The amorphous Fe(100-x)B(x) alloys with 18 ≤ x ≤ 42 were prepared by applying a rf-sputtering technique. The chemical composition of the sputtered films was well controlled by varying the area ratio of B plate to Fe plate, which were used as a composite target. The crystallization temperature of the amorphous films linearly rises with increasing of B content up to x = 36, but falls in a composition range of 36 ≤ x ≤ 42. The amorphous Fe(100-x)B(x) films exhibited ferromagnetism in the whole compositions studied in the present work. The internal magnetic field of the amorphous films decreases with increasing of B content, since the charge transfer increases with B atom in the system Fe(100-x)B(x)

Kanamaru, Fumikazu

Miyazaki, Susumu

Oda, Kiichi

Takahashi, Katsuaki

Yoshio, Tetsuo

Okayama University Scientific Achievement Repository

Memoirs of the School of Engineering, Okayama University Vol. 14-2, February 1980Properties of the Amorphous FelOO-xBx AUoyPrepared by rf-SputteringlTechniqueFumikazu KANAMARU*,Kiichi ODA*,susumu MIYAZAKI*,Tetsuo YOSHIO***and Katsuaki TAKAHASHI(Received January 31,1980)SynopsisThe amorphous FelOO_xBx alloys with 18 2 x 2 42were prepared by applying a rf-sputtering technique.The chemical composition of the sputtered films waswell controlled by varying the area ratio of B plate toFe plate, which were used as a composite target.The crystallization temperature of the amorphousfilms linearly rises with increasing of B content up tox = 36, but falls in a composition range of 36 < x 2 42.The amorphous FelOO_xBx films exhibited ferromagnetismin the whole compositions studied in the present work.-The internal magnetic field of the amorphous filmsdecreases with increasing of B content, since thecharge transfer increases with B atom in the systemFelOO_xBx'1. IntroductionRecent progress of the technique for glass formation has made itpossible to produce various non-crystalline materials such as ferro-magnetic amorphous alloys, which were difficult to obtain by a con-ventional glass-melting method.Ferromagnetism in an amorphous alloy was first observed in vapor-deposited Co-Au filmCl). Unfortunately, the alloy was structurallyunstable at room temperature. More stable ferromagnetic amorphousalloys were subsequently obtained in the system of transition metals>'< Research Institute for Non-Crystalline Materials** Department of Industrial Chemistry111LIZ Fumikazu KANAMARU, Kiichi ODA, Susumu MIYAZAKI, Tetsuo YOSHIO and Katsuaki TAKAHASHIand metalloids (2-3). The amorphous Fe80B20 alloy, which is one ofsuch alloys, exhibits ferromagnetism with saturation induction ofabout 16 kG and low coercive force, ranging from 0.1 to 0.2 Oe, beingpromised as an excellent soft magnetic material. The amorphousFelOO_xBx alloy has been prepared by a continuous rapid-quenchingtechnique, but their chemical composition was limited in a range of12 < x < 25 (4-5).In the present work, synthesis of the amorphous FelOO_xBx alloywith a wide range of chemical composition was attempted by applyingrf-sputtering technique, and then the effects of boron atoms, ametalloid element, on the properties of the sputtered anorphous filmswere studied by measuring the dependence of the properties for thecomposition. It was also examined whether the properties of theamorphous alloy obtained by rapid-quenching were different from thoseof the sputtered film with the same composition or not.2. Experimental ProcedureThe rf-sputtering apparatusused for preparation of amorphousfilm is a ULVAC-SBR-ll04 type.The electrode construction is shownin Fig. 1. The chamber includesa pair of water-cooled electrodesand a shutter. A target wasplaced on the lower electrode anda substrate was attached to thecenter of the upper electrode.The target used for co-sputteringwas composed of a Fe disk of 100mm¢, geometrically arranged B disksof 11.3 mm¢ and small Fe squaresheets with dimension ranging from3 -x 3 mm 2 to 8 x 8 mm2 • The arearatios of B to Fe were controlledby varying the number of the B diskand the dimension of the Fe sheet.