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Re-entrant ferromagnetism in the ThFe3-x Alx system
de Groot, C.H.; Buschow, K.H.J.; van Bockstal, L.
Publication date
1996
Published in
Journal of Magnetism and Magnetic Materials
Link to publication
Citation for published version (APA):
de Groot, C. H., Buschow, K. H. J., & van Bockstal, L. (1996). Re-entrant ferromagnetism in
the ThFe3-x Alx system. Journal of Magnetism and Magnetic Materials, 157&158, 641-642.
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N
ELSEVIERJournal of Magnetism and Magnetic Materials 157/158 (1996) 641-642
journal of
magnetism
and
magnetic
materials
Re-entrant ferromagnetism in the ThFe3_xA1 x system
C.H. de Groot a,b,*, K.H.J. B u s c h o w a, F.R. de Boer a
a v / d Waals-Zeeman Institute, University o f Amsterdam, Valckenierstraat 65, 1018 XE Amsterdam, The Netherlands b Philips Research Laboratories, Prof. Holstlaan 4, 5656 AA Eindhouen, The Netherlands
A b s t r a c t
The magnetic behaviour of ThFe3_xA1 x of which the parent compound displays re-entrant ferromagnetism, has been studied. Substitution of A1 leads to an expansion of the lattice which is the largest in the basal plane. The Curie-temperature decreases monotonously from 428 K for x = 0 to 341 K for x = 0.33. The antiferromagnetic temperature range decreases and is completely suppressed for x > 0.33.
Keywords: Re-entrant ferromagnetism; Antiferromagnetism
All RFe 3 compounds with R = rare-earth, Y or Th crystallize in the rhombohedral Be3Nb-smacmre [1], (space group R3m, also called PuNi3-smacture) which has three inequivalent Fe-sites and t w o inequivalent R-sites. The F e - F e distances are m u c h smaller than the F e - R dis- tances. The compound ThFe 3 is exceptional in its mag- netic properties because it displays so-called re-entrant ferromagnetism [2]. This feature makes the series ThFe3_xA1 x interesting for studying the origin of antifer- romagnetism and its dependence on interatomie distances in Fe-based intermetallics.
Samples ThFe3_xA1 x with x = 0, 0.033, 0.083, 0.167, 0.333 were prepared by arc melting starting materials of at least 99.9% purity. After 'arc-melting the samples were wrapped in Ta-foit, sealed in an evacuated quartz tube and
annealed for two weeks at 1000°C. The X-ray diffraction
diagrams showed that the crystal structure of all samples corresponds to the rhombohedral Be3Nb-stmcture. The samples with x = 0.033 and x = 0.083 were single phase while the parent compound showed a small ( ~ 5%) amount of T h z F e 7 (a ferromagnetic phase, also identified by its T c of 570 K [3]). The samples with higher A1 concentration showed a small amount of an unidentified second phase. In Fig. 1 the lattice constants are plotted versus the A1 concentration. The expansion is monotonous in both direc- tions and slightly larger in the basal plane than in the c-direction.
* Corresponding author. Fax: + 31-40-2744-282; emaiI: grootc @ natlab.research.philips.com.
o~
5.26 25.3 5.24 ~ c I ~ ~ ~EI~ 5.22 5.20 I ~ I 25.0 0 0.1 0.2 .... 0.3 0.4 X ' ' ':Fig. I. Lattice constants o f ThEe 3_ x A l x compounds. 25.2
°Z
25.1 4 ¸ ' ~ ' 3 ::t ~ 2 ¸~ i i i i i i i i i i i
= i i
¢ ~ x x X X X X X X X X X X X ~ x x x x O O D O O O D O O O O ~ O O O O O O O O o I [ J I I 1 2 3 4 5Brr]
Fig. 2. Magnetic isotherms at 5.0 K for ThFe 3_ xA1x compounds, taken in decreasing field. The solid line is a guide to the eye. 0304-8853/96/$15.00 Copyright © 1996 Elsevier Science B.V. All rights reserved.
