Anomalous physical properties of the low carrier concentration state in f-electron systems

ELSEVIER

Physica B 206 & 207 (1995) 771-779

Anomalous physical properties of the low carrier concentration state in f-electron systems T. Suzuki a'*, Y. Haga a, D.X. Li a, T. Matsumura a, E. Hotta a, A. Uesawa ~, M. Kohgi a, T. Osakabe ~, S. Takagi a, H. Suzuki a, T. Kasuya a, Y. Chiba b, T. Goto c, S. Nakamura c, R. Settai c, S. Sakatsume d, A. Ochiai d, K. Suzuki d, S. Nimori d, G. Kido d, K. Ohyama d, M. Date e, Y. Morii ~, T. Terashima f, S. Uji f, H. Aoki f, T. Naka f, T. Matsumoto f, Y. Ohara g, H. Yoshizawa g, Y. Okayama g, Y. Okunuki g, A. Ichikawa g, H. Takahashi g, N. Mori g, T. Inoue h, T. Kuroda h, K. Sugiyama h, K. Kindo h, A. Mitsuda i, S. Kimura j, S. Takayanagi k, N. Wada ~, A. Oyamada m, K. Hashi m, S. Maegawa m, T. Goto m, Y.S. Kwon n, E. Vincent °, P. Bonville ° aDepartment of Physics, Tohoku University, Sendai, Japan bMiyagi University of Education, Sendai, Japan CResearch Institute for Scientific Measurements, Tohoku University, Sendai, Japan dlnstitute for Materials Research, Tohoku University, Sendai, Japan eJapan Atomic Energy Research Institute, Tokai, Ibaraki, Japan ~National Research Institute for Metals, Tsukuba, Japan ~lnstitute for Solid State Physics, University of Tokyo, Japan hDepartment of Physics, Osaka University, Osaka, Japan iFaculty of Science, Science University of Tokyo, Japan Jlnstitute for Molecular Science, Okazaki, Japan kHokkaido University of Education, Sapporo, Japan ~College of General Education, University of Tokyo, Japan "Graduate School of Human and Environmental Studies, Kyoto University, Kyoto, Japan "Department of Physics, Sung Kyun University, Seoul, South Korea °CEA, C.E. Saclay, DRECAM/SPEC, 91191, Gif-sur-Yvette, France

Abstract Recent progress in studies on low cartier concentration systems of magnetically ordered and non-magnetic heavy Fermion metals are discussed. Successive steps in the high field magnetisation, the magnetic structure, and the influence of high pressure are reported and the relation with the observed Fermi surface for CeP is discussed. The origin of the low cartier concentration in USb is also discussed based on the first observation of dHvA oscillations. It is also unambiguously demonstrated that the unconventional heavy Fermion state of Yb4As 3 is intrinsic and not due to impurities.

1. Introduction D u e to t h e s t r o n g e r c o r r e l a t i o n effects, f-electron * Corresponding author.

m e t a l s exist in various a n o m a l o u s states such as h e a v y f e r m i o n m e t a l s with s u p e r c o n d u c t i n g or m a g n e t i c o r d e r e d p h a s e s , a n d a rich variety of strange insulators as in t h e case of S m B 6. Study of t h e m e t a l - i n s u l a t o r t r a n s i t i o n by applying pressure to these strange in-

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T. Suzuki et al. / Physica B 206 & 207 (1995) 771-779

sulators, reveals peculiar properties, and the case of SmS may serve as an example. The criteria for the f-electron metal being in one of the above-mentioned states are not clear. Low-carrierdensity systems find themselves just between insulators and metals, and may therefore provide the key for clarification of the appropriate criteria. Several anomalous properties of low-carrier-density systems have been studied recently [1]. In this paper the progress on the strongly magnetic Ce monopnictides and USb, and the non-magnetic heavy fermion system Yb4As 3 are reported. Investigation of low-carrier-density systems demands high quality single crystal samples, because impurity effects are always mediated by the long range Coulomb interaction. Typical examples include the Gd-monopnictides. These are intrinsically all simple antiferromagnets, but for even a small deviation from stoichiometry, large deviations in the magnetisation curve are found (see Fig. 1) [2]. This phenomenon is very similar to the case of Eu-chalcogenides studied in the past [3]. However, there are essential differences between the Eu-chalcogenides and Gd-monopnictides. In the case of Eu, the magnetic ordering temperatures remain the same as in the pure insulating crystal, when the number of chalcogenide vacancies introduced is small. On the other hand, a strong reduction of T N is found in the Gd-monopnictides because the intrinsic carriers present in this case can distribute the local magnetic polaron nature over the entire sample and so produce profound effects. This also applies to CeP and

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CeAs, where strong sample dependence of the physical properties was found [4]. We could establish that this is due to the low screening, characteristic of extremely low-carrier-densities [5]. Therefore, it is very important to have high quality samples for the study of low-carrier-density systems. In the study of the metal-insulator transition by means of high pressures, it is therefore also very important to select high quality crystals for the insulator, as illustrated by TmTe [6] and SmTe [7].