(Fig. 2) Rf-sputtering was car-ried out by using Ar gas as a sput-tering gas. An optimum rf-sputter-ing condition is sho,~ in Table 1.Water coolingFig.l Rf-sputtering apparatusFig.2 Typical assembly of thetarget for co-sputteringProperties of the amorphous FelOO_xBx prepared by rf-sputtering 113Table 1 The rf-sputtering conditions forthe film preparationTarget Fe, B diskSubstrate Slide glass, Polyimide filmGas ArPressure -210 nnn HgPower 100 wTime 2-6 hrThe chemical composition of rf-sputtered films was determined withusing atomic absorption spectrometer and EMX. The X-ray diffractionpatterns were taken by using Cu-Ka. radiation monochromatized by agraphite monochrometer. DTA was carried out up to 600°C in N2 atmos-phere with a heating rate 10°C/min.. The MBssbauer spectra weremeasured at room temperature using radiation from S7 Co in Pd metalwith multichannel analyzer(200 channel). Calibration was based onthe MBssbauer spectrum of Fe metal.B Area Cov....age (at~'" )Chemical composition ofthe sputtered FelOO_xBxfilms vs. B area coverageon targeto Present Work405o...-----------...,.....--,III 10 ~.-/"-/o0~----:,:';:0-'---:t20;---;'30~----:4;';;0-<';50;--~60Fig.3Fig. 3, it was confirmed that theaverage composition of the film was3. Results and Discussion3.1 Chemical compositionIn connnon sputtering method fabrication of a number of targetswith various compositions were necessary to obtain the alloy filmswith a wide composition range. In addition to ;this laborious work, itwas practically difficult to fabricate a large size of targets con-taining elements with high melting point. To avoid these inconven-iences, the co-sputtering techniquewas attempted to prepare Fe-B amor-phous alloys. The target used forthe co-sputtering was composed ofa Fe disk, B disks and Fe sheets asshown in Fig. 2. The B disks, onwhich Fe sheets were placed, weredistributed on the Fe disk as uni-formly as possible. The chemicalcomposition of the co-sputteredfilms was controlled by varying thenumber of theB disk or the dimen-sion of the Fe sheet. As shown in114 Fumikazu KANAMARU. Kiichi ODA, Susumu MIYAZAKI" Tetsuo YOSHIO and Katsuaki TAKAHASHI4 6Time ( hr)Line analysis of EMXfor Fe and B1.21.0III 0.8IIIQ>~. 0.6u:;:I-Fig.43.2 Film thicknessA linear relationship betweenthickness of the film and thesputtering time is observed asshown'in Fig. 5. The growth rateof Fe62B38 film is 0.18 ~m/hr,.which 'is larger than that ofthe'Brich alloy film because of thelower melting point of Fe metal.in proportion to the area ratio of Bmetalloidto Fe metal on thetarget. On comparing the area ratio of Bto Fe, the amount of the Batoms contained in the sputtered films ~s less b~cause of great dif-ference in the melting;points between B~2225°C) and Fe(1535°C) metal.The homogeneity of the compo-sition of the films was examined bymeans of EMX. Fig. 4 shows theresults of line scanning analysisfor Fe-Ka andB-Ka radiation fromthe Fe69B31 film deposited ontothe sl:ide glass-substrate. 'Fromthat results, it is confirmed thattheal16Y film prepared by co-sputtering has'a homogeneous com-position'over the whole film.sputt,ering timeFilm thickness of the.sputtered FelOO_xBxfilms as a function ofFig.5of Fen B23 filmpattern as shownStructure and crystallizationThe reflection electron dif-3.3fraction patternshowed only haloin Fig. 6.The X-ray dif~rad:ion pattern of the film also showed a typicalamorphous pattern as shown in Fig. 7a).'