This paper reports the influence of the deposition temperature and the wavelength of the periodicity on the effective interdiffusivity, microstructure, and magnetic properties of annealed [Fe/Pt](n) multilayer films (MLs). It was found that both the deposition temperature and periodicity of [Fe/Pt](n) MLs have a significant influence on the effective Fe-Pt interdiffusivity, microstructure, and magnetic properties of the annealed films. It was also observed that the magnitude of the effective interdiffusion coefficient, the L1(0) grain size, and the long-range order parameter were positively correlated. This result suggests that nonequilibrium reaction kinetics are desirable for the reduced temperature formation of the L1(0) FePt phase

Coffey, Kevin R.

Yao, Bo

English

University of Central Florida (UCF): STARS (Showcase of Text, Archives, Research & Scholarship)

University of Central Florida STARS Faculty Bibliography 2000s Faculty Bibliography 1-1-2008 The effective interdiffusivity, structure, and magnetic properties of Fe/Pt (n) multilayer films Bo Yao University of Central Florida Kevin R. Coffey University of Central Florida Find similar works at: https://stars.library.ucf.edu/facultybib2000 University of Central Florida Libraries http://library.ucf.edu This Article; Proceedings Paper is brought to you for free and open access by the Faculty Bibliography at STARS. It has been accepted for inclusion in Faculty Bibliography 2000s by an authorized administrator of STARS. For more information, please contact STARS@ucf.edu. Recommended Citation Yao, Bo and Coffey, Kevin R., "The effective interdiffusivity, structure, and magnetic properties of Fe/Pt (n) multilayer films" (2008). Faculty Bibliography 2000s. 1174. https://stars.library.ucf.edu/facultybib2000/1174 J. Appl. Phys. 103, 07E107 (2008); https://doi.org/10.1063/1.2828978 103, 07E107© 2008 American Institute of Physics.The effective interdiffusivity, structure, andmagnetic properties of  multilayerfilmsCite as: J. Appl. Phys. 103, 07E107 (2008); https://doi.org/10.1063/1.2828978Submitted: 07 September 2007 . Accepted: 27 September 2007 . Published Online: 22 January 2008Bo Yao, and Kevin R. CoffeyARTICLES YOU MAY BE INTERESTED INThickness dependence of structure and magnetic properties of annealed  multilayerfilmsJournal of Applied Physics 105, 07A726 (2009); https://doi.org/10.1063/1.3073842Reduction of ordering temperature of an FePt-ordered alloy by addition of CuApplied Physics Letters 80, 2147 (2002); https://doi.org/10.1063/1.1463213 Review Article: FePt heat assisted magnetic recording mediaJournal of Vacuum Science & Technology B 34, 060801 (2016); https://doi.org/10.1116/1.4965980The effective interdiffusivity, structure, and magnetic properties of †Fe/Pt‡nmultilayer filmsBo Yaoa and Kevin R. CoffeyAdvanced Materials Processing and Analysis Center and Department of Mechanical, Materialsand Aerospace Engineering, University of Central Florida, Orlando, Florida 32816, USAPresented on 9 November 2007; received 7 September 2007; accepted 27 September 2007;published online 22 January 2008This paper reports the influence of the deposition temperature and the wavelength of the periodicityon the effective interdiffusivity, microstructure, and magnetic properties of annealed Fe /Ptnmultilayer films MLs. It was found that both the deposition temperature and periodicity ofFe /Ptn MLs have a significant influence on the effective Fe–Pt interdiffusivity, microstructure, andmagnetic properties of the annealed films. It was also observed that the magnitude of the effectiveinterdiffusion