Journal of Magnetism and Magnetic Materials 157/158 (1996) 537-538 Journal of

N magnetism and magnetic materials

ELSEVIER

Elastic and magneto-elastic properties of Mn-rich manganese ferrites

v ° v

Y. K a w a i a V . A . M . Brabers b,* Z. S l m s a c

a Gakushuin University, 1-5-1 Meijiro, Toshima-ku, Tokyo, 171, Japan b Eindhoven University o f Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands

° Institute o f Physics AS CR, Cukrovarnickfi 10, 162 O0 Praha 6, Czech Republic

Abstract Measurements of the elastic tensor elements and magnetostriction constants in the temperature range of 100 to 300 K are

reported for MnxFe3_xO 4 (x = 1.05, 1.7 and 1.8), from which the magneto-elastic anisotropy K ' I and the coefficients B 1 and B 2 are deduced. The magneto-elastic anisotropy contribution to K 1 is found to be small compared with the magnetocrystalline anisotropy.

Keywords: Ferrites; Elastic coefficients; Magnetostriction constants; Jahn-Teller effect

The magnetostrictive properties of the cubic spinel ferrites are well documented in the literature [1] but there is only a rare knowledge of the magneto-elastic coeffi- cients B 1 and B 2 [2], which are determined by the magne- tostriction coefficients Ahk l and the elastic coefficients cij

according to the equations

B 1 = 3Amo(C12 - C i l ) / 2 , (1)

02 = -- 3/~111 C 4 4 " , (2)

In particular, this is due to the lack of data o n the elastic properties of the spinel ferrites.

Besides the fundamental interest in the study of mag- neto-elastic phenomena, the elastic properties are of tech- nological importance in the production, characterization and the physical properties of spinel ferrite films and multilayers. Having this in mind we measured the magne- tostriction and elastic coefficients of single crystalline manganese ferrites MnxFe3_xO 4 with x = 1.05, 1.7 and 1.8. For high manganese concentrations the magnetocrys- talline anisotropy K~ and the magnetostriction coefficient amo increase significantly with decreasing temperature, which is both attributed to the Jahn-Teller effect of the octahedral Mn 3+ ions [3,4].

An additional question arises now whether the mag-

* Corresponding author. Fax: +31-40-245-3587; email: brabers @tna.phys.tue.nl.

netic anisotropy K 1 is dominated by the magneto-elastic contribution K'I, determined by

K i = Bl~/(C~l -- c12 ) - B ] / 2 , 4 4 , (3)

or whether the crystal field contributions of magnetic ions dominate [5].

The magnetostriction was measured by means of the strain gauge technique on single crystals, which were grown from the melt with a floating zone method [4].

To obtain the complete set of elastic coefficients Cij two measuring set ups were used. By means of the first, Young's moduli were measured using a composite-bar resonator system [6] in the frequency range of 90 to 150 kHz in the longitudinal mode and at temperatures between 100 and 300 K. These measurements were performed on crystal bars of approximate dimensions 2.5 × 2.5 × 20 mm 3 oriented along the three principal crystallographic direc- tions (111), (110) and (100) in which also the external mechanical stress was applied. The ultra, sound velocity was measured by means of the second set up using a puls-echo technique [7] on plane-parallel polished crystals ( ~ = 5 mm, 12 m m ) i n the (110) direction at frequencies of 7 and 10 MHz and in the temperature range of 100 to 300 K. A longitudinal mode as well as two transversal modes, polarized in the (001) and (110), respectively, were used.

The results of the magnetostriction and elastic measure- ments for x = 1.05 and 1.8 are presented in Fig. 1 and Fig. 2, respectively. The coefficient A100 for x = 1.8 depends at temperatures below 180 K upon the rotation rate of the

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538 Y. Kawai et al. / Journal of Magnetism and Magnetic Materials 157/158 (1996) 537-538

cd 250 [3_

03 ; ~5o

0)

,4--

o 5 0 O

O +., ¢0 ¢6 klJ

Oll

Ol 2

0 4 4

, -=-- e - e - .-o- .~ - e- - o - e - e. -.o- .~ - ~ - o - ~ - e - o - - o - e - o - .

