Regular nanosized structures are considered to be promising materials for magnetic information storage media with high density of information. Recently attention was paid to static and dynamic magnetic properties arising from dimensional confinement in such nanostructures. Here we present an investigation of permalloy antidot arrays of different thicknesses. Thin permalloyfilms of thickness ranging from were deposited on nanoporous membranes with a pore size of . It was found that additional ferromagnetic resonance peaks appear for film thicknesses below , while films with larger thicknesses show resonanceproperties similar to continuous films. A comparison between the filmsdeposited onto Si wafers and porous media was done. An evolution of the domain structures observed in MFM experiments was confirmed by micromagnetic calculations

Jung, Jin-Seung

Malkinski, Leszek M.

Min, Suk-Hong

O\u27Connor, Charles

Vovk, Andriy

Whittenburg, Scott L.

English

University of Montana

University of Montana ScholarWorks at University of Montana Chemistry and Biochemistry Faculty Publications Chemistry and Biochemistry 5-12-2005 Preparation, Structural Characterization, and Dynamic Properties Investigation of Permalloy Antidot Arrays Andriy Vovk University of New Orleans, avovk@uno.edu Leszek M. Malkinski University of New Orleans Scott L. Whittenburg University of Montana - Missoula, scott.whittenburg@umontana.edu Charles O'Connor University of New Orleans Jin-Seung Jung Kangnung National University See next page for additional authors Follow this and additional works at: https://scholarworks.umt.edu/chem_pubs  Part of the Biochemistry Commons, Chemistry Commons, and the Physics Commons Let us know how access to this document benefits you. Recommended Citation Vovk, Andriy; Malkinski, Leszek M.; Whittenburg, Scott L.; O'Connor, Charles; Jung, Jin-Seung; and Min, Suk-Hong, "Preparation, Structural Characterization, and Dynamic Properties Investigation of Permalloy Antidot Arrays" (2005). Chemistry and Biochemistry Faculty Publications. 62. https://scholarworks.umt.edu/chem_pubs/62 This Article is brought to you for free and open access by the Chemistry and Biochemistry at ScholarWorks at University of Montana. It has been accepted for inclusion in Chemistry and Biochemistry Faculty Publications by an authorized administrator of ScholarWorks at University of Montana. For more information, please contact scholarworks@mso.umt.edu. Authors Andriy Vovk, Leszek M. Malkinski, Scott L. Whittenburg, Charles O'Connor, Jin-Seung Jung, and Suk-Hong Min This article is available at ScholarWorks at University of Montana: https://scholarworks.umt.edu/chem_pubs/62 Preparation, structural characterization, and dynamic properties investigation ofpermalloy antidot arraysAndriy Vovk, Leszek Malkinski, Vladimir Golub, Scott Whittenburg, Charles O’Connor, Jin-Seung Jung, and Suk-Hong Min  Citation: Journal of Applied Physics 97, 10J506 (2005); doi: 10.1063/1.1853691 View online: http://dx.doi.org/10.1063/1.1853691 View Table of Contents: http://scitation.aip.org/content/aip/journal/jap/97/10?ver=pdfcov Published by the AIP Publishing                    Advertisement:  [This article is copyrighted as indicated in the abstract. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP:150.131.77.62 On: Mon, 28 Oct 2013 20:09:37Preparation, structural characterization, and dynamic propertiesinvestigation of permalloy antidot arraysAndriy Vovk,a!,b! Leszek Malkinski, Vladimir Golub,a! Scott Whittenburg, andCharles O’ConnorAdvanced Materials Research Institute, University of New Orleans, 2000 Lakeshore Dr., New Orleans,Louisiana 70148Jin-Seung JungDepartment of Chemistry, Kangnung National University, Kangnung 210702, South KoreaSuk-Hong MinDepartment of Metal and Material Engineering, Kangnung National University, Kangnung 210702,South KoreasReceived 1 September 2004; accepted 22 November 2004; published online 12 May 2005dRegular nanosized structures are considered to be promising materials for magnetic informationstorage media with high density of information. Recently attention was paid to static and dynamicmagnetic properties arising from dimensional confinement in such nanostructures. Here we presentan investigation of permalloy antidot arrays of different thicknesses. Thin permalloy films ofthickness ranging from 10 to 500 nm were deposited on nanoporous Al2O3 membranes with a poresize of 100 nm. It was found that additional ferromagnetic resonance peaks appear for filmthicknesses below 100 nm, while films with larger thicknesses show resonance properties similar tocontinuous films. A comparison between the films deposited onto Si wafers and porous media wasdone. An evolution of the domain structures observed in MFM experiments was confirmed bymicromagnetic calculations. ©2005 American