coefficient, the L10 grain size, and the long-range order parameter were positivelycorrelated. This result suggests that nonequilibrium reaction kinetics are desirable for the reducedtemperature formation of the L10 FePt phase. © 2008 American Institute of Physics.DOI: 10.1063/1.2828978I. INTRODUCTIONThe L10 FePt phase has received research interest be-cause of its potential application for high-density magneticrecording media and high-energy permanent magnets,mainly due to its large magnetocrystalline anisotropy energydensity Ku107 ergs /cm3.1 For many potential applica-tions it is desirable to obtain the ordered L10 phase at aminimal processing temperature. Multiple layers of elemen-tal Fe and Pt films, Fe /Ptn, have attracted attention, due tothe observation of the L10 FePt phase at reduced annealingtemperatures, as low as 300 °C for both epitaxial2–6 andpolycrystalline7,8 films. Although the mechanism of this re-action is still poorly understood, the rapid interdiffusion ofFe and Pt at the interface is generally believed to be respon-sible for the formation of L10 FePt. Efforts4,9–11 have beenmade to measure the bulk Fe–Pt interdiffusivity and to un-derstand the relationship between interdiffusivity and forma-tion of L10 FePt phase. However, it has been demonstrated inboth theory and experiments that the effective interdiffusivityD in nanoscale multilayer films MLs can deviate signifi-cantly from the bulk interdiffusivity due to the influence ofthe steep composition gradient and coherent strains inMLs.12–16 Therefore, it may not be useful to use the mea-sured bulk diffusivity to understand the interdiffusion ofMLs.Instead, the effective interdiffusivity in MLs can be di-rectly determined from the decay rate of the intensity ofsmall angle x-ray diffraction XRD peaks due to thermaltreatments. The repetitive layer pairs of different x-ray scat-tering strength in the MLs induce small angle XRD peaksaround the 000 reflection direct beam, and the decay ofthese peaks due to annealing is directly related to the homog-enization of these compositionally modulated layers. The ef-fective interdiffusivity D is given by the decay rate of thefirst small angle peak intensity It during annealing re-viewed in Ref. 17:D = − 2/82dlnIt/I0/dt , 1where I0 is the initial intensity of as-deposited films,  isthe bilayer period i.e., sum of the thickness of a single Ptand a single Fe layer, and t is the annealing time. The valuesof It and I0 can be measured through small angle XRD,and the values of t and  are known. This method has beenapplied to measure the interdiffusivity of a large variety ofmaterial systems such as Si /SiG,18,19 Mo /Si,20 Cu /Pd,15GaAs /AlAs,21 and Au /Ag Ref. 16 MLs. Most recently,Se-Young et al.22 and Zotov et al.17 used this approach tomeasure the effective Fe–Pt interdiffusivity of Fe /Ptn MLs.Interestingly, they found that the effective interdiffusivitydiffered for different Fe–Pt MLs, which, in part, motivatesthis more comprehensive study.The aim of this paper is to investigate the influence ofthe deposition temperature and the wavelength of the period-icity of the Fe /Ptn MLs on the effective interdiffusivity,microstructure, and magnetic properties of the films after an-nealing. As will be shown, both the deposition temperatureand periodicity of Fe /Ptn MLs have a significant influenceon the effective Fe–Pt interdiffusivity and upon the micro-structure and magnetic properties of the annealed films. Itwas also found that the magnitude of the effective interdif-fusion coefficient, the L10 grain size, and the long-range or-der parameter were