Journal of Magnetism and Magnetic Materials MO-144 tlY!ki; 2;: 1?7

ELSEVIER

Miissbauer spectra of Hf ,-,Ta,Fe, during ball milling T. Saito, H. Takano *, S. Murayama, K. Hoshi

Mutoran Institute of Technoiogy, Mumran, Hokkddo 0.50, Jopon

Abstract Changes in the magnetic properties of the intermetallic compound Hf,L,Ta,Fe:e, upon high-energy ball milling are

investigated by MSssbauer spectroscopy. X-ray diffraction and magnetization measurements suggested that a little disorder generated by ball milling significantly affected the magnetic properties in this compound system. The features of the Mijssbauer spectra of ball-milled samples are clearly different from those of the unmilled sample. This indicates that the baE milling produces a different phase from that of the unmilled sample.

We have studied the structural features and the mag- netic properties of pseudobinary alloy Hf -,Ta,Fe, after h-11 m;ll;nn I.., s.,.P.I..c. -4 Y m.. A:cFm, rrms,e, . ..nm..dkn ““I. . . . . . . ..I 6 Y, LIIIua..l “A xx-e”, Y.aLaUI.“L,.CI ..,I ~~~Yp.~.s&.U-

tion measurements and Mtissbauer sp:ctroscopy. We re- ported the changes of the X-ray diffract ion patterns and the magnetization for crystalline Hfo,sTa0,5 Fe, after milling in Ref. 111. The crystalline compound tlf,,Ta,,Fe, with MgZn,-type structure is antiferromagnetic below TN = 260 K [2] and the amorphous Hf,5Ta,,5Fe, ferromagnetic below T, = 120 K [3]. In Arrott plot analyses of magneti- zation, Hf,sTa,,Fe, milled for 6 h was ferromagnetic. This indicates that a transition from antiferromagnetic to ferromagnetic state occurs with increasing milling time. The crystalline Hf,,3Ta,,Fe2 is also antiferromagnetic below TN = 220 K and the amorphous Hf,,Ta,,Fe, fer- romagnetic below ‘Z’., = 70 K. Since the N&e1 temperature TN and the Curie temperature T’ for Hf,,Ta,,Fe, are iuwer iii&i ihose r”rjt i-i~o,5T;ilo,sFC2, we Ciiri 0bkiii i8 p21i& magnetic state in the Hf,-,Ta,Fe, at room temperature foi x = 5.7 more wily ,I~, .“, p... A.- x Y!T 0.5, so !#e in\*&- gated the magnetic properties of Hfe,,Ta,,Fe, by MSssbauer spectroscopy. MSssbauer spectra are collected on a conventional constant-acceleration spectrometer with “CoRb source. This system can be operated between 20 and 300 K.

The intermetallic compound Hfe,,Ta,,Fe, was ob- tained by the sazte method as Hf,,Ta,,Fe, El]. The annealing of the alloy was performed at 1000°C for a week in a high vacuum, and was crushed in a ceramic mortar with a pestle. The sample was milled in a MlTSUI AT- TRITOR (Mitsui tdiike Eng. Corp., MAOlD) with a balt- to-powder ratio of 20: 1. The milling ball was made from AlaO, having a purity of 92%.

’ Corresponding author. Fax: +81-14347-313 7.

X-ray diffraction and the magnetization measurements were performed before Miissbauer specuoxopy. X-ray d:cc”nn*:r.r m.d+amr .,,PCP *nlrpn at rnnm ,apmnrrrhrrp Id”” Y~A..UYI~Y”. L’U..“L.W 1.w.1 .U.“Y U. .“V... .“.qa-.U”.- .%.#.a.~

Cu Kol radiation. The magnetization between 10 and 340 K in fields of up to 5 T was measured with a SQUlD magnetometer. The intensity of the Bragg peaks decreased gradually and the peaks became broader with increasmg milling time. The magnetization between 10 and 340 K increased with increasing milling time. We found that Hf,,Ta,,Fe, after n.illing was ferromagnetic and the Curie temperature (T,) was around 200 K. The changes of the X-ray diffraction pattern and the feature of the magne- tization for Hf0.3Tae.7Fe2 after milling were similar to those for Hf,sTa,-,,Fe, [l]. These imply that for Hf,sTa,,,Fe, as well as Hf,,,Tae,,Fe, a little disorder is generated by ball milling and the material did not begin amorphization.