2. Strongly magnetic case: Ce-monopnictides After the successful growth of high quality single crystals, there has been much progress made in the study of the anomalous properties of these compounds. A typical example is magnetisation of CeP measured by Date et al. [8]. Successive steps were observed in the magnetisation at magnetic fields above the saturation of the moments of the F7 level. The critical fields of these steps, A - F in Fig. 2, are almost temperature independent and, except for A, are equally spaced on a 1 / H scale. They correspond to the crossing of the Landau levels through the Fermi surface (which was obtained from de Haas van Alphen oscillations). Date et al. [8] explained their results by a Stoner-Landau model assuming that the population change in the levels of carriers for different spin at the crossing field induced a modification of the magnetic phase consisting of the network of localised Ce spins. A neutron diffraction study by Kohgi et al. [9] in magnetic fields up to 5 T along the [0 0 1] axis indi-

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Fig. 2. Magnetic phase diagram of CeP, from Date et al. [8]. The steps in the magnetisation are labeled A-F.

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T. Suzuki et al. / Physica B 206 & 207 (1995) 771-779

cated the coexistence of double F8 layers with groundstate F7 layers. These layers were stacked in the direction parallel to the field direction. The crystalline field splitting was large as 170 K [9], i.e. much larger than the effect of the external field of 5 T. The most probable explanation for the stability of the F8 layers is the creation of a magnetic polaron state [10]. The magnetic structures are shown in Fig. 3 with the corresponding phase diagrams. In the lowest temperature phase I, there are nine sheets of F7 layers, antiferromagnetically coupled, and a double sheet of F8 layers which are ferromagnetically aligned. The coupling between the F8 sheet and its nearest neighbour F7 layers is antiferromagnetic. In these phases there is an additional period of 11 layers. The ordering

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of the F7 layers is destroyed in phase III where only the double F8 sheet remains ordered. A t higher temperatures, the ferromagnetic F8 order disappears in a first order phase transition. Thus, the slope of the phase boundary is mainly determined by the magnetic moments and entropy of the F8 state. In higher fields, above about 12 T, there is no phase transition corresponding to the melting of the F7 order. So a change in slope was expected (see Fig. 2) when the F7 moment remained aligned with the magnetic field [9]. Recently, detailed de Haas van Alphen (dHvA) measurements [11] were carried out, including the dependence on the orientation of the applied magnetic field, and Fig. 4 shows the oscillations observed in lower fields, down to 100 mK, and a typical Fourier spectrum. The 11 layer period of the magnetic structure corresponds precisely to the frequency with the strongest spectral intensity obtained in the low field traces. The periods of the steps in the magnetisation exactly correspond to another frequency, namely that with the highest intensity found in the higher field traces. Furthermore, the angular dependence of the Fourier frequencies and the period of the magnetisation steps were consistent, as shown in Fig. 5. Therefore the period of the

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magnetic structure and magnetisation steps are strongly connected with the special Fermi surface. What is this Fermi surface? A t present, the spectrum is not complete, however it can be tentatively determined that this Fermi surface is the electron Fermi surface located at the X z point of the Brillouin zone, split into two parts by the spin exchange interaction in high fields. Effects on the Fermi surface due to the new zone resulting from the magnetic order were expected only for the low field spectrum as illustrated in Fig. 4. This is also supported by the results of dHvA effect for YbAs [12] and SmSb [13] which are antiferromagnets with low TN, and where the spectrum did not change below and above T N. Here, magnetic breakdown occurred for relatively low fields. The systematic investigation of the d H v A oscillations in rare earth monopnictides was split into two groups. The members of the first group (LaBi [14], LaSb [14], LaAs [151, PrSb [16], SmSb, GdSb [171, TmSb [181, YbAs) were qualitatively similar to each other. Their Fermi surfaces consisted of two-hole pockets at the F point and three equivalent electron pockets at the X points. The second group were CeSb and CeBi [17,19-21].