positively correlated. This result suggeststhat nonequilibrium reaction kinetics are desirable for thereduced temperature formation of the L10 FePt phase.II. EXPERIMENTSTwo sets of Fe /Ptn samples were sputtered on oxidizedSi substrates, as listed in Table I. The first set of sampleslabeled as “a,” “b,” “c,” “d,” and “e” have the same layerstructure, Fe22 ÅPt28 Å12 but different deposition substrateaElectronic mail: bo555252@pegasus.cc.ucf.edu.JOURNAL OF APPLIED PHYSICS 103, 07E107 20080021-8979/2008/1037/07E107/3/$23.00 © 2008 American Institute of Physics103, 07E107-1temperatures, in the range of −50–250 °C. Among them,samples a, b, and d were selected to examine the influence ofdeposition temperature on the effective interdiffusion coeffi-cient. The second set of samples, labeled as “f,” “g,” “h,” “i,”and “j,” have a common deposition temperature, 250 °C, butvarying periodicity, in the range of 11.4–182.6 Å. Amongthem, samples g, h, and i were chosen to determine the in-fluence of periodicity on the interdiffusivity. The details ofthe ML sample preparation have been previously reported.23The ML film samples were annealed in a modified tube fur-nace in 1 atm of flowing Ar+5% H2 process gas, describedalso in Ref. 23. The modified furnace allows a rapid heatingand cooling of samples without breaking the annealing am-bient.Small angle XRD patterns were acquired in a RigaKux-ray diffraction instrument with a Cu K source. Magneticproperties were measured with an alternate gradient forcemagnetometer Princeton Measurements Corp. MicroMagmodel 2900 with a maximum field of 22 kOe. The micros-copy was performed in a Tecnai F30 microscope operating at300 kV. Hollow-cone annual dark field ADF transmissionelectron microscopy TEM images were used to analyze thestructure of L10 phase. The TEM samples were preparedusing a back-etch technique.III. RESULTS AND DISCUSSIONSmall angle XRD patterns confirm that the multilayerstructures were preserved in good condition for all as-deposited samples.23 Figure 1a shows the evolution of thesmall angle x-ray diffraction pattern for sample i a represen-tative example annealed for different times at 325 °C. Theintensity of the satellite peak decreases with annealing timedue to the interdiffusion of Fe and Pt at the interface. Figure1b shows plots of lnIt / I0 versus t for samples g, h,and i annealed for different times at 325 °C. It can be seenthat lnIt / I0 falls almost linearly with the annealing timeafter the first anneal. The fitted lines do not meet the Y axisat 0, due to an initial drop in intensity, which has been widelyobserved and investigated in many systems.17 As a commonpractice, the linear decay after the initial rapid drop is takento determine the effective interdiffusivity for each sample atthe annealing temperature studied.All six samples a, b, d, and g, h, i were annealed fordifferent times at 275, 300, and 325 °C. The measured ef-fective interdiffusivities, according to Eq. 1, are shown inFig. 2 in the form of lnD plotted as a function of 1 /T. Itcan be seen from Fig. 2b that the effective interdiffusivityincreases with the increase of periodicity for samples g, h,and i, with approximately similar interdiffusion activationenergies ranging from 1.3 to 1.8 eV. This trend is consis-tent with the greater effective interdiffusivity reported forlarger periodicity Fe /Pt MLs by Zotov et al.17 In the set ofsamples deposited at different temperatures, as shown in Fig.2a, sample a deposited at −50 °C has a lower interdiffu-sivity and activation energy, while the effective interdiffusiv-ity of samples b and d is