642 C.H. de Groot et al. / Journal of Magnetism and Magnetic Materials 1 5 7 / 1 5 8 (1996) 641-642
Table 1
Magnetic properties of T h F e 3 _ x A l x . T m is the minimum of the magnetization, 7"1, 2 are the points of steepest slope. For the compound with x = 0 a correction has been made for the amount of Th 2 Fe 7 Compound x 0 0.033 0.083 0.167 0.333 M s ~ 5 K ( ~ B / L u . ) 4.79 4.65 4.65 4.43 4.19 MR ( ~ B ) 1.60 1.55 1.56 1.49 1.42 T 1 (K) 188 214 229 T m (K) 264 257 245 229 176 T2(K) 300 287 268 Tc(K) 428 422 411 393 341
The magnetic measurements were made on powdered samples in a SQUID magnetometer in the temperature range 5 - 3 0 0 K in magnetic fields up to 5.5 T. A b o v e 300 K, the measurements were made on polycrystalline mate- rial on a home-built Faraday balance. The magnetization in decreasing magnetic field is displayed in Fig. 2, and shows ferromagnetic behaviour for all samples at 5 K. Magnetic measurements on the parent compound using the neutron depolarization technique show ferromagnetic behaviour at 5 K in zero field [2], therefore we can conclude that the decrease in magnetization at low fields is due to domain formation. Substitution of Fe by A1 causes a decrease in the saturation magnetization, which is due to the dilution of the Fe-sublattices as well as to a decrease in F e - m o m e n t from 1.6 / ~ B / F e for x = 0 to 1.4 / x B / F e for x = 0.33 (see Table 1).
Fig. 3 displays the magnetization as function of temper- ature in a field of 0.1 T (two samples are left out for reasons of clarity). It shows a decrease in Curie-tempera- ture with increasing A1 concentration as can be explained by the dilution and the decrease in Fe-moment.
3 2.5 2 -4 .,,z. " ~ 1 5 . = . 0.5 0
I+×=o.o<
100 2 0 0 3 0 0 1" [K]Fig. 3. Temperature dependence of the ThFe3_xA1 x compounds at 0.1 T. 4 0 0 500 magnetization of ...I 0 0.1 0.2 0.3 0.4 0.5 B [U
Fig. 4. Magnetic isotherms for ThFe 3. The lines are guides to the eye.
In the parent compound antiferromagnetism sets in at T 2 = 300 K and disappears at T 1 = 188 K. Fig. 4 shows the magnetic behaviour just below and above the second tran- sition. The transitions are not accompanied by a structural change or sudden change in lattice constants [2]. At 275 K, a metamagnetic transition appears around 0.15 T and at 0.5 T the antiferromagnetic behaviour is completely sup- pressed.
A1 substitution limits the temperature range in which antiferromagnetism appears and for x = 0.167, the antifer- romagnetic behaviour is barely visible. The transition T 2 can tentatively be explained as a first-order antiferro-fer- romagnetic transition, which is driven by the thermal expansion. A1 substitution expands the lattice which causes a decrease in transition temperature.
The inset of re-entrant ferromagnetism ( T 1) shifts to higher temperatures with increasing A1 concentration, while
the compounds Th0.9R0.1Fe 3 ( R = Y , Gd or Lu) show
antiferromagnetic behaviour down to 5 K [4,5]. Since neither Th nor Y or Lu have a magnetic moment, this indicates that the re-entrant ferromagnetism also critically depends on the F e - F e distances. More detailed explanation should await for neutron diffraction measurements, which are currently in progress.
Acknowledgement: This work has been supported by
the Dutch Technology Foundation (STW).
References
[1] J.R. Thomson, J. Less-Common Metals 10 (1966) 432. [2] A.M. van tier Kraan, J.N.J. van der Velden, J.H.F. van
Apeldoorn, P.C.M. Gubbens and K.H.J. Buschow, Phys. Sta- tus Solidi (a) 35 (1976) 137.
[3] K.H.J. Buschow, J. Appl. Phys 42 (1971) 3433. [4] J.E. Greedan, AIP Conf. Proc. no. 5 part 2 (1971) 1425. [5] C.J. Kunesh, K.S.V.L Narasimhan and R.A. Butera, J. Phys.
