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TEXTURE FUNCTION IN γ-Fe2O3 MAGNETIC TAPES
B. Martinez, A. Labarta, X. Obradors, J. Cusidó, J. Tejada
To cite this version:
B. Martinez, A. Labarta, X. Obradors, J. Cusidó, J. Tejada. TEXTURE FUNCTION IN γ- Fe2O3 MAGNETIC TAPES. Journal de Physique Colloques, 1985, 46 (C6), pp.C6-379-C6-382.
�10.1051/jphyscol:1985670�. �jpa-00224925�
JOURNAL DE PHYSIQUE
Colloque C6, suppl6ment au n09, Tome 46, septembre 1985 page C6-379
TEXTURE FUNCTION IN y-Fe203 MAGNETIC TAPES
B. Martinez, A. Labarta, X. Obradors, J.A. ~usid6' and J. Tejada Facultat de ~ z ' s i c a , Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Spain
*E. T.S.A. Vs., Universitat Polit2cnica de Catalunya, Apartat de Correus 508, Terrassa, Barcelona, Spain
~&um6 - La fonction de texture des particules de a-Fe20 monodomaines constituant les bandes magnetiques a 6t6 d6termin6e quan2itativement par l'exploitation des spectres d'absorption Mossbauer et des cycles d'hys- t6r6sis. I1 a 6t6 v6rifi6 que la contribution des termes d'ordre sup6- rieur G 1 = 4 peut Stre n8gligCe.
Abstract - The texture function of single domain a-Fe20 particles belonging to magnetic tapes has been quantitatively evaguated by using data of Mossbauer spectroscopy and magnetic hysteresis loop measurements.
It has been verified that the contribution of the terms having 1 > 4 can be neglected.
I - INTRODUCTION
A very interesting approach to the development of longitudinal (perpendicular) aniso- tropy particula media involves the employement of small acicular particles with pre- dominant shape anisotropy oriented with their easy axes parallel (perpendicular) to the substrate.
The texture of single domaing-Fe 0 particles in magnetic recording tapes is of ma- jor technological interest due to2tge dependence of magnetic recording characteris- tics on the texture of the particles /1,2/.
Mossbauer spectroscopy can be used to measure the orientation of the magnetic single domain particles in the film /3,4/. The measurement of the magnetic properties, such as coercivity, magnetization and the squareness of the hysteresis loop (sq=Mr/M where M and M are the remanence and the saturation magnetization respectivelys), allows rto chaFacterize the single domain particles and to determine the particle orientation with respect to the direction of the applied magnetic field /5 - 7/.
In this work we use recently published Mossbauer and hysteresis loop data /8/ on 8-Fe20 magnetic tapes to determine the coefficients of the real harmonics in which the texgure function may be developed /9/. In Table I we summarize the different data used in this paper.
Geometry (6 $9,) (Icos Q RI> (3) < cos 2 8 R ) (Mossbauer ) 9 = O @ = a n y 0.19 (1) 0.11 (1)
M M
e M = % p M = n / ~ 0.85 (1) 0.40 (1)
8, =n/Z 9, = 0 0.45 (1) 0.23 (1)
Table I - Different experimental data used in this work
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1985670
C6-380 JOURNAL DE PHYSIQUE
In Figure 1 are indicated the geometrical arrangements used for Mossbauer spectrosco- py measurements. In the hysteresis loop measurements the external magnetic field was applied along the X, Y and Z directions defined in Figure 1.
Figure 1 - Geometrical arrengements used for Mossbauer spectroscopy and hysteresis loop measurements
I1 - RESULTS AND DISCUSSION
2 Y
The deviation of the hysteresis loop squareness (sq) from (<cos 8 ) 1"s it is de- termined from the Messbauer data could be understood in terms of both the demagneti- R zing field associatsd to the remanence and the different effect of the texture on (Icos OR[> and <cos B R > . In particulate media formed by independent needle-like particles shape anisotropy imposes the easy axis of magnetization for each particle.
Then, ifathe zagnetic interaction among the particles is negligible the deviation of sq/(<cos eR)) ratio from one must be attributed to the texture.
In order to determine if the demagnetizing field associated to the remanence of the tape has soms influence on the single domain magnetic moment orientation, we can measure (cos 8 > values in the zero field Mossbauer spectra of magnetized and demag- netiz d samples? We have indeed verified that no differences exist among both <cos 8 8 ) values. There ore, wg may safely attribute to the texture the differences
R h
among <IcosQRl> and ( < cos eR) ) as deduced by hysteresis loop and Mossbauer spec- troscopy respectively.
