Hostname: page-component-cd9895bd7-hc48f Total loading time: 0 Render date: 2024-12-17T11:54:54.044Z Has data issue: false hasContentIssue false
  • English
  • Français

Temperature dependence of static and dynamic magnetic properties in NiFe/IrMn bilayer system

Published online by Cambridge University Press:  10 June 2014

Faris Basheer Abdulahad ,
Dung-Shing Hung Open the ORCID record for Dung-Shing Hung [Opens in a new window]  and
Shang-Fan Lee
Faris Basheer Abdulahad
Affiliation:
Institute of Physics, Academia Sinica, Taipei 11529, Taiwan; Nano Science and Technology Program, TIGP, Academia Sinica, Taipei 11529, Taiwan; and Department of Engineering and System Science, National Tsing Hua University, Hsinchu 300, Taiwan
Dung-Shing Hung
Affiliation:
Department of Information and Telecommunications Engineering, Ming Chuan University, Taipei 111, Taiwan
Shang-Fan Lee*
Affiliation:
Institute of Physics, Academia Sinica, Taipei 11529, Taiwan; and Nano Science and Technology Program, TIGP, Academia Sinica, Taipei 11529, Taiwan
*
a)Address all correspondence to this author. e-mail: [email protected]
Get access

Abstract

A systematic experimental study on the exchange bias (EB) effect in a ferromagnet/antiferromagnet bilayer system is performed both in the static (dc) and dynamic (high frequency) timescale to clarify the effects of temperature and antiferromagnetic (AFM) layer thickness on the system's stability and magnetic properties. Our system consists of NiFe/IrMn. Both parallel and perpendicular domain walls are suggested to explain the static EB and coercivity behaviors. In the microwave region, peaks, which can only be suppressed at high temperatures with strong external fields, were observed in the AFM thickness dependencies of the dynamic effective field and resonance frequency. The temperature dependence of both static and dynamic parameters suggests different values of Néel temperatures. The dynamic results show a rotatable anisotropy contribution, which has a peak value at the blocking temperature and vanishes at the dynamic Néel temperature.

Type
Articles
Information
Journal of Materials Research , Volume 29 , Issue 11 , 14 June 2014 , pp. 1237 - 1247
Copyright
Copyright © Materials Research Society 2014 

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

REFERENCES

Meiklejohn, W.H. and Bean, C.P.: New magnetic anisotropy. Phys. Rev. 102(5), 1413 (1956).Google Scholar
Meiklejohn, W.H. and Bean, C.P.: New magnetic anisotropy. Phys. Rev. 105(3), 904 (1957).Google Scholar
Nogues, J. and Schuller, I.K.: Exchange bias. J. Magn. Magn. Mater. 192(2), 203 (1999).Google Scholar
Kiwi, M.: Exchange bias theory. J. Magn. Magn. Mater. 234(3), 584 (2001).CrossRefGoogle Scholar
Stiles, M.D. and McMichael, R.D.: Coercivity in exchange-bias bilayers. Phys. Rev. B 63(6), 064405 (2001).Google Scholar
McMichael, R.D., Stiles, M.D., Chen, P.J., and Egelhoff, W.F.: Ferromagnetic resonance studies of NiO-coupled thin films of Ni80Fe20 . Phys. Rev. B 58(13), 8605 (1998).CrossRefGoogle Scholar
Rubinstein, M., Lubitz, P., and Cheng, S.F.: Ferromagnetic-resonance field shift in an exchange-biased CoO/Ni80Fe20 bilayer. J. Magn. Magn. Mater. 195(2), 299 (1999).Google Scholar
Hu, J.G., Jin, G.J., and Ma, Y.Q.: Ferromagnetic resonance and exchange anisotropy in ferromagnetic/antiferromagnetic bilayers. J. Appl. Phys. 91(4), 2180 (2002).CrossRefGoogle Scholar