· On annealing above thecrystallization temperature descrived later, several diffractionlines were appeared as seen in Fig. 7 b)'. The results of X-ray. .analysis of the as-sputtered and heat-treated films are summarizedin Table 2. . The. chemical composition of the amorphous FelO:O_xBxfilms prepared by rapid-quenching was limited within 12 < x < 25.As seen in Table 2, the upper limit of B content was extended to 42Properties of the amorphous FelOO_xBx prepared by r{-sputtering 115____--.JA....._..,+"-"__........~__....... __as-sputtered8027060480°C-O.5hr in50Cu -K.30 402 e ( 0'20b)-----------10Fig.6 Reflection electrondiffraction patternof Fe n B23Fig.7 X-ray diffraction patternsof the sputtered Fe71B29film before and after heat-treatmentTable 2 Heat-treatment conditions and precipitated crystal phasesComposition As-sputtered film Temperature Crystal phasesFen B23 amorphous 440°C a-Fe, Fe2B460°C a'-Fe, Fe 2BFen B29 amorphous 480°C a-Fe, Fe2BFe 62 B38 amorphous 460°C Fe2B, FeB, a-FeFe58B42 amorphous 460°C Fe2B, FeB, a-Feby applying the co-sputtering technique. Nowick and Mader pointedout that amorphous structures were not obtained at any compositons foralloys composed of elements differing in size by less than 14 %, butamorphous structures were obtained in the composition range of ca. 30- 50 % in the case of differing in size by 27 % (1). In the presentcase the difference of size between Fe and B atoms is ca. 29 %, re-sulting in a wide composition range for the amorphous FelOO_xBx films.DTA of the amorphous FelOO_xBx films was carried out to determinethe crystallization temperature. An example of DTA curve is shown inFig. 8, where an exothermal peak assigned to crystallization of theamorphous film is observed at 458°C. The crystallization temperatureof the amorphous FelOO_xBx films rises with increasing the amount of Bcontent in the composition range of 23 < x ~ 36, but the crystalliza-tion temperature falls with increasing B atom in the range x > 36 asshown in Fig 9.The structure of amorphous Fe80B20 involves the fundamental units116 Fumikazu KANAMARU, Kiichi ODA; Susumu MIYAZAKI, Tetsuo YOSHIO and Katsuaki TAKAHASHIOTA600.-------------,After Masumoto et al.I rapid- quenching)Present Work,--o400uo~:;)~ 500tilg-till-e,Q.~'iijiii>-...uDTA-curve of the amor-phous Fe71B29 film, . , , , ,100 200 300 400 500 600Temperature I ·C Jci"t:Ic:LUci"LU1'qt-----------J1Fig.8corresponding to the smallest formof a close-packed structure asface centered cubic and B atoms300~-~-_;;!;;:-__='::__-_=__-...Jo 10 20 30 40 50B Content (atOJo)Crystallization tempera-ture vs. B content for theamorphous FelOO_xBx filmsFig.9located at the center of the Fe6trigonal prism (6-7). Since theamorphous structure is stabilizedby the BFe6 units, it is reasonablethat the crystallization temperature of the amorphous FelOO_xBx filmsrises with increasing B atom in the film with x less than 36. On theother hand, the crystallization temperature falls with increasing Batoms in the composition range of x > 36. Furthermore, as shown inTable 2 three crystal phases, FeB, FeZB and a-Fe(minor),precipitatedin the amorphous films with the composition of x > 36, even thoughcoexistance of three crystal phases was not expected from the phasediagram (8). From 'these experimental results in the composition rangeof x > 36 the following structural models are deduced.1) The structure of the amorphous FelOO_xBx film with x > 36seems to contain a large number of B-B bond to form a zigzag chain ofB atoms, resulting in the formation of the small structure unit asFeB, in which B atoms form infinite chains. Increasing the numberof the