similar in magnitude and tempera-ture dependence activation energy.Figures 3a and 3b show the measured in-plane coer-civity for samples annealed at 400 and 500 °C. The resultsshow that both the deposition temperature and periodicity offilms have a great influence on this magnetic property. Moreinterestingly, by comparing the coercivities Fig. 3 and in-terdiffusivities Fig. 2 for the two sets of samples, it can benoted that samples having large effective interdiffusivitiesgenerally have large coercivity. To further understand thesefilms, hollow-cone ADF TEM microscopy and electron dif-TABLE I. A list of Fe /Ptn MLs.SamplelabelMultilayerstructurePeriodÅDepo.temp. °Ca Fe22 ÅPt28 Å12 50 −50b Fe22 ÅPt28 Å12 50 25c Fe22 ÅPt28 Å12 50 150d Fe22 ÅPt28 Å12 50 200e Fe22 ÅPt28 Å12 50 250f Fe5 ÅPt6.4 Å48 11.4 250g Fe10 ÅPt12.8 Å24 22.8 250h Fe20 ÅPt25.6 Å12 45.6 250i Fe40 ÅPt51.3 Å6 91.3 250j Fe80 ÅPt102.6 Å3 182.6 250FIG. 1. Color online a The decay of the first satellite peak due to an-nealing for sample “i” annealed at 325 °C. b The plots of lnIt / I0 vsannealing time t for samples “g,” “h,” and “i” annealed for different timesat 325 °C.FIG. 2. a The lnD vs 1 /T for samples “a,” “b,” and “d.” b ThelnD vs 1 /T for samples “g,” “h,” and “i.” D has the unit of m2 /s.FIG. 3. a The in-plane Hc vs deposition temperature for samples “a,” “b,”“c,” “d,” and “e.” All samples were annealed at 500 °C for 30 min. b Thein-plane Hc vs periodicity for samples “f,” “g,” “h,” “i,” and “j” annealed attemperatures of 400 and 500 °C for 30 min.07E107-2 B. Yao and K. R. Coffey J. Appl. Phys. 103, 07E107 2008fraction studies were undertaken to examine the structure ofL10 FePt phase and its long-range order parameter in thesesamples.The as-deposited films were found to consist of fccphase Fe and Pt except samples i and j which have a bccphase Fe present while the annealed films showed evidenceof both fcc and L10 phases, but lacked evidence of the Fe3Ptand FePt3 L12 phases that have been reported by others inmuch larger periodicity Fe /Pt MLs.2 We hypothesize that theabsence of the L12 phases is due to a lack of driving force fortheir nucleation in our small periodicity samples. Figures4a–4e show the hollow-cone ADF TEM images from the001 and 110 superlattice reflections of samples a, b, c, d,and e, respectively, annealed at 500 °C for 30 min. The illu-minated regions in the images show the L10 FePt grains with001 or 110 planes parallel to the electron beam. Figure4f shows the c /a ratio of the L10 phase of these five an-nealed samples. Figures 5a–5e show the ADF TEM im-ages from the 001 and 110 L10 superlattice reflections forsamples f, g, h, i, and j, respectively, annealed at 500 °C for30 min. Figure 5f shows the c /a ratio of the L10 phase ofthese five annealed samples. It can be noted from examina-tion of Figs. 4 and 5 that both a larger grain size and a lowerc /a ratio of L10 FePt phase indicating a greater value for thechemical order parameter24 are observed for samples havinghigher effective interdiffusivities Fig. 2 and in-plane coer-civities Fig. 3. Specifically, samples with larger interdiffu-sivities generally have larger L10 FePt grains, larger long-range order parameters indicated by small c /a ratio, andlarger coercivities. This correlation of structural and mag-netic properties to the effective interdiffusivity suggests thatnonequilibrium reaction kinetics are desirable for the re-duced temperature formation of the L10 FePt phase.IV. CONCLUSIONSThis paper reports the influence of the deposition tem-perature and the wavelength of the periodicity of Fe /PtnMLs on the