Lubitz, P., Krebs, J.J., Miller, M.M., and Cheng, S.: Temperature dependence of ferromagnetic resonance as induced by NiO pinning layers. J. Appl. Phys. 83(11), 6819 (1998).Google Scholar
Meiklejohn, W.H.: Exchange anisotropy—A review. J. Appl. Phys. 33(3), 1328 (1962).CrossRefGoogle Scholar
Nogues, J., Sort, J., Langlais, V., Skumryev, V., Surinach, S., Munoz, J.S., and Baro, M.D.: Exchange bias in nanostructures. Phys. Rep. 422(3), 65 (2005).CrossRefGoogle Scholar
Yang, P.Y., Song, C., Fan, B., Zeng, F., and Pan, F.: The role of rotatable anisotropy in the asymmetric magnetization reversal of exchange biased NiO/Ni bilayers. J. Appl. Phys. 106(1), 013902 (2009).Google Scholar
Stamps, R.L.: Mechanisms for exchange bias. J. Phys. D: Appl. Phys. 33(23), R247 (2000).Google Scholar
Dieny, B., Speriosu, V.S., Parkin, S.S.P., Gurney, B.A., Wilhoit, D.R., and Mauri, D.: Giant magnetoresistive in soft ferromagnetic multilayers. Phys. Rev. B 43(1), 1297 (1991).Google Scholar
Chappert, C., Fert, A., and Nguyen Van Dau, F.: The emergence of spin electronics in data storage. Nat. Mater. 6, 813 (2007).CrossRefGoogle ScholarPubMed
You, C.Y., Goripati, H.S., Furubayashi, T., Takahashi, Y.K., and Hono, K.: Exchange bias of spin valve structure with a top-pinned Co40Fe40B20/IrMn. Appl. Phys. Lett. 93(1), 012501 (2008).Google Scholar
Stoecklein, W., Parkin, S.S.P., and Scott, J.C.: Ferromagnetic resonance studies of exchange-biased permalloy thin films. Phys. Rev. B 38(10), 6847 (1988).Google Scholar
Kuanr, B.K., Camley, R.E., and Celinski, Z.: Exchange bias of NiO/NiFe: Linewidth broadening and anomalous spin-wave damping. J. Appl. Phys. 93(10), 7723 (2003).Google Scholar
Queste, S., Dubourg, S., Acher, O., Barholz, K.U., and Mattheis, R.: Exchange bias anisotropy on the dynamic permeability of thin NiFe layers. J. Appl. Phys. 95(11), 6873 (2004).Google Scholar
Lamy, Y. and Viala, B.: NiMn, IrMn, and NiO exchange coupled CoFe multilayers for microwave applications. IEEE Trans. Magn. 42(10), 3332 (2006).Google Scholar
Phuoc, N.N., Lim, S.L., Xu, F., Ma, Y.G., and Ong, C.K.: Enhancement of exchange bias and ferromagnetic resonance frequency by using multilayer antidot arrays. J. Appl. Phys. 104(9), 093708 (2008).Google Scholar
Phuoc, N.N., Xu, F., and Ong, C.K.: Ultrawideband microwave noise filter: Hybrid antiferromagnet/ferromagnet exchange-coupled multilayers. Appl. Phys. Lett. 94(9), 092505 (2009).Google Scholar
O’Grady, K., Fernandez-Outon, L.E., and Vallejo-Fernandez, G.: A new paradigm for exchange bias in polycrystalline thin films. J. Magn. Magn. Mater. 322(8), 883 (2010).CrossRefGoogle Scholar
Chen, X., Ma, Y.G., and Ong, C.K.: Magnetic anisotropy and resonance frequency of patterned soft magnetic strips. J. Appl. Phys. 104(1), 013921 (2008).Google Scholar
Chai, G., Yang, Y., Zhu, J., Lin, M., Sui, W., Guo, D., Li, X., and Xue, D.: Adjust the resonance frequency of (Co90Nb10/Ta)n multilayers from 1.4 to 6.5 GHz by controlling the thickness of Ta interlayers. Appl. Phys. Lett. 96(1), 012505 (2010).Google Scholar
Phuoca, N.N., Hungb, L.T., and Ong, C.K.: Ultra-high ferromagnetic resonance frequency in exchange-biased system. J. Alloys Compd. 506(2), 504 (2010).Google Scholar