B-B bond makes more easy the crystallization of FeB.2) On heating the film, FeB was preferentially precipitated in thefilm, subsequently the crystallization of Fe2B and a-Fe in the Fe richamorphous matrix.3.4 MBssbauer spectraMBssbauer spectra of the amorphous FelOO_xBx films show broad sixlines as shown in Fig. 10. The broadness of the line is caused byhyperfine field distribution commonly observed in amorphous magneticmaterials. It is well known that the intensities of the six linesProperties of the a'ITUJrphous Fe100.xBx prepared by rf·sputtering 117in H. t with in-l.n .atoms indicates that.',I.':.:. :',' . '.:.:".':221 KOei :...~".Hint. =248 KOeo Present WorkX after C.L. Chien et al., , , ,-5 0 +5 +10V (mm/sec)i ..........:".::".", ...~'...M~ssbauer spectra ofthe FelOO_xBx filmso0~--:'10::--""-:2:":0~---:3:'::0-"""""4'="O-""'5=-'OB Content (at"lo)Internal magnetic fieldvs. B content for theamorphous FelOO_xBx filmsFig. 11Fig.10-10"li 300i.Lu:;c:f 200~iiic..CII:5 100electrons localized onthe reductioncreasing of Bvalue of H. t monotonously de-"l.n .creases with increasing B content.G.Shirane et al. found a linearrelationship between magneticmoment and H. t in alloys of Fel.n .and metalloids (11). Because thereduction of magnetic moment meansan increase of the amount of 3dFe atoms,have an angular dependence betweenthe direction of the magnetic fieldaxis of quantization and the direc-tion of the emmission of the y-ray,i.e. those have an area ratio of3:2:l:l:2:3( randomly oriented mag-netization axis ); 3:4:l:l:4:3( mag-netization axis in perpendicular tothe y-ray ) (9). It is apparentfrom Fig. 10 that the spectra ofthe as-sputtered film at 300 Kshow an area ratio close to 3:4:1:1:4:3. It is indicated that themagnetization axis remains complete-ly in the plane. This resultagrees precisely with one thatChien et al. observed on theM~ssbauer spectrum of the FeSOB20amorphous alloy prepared by rapid-quenching (10). Consequently,there is no difference of magneticstructure between the rf-sputteredfilm and the amorphous ribbon pre-pared by rapid-quenching.In M~ssbauer spectra the in-ternal magnetic field, H. t ' isl.n .evaluated by the width between leftand right end line of all the sixlines. As shown in Fig. 11, the118 Fumikazu KANAMARU, Kiichi ODA, Susumu MIYAZAKI. Tetsuo YOSHIO and Katsuaki TAKAHASHIthe charge transfer of the p electrons of B atoms to Fe atoms takesplace to result the increasing of number of the localized electrons onFe atoms in the amorphous FelOO_xBx films within composition range of23 < x < 42.AcknowledgementsThe authors wish to thank Dr.M.Shimada( Osaka University) forthe M~ssbauer effect measurement.This research was supported in part by a Grant-in-Aid for Scien-tific Research from the Ministry of Education.References(1) S.Mader and A.S.Nowick, App1. Phys. Lett., 2(1965), 57-59.(2) D.E.Po1k and H.S.Chen, J. Non-Cryst. Solids, 15(1974), 165-173.(3) D.E.Polk and H.S.Chen, ibid. , 15(1974), 174-178.(4) H.S.Chen and C.E.Miller, Rev. Sci. Instrum., 11(1970), 1237-38.(5) N.Tsua, K.I.Arai and T.Ohsaka, IEEE Trans. Magn. ,MAG-14(1978),941.(6) U.Herold and U.K~ster, Z. Meta1k., 69(1978), 326.(7) U.Herold and U.KBster, Rapid Quenched Metals III, !(1978), 281.(8) William G.Moffatt, " The handbook of binary phase diagrams"vo1.1, General Electric Co. (1978).(9) G.K.Wertheim," M~ssbauer Effect; Principles and Applications"Academic Press (1964), pp.69.(10) C.L.Chien and R.Hasegawa, " Amorphous Magnetism II ", PlenumPress (1977), pp.225.(11) G.Shirane, W.J.Takei and S.L.Ruby, Phys. Rev., 126(1962), 49-52.

Properties of the Amorphous Fe(100-x)B(x) Alloy Prepared by rf-Sputtering Technique

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