effective interdiffusivity, microstructure, andmagnetic properties of the films after annealing. It was foundthat both the deposition temperature and periodicity ofFe /Ptn MLs have a significant influence on the effectiveFe–Pt interdiffusivity, microstructure, and magnetic proper-ties of the annealed films. It was also observed that the mag-nitude of the effective interdiffusion coefficient, the L10grain size, and the long-range order parameter were posi-tively correlated. In all cases studied, the L12 phases werebypassed. This result suggests that nonequilibrium reactionkinetics are desirable for the reduced temperature formationof the L10 FePt phase.1R. Skomski, J. Phys.: Condens. Matter 15, R841 2003.2M. Verdier, M. Veron, F. Bley, F. Ingwiller, N. M. Dempsey, and D.Givord, Philos. Mag. 85, 3157 2005.3Y. Endo, N. Kikuchi, O. Kitakami, and Y. Shimada, J. Appl. Phys. 89,7065 2001.4Y. Endo, K. Oikawa, T. Miyazaki, O. Kitakami, and Y. Shimada, J. Appl.Phys. 94, 7222 2003.5S. C. Chou, C. C. Yu, Y. Liou, and Y. D. Yao, Phys. Status Solidi A 201,1755 2004.6S. C. Chou, C. C. Yu, Y. Liou, Y. D. Yao, D. H. Wei, T. S. Chin, and M.F. Tai, J. Appl. Phys. 95, 7276 2004.7C. P. Luo and D. J. Shellmyer, IEEE Trans. Magn. 31, 2764 1995.8V. Raghavendra Reddy, S. Kavita, and A. Gupta, J. Appl. Phys. 99,113906 2006.9H. Mehrer, Diffusion in Solid Metals and Alloys, Landott-Bornstein, NewSeries, Group III, Vol. 26 Springer, Berlin, 1990.10Kushida, K. Tanaka, and H. Numakura, Mater. Trans. 44, 59 2003.11Y. Nose, T. Ikeda, H. Nakajima, and H. Numakura, Defect Diffus. Forum237–240, 450 2005.12A. Lindsay Greer, Curr. Opin. Solid State Mater. Sci. 2, 300 1997.13L. Chang and B. C. Giessen, Synthetic Modulated Structures Academic,New York, 1985.14D. Gupta and P. S. Ho, Diffusion Phenomena in Thin Films and Micro-electronic Materials Noyes, Park Ridge, NJ, 1988.15E. M. Philofsky and J. E. Hilliard, J. Appl. Phys. 40, 2198 1969.16H. E. Cook and J. E. Hilliard, J. Appl. Phys. 40, 2191 1969.17N. Zotov, J. Feydt, A. Savan, and A. Ludwig, J. Appl. Phys. 100, 0735172006.18S. M. Prokes, M. Fatemi, and K. L. Wang, J. Vac. Sci. Technol. B 8, 2541990.19D. B. Aubertine, N. Ozguveen, P. C. McIntyre, and S. Brenan, J. Appl.Phys. 94, 1557 2003.20H. Nakajima and H. Fujimori, J. Appl. Phys. 63, 1046 1988.21R. M. Fleming, D. B. McWhan, A. C. Gossard, W. Wiegmann, and R. A.Logan, J. Appl. Phys. 51, 357 1980.22O. Se-Young, D. P. Nguyen, C. G. Lee, B. S. Lee, B. H. Koo, H. Y. Liu,J. H. Yoo, and K. Shin, Diffus. Defect Data, Pt. A 258–260, 199 2006.23B. Yao and K. R. Coffey, J. Magn. Magn. Mater. 320, 559 2008.24B. W. Roberts, Acta Metall. 2, 597 1954.FIG. 4. Color online a–e ADF TEM images from L10 001 and 110superlattice reflections of samples “a,” “b,” “c,” “d,” and “e” annealed at500 °C for 30 min. f The c /a ratio vs deposition temperature. The barshows 100 nm.FIG. 5. Color online a–e ADF TEM images from L10 001 and 110superlattice reflections of samples “f,” “g,” “h,” “i,” and “j” annealed at500 °C for 30 min. f The c /a ratio vs deposition temperature. The barshows 100 nm.07E107-3 B. Yao and K. R. Coffey J. Appl. Phys. 103, 07E107 2008

The effective interdiffusivity, structure, and magnetic properties of Fe/Pt (n) multilayer films

Crossref

https://stars.library.ucf.edu/cgi/viewcontent.cgi?article=2173&amp;context=facultybib2000

The effective interdiffusivity, structure, and magnetic properties of Fe/Pt (n) multilayer films

Abstract

Similar works

Full text

Available Versions

University of Central Florida (UCF): STARS (Showcase of Text, Archives, Research & Scholarship)

Crossref