Takano, K., Kodama, R.H., Berkowitz, A.E., Cao, W., and Thomas, G.: Interfacial uncompensated antiferromagnetic spins: role in unidirectional anisotropy in polycrystalline Ni81Fe19/CoO bilayers. Phys. Rev. Lett. 79(6), 1130 (1997).CrossRefGoogle Scholar
Takano, K., Kodama, R.H., Berkowitz, A.E., Cao, W., and Thomas, G.: Role of interfacial uncompensated antiferromagnetic spins in unidirectional anisotropy in Ni81Fe19/CoO bilayers. J. Appl. Phys. 83(11), 6888 (1998).Google Scholar
Stiles, M.D. and McMichael, R.D.: Model for exchange bias in polycrystalline ferromagnet-antiferromagnet bilayers. Phys. Rev. B 59(5), 3722 (1999).CrossRefGoogle Scholar
Moran, T.J., Gallego, J.M., and Schuller, I.K.: Increased exchange anisotropy due to disorder at permalloy/CoO interfaces. J. Appl. Phys. 78(3), 1887 (1995).Google Scholar
Nogués, J., Moran, T.J., Lederman, D., Schuller, I.K., and Rao, K.V.: Role of interfacial structure on exchange-biased FeF2−Fe. Phys. Rev. B 59(10), 6984 (1999).CrossRefGoogle Scholar
Scholl, A., Nolting, F., Stohr, J., Regan, T., Luning, J., Seo, J.W., Locquet, J-P., Fompeyrine, J., Anders, S., Ohldag, H., and Padmore, H.A.: Exploring the microscopic origin of exchange bias with photoelectron emission microscopy. J. Appl. Phys. 89(11), 7266 (2001).Google Scholar
Kuch, W., Offi, F., Chelaru, L.I., Kotsugi, M., Fukumoto, K., and Kirschner, J.: Magnetic interface coupling in single-crystalline Co/Fe Mn bilayers. Phys. Rev. B 65(14), 140408(R) (2002).Google Scholar
Martinez, B., Obradors, X., Balcells, Ll., Rouanet, A., and Monty, C.: Low temperature surface spin-glass transition in γ-Fe2O3 nanoparticles. Phys. Rev. Lett. 80(1), 181 (1998).CrossRefGoogle Scholar
Skumryev, V., Stoyanov, S., Zhang, Y., Hadjipanayis, G., Givord, D., and Nogues, J.: Beating the superparamagnetic limit with exchange bias. Nature 423, 850 (2003).Google Scholar
te Velthuis, S.G., Felcher, G.P., Jiang, J.S., Inomata, A., Nelson, C.S., Berger, A., and Bader, S.D.: Magnetic configurations in exchange-biased double superlattices. Appl. Phys. Lett. 75(26), 4174 (1999).Google Scholar
Yuan, F-T., Lin, J-K., Yao, Y.D., and Lee, S-F.: Exchange bias in spin glass (FeAu)/NiFe thin films. Appl. Phys. Lett. 96(16), 162502 (2010).Google Scholar
Peng, D.L., Sumiyama, K., Hihara, T., Yamamuro, S., and Konno, T.J.: Magnetic properties of monodispersed Co/CoO clusters. Phys. Rev. B 61(4), 3103 (2000).Google Scholar
Malozemoff, A.P.: Random-field model of exchange anisotropy at rough ferromagnetic-antiferromagnetic interfaces. Phys. Rev. B 35(7), 3679 (1987).Google Scholar
Mauri, D., Siegmann, H.C., Bagus, P.S., and Kay, E.: Simple model for thin ferromagnetic films exchange coupled to an antiferromagnetic substrate. J. Appl. Phys. 62(7), 3047 (1987).CrossRefGoogle Scholar
Koon, N.: Calculations of exchange bias in thin films with ferromagnetic/antiferromagnetic interfaces. Phys. Rev. Lett. 78(25), 4865 (1997).CrossRefGoogle Scholar
Schulthess, T.C. and Butler, W.H.: Consequences of spin-flop coupling in exchange biased films. Phys. Rev. Lett. 81(20), 4516 (1998).Google Scholar
Wee, L., Stamps, R.L., and Camley, R.E.: Temperature dependence of domain-wall bias and coercivity. J. Appl. Phys. 89(11), 6913 (2001).Google Scholar
Schulthess, T.C. and Butler, W.H.: Coupling mechanisms in exchange biased films. J. Appl. Phys. 85(8), 5510 (1999).CrossRefGoogle Scholar
