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Submitted on 1 Jan 1979
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Magnetic properties of RE(FexRh1-x)2, RE = Y, Gd, Dy, Ho
J. Hrubec, W. Steiner
To cite this version:
J. Hrubec, W. Steiner. Magnetic properties of RE(FexRh1-x)2, RE = Y, Gd, Dy, Ho. Journal de Physique Colloques, 1979, 40 (C5), pp.C5-198-C5-199. �10.1051/jphyscol:1979573�. �jpa-00218990�
Magnetic properties of RE(Fe^Rh
1_
JC)
2, RE = Y, Gd, Dy, Ho
J. Hrubec and W. Steiner
Inst. f. Angew. Physik, T.U. Wien, Karlsplatz 13, A, 1040 Wien, Austria
Abstract. — YRh2 can be characterized as a Pauli-paramagnet. At 4 K no ordering temperatures could be detected for Y(Fe, Rh)2 from bulk magnetic measurements, whereas at 5 K the 57Fe Mossbauer investigations reveal magnetic hyperfine interactions. For RE = Gd, Dy, Ho a ferrimagnetic coupling is observed in the Fe substi- tuted compounds. The Curie temperatures can be analyzed for constant x using a de Gennes function. The con- centration dependence of Tc might be explained by a distance dependent Fe-Fe interaction.
In cubic Laves phases R E C F e ^ M ^ J j , RE = Y, Gd, Dy, Ho and M = Al, Co the Fe-Fe interaction is mainly determined by the M atoms. For Y(Fe, Al)2
no magnetic ordering could be detected at 4 K from bulk magnetic measurements and also from Moss- bauer investigations only quadrupole split spectra are obtained at 5 K up to x = 0.3 [1]. Whereas for Y(Fe, Co)2 (x < 0.1) from <r2(H/cr) diagrams no magnetic ordering temperatures could be extrapo- lated, magnetically hyperfine split spectra were observed at 5 K [2]. To get further informations about the Fe exchange interaction in isostructural compounds, the isoelectronic Rh has been exchanged for Co, since the existence of RERh2 cubic Laves phases was reported [3, 4].
Samples with MgCu2 structure could only be prepared up to x = 0.3. For all series the lattice spacings decrease with increasing x. Magnetic mea- surements in fields up to 6.5 T have been performed in the temperature range 2-270 K. 5 7Fe Mossbauer spectra were recorded at 5, 80 and 300 K.
From the temperature independent susceptibility of YRh2 (x = 2.06 x 10~4 emu/mole) a Pauli-para- magnetic behaviour can be concluded similar to YCo2 [5]. At the lowest temperature for Y(Fe, Rh)2
no magnetic ordering could be detected neither from plots a2{Hja) nor from the initial susceptibility. The susceptibility was determined using the linear part of a{H) (H > LOT) at a fixed temperature. Sub- tracting XvRh, from
XY(Fe,Rh>2 a n^ assuming a Curie Weiss law (6 = — 25 K independent of x) jUrff/Fe = 3.5 ( + 0.25) ^B was calculated for x < 0.2 and 3.9 ( ± 0.25) (i* for x = 0.3 (figure 1). These values might be attributed to the Fe atom itself and
to the surrounding Rh atoms and are in view of the overall error in agreement with Ateff/Fe = 3.87 jtB
extrapolated for binary (Fe, Rh) alloys with compa- rable Fe concentrations [6]. At low temperatures the deviations from the Curie Weiss behaviour (figure 1) might be due to Fe-Fe exchange interactions as indicated by the magnetically hyperfine split Mossbauer spectra at 5 K. Similar results are also obtained for Y(Fe, Co)2 (x < 0.1) [2].
Fig. 1.—Reciprocal susceptibility of Y(Fe. Rh)2 (+ x = 0 1.
A x = 0.2, D x = 0.3).