%,2--L ^..^_ l-r3.- c c,, TmT T.. ..r..&ll..A ..“..I ivIusJIJIucI zq.rGbblO LVI Luo.p~.,Fc~ ULIIIIUICU muu milled for 24 h are shown in Figs. 1 and 2, respectively. Above T 1 N or Tc the spectrum SLOWS a Sdi doub!tt. Nishihara and Yamaguchi [2] reported the magnetic and Miissbauer study of crystalline Hf,-,Ta,Fea, and ob- served a quadrupole doublet above 340 K for x = 0.2. The doublet at 294 K for unmilled and milled samples seems to be mainly due to electric-quadrupofe interaction. The width of the doublet is a little broader than a natural width, and we need to consider the other contribution besides quadrupole interaction. For crystalline HfcJTa,,Fe, mag- netic splitting is observed with decreasing temperature, and simultaneously a weak non-magnetic subspectrum remains below 200 k. After 24 h of ball milling, the spectrum at 200 or 150 K shows a strong ncm-magnetic spe&um superposed on a weak broader specmrm due to the occur- rence of the static internal field, The spectrum after 24 h of h!l milling at 20 K is similar to one of the ttnmilled sampic ai 29 ii. We z+suineri that the contrbutiou tu tbf:

03048853/95/@9.50 6 1995 Elsevier Science B.V. All rights reserved SSDI 0304-8853(94)01336-5

312 T. Saito et 01. /Journal of Magnetism and Mugnetic Materials 140-144 (1995) 311-312

, 7 I 1 I I I

Hf*.aTao.,Fe2 6

t\

-e-- unmilled -+-- milled for 6h ++- milled for 24h

-I (K)

Fig, 1. Miissbauer spectra at various temperatures for unmilled %Jade2.

broadening and !hc splitting of these spectra except for qiradntpole interaction was the distribution of the internal field. and analyzed them by the method of Hesse and Ribartsch [4]. The sharp peak centered at 2 T characterizes the distributiorr of the internal field Car Hf,,,Ta,,Fe, unmilled and milled for 24 h at 294 K. The distribution of

1 . A

Hfo aTa,, ,Fe$milled for 24h) . I I I I a I .I,

-6 -4 -2 0 2 4 6 velocity (mmlsec)

Fig. 2. Miissbauer spectra at various temperatures for HC,,Ta, ,Fe2 milled for 24 h.

!O

Fig. 3. Temperature dependence of the hyperfine field for Hf,,3Ta,,,Fe2 unmilled and milled for 6 and 24 h. Solid lines are guides for the eye.

the internal field for these two samples has three peaks under 200 K. The broadest peak of the distribution is over he range uL 5 iu B T ior iuc uo&iiu~ sumyic i& 4 IV “r T for the milled sample. Milling time dependence of the spectrum broadening seems in agreement with that of the magnetization. Next we estimated the average field (H) using the same procedure as Murayama et al. [3]. We regard the average field (H) as the static hyperfine field (Hhl) as well as Murayama et al. Temperature depen- dence of ( H,,) is shown in Fig. 3, where we consider the value of (Hhf ) at 294 K a starting point. The static hyperfine field (Hhf) changes greatly with increasing milling time, especially around 200 K. The large change around 200 K seems to be consistent with a ferromagnetic transition in a milled sample.

In conclusion, the ball miHing process generates a little disorder in a crystai, and the magnetic siaie after miiiinp is different from that of the unmilled sample.

References

[l] H. Takanc, T. Saito, S. Murayama and K. Hoshi, Jpn. J. Appl. Phys. 32 (1993) Suppl. 32-3, 421.

[2] Y. Nishihara and Y. Yamaguchi, J. Phys. See. Jpn. 52 (1983) 3630.

[3j S. Murayama, H. Inaba, K. Hoshi and Y. Obi, J. Phys. Sot. Jpn. 61 (1992) 3699.

[4j J. Hesse and A. Riibartsch, J. Phys. E: Sci. !cz!zm. ? (1974) 526.