Magnetic properties and magnetostriction in Tb0.5Dy0.5(Fe0.9MnxAl0.1 − x)1.95 compounds

Jewnal of nT netlsm

•IM ELSEVIER

Journal of Magnetismand Magnetic Materials 152 (1996) 379-382

magnetic materials

Magnetic properties and magnetostriction in Tb0.sDy0.5(Fe0.9MnxAl0.1-x) 1.95 compounds Gao Youhui

*, J . H . Z h u , L i - C h i T a i

Central Iron and Steel Research Institute, Beijing 100081, China

Received 31 March 1995; revised 12 June 1995

Abstract The discovery of the giant magnetostriction in RFe 2 alloys was a breakthrough. However, the compounds possessing huge magnetostriction at room temperature have large magnetic anisotropy. A number of papers have reported work to reduce the anisotropy by substituting the elements in RFe 2 with other rare earth, transition metal and group III elements. In this paper, samples of Tb0.sDyo.sFeL95 were prepared by substituting part of the Fe by Mn and Al. The metallographic organization of these compounds, depending on Mn and A1, and the magnetization and magnetostriction of the compounds Tbo.sDyo.5(Feo.9MnxAlo.1_x)1.95 were studied. It is found that AI can improve the crystalline state of Tb0.sDyo.~Fel.95, and that both Mn and AI can reduce the magnetic anisotropy.

1. Introduction The huge magnetic moments and high anisotropy found in the rare-earth-iron intermetallic compounds have been attractive in the study of magnetic materials. The Laves phase rare earth-iron compounds with high magnetostriction values have attracted the attention of many researchers, a great deal of work has been carried out since Clark and his co-workers reported their findings for Tb(Dy)Fe 2 [1]. It seems that a final stage was reached when the compound Tbo.27DYo.73Fe2 (Terfenol-D) was found with to have a low anisotropy, a high ordering temperature and optimal magnetic properties. The material possesses low crystalline anisotropy, large magnetostriction and has great application potential in transducers and actuators [2]. However, the material suffers from some disadvantages: (1) it does not stand intense

* Corresponding author.

shear forces [3], (2) the skin effect limits the actuation speed (unless the alloy is laminated, but it is difficult to load with high-pressure forces) [4]. Based on this composition, researchers have modified the magnetic properties of the alloy by the addition of 3d transition metal or some group III elements to replace iron, such as Mn, Co, etc. Substituting iron with Mn reduces the anisotropy of the alloy, and with Co raises the Curie temperature. However, by replacing some iron with Mn or with Co it is difficult to obtain high orientated samples [5]. Many researchers have recently chosen AI as a substitute to improve the magnetic properties of Tb0.zTDy0.73Fe2 alloy because the addition of A1 to a binary F e - A I system can increase the magnetostriction and electrical resistivity, and can reduce the magnetocrystalline anisotropy. Prajapati [6] investigated the remanence, coercivity, magnetomechanical coupling, resistivity and other physical properties of the alloy Tbo.27Dyo.73(Feo.9Alo.1)l.95.

0304-8853/96/$15.00 © 1996 Elsevier Science B.V. All rights reserved SSDI 0304-8853(95)00470-X

380

G. Youhui et aL /Journal of Magnetism and Magnetic Materials 152 (1996) 379-382

The present paper reports on the magnetostriction, microstructure and some other properties of the alloys Tbo.sDyo.sFel.95 and Tbo.sDyo.5(Feo.9