JOURNAL DE PHYSIQUE Colloque C5, supplément au n° 5, Tome 40, Mai 1979, page C5-198
Résumé. — Dans cette série : YRh2 est un paramagnétique de Pauli. Y(Fe, Rh)2 présente une structure hyperfine magnétique en effet Môssbauer sur le fer 57 à 5 K, mais les mesures macroscopiques d'aimantation à 4 K ne permettent pas de détecter un ordre magnétique. Enfin les composés avec RE = Gd, Dy, Ho sont ferrimagné- tiques ; leurs températures de Curie Tc h x fixé sont en accord avec une fonction de de Gennes ; par ailleurs la variation de Tc(x) avec x pourrait s'expliquer par une interaction fer-fer dépendant de la distance.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979573
MAGNETIC PROPERTIES OF RE(Fe,Rh,-J,, RE = Y, Gd, Dy, Ho C5-199
Above the Curie temperature the susceptibility of RERh,, RE = Gd, Dy, Ho leads to
respectively assuming a Curie Weiss behaviour.
Comparing this with the value for Gd3+ a negligible peff/Rh can be concluded in the paramagnetic region.
Using the above peff/Ho and assuming the same peff/Fe as determined in Y(Fe, Rh), agreement was found for Ho(Feo.,Rh0.,),. A comparison with other samples was not practicable because of the high Curie temperatures and the possible presence of small amounts of second phases, not observed in Debye Scherrer photographs.
The saturation magnetization, defined as ~ ( 4 . 2 K, 6.5 T), for RE = Gd, Dy, Ho indicates a ferrimagnetic coupling between the RE and Fe moments (figure 2).
From GdRh, pRh
-
0 pB has to be concluded, accep-ting pG, = 7.0 y. Assuming this to be valid for Fig. 2. - a ) Magnetization v (at 4.2 K and 6.5 T) open symbols and remanence a, (at 4.2 K) full symbols ( 0 Gd, A Dy, Ho)
Gd(Fe, Rh)2 p ~ e = 2.6y 2.5 and 2.2 can be eva- and b) Curie temperature of RE(Fe,Rh,-,)2 ( 0 x = 0.0,
luated for x = 0.1, 0.2 and 0.3 respectively. Never-
+
x = 0.1, A x = 0.2, x = 0.3). The lines connect thetheless these values are too large compared with pFe 1 pB in Gd(Fe,,,Al0~,), [I], indicating that a certa~n amount of the observed moment should be ascribed to the Rh atoms. No complete saturation was obtained for RE(Fe, Rh),, RE = Dy, Ho caused by a high anisotropy. This is also supported by the appearance of a remanent magnetization (figure 2) and a critical field at 4.2 K, both increasing with increasing x. Furthermore maxima in o(T) were obtained at low fields with increasing temperature after cooling the sample in zero field, indicating small domain wall widths. Assuming pRh -- 0 pB to be valid for RERh,, RE = Dy, Ho the RE moments must be reduced compared with those of RE3+ due to crystalline electric field effects.
Starting from RERh, the Curie temperatures (determined from plots 02(H/o) and initial suscep- tibility measurements) are drastically elevated for
values calculated by a de Gennes function normalized to Gd(Fe, Rh), according to T, = a(g - 1)' J(J
+
1).x = 0.1, followed by a much smaller increase for further Fe substitution (figure 2). The Curie tempe- ratures of RERh, can be described by a de Gennes function
171.
Also for constant x the ordering tem- peratures of the Fe containing samples could be analyzed using the same relation (figure 2). Assuming a statistical distribution, for all investigated series the most probable Fe-Fe distance is 40, 19 and 9%
larger than the appropriate nearest neighbour dis- tance for x = 0.1, 0.2 and 0.3 respectively. Therefore the striking change of the concentration dependence of the Curie temperature at x = 0.1 could be ascribed to a distance dependent Fe-Fe interaction.
References
[I] GROSSINGER, R., STEINER, W., KREC, K., J. Magn. Magn. [5] SCHINKEL, C. J., J. Phys. F 8 (1978) L 87.
Mat. 2 (1976) 196. [6] VOGT, E., BOLLING, F., TREUTMANN, W., Ann. Phys. 25 (1970)
[2] ORTBAUER, H., STEINER, W., HAFERL, R., Phys. Status Solidi (a) 280.
39 (1977) 157. [7] DE GENNES, P.-G., C.R. Hebd. S6an. Acad. Sci. 247 (1958) [3] LOEBICH, O., RAUB, E., J. Less-Common MetaN. 46 (1976) 1 . 1836.
[4] GHASSEM, H., RAMAN, A,, 2. Met. 64 (1973) 197.
