Amorphous and crystalline properties of thin films of NdFe(B)M. Gasgnier, C. Colliex, and T. Manoubi Citation: Journal of Applied Physics 59, 989 (1986); doi: 10.1063/1.336583 View online: http://dx.doi.org/10.1063/1.336583 View Table of Contents: http://scitation.aip.org/content/aip/journal/jap/59/3?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Magnetic properties and magnetic domains of Nd–Fe–B thin films J. Appl. Phys. 103, 023922 (2008); 10.1063/1.2836957 Effect of rare earth content on microstructure and magnetic properties of SmCo and NdFeB thin films J. Appl. Phys. 91, 8180 (2002); 10.1063/1.1453940 Exchange coupling in crystalline/amorphous Nd–Fe–B nanoassemblies J. Appl. Phys. 87, 6113 (2000); 10.1063/1.372626 Magnetic properties of NdFeB thin films synthesized via laser ablation processing J. Appl. Phys. 83, 6620 (1998); 10.1063/1.367927 Magnetic properties and growth texture of high-coercive Nd–Fe–B thin films J. Appl. Phys. 83, 2735 (1998); 10.1063/1.366635

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tration Report NASA S),·3012, (1964). polation of the tabulated results is required in our proposed expression, which shows its simplicity including only two constants.

lE. Bertel, H. Joffre, L Pagei:, arid L Sklavenitis, Atomic Energy Commis­sion (France) Rep-:Jrt No. CEACONE··1087 (1968).

We wish to thank Dr. S. C. Gupta (Principal, S. V. Col­lege, Aligarh) and Professor M. L. Sehgal (Chairman, De­partment of Physics, Aligarh Muslim University, Aligarh) for providing research and library facilities. P. B. Pal is grateful to Sri S. L. Rathore (Principal, Ganjdundwara Col­lege, Ganjdundwara, Btah) for constant encouragement during this work. The financial assistance from the U.G.C. in the form of a minor research project is also gratefully acknowledged.

.oM. J. Berger and S. M. Seltzer, Nat. BUT. Stand. Report No.. NBSIR 82-2550-A (1982).

'So E. Liverhant, Eillmimtary introduction toVuclear Reactor Physics (Wi­ley, Toppan, 1960), p. 338.

6L. Katz and A. S. Peniold, Rev. Mod. Phys. 24, 28 (1952). 7H. H. Selizer, PhYi::. Rev. 100, 1029 (1955). 8p. J. Ebert, A. F. Lauzoll, Imd E. M. Lent, Phys. Rev. 183,422 (1969). 1>'[. Tabata, R. Ito,ar.d S Okaoe, J. Appl. Pllys. 42, 3361 (1971). I"T. Tabata, R. Ito, :lnd S. Okabe. Nuel. Instmm. Methods 103, 85 (1972). JlR. R. Wilson, Phys. Rev. 84, 100 (l95J). '2p. B. Pal, S. K. Gupta, V. P. Van>hney, and D. K. Gupta, Indian J. Pure

Appl. Phys. 23, 244 (1985). "D. Harder and G. Posehet, Phys. Lett. B 24,519 (1967). ,.oK. H. Weber, Nucl. lnstrum. Methods 25,261 (1964). ISR. K. Batra and M. L. Sehgal, Phys. Rev. B 23, 4448 (1981). 1"1'. M. Knasel, Nucl. Instrum. Methods 83,217 (1970). IA. T. Nelms, Nat. Bur. Stand. Cire. 577 (1956) (unpublished); Nat. Bur.

Stand. Cire. 577, Suppl. (1958) (unpublished). 2M. J. Berger and S. M. Seltzer, National Aeronautics and Space Adminis-

I7H. A. Bethe, M. E. Rose, and L. P. Smith, Proc. Am. Philos. Soc. 78, 573 (1938).

Amorphous and crystalline properties of thin films of Ndfe(8) M. Gasgnier E. R. 060210, I, place A. Briand 92195 Meu.don Cedex, France

C. Colliex and T. Manoubi Unite de Service du C.NR.S., 120041 Bat. 510, Universile Paris-Sud, 914050rsay Cidex, France

(ReceiveCi 23 July 1985; accepted for publication 15 October 1985)

NdFe(B) thin films are deposited onto gbs,<; substrates by means of a tungsten crucible. The as­deposited films are studied hy the Lorentz microscopy method in order to observe the different magnetic domains, STEM analysis (EELS method) permits us to obtain the characterjstic absorption edges of Fe and Nd (but not of boron). The crystallization behavior, inside the electron microscope, by m("llllS oftlle ek"etron beam, allows us to observe the formation of the a­Fe, A-Nd20 3 , and NdFeO j phases. The different stages of appearances of these structures are discussed.