Institute of Physics. fDOI: 10.1063/1.1853691gWell-ordered arrays of nano-size objects attract a lot ofattention due to their potential applications for ultrahigh den-sity magnetic information storage. Among them are so-calledantidot structures, which are arrays of pores instead of dots.Antidots are believed to have an advantage over nanodots asthey are easier to prepare. Also, there is no superparamag-netic limit of information bit size, as there is for dot struc-tures. Recently, numerous publications reported on the staticand dynamic magnetic properties of antidot structures. Inmost cases, these antidots are submicron or micron size. Forexample, magnetic anisotropy and domain structure wereanalyzed for an antidot array of 1.6mm size.1 Dynamicproperties of rectangular antidot structures with a pore sizeof 1.5 mm and interpore distance of 3–5mm were reported.2Magnetic reversal for asymmetric antidots of 6–10mm sizewas presented in Ref. 3. In contrast, there are only a fewinvestigations that study structures with characteristic sizesaround 100 nm. It was shown in Ref. 4 that it is possible toprepare an antidot structure with a pore size as small as20 nm by deposition of Ni film on anodic aluminum oxidesAAOd. The magnetic reversal and magnetotransport proper-ties were analyzed and it was suggested that such technologyis suitable to prepare materials that can be used for ultrahighdensity storage media. However, in the quoted work no re-sults on magnetic domain structure and dynamic propertieswere reported. In this work we report on the preparation ofpermalloy antidot structure on AAO substrates and an inves-tigation of its magnetic structure, as well as static and dy-namic magnetic properties.Nanoporous AAO substrates were prepared using oxida-tion of high purity s99.999%d aluminum sheets. The detailsof the preparation procedure were reported elsewhere.5 Thethicknesses of the membrane and pore sizes were controlledby the current density and the anodizing time. AAO mem-branes with regular hexagonal arrangement of pores of100 nm in diameter, about 100 nm spacing, and 280 nmthickness, were fabricated. Field emission scanning electronmicroscopy cross-sectional images5 of the AAO membranerevealed uniformity of the pore diameter and high orderingof the array.Permalloy films were deposited on the AAO membranesusing a magnetron sputtering system with research S-guns.The base pressure before deposition was 1.1310−7 Torr, andthe argon pressure during deposition was 3.0 mTorr. Thedeposition rate was controlled by an INFICON IC 6000quartz monitor and was kept at 0.1 nm/s. The films withthicknessessdd in the range from 10 to 500 nm were pre-pared. Reference samples with the same thicknesses weredeposited simultaneously on Si wafers. Magnetic propertiesof the films were studied using a Quantum Design MPMS 5SSQUID magnetometer at 300 K. The ferromagnetic reso-nance sFMRd was measured at 300 K using anX-bandBruker EMX300 EPR spectrometer with magnetic field inthe film plane. The surface and domain structures of the de-posited films were studied using a Digital Instruments Nano-scope IIIa scanning probe microscope.adOn leave from Institute of Magnetism NAS of Ukraine, 36b VernadskogoBlvd., 03142 Kiev, Ukraine.bdAuthor to whom correspondence should be addressed; electronic mail:avovk@uno.eduJOURNAL OF APPLIED PHYSICS97, 10J506s2005d0021-8979/2005/97~10!/10J506/3/$22.50 © 2005 American Institute of Physics97, 10J506-1 [This article is copyrighted as indicated in the abstract. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP:150.131.77.62 On: Mon, 28 Oct 2013 20:09:37It was found that increasingd up to 100 nm did notaffect the size and the shape of the pores. The atomic forcemicroscopy and magnetic force microscopy images of100 nm thick film are represented in Fig. 1. It is clearly seenthat the antidot structure retains the structure of the AAOmembrane. Further increase ofd leads to a rapid decrease inthe pore size, and the film becomes continuous for thicknessd.200 nm. The effect of film thicknesssfor d,100 nmd onthe pore size is different from what was reported earlier4 foNi antidotes. Most probably, this discrepancy is caused bythe structure of the AAO membranes and the difference inthe deposition rates, which was lower in our case. MagneticForce Microscope images also show that the barlike domainsare pinned along the lines of poresssee the insets in Fig. 1d.Micromagnetic calculations performed using JaMM code6confirm the pinning of the domain walls along the rows ofthe holessFig. 