Malozemoff, A.P.: Mechanisms of exchange anisotropy. J. Appl. Phys. 63(8), 3874 (1988).Google Scholar
de Almeida, J.R.L. and Rezende, S.M.: Microscopic model for exchange anisotropy. Phys. Rev. B 65(9), 092412 (2002).Google Scholar
Nowak, U., Misra, A., and Usadel, K.D.: Domain state model for exchange bias. J. Appl. Phys. 89(11), 7269 (2001).Google Scholar
Xi, H. and White, R.M.: Antiferromagnetic thickness dependence of exchange biasing. Phys. Rev. B 61(1), 80 (2000).Google Scholar
Fulcomer, E. and Charap, S.H.: Thermal fluctuation aftereffect model for some systems with ferromagnetic-antiferromagnetic coupling. J. Appl. Phys. 43(10), 4190 (1972).Google Scholar
Soeya, S., Imagawa, T., Mitsuoka, S., and Narishige, S.: Distribution of blocking temperature in bilayered Ni81Fe19/NiO films. J. Appl. Phys. 76(9), 5356 (1994).Google Scholar
Baltz, V., Sort, J., Rodmacq, B., Dieny, B., and Landis, S.: Thermal activation effects on the exchange bias in ferromagnetic-antiferromagnetic nanostructures. Phys. Rev. B 72(10), 104419 (2005).CrossRefGoogle Scholar
Baltz, V., Rodmacq, B., Zarefy, A., Lechevallier, L., and Dieny, B.: Bimodal distribution of blocking temperature in exchange-biased ferromagnetic/antiferromagnetic bilayers. Phys. Rev. B 81(5), 052404 (2010).Google Scholar
Safeer, C.K., Chamfrault, M., Allibe, J., Carretero, C., Deranlot, C., Jacquet, E., Jacquot, J-F., Bibes, M., Barthelemy, A., Dieny, B., Bea, H., and Baltz, V.: Anisotropic bimodal distribution of blocking temperature with multiferroic BiFeO3 epitaxial thin films. Appl. Phys. Lett. 100(7), 072402 (2012).Google Scholar
Ventura, J., Araujo, J.P., Sousa, J.B., Veloso, A., and Freitas, P.P.: Distribution of blocking temperatures in nano-oxide layers of specular spin valves. J. Appl. Phys. 101(11), 113901 (2007).Google Scholar
Ali, M., Adie, P., Marrows, C.H., Greig, D., Hickey, B.J., and Stamps, R.L.: Exchange bias using a spin glass. Nat. Mater. 6, 70 (2007).Google Scholar
Yuan, F.T., Yao, Y.D., Lee, S.F., and Hsu, J.H.: Coercive mechanism and training effect in Fe-Au/Ni-Fe bilayer films. J. Appl. Phys. 109(7), 07E148 (2011).Google Scholar
Biternas, A.G., Nowak, U., and Chantrell, R.W.: Training effect of exchange-bias bilayers within the domain state model. Phys. Rev. B 80(13), 134419 (2009).Google Scholar
Gruyters, M.: Spin-glass-like behavior in CoO nanoparticles and the origin of exchange bias in layered CoO/ferromagnet structures. Phys. Rev. Lett. 95(7), 077204 (2005).Google Scholar
Ercole, A., Fujimoto, T., Patel, M., Daboo, C., Hicken, R.J., and Bland, A.C.: Direct measurement of magnetic anisotropies in epitaxial FeNi/Cu/Co spin-valve structures by Brillouin light scattering. J. Magn. Magn. Mater. 156(1–3), 121 (1996).Google Scholar
Miller, B.H. and Dan Dahlberg, E.: Use of the anisotropic magnetoresistance to measure exchange anisotropy in Co/CoO bilayers. Appl. Phys. Lett. 69(25), 3932 (1996).Google Scholar
Strom, V., Jonsson, B.J., Rao, K.V., and Dahlberg, D.: Determination of exchange anisotropy by means of ac susceptometry in Co/CoO bilayers. J. Appl. Phys. 81(8), 5003 (1997).Google Scholar
Abdulahad, F.B., Hung, D.S., Chiu, Y.C., and Lee, S.F.: Exchange bias effect on the relaxation behavior of the IrMn/NiFe bilayer system. IEEE Trans. Magn. 47(10), 4227 (2011).Google Scholar