Production of permanent magnets, such as NdxByFeIOO-x_y, has been developed recently. CrystaLline and magnetic properties of sintered or heat-treated melt­spun bulk. materials 1--6 and thinned crystalline samples 7-9

have been reported. To have new results in this field of inves­tigation, we have used here the thin-film method.

Initial ingots with a NdJIJFe76:Bs (or Nd t Fe14B) compo­sition are evaporated in a tungsten crudb}(!. The vacuum system, supplied with a nitrogen traJ), is pumped to about 7X 10-5 Pa. The films (e-60 n:rn) are deposited onto NaCl substrates. Then they are removed by floaHng on deionized water and deposited on copper grids to be observed by elec­tron microscopy. Three methods have heen used: Lorentz electron microscopy; conventional transmission electron microscopy (CTEM) to anneal the film by means of the electron beam; and scanning transmission electron micros­copy (STEM) to analyze the material by means of the elec­tron energy loss spectroscopy (EELS) method.

Lorentz microscopy: The as-deposited films are amor­phous (Fig. 1). Lorentz microscopy micrographs are ob­tained with the electron beam oriented perpendicuJar to the film plane. Two sorts of domain walls (Figs. 2 and 3) show FIG. 1. Electron diffraction pattern of an as-deposited film.

989 J. Appl. Phys. 59 (3), 1 February 1986 0021-8979/66/030989-04$02.40 @ 1986 American Institute of Physics 989

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FIG. 2. Fine magnetic domains of as-deposited films.

FIG. 3. Ripple domains of as-deposited films.

FIG. 4. New magnetic domains after application of the magnetic induction of the objective lens.

FIG. S. Sharp misoriented single walls for a zone near an annealing area.

990 J. Appl. Phys., Vol. 59, No.3, 1 February 1986

very fine and ripple domain patterns. By application of the magnetic induction of the objective lens (-10 kG), new domains are generated (Fig. 4). These are roughly perpen­dicular to the main ripple's direction. The electron beam is used to anneal a small area of the film. A weak heating de­stroys all the magnetic domains. But it generates, for neigh­boring zones, new magnetic structures as sharp misoriented single walls (Fig. 5). All. these contrasts are characteristics of an in-plane magnetization. 10--13

STEM analysis: A STEM, VG-HB5 system, linked with a GATAN 607 detector is used for EELS method. This per­mits to analyze thinned materials, and to determine the ratio of an element throughout a very small volume (typically some nm3

). 14 But it is more difficult to detect a very small minority of components randomly distributed throughout a given matrix. In Fig. 6(a), the recorded spectrum shows the characteristic absorption edges of Fe(M2.3 ) and of Nd(N4.5 ). The presence of carbon and oxygen was observed within the film thickness. As in the initial ingot, the weight % of boron is about 1.3, so it seems possible that it be scat­tered in the whole layer volume. Therefore, it is very difficult to record the boron K edge at 200 eV [Fig. 6(b) J.

On another part, it has not been possible to use the ener­gy dispersive x-ray (EDX) method in order to analyze the NdlFe ratio content. Indeed., the Ka emission ray relative to Nd is too high in energy (37 350 eV) to be recorded. And to

FIG. 6. (a) Electron energy loss spectrum: the first peak is relative to the M 2_3 iron·absorption edge (60 eV), the second one, indicated by the spot, is relative to the N .... , neodynium.absorption edge (133 eV). (b) RedU«d scan (between 141 and 241 e V) in order to research the boron Kedge ( 190 eV) (see text).

Gasgnier, Colliex, and Manoubi 990

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FIG. 7. Electron diffraction pattern after total crystallization: theA-Nd20) and the a-Fe structures are well defined.

have a good accuracy, it must be compared to two Ka rays. Crystallization behavior: The as-deposited films are

amorphous (Fig. 1). This has been observed with numerous other alloys, obtained according to the same experimental procedure. 10 By means of the electron beam, the films were annealed progressively from 300 K up to about 1500-1800 K. This method permits us to observe the different stages of crystallization and recrystallization. In the first stage of the heating, the first two haloes (Fig. 1) are better resolved and centered at about 3.00 and 2.00 A. Upon heating at a higher temperature, the electron diffraction pattern shows clearly resolved rings when the material is wen crystallized (Fig. 7). There are two sorts of rings: the ones that are dashed and relative to a-Fe (a = 2.84 A) and the ones which, as full

FIG. 8. After annealing at very high temperature, the NdFe03 orthoferrite structure is observed.