3. Results and discussion

In a metallographic examination, the three samples Tb0.5Dyo.5Fe 1.95, Tbo.5Dy0.5(Fe0.9Mn 0.1)1.95 and Tbo.sDY0.5(Fe0.gAlo.i)l,95, obtained using the same technical procedures, were investigated by optical microscopy (Fig. 1). It was found that: (1) in the alloy Tbo.sDy0.sFe1.95 the cylindrical crystalline grains that grow are very tiny. An X-ray diffraction examination showed that this sample contained an excess RE-rich phase besides the main phase (RFe 2 Laves phase). (2) In the alloy Tbo.sDyo.5(Fe0.9 Mn0.1)1.95, the cylindrical grains are very bulky, but not quite regular. It grows branched grains that deviate from the axis direction. (3) In the alloy Tb0.sDYo.5(Fe0.9Alo.1)1~95 the grains are not only bulky, but also parallel to the axis direction of the rod sample. For the last two samples, X-ray diffraction analysis showed that the proportion of the second phase is markedly reduced in the alloy. The magnetization curves of the compounds are shown in Fig. 2. The substitution of iron with Mn and Al in Tbo.sDYo.sFe1.95 can increase the magnetization at low field and can yield saturatation easily. It can therefore be inferred that the addition of Mn and AI apparently reduces the magnetocrystalline anisotropy of the alloys; but also reduces the saturation magnetization. However, by replacing some of the Mn of Tb0.sDyo.5(Fe0.gMn0.1)l.95 with A1, it re-

M n x m l o . l _ x ) l . 9 5 (0 < X < 0 . l ) .

2. Experimental

The alloys were prepared from metals of high purity - Dy 99.9%, Tb 99.9% - and electrolytic iron, aluminum and manganese. According to molecular equations Tbo.sDyo.5(Feo.9MnxA10.1_x)1.95 (x = 0, 0.03, 0.05, 0.1), these metals were weighed and mixed; initially alloyed together by arc melting in a water-cooled copper crucible several times to obtain homogeneous ingots; and then cast into polycrystalline alloy rods. All samples were prepared using the directional solidification method. Transverse sections of the rod samples were polished and macroetched with a reagent (4 ml nitric acid and 96 ml alcohol), and then examined by optical microscopy. Under protective Ar, the polycrystalline samples were held at 950°C for 30 h, ground into powder, and investigated by X-ray diffraction. The magnetostriction, magnetization and Curie temperatures of all the samples were measured using the standard strain gauge technique, VSM and a Faraday magnetometer, respectively.

a

b

c

axis direction. Fig. 1. Metallographic organization of (a) Tbo.5 Dyo.5 Fe 1.95, (b) Tbo. 5Dyo. 5(Feo. 9 Mn o.J )1.95, and (c) Tbo. 5 Dyo.5(Feo.9 AI o.1)1.95. Magnification ×40.

381

G. Youhui et al. /Journal of Magnetism and Magnetic Materials 152 (1996) 379-382

O3 0 •

•

I

"

•

I

"

"

I

"

"

!

"

"

!

"

"

!

'

O.8 0.7

Eu

(14

1

•

0

.

.

L

.

.

.

I

2

0

.

.

.

4

I

.

I

,

,

S

k-r~m

I

.

.

.

II

I

•

I

10

I

12

F.= n (KOe)

duces the anisotropy and does not alter the saturation magnetization of the compounds (see Fig. 2). For the magnetostriction versus applied field curves the same reasoning applies, which explains the above results (Fig. 3). The curves of the differential susceptibility versus the applied field (Fig. 4) indicate that the peaks of the differential susceptibility, XO, increase, and simultaneously move toward the low field after substituting the iron with Mn and A1 in Tbo.sDyo.sFel.95. For Tb0.sDyo.sFet.95, when ( Xd)~a~ = 9.66, H = 20 k A / m ; for Tb0.sDy0.5(Feo.9Mn0.t)1.95, when (Xd)max = 12.68, H = 14 k A / m ; and for Tb0.sDyo.5(Feo.9 Alo.1)t.95, when (Xd)m~x = 14.65, H = 11 k A / m . According to these data, the effect of AI on the susceptibility is more remarkable than that of Mn. The effect is quite beneficial to the design of transducers and actuators: the addition of A1 can (1) decrease the dc field-biased intensity at the device work point, (2) increase the actuation speed and

Fig. 2. Magnetizationcurves. 4 44 t e [ i. ~ , • • . . . . 21mr}

14

!:

12

i

84 1 ....

la4 ~, •.