Philipps, T.G. and Rosenberg, H.M.: Spin waves in ferromagnets. Rep. Prog. Phys. 29(1), 285 (1966).Google Scholar
Heinrich, B. and Cochran, J.F.: Ultrathin metallic magnetic films: Magnetic anisotropies and exchange interactions. Adv. Phys. 42(5), 523 (1993).Google Scholar
Farle, M.: Ferromagnetic resonance of ultrathin metallic layers. Rep. Prog. Phys. 61(7), 755 (1998).Google Scholar
Adam, J.D. and Stitzer, S.N.: A magnetostatic wave signal-to-noise enhancer. Appl. Phys. Lett. 36(6), 485 (1980).Google Scholar
Ishak, W.S.: Magnetostatic wave technology: A review. Proc. IEEE 76(2), 171 (1988).Google Scholar
How, H., Hu, W., Vittoria, C., Kempel, L.C., and Trott, K.D.: Single-crystal yttrium iron garnet phase shifter at X band. J. Appl. Phys. 85(8), 4853 (1999).Google Scholar
Cramer, N., Lucic, D., Camley, R.E., and Celinski, Z.: High attenuation tunable microwave notch filters utilizing ferromagnetic resonance. J. Appl. Phys. 87(9), 6911 (2000).Google Scholar
Wolf, S.A., Awschalom, D.D., Buhrman, R.A., Daughton, J.M., von Molnar, S., Roukes, M. L., Chtchelkanova, A.Y., and Treger, D.M.: Spintronics: A spin-based electronics vision for the future. Science 294, 1488 (2001).Google Scholar
Seu, K.A., Huang, H., Lesoine, J.F., Showman, H.D., Egelhoff, W.F., Gan, L., and Reilly, A.C.: Co layer thickness dependence of exchange biasing for IrMn/Co and FeMn/Co. J. Appl. Phys. 93(10), 6611 (2003).Google Scholar
Jungblut, R., Coehoorn, R., Johnson, M.T., aan de Stegge, J., and Reinders, A.: Orientational dependence of the exchange biasing in molecular-beam-epitaxy-grown Ni80Fe20/Fe50Mn50 bilayers. J. Appl. Phys. 75(10), 6659 (1994).Google Scholar
Phuoc, N.N., Chen, H.Y., and Ong, C.K.: Effect of antiferromagnetic thickness on thermal stability of static and dynamic magnetization of NiFe/FeMn multilayers. J. Appl. Phys. 113(6), 063913 (2013).Google Scholar
Ali, M., Marrows, C.H., Al-Jawad, M., Hickey, B.J., Misra, A., Nowak, U., and Usadel, K.D.: Antiferromagnetic layer thickness dependence of the IrMn/Co exchange-bias system. Phys. Rev. B 68(21), 214420 (2003).Google Scholar
Gloanec, M., Rioual, S., Lescop, B., Zuberek, R., Szymczak, R., Aleshkevych, P., and Rouvellou, B.: Temperature dependence of exchange bias in NiFe/FeMn bilayers. Phys. Rev. B 82(14), 144433 (2010).Google Scholar
Chen, H.Y., Phuoc, N. N., and Ong, C. K.: Thermal stability of exchange-biased NiFe/FeMn multilayered thin films. J. Appl. Phys. 112(5), 053920 (2012).Google Scholar
McCord, J., Mattheis, R., and Elefant, D.: Dynamic magnetic anisotropy at the onset of exchange bias: The NiFe/IrMn ferromagnet/antiferromagnet. Phys. Rev. B 70(9), 094420 (2004).Google Scholar
Steenbeck, K., Mattheis, R., and Diegel, M.: Antiferromagnetic energy loss and exchange coupling of IrMn/CoFe films: Experiments and simulations. J. Magn. Magn. Mater. 279(2–3), 317 (2004).Google Scholar
McCord, J., Kaltofen, R., Gemming, T., Hühne, R., and Schultz, L.: Aspects of static and dynamic magnetic anisotropy in Ni81Fe19-NiO films. Phys. Rev. B 75(13), 134418 (2007).Google Scholar
Liu, H.Y., Wang, Z.K., Lim, H.S., Ng, S.C., Kuok, M.H., Lockwood, D.J., Cottam, M.G., Nielsch, K., and Gösele, U.: Magnetic-field dependence of spin waves in ordered permalloy nanowire arrays in two dimensions. J. Appl. Phys. 98(4), 046103 (2005).Google Scholar