991 J. Appl. Phys., VOl. 59, No.3, 1 February 1986

FIG. 9. Different modes of crystallization in the course of the annealing.

circles, belong to the A-Nd20 3 hexagonal structure (a = 3.63 Aandc = 6 A). Ata higher temperature, it forms new compounds as the orthoferrite NdFe03 (Fig. 8) and an unidentified phase (either cubic or hexagonal). The micro­graph (Fig. 9) shows the different degrees of the heating modes and the presence of holes.

As some analyses are very difficult to carry out, the "as­deposited" material must be labeled as "NbxFey (B)," which presents classical magnetic domains as for GdFe, GdCo, ThFe, etc., samples. \0 From the crystallization be­havior two conclusions can be made. Firstly, the haloes be­long to a-Fe andA-Nd20 3• So there is a decomposition into a metallic and an insulating phase. The presence of oxygen within the film, as revealed by EELS, should explain the formation of neodynium sesquioxide. But it is surprising to observe the A-structure, which is formed ordinarily at high temperature. Indeed, for rare-earth (R) thin films, the low­temperature C-R20 3 bec phase always appears at first. 15

This result can be compared to the ones reported for amor­phous GdCo and ThFe thin films contaminated with oxy­gen. 16

•I7 The electron diffraction patterns then present two

halo characteristics of the metal (Co and Fe) and of the monoclinic high-temperature phase of the rare-earth ses­quioxide. Secondly, it was not possible to observe the forma­tion of metallic phases (as Nd2F I7) of ternary compounds (as Nd2FeI4B), or of iron-boron alloys (as Fe3B).2.7,9 (If this one is present, it is possible that it might be epitaxiaUy grown within some a-Fe crystals. 18) Lastly, one must n~tice that the so-called unidentified bee structure (a = 2.9 A as reported) observed by Hiraga et al.9 should in fact be the a­Fe phase.

Further experiments will be done soon with thicker films to visualize magnetic domains and to determine the presence of boron.

1M. Sagawa, F. Fujimura, N. Togawa, H. Yamamoto, and Y. Matsuura, J. Appl. Phys. 55, 2083 (1984).

2E. Burzo, Proceedings o/the 6th International Symposium on High-Purity Materials in Science and Technology (Dresden RDA 1985, Proc. III), p.51.

31.1. Croat,J. F. Herbst, R. W. Lee, andF. E. Pinkerton,J. Appl. Phys. 55, 2078 (1984).

4A. Kostikas, V. Pupaefthymion, A. Simopoulos, and G. Hadjipanayis, J.

Gasgnier, Colliex, and Manoubi 991

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Phys. F 15, L 129 (1985). 5J. O. Livingston, J. Appl. Phys. 57, 4137 (1985). 60. Li and J. Stmat, J. Appl. Phys. 57, 4143 (1985). 7F. Fidler, P. Skalicky, M. Sagawa, and Y. Matsuura, Proceedings of the 8th European Congress on Electron Microscopy, edited by A. Csanody, P. Roh­lich. and O. Szabo (Budapest, 1984), Vol. 1, p. 811.

IVI. Suzuki, K. Hiraga, and M. Sagawa, Jpn. J. Appl. Phys. 23, L 421 (1984).

9K. Hiraga, M. Hirabayaski, M. Sagawa, and Y. Matsuura, Jpn. J. Appl. Phys. 24, L 30 (1985). I~. Gasgnier, Handbook on the Physics and the Chemistry of Rare Earth,

edited by K. A. Gschneider, Ir. and L. Eyring (North-Holland, Amster­dam, 1982), Vol. 5, Chap. 41.

lIT. Suzuki, Jpn. J. Appl. Phys. 20, 2079 (1981). 12H. J. Leamy andA. G. Dirks, J. Appl. Phys. 50, 2871 (1979). '1". Tymosz, Acta Phys. Polonica A 63, 379 (1983). I·C. Colliex, Proceedings of the 8th European Congress on Electron Micros­

copy, edited by A. Csanady, P. Rohlich, and O. Szabo (Budapest, 1984), p.349.