~Lll 1

-50 --,-,-,---,-,-*--,--*.-r-*-'-*- : , -50 100 150 200 250 ~300

Fig. 1. The M n L o s F e ~ . 9 5 0 4 •

250 o ~. 2.5 X " -3

150 o c o ¢6

O c - 4 ~ O O

50 c_ f / ) ~ . O

C- O) t6

Temperature (K)

elastic and magnetostriction coefficients of

. ..o, e _e . _c,. e . e , ..o- " e - • - o - - o - e --o- - e - e --o- -e - e - o . .

KI' =~=.,~"~" -2.5 ~c~.j~r-=~'~'~"

J o -7.5 j~ /=

o K 1 +_.

o~° _12.51 '~ 00 150 200 250 300 <

Tempera ture (K)

Fig. 4. The anisotropy constants K 1 (after Ref. [10]) and K'~ (this article) for MnLsFeL204.

200 C.b

c 100

0) o 0 O

O 4-, o)

--~ -1OO1o o klJ

Fig. 2. The MnLsFeL204.

200 ~-'a" ' e t ' e ' " ~ - e " - z - ' e - ~ - e ' ~ " e " a ' "1~'-~ " l ~ ' - m ' - ' l ~ la.-n.

O l l

~ .-0- e _ ~ . . c - e - e . -¢~ e - ~- .-o- "e - e ~ -e - e _e_ ,.o_ e _ e . "

0 4 4

~ ' 1 1 1

Z - : I Y ~ [ . . . . . . . . - ~ 1 0 , 0 Z

100

150 200 250 300 -1°°

Temperature (K)

elastic and magnetostriction coefficients of

X

0 0

c -

O

0

0 4 - .

C O 3

magnet ic f ield dur ing the measurement , showing an in- crease in absolute value wi th decreasing rota t ion rate. This implies that Am0 is t ime dependent , wh ich can be at- t r ibuted to the f reezing of the local J a h n - T e l l e r deforma-

t ions as suggested in Ref. [4]. This is also ref lected in the anomalous tempera ture dependence of the magneto-elas t ic coeff icient B 1 be low 180 K as shown in Fig. 3. For x = 1.7 a similar (but less pronounced) behav io r is ob- served as for x = 1.8. The room temperature data for the elastic coefficients c/j reported by Sakurai [8] for x = 1 are in close agreement with our data for x = 1.05. I f we include our early room temperature elastic data [9] for

Fe304 (Cll = 270, c12 = 157 and c44 = 63 GPa), we can observe a gene ra l t rend of the latt ice sof tening wi th the increase of Mn-concent ra t ion .

In Fig. 4 the exper imental data for K 1 for x = 1.8 [10] are compared wi th the magneto-e las t ic contr ibut ion K'~ calculated wi th formula (3). It appears that the magneto- elastic cont r ibut ion K~ is a lways posi t ive and small as compared wi th the exper imenta l values of K 1. It implies the magne t ic anisotropy of manganese- r i ch manganese fer- rites be low room tempera ture is domina ted by the crystal- field contr ibut ions of the magnet ic ions.

R e f e r e n c e s

¢6 4500

l

3 0 0 0 0 0

0 1500

©

, 0 O

©

C

-150~00 ¢6

~ ..ll~l -m - n~-u--m" =

.Y" [32

150 200 250 300

Tempera ture (K)

Fig. 3. The magneto-elastic coefficients of Mnl.05Fel.9504 (open symbols) and Mnl.sFel.204 (closed symbols).

[1] Landolt-B/Srnstein, Numerical Data and Functional Relation- ships in Science and Technology, New Series, Vols. l / I / 4 b (1970), I l I /12b (1980) and I I I /27a (1991).

[2] Y. Ishikawa and Y. Syono, J. Phys. Soc. Japan 31 (1971) 461.

[3] Z. Sim~a, V. Roskovec, P. Nov~k and V.A.M. Brabers, Czech. J. Phys. B21 (1971) 1181.

[4] V.A.M. Brabers, J. Klerk and Z. Sim§a, Physica B + C 86-88 (1976) 1461.

[5] P. Nov~k, Czech. J. Phys. B21 (1970) 259. [6] Y. Kawal and T. Ogawa, Phys. Status Solidi (a) 76 (1983)

375. [7] B. Chick, G. Anderson and R. Tmell, J. Ac. Soc. Am. 32

(1960) 186. [8] J. Saloarai, J. Phys. Soc. Japan 19 (1964) 311. [9] V.A.M. Brabers, unpublished results.

[10] W. Palmer, J. Appl. Phys., Suppl. 33 (1962) 1201.