--F~e

,.--171S77~7" - - -

1500

r.~.

~,

t. f i.l ,

f

t,

1'

- ' n' ,~ a, " ~ ~ ¢r.,, "ul

/// , "

4

II~/ '

..... ~ . ~

~ 2

0 008 I

O 0

,

,

,

I

,

4O0

,

,

,

|

800

t

i

A

,

I

A

,

1200

APPt.L;O MELO (r~/m)

Fig. 3. Magnetostrictioncurves.

,

nJ~

1.08

1,B

,

1800

~ ~

tKt~

Fig. 4. Differential susceptibilities of RFe].95 (--), R(Feo.gMno.05Alo.05)l.95 ( - - - ) , R(Feo.gAloA)I.95 ( . . . ) and R(Feo.gMno.1)]95 (---) (R is rare-earth Tbo.sDyo.5).

382

G. Youhui et al. /Journal of Magnetism and Magnetic Materials 152 (1996) 379-382

Table 1 Magnetic properties of the samples (R is rare-earth Tb0.sDy0.5) Alloys Density (g/cm 3) Tc (K) As (ppm) RFel.95

8.8749 8.7515 R(Fe0.9Mn0.o3AIo.07)1.95 8.7771 R(Feo.9Mn0.05Alo.o5)1.95 8.8448 R(Feo.sMn0.l)l.95 8.9887

R(Feo.9 Alo. 1)1.95

643 558 562 568 588

2230 1641 1500 1855 1650

wall motion. But compared with the effect of adjusting the T b / D y ratio, the effects of Mn and A1 on the anisotropy are weak. Thus, under the proper T b / D y ratio, the compounds whose properties can be improved with the addition of A1 must be more advanced.

4. Conclusions magnetomechanical coupling, and (3) reduce energy losses. Fig. 4 shows the effect of the addition of Mn and A1, which also reduces the magnetocrystalline anisotropy of the compounds. Compared with Tb0.sDyo.sFel.95, the Curie temperatures and densities of compounds of nominal composition Tbo.sDyo.5(Feo.9MnxA10.1 x)1.95 show some reductions (see Table 1). During the metallographic examination using the reagent 4% nitric acid/alcohol, we found that it was more difficult to macroetch the samples with added AI than the other samples. Therefore, in the alloy Tbo.sDyo.sFel.95 the replacement of iron with A1 can improve the anticorrosion properties of the compound. The reason for the above results, generally speaking, is that A1 greatly improves the crystalline condition, and the sample easily grows regular bulky cylindrical grains, which greatly reduce the boundary energy in the alloys, and weaken the factors that hinder the domain

(1) AI improves the crystalline condition, and cylindrical grains grow easily in the compounds. (2) Both Mn and A1 reduce the magnetocrystalline anisotropy, and extend the applications of the alloy. (3) A1 and Mn decrease the Curie temperatures and densities of the compounds generally.

References [1] A.E. Clark, in: Ferromagnetic Materials, vol. 1, ed. E.P. Wohlfarth (North-Holland, Amsterdam, 1980), p. 531. [2] D.C. Jiles, J. Phys. D: Appl. Phys. 27 (1994) 1. [3] J.R. Oswin, R.J. Edenborugh and K. Pitman, Aerospace Dynam. 24 (1988) 9. [4] N. Galloway, R.D. Greenough and M.P. Schulze, J. Magn. Magn. Mater. 119 (1993) 107. [5] E. Clark, J.P. Teter and M. Wun-Fogle, J. Appl. Phys. 69 (1991) 15. [6] K. Prajapati, A.G. Jenner and R.D. Greenough, IEEE Trans. Magn. 29 (1993) 3514.