15M. Gasgnier, Phys. Status Solidi A 57, 11 (1980). 'lig. R. Herd, Phys. Status Solidi A 44, 363 (1977). I7A. G. Dirks and I. R. M. Gijsbers, J. Phys. D 12,149 (1979). 18A.Quivy,J. Rzepski, J. P. Chevalier, and Y. Calvayrac, Proceedings of the

Rapidly Quenched Metals 5, Wurzburg, 1985, edited by S. Steeb and H. Warlimont (msevier, Lausanne, Switzerland, 1985), p. 315.

AUoy scattering Umited mobmty of two-dimens6ona.r electron gas ~n quaternary aUoy semiconductors

P. K. Basu and Keya Bhattacharya Institute of Radio Physics and Electronics, 92 Acharya Prafulla Chandra Road. Calcutta 700009, India

(Received 28 May 1985; accepted for publication 23 October 1985)

A theory of alloy scattering of two-dimensional electron gas in quaternary III -V semiconductors is developed by assuming spherically symmetric square scattering potential randomly distributed in the crystal. The theory predicts a temperature-independent mobility. Electron mobilities have been calculated for two-dimensional. electrons in Gal _ x lnx PI _ y Asy and Gal _ x lnx PI _ y

Sby, with scattering potentials expressed in terms of the differences in the band gaps, the electron affinities, and the electronegativities of the constituent materials.

Modulation-doped field-effect transistors (MOD­FETs) using semiconductor heterojunctions 1 and quantum well <QW) lasers,2 in which a layer oflower band-gap semi­conductor is sandwiched between two layers of a higher band~gap semiconductor, are receiving attention from dif­ferent workers because of their superior device performance. In these devices a narrow one-dimensional potential. well quantizes the motion of electrons, and a two-dimensional electron gas (2DEG)3 is formed. The mobility of2DEG is an important device parameter, and some knowledge about the mobility behavior is needed for optimization of devices. The variation of mobility at l.ow temperature is also useful for the study of the quantum Hall effect.4 To date, mobility behavior of 2DEG has been studied in detail in heterojunc­tions and QW's made of GaAs and AJ.GaAs.5 Recently, 2DEG in ternaries like InGaAs with either lnAlAs or loP as the barrier layer is receiving attention from workers.5

-IO It

has been conduded that in ternaries alloy scattering is the dominant mechanism at low temperature and, if impurity scattering is properly eliminated, a study of alloy scattering limited mobility may lead to a correct estimate of alloy scat­tering potential.

Quaternary alloy (QA) semiconductors like InGaAsP form an important class of materials finding widespread ap­p!.ication in optoelectronic devices. II Recently laser action in InGaAsP QW lasers has been reported,12 and it is likely that properties of 2DEG in heterojunctions made of quaternary alloys win soon be reported as well In order to study the mobility behavior of 2DEG in QAs, the formuJ!as developed for phonon and impurity scattering may be employed; the

formula for alloy scattering in ternaries, however, is not ap~ plicabJ.e.

Recently, Brum and Bastard 13 have presented the calcu­lated values of mobility in QW's formed in QAs by assuming that the scattering potentials are 8 functions in space. We propose to develop in this paper the theory of transport due to alloy scattering in heterojunctions. The scattering poten­tial is a spherically symmetric square well, and therefore the theory may be applicable when alloy clustering is present. 14

The theory and the results for low-temperature mobilities in GalnPAs and GalnPSb are given below.

Let us assume that the 2DEG is formed in A ~I~ x B !I1 C i _ y D ~ QA semiconductor (lnd z represents the direction of quantization. The 2DEG is assumed to occu­py the lowest subband, and the wave function3.8 is given by

if! = S 1/2XO (Z) exp(i k'r) (la)

and

xo(z) = Ob3)ll2zexp( -bz/2), (lb)

where S is the surface area and b is the variational parameter. The scattering potentials are assumed to be spherically

symmetric square wens of radius r 0 with heights 6.E A , I1E B'

11Ec> and ~D atA,B,C, andD atom sites, respectively. Con­sider a sphere centered at (r;, Z; ). The potential due to a circular disc at z in this sphere may then be expressed in terms of the following 2D Fourier series:

V(r,z) = L2m~En{r (z)JI[qr (z)]lq} q

X {1 - H [r - r(z) nexpUq-\r - riD, (2)

992 J. Appl. Phys. 59 (3),1 February 1986 0021-8979/86/030992-03$02.40 @ 1986 American Institute of PhYSics 992

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