Youssef, J.B., Castel, V., Vukadinovic, N., and Labrune, M.: Spin-wave resonances in exchange-coupled permalloy/garnet bilayers. J. Appl. Phys. 108(6), 063909 (2010).Google Scholar
Awad, A.A., Lara, A., Metlushko, V., Guslienko, K.Y., and Aliev, F.G.: Broadband probing magnetization dynamics of the coupled vortex state permalloy layers in nanopillars. Appl. Phys. Lett. 100(26), 262406 (2012).Google Scholar
Demand, M., Oropesa, A.E., Kenane, S., Ebels, U., Huynen, I., and Piraux, L.: Ferromagnetic resonance studies of nickel and permalloy nanowire arrays. J. Magn. Magn. Mater. 249(1–2), 228 (2002).CrossRefGoogle Scholar
Lin, C.S., Lim, H.S., Wang, Z.K., Ng, S.C., and Kuok, M.H.: Band gap parameters of one-dimensional bicomponent nanostructured magnonic crystals. Appl. Phys. Lett. 98(2), 022504 (2011).Google Scholar
Fukumoto, K., Kuch, W., Vogel, J., Camarero, J., Pizzini, S., Offi, F., Pennec, Y., Bonfim, M., Fontaine, A., and Kirschner, J.: Mobility of domain wall motion in the permalloy layer of a spin-valve-like Fe20Ni80/Cu/Co trilayer. J. Magn. Magn. Mater. 293(3), 863 (2005).Google Scholar
Mathon, J. and Ahmad, S.B.: Quasi-two-dimensional behavior of the surface magnetization in a ferromagnet with softened surface exchange. Phys. Rev. B 37(1), 660 (1988).Google Scholar
Kittel, C.: Introduction to Solid State Physics, 8th ed. (John Wiley & Sons, New York, NY, 2005).Google Scholar
Xi, H., Rantschler, J., Mao, S, Kief, M.T., and White, R.M.: Interface coupling and magnetic properties of exchange-coupled Ni81Fe19/Ir22Mn78 bilayers. J. Phys. D: Appl. Phys. 36(13), 1464 (2003).Google Scholar
Tripathy, D., Adeyeye, A.O., and Singh, N.: Exchange bias in nanoscale antidot arrays. Appl. Phys. Lett. 93(2), 022502 (2008).Google Scholar
Kim, J.V. and Stamps, R.L.: Hysteresis from antiferromagnet domain-wall processes in exchange-biased systems: Magnetic defects and thermal effects. Phys. Rev. B 71(9), 094405 (2005).Google Scholar
Nikitenko, V.I., Gornakov, V.S., Shapiro, A.J., Shull, R.D., Liu, K., Zhou, S.M., and Chien, C.L.: Asymmetry in elementary events of magnetization reversal in a ferromagnetic/antiferromagnetic bilayer. Phys. Rev. Lett. 84(4), 765 (2000).Google Scholar
Leighton, C., Fitzsimmons, M.R., Hoffmann, A., Dura, J., Majrkzak, C.F., Lund, M.S., and Schuller, I.K.: Thickness-dependent coercive mechanisms in exchange-biased bilayers. Phys. Rev. B 65(6), 064403 (2002).Google Scholar
Aley, N.P., Fernandez, G.V., Kroeger, R., Lafferty, B., Agnew, J., Lu, Y., and O’Grady, K.: Texture effects in IrMn/CoFe exchange bias systems. IEEE Trans. Magn. 44(11), 2820 (2008).Google Scholar
Ali, M., Marrows, C.H., and Hickey, B.J.: Onset of exchange bias in ultrathin antiferromagnetic layers. Phys. Rev. B 67(17), 172405 (2003).Google Scholar
Ambrose, T. and Chien, C.L.: Dependence of exchange coupling on antiferromagnetic layer thickness in NiFe/CoO bilayers. J. Appl. Phys. 83(11), 6822 (1998).Google Scholar
Stiles, M.D. and McMichael, R.D.: Temperature dependence of exchange bias in polycrystalline ferromagnet-antiferromagnet bilayers. Phys. Rev. B 60(18), 12950 (1999).Google Scholar
Fernandez, G.V., Outon, L.E.F., and O’Grady, K.: Antiferromagnetic grain volume effects in metallic polycrystalline exchange bias systems. J Phys. D: Appl. Phys. 41(11), 112001 (2008).Google Scholar