.E. Dragunov, V. Neu, et al., Theoretical analysis of magnetic force microscopy contrast in multidomain states of magnetic superlattices with perpendicular anisotropy, J. Appl. Phys., 103(2008), No.4, art. No.043907.

[21] Z.Y. Liu, B. Xu, J.L. He, et al., Effect of cooling field on the antiferromagnetic interlayer coupling and exchange biasing in two antiferromagnetically coupled Co/Pt multilayers, J. Appl. Phys., 102(2007), No.7, art. No.073904.

[22] Z.Y. Liu, F. Zhang, N. Li, et al., Oscillatory antiferromagnetic interlayer coupling in Co(0.4 nm)/Pt(t nm)/[Co(0.4 nm)/Pt(0.6 nm)/Co(0.4 nm)]/NiO(2 nm) multilayers with perpendicular anisotropy, Phys. Rev. B., 77(2008), No.1, art. No.012409.

[23] Johnson M.T., Bloemen P.J.H., den Broeder F.J.A., et al. Magnetic anisotropy in metallic multilayers. Rep. Prog. Phys., 1996, 59(11): 1409.

[24] Walser P., Hunziker M., Speck T., et al. Heat-induced antiferromagnetic coupling in multilayers with ZnSe spacers. Phys. Rev. B, 1999, 60(6): 4082.

[25] J. Faure-Vincent, C. Tiusan, C. Bellouard, et al., Interlayer magnetic coupling interactions of two ferromagnetic layers by spin polarized tunneling, Phys. Rev. Lett., 89(2002), No.10, art. No.107206.

[26] Margulies D.T., Schabes M.E., McChesney W., et al. Interlayer coupling and magnetic reversal of antiferromagnetically coupled media. Appl. Phys. Lett., 2002, 80(1): 91.