The assembly of magnetic moments along the direction ( 8 , d ) associated to each par- ticle, constitutes the set of elements of the magnetic texture of magnetic tape~.~The magnetic texture function D(8 4 ) may be developped in terms of real harmonics Z
/9/ : M' M 1
where e M and are the polar and azimuthal angles of both the quantization axes of
C?
the J'~e absorber nuclei in the tape and the magnetic moment of the single domain
8 -Fe 0 particles. The contribution of the different terms on equation (1) depends on bogh the symmetry of the particle distribution in the tape and on the experimental 3 technique used.
In the case of zero magnetic field Mossbauer measurements, relative angles between the direction of propagation of$-ray and the direction of the local magnetic moments can be calculated from :
where A / Atot is the relative area of the middle lines in the six lines Mossbauer spectra. 2.5
Therefore, ig order to evaluate the te3ture function D(8 ,d ) it is necessary to cal- M M
culate (cos Q R ) . By expressing<cos Q ) in terms of the texture function and using the values o f B R experimentally obtained by means of equation (2) it is possi- R
ble to calculate the coefficientes Dm of the equation (1):
1 2R
< ~ o s ~ @ ~ > = 1 cos 2 0 R D(oM,dM) d o M d a M
In the case of acicular particles oriented with a magnetic field along ,the travelling direction of the magnetic tape (Y axis), the particles distribution own an orthorho- mbic symmetry with the three two-fold axes directed along the X, Y and Z directions shown in figure 1. This symmetry is experimentally confirmed by both the Mijssbauer spectroscopy and hysteresis loop measurements (Table I) which sow that X, Y and Z are unequivalent axes and that they are two-fold axes.
Therefore, taking into account both that the Mijssbauer spectroscopy measurements only depend on the terms of equation (1) having 1 2 with 1 and m even and the ulterior reduction in the expansion coefficients introduced by the ortkorhombic symmetry for the texture, equation (3) is rewritten as:
2n n 2
1 2 m m
<cos2 8 > = / / X 2 cos 8 Dl Z 1(8 ,O M M) sin8 dB dOM ( 4 )
R M M
0 0 1=0 m = O
even 1
The squareness of the hysteresis loop (sq) which directly measures ccose >can also R .
be developped using the texture function. In this case, the unique reduction In the number of terms is due to the symmetry of the texture. Therefore it can be written:
2a n
1 m m
~ C O S 8 I > = / / c C lcos OR\ Dl Z1(eM,OM) sineM doM dOM ( 5 ) R 0 0 1=0 m =O
even 1
First of all, we have evaluated the coefficients a? of the Dm parameters which are
defined as: 1
These al are function of geometry through: m
cos 6 = COSS cos 6 +sin6 sin 8 cos 4 cos $ m+ sin 8 sin 8 sin 6 sin # (7) m
The values of these coefficients for both Midssbauer and hysteressis loop measurements are summarized in table 11.
As it can be noticed, the a; coefficients with 1=6 are one order of magnitude smaller than those corresponding to 1<6. Hence, we will only take into consideration the contribution to the texture of the D; for 164. Finally thanks to 3 differents geome- tries, a set of six independent linear equations are obtained which allow us to dedu- ce six Dl coefficients m
The values of the different D~ paramete:s resulting from these equations are:
0 0 2 l O 2 4
D 0 = 0.28, D2 = -0.21, D = -0.1, D = 0.45, D = -1.13, D = 0.11. In Figure 2
2 4 4 4
we draw the resulting texture function D(0 M, @ ) for the 8 - ~ e 0 magnetic tapes as it is obtained from the obove mentioned procedure. M 2 3
JOURNAL DE PHYSIQUE
M6aabauer am ( 1 ) m
1 Squareness a1 (2)
Table I1 - Coefficients al of the different D~ parameters defining the texture rn
4 -1
Fig. - ~extu& as a function of-the polar angles ( REFERENCES
/1/ B.Spuznar and J-Spuznar, J.Magn.Magn.Mater. 43 (1983) 317
/2/ J.M.Greneche and F.Varret, J.Phys. C: Solid =ate Phys. 5 (1982) 317 /3/ K.Hanada and A.H.Morrish, IE& Trans. on Magn. MAG-12 (1976) 6
/4/ M.Kishimoto, S.Kitahorta and M.Amemiya, IEEE Trans. on Magn. MAG-19 (1983) 5 /5/ G.Bate in Ferrrornagnetic Materials, vol. 2, E.P.Wohlfarth ed. (North-Holland,
Amsterdam, 1980) p. 380
/6/ J.Crangle, Magnetic Properties of Solids, (Arnold, London, 1977)
/7/ S.Kitahata,M.Kishimoto and M.Amemiya, Magn. Magn. Mater. Conf., San Diego (1984).
J.App1. Phys. ( in press)
/8/ B.Martinez, J.A.Cusid6, A.Isalgu6, X.Obradors and J.Tejada, submitted for publi- cation
/9/ H.D.Pfanes and H.Fischer, Appl. Phys. 13 (1977) 317