2d. Formation of such domain structure is aclear indication that the density of magnetic recording,10 Gbits/cm2 can be achieved using 100 nm antidotearrays.Magnetic hysteresis loops for the films of different thick-ness deposited on AAO and Si are presented in Fig. 3. Ford=10 nm the loops are narrow and have a square shape forthe films on both the AAO and on Si. However, the rema-nence is lower in the case of the AAO substrate. Ford=500 nm hysteresis loops for the films on the AAO and Sisubstrates practically coincide. This is in good agreementwith structural studies and confirms that for this thickness thefilm is continuous. Thus the pores are covered and the struc-ture of the substrate does not affect the magnetization rever-sal. For the intermediate range of thicknesses, a gradual evo-lution of the hysteresis loops shape was observed. The loopsfor the films deposited on Si show higher remanence andsquareness. The difference in magnetization reversal isFIG. 1. Atomic Force Microscopesad and Magnetic Force Microscopesbdimages of 100 nm thick Permalloy film deposited on an AAO membrane.FIG. 2. Micromagnetic simulation of antidote spin structure using theJaMM code.FIG. 3. Magnetic hysteresis loop of permalloy films of thickness 10 nmsad,100 nmsbd, and 500 nmscd deposited on Si wafersssolid squared and AAOmembranesopen circled.10J506-2 Vovk et al. J. Appl. Phys. 97, 10J506 ~2005! [This article is copyrighted as indicated in the abstract. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP:150.131.77.62 On: Mon, 28 Oct 2013 20:09:37caused by the differences in the topology of the films depos-ited on AAO. Computer simulations of the magnetizationprocess show that the reversal begins in the vicinity of thepores where vortex states are formed. This noncollinear spinconfiguration around the pores promotes incoherent magne-tization reversal, which results in reduced remanence.FMR measurements provide additional informationabout magnetic properties of the films. FMR spectra re-corded in the films are summarized in Fig. 4. A single sharpresonance line was observed in all of the films deposited onSi wafers. In contrast, the FMR spectra of the films depositedon AAO substrate consisted of multiple, broad resonancepeaks. The appearance of additional modes is associated withthe patterned structure of the films and reflects a lateral di-mensional confinement. Previously, similar multipeak spec-tra were reported for magnetic dot arrays.7,8 However, this isjust a rough analogy, due to the different character of inter-action inside dot and antidot arrays. Unfortunately, so far,there is no well-defined theory describing FMR for antidotstructure. For smalld, the main resonance peak is shiftedtoward high fields. This is connected with the decrease of thedemagnetizing factor of the film due to the roughness of thesurface. The increase ofd leads to the shift of the resonancepeak to a low fields area. For certaind the value of theresonance field becomes lower than that observed for thefilm deposited on Si substrate. This fact reflects the presenceof an in-plane anisotropy in the antidot structure. However,to investigate the origin of such anisotropy, lithographicallypatterned antidot structures on flat surfaces are preferable.Finally at the highestd the spectrum became pretty close tothe one observed in the film deposited on a Si wafer, whichcorrelates with the magnetic data.This work was supported through the grants fromDARPA sMDA972-04-1-0029d and from the National Sci-ence FoundationsCCF-0403673d.1C. T. Yu, H. Jiang, L. Shen, P. J. Flanders, and G. J. Mankey, J. Appl.Phys. 87, 6322s2000d.2Chengtao Yu, Michael J. Pechan, and Gary J. Mankey, J. Appl. Phys.83,3948 s2003d.3C. C. Wang, A. O. Adeyeye, and Y. H. Wu, J. Appl. Phys.94, 6644s2003d.4Z. L. Xiao, Catherine Y. Han, U. Welp, H. H. Wang, V. K. Vlasko-Vlasov,W. K. Kwok, D. J. Miller, J. M. Miller, R. E. Cook, G. A. Willing, and G.W. Crabtree, Appl. Phys. Lett.81, 2869s2002d.5A. Chalastaras, L. M. Malkinski, J. S. Jung, S. L. Oh, J. K. Lee, C. A.Ventrice Jr., V. Golub, and G. Taylor, IEEE Trans. Magn.40, 2257s2004d.6S. L. Whittenburg, http://jamm.uno.edu7S. Jung, B. Watkins, L. DeLong, J. B. Ketterson, and V. Chandrasekhar,Phys. Rev. B66, 132401s2002d.8G. N. Kakazei, P. E. Wigen, K. Yu. Guslienko, V. Novosad, A. N. Slavin,V. O. Golub, N. A. Lesnik, and Y. Otani, Appl. Phys. Lett.85, 443s2004d.FIG. 4. FMR spectra of permalloy films of thicknesses 10 nmsad, 100 nmsbd, and 500 nmscd deposited on Si waferssolid squared and on AAOmembranessopen circled. Magnetic field was applied in the film planes.10J506-3 Vovk et al. J. Appl. Phys. 97, 10J506 ~2005! [This article is copyrighted as indicated in the abstract. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP:150.131.77.62 On: Mon, 28 Oct 2013 20:09:37

Preparation, Structural Characterization, and Dynamic Properties Investigation of Permalloy Antidot Arrays

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Preparation, Structural Characterization, and Dynamic Properties Investigation of Permalloy Antidot Arrays

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