However, with CeSb and CeBi, with a F8 ground state, there were four-hole pockets due to the removal of the spin degeneracy by strong p - f mixing, and the electron pocket at X z was not equivalent to those at X r and X z , reflecting the effect of the anisotropic p - d mixing around X z . In the case of CeP, F8 and F7 layers coexisted. Therefore, coexistence of the two types of Fermi surface mentioned above should be expected. Which one belongs to the observed electron Fermi surface at the X z point? There are two crucial points. Firstly, whether there are spin split bands or not (in the CeSb case there is no more splitting because it is a single spin band). Secondly, whether a difference exists between the electron Fermi surface at X z and X r , X x or not. In this study there were two spin split branches and the frequency spectrum degenerated at the 11 1 0] point. Thus, the electron Fermi surface can be determined around X z from the F7 state in CeP (See Fig. 5). Then one would expect a change in frequency for the Fermi surfaces in low and high fields, because the spin state in F7 is canted in the high field region as revealed by neutron diffraction (see Fig. 3). The next question was to determine why this Fermi surface would generate the magnetic structure and steps of the magnetisation. Simple nesting was excluded. It is the field parallel to the stacking direction that determines the magnetic structure, while the observed frequencies correspond to the extremal areas of the Fermi surface perpendicular to the applied magnetic field, and all pockets have a simple parallelelipsoidal shape. Previous theoretical predictions suggest that the exchange interaction of electrons at X z of the d x r type as a result of strong anisotropic d - f Coulomb interaction [22]. Why would this type of exchange be so effective in realising the additional periodicity of the F8 layers? This requires further theoretical investigation, but we can point out the following facts. There are no quantitative differences in Fermi surface area between LaAs and CeAs, which has a F7 ground state. The dHVA effect was measured on La0.98Ceo.02P 125], and it was found that the extremal area of the electron Fermi surface at X z was nearly half of that of CeP, quite different from the L a A s / C e A s case. ESR measurement showed that the Ce site was in a F7 state in this dilute alloy [24]. Why would such a difference exist between CeP and its dilute alloy? A possible explanation for the difference with the L a A s / C e A s case is as follows CeP contains periodic F8 layers stabilised by the formation of a magnetic polaron state by strong p - f mixing in the F7 layers; then electrons from the F8 state may be

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T. Suzuki et al. / Physica B 206 & 207 (1995) 771-779

redistributed to the Fv layers to save the increase in kinetic energy in the F8 layer. So we have nearly twice the Fermi surface area in CeP compared to that of Lao.98Ceo.02P. Detailed studies were carried out under high pressure [25]. Remarkably, the phase diagram obtained is very similar to the magnetic phase diagram. Fig. 6 shows the close similarity between the temperature dependence of the magnetisation under constant pressure (a) and magnetic field (b) [26]. This result strongly suggests that there is some close connecting mechanism between volume and magnetisation. This

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776

T. Suzuki et al. / Physica B 206 & 207 (1995) 771-779

3. Strongly magnetic 5f electron case: USb There have been extensive studies on U-monopnictides. Among these compounds, USb has very prominent physical properties [29]. Resistivity at room temperature can be as high as 700 mW cm exceeding that of the extremely low-carrier-density system of CeAs mentioned above. The resistivity is essentially constant to 210 K, corresponding to TN, with a high maximum around 140 K, and then starts to decrease like a metal [30]. This strongly suggests that the systems have an extremely low carrier density. This is supported by the rather low electronic specific heat coefficient of 4 mJ/mol K 2 compared to 53 mJ/mol K 2 for UAs [31]. What is the origin of this low carrier concentration? There are two possible origins. Firstly, USb with the trivalent U atom and localised 5f electrons similar to the case of the semimetallic rare earth monopnictides discussed above. Another possibility is that the 5f electrons are itinerant. Photoemission and angular resolved photoemission experiments also showed a low density of states at the Fermi level and good agreement with theoretical band calculations [32] which predicted a strong hybridisation of the f and d bands, although the bands located just below Ef are flat. It was necessary to observe the d H v A effect to determine the ground state. The difficulties of purification of the raw uranium metal and growth of high quality crystals of these compounds have prevented the observation of this series so far. After enormous effort, for both purification of raw U metal and crystal growth of USb, we have succeeded in producing a high quality single crystal and were able to observe some quantum oscillations of the d H v A effect [33]. The two most intense frequencies in the Fourier spectrum shown in Fig. 8 can be seen at 0.015 and 0.033 ,~-2, respectively. These cross sections are very similar to the case of extremely low carrier concentrations in CeAs and LaAs, and it is reasonable to assume that this is due to the electron Fermi surface at X z with large spin splitting. If this is the case, then the splitting energy may be estimated as several orders of magnitude larger than in the 4f electron case. The effective mass along the [1 0 0] direction was measured to be 1.2/~0. This is nearly six times that of LaAs and suggests strong d - f mixing. However, at present, there are no detailed theoretical calculations and unobserved branches still remain because of the insufficient quality of the samples. A definite conclusion therefore cannot be drawn and further studies are necessary.

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4. Nonmagnetic heavy fermion: Yb4As 3 It is an interesting question as to why the heavy Fermion character is realised in low-carrier-density Yb4As 3. The low temperature behaviour is very strange and the unconventional heavy Fermion state has been attributed to the 'impurity state'. A typical example illustrating the ambiguity of the results due to impurity effects is the behaviour of the magnetic susceptibility c [34]. It appears as a deviation from the Curie-Weiss law followed by a plateau below 20 K, with a value c o = 2.75 x 10 - 2 e m u / m o i . However, below 10 K the susceptibility increases anew and even more rapidly below 2 K. This was attributed to the presence of 'impurity' Yb 3+ ion. There are also some delicate changes in the specific heat. A linear relationship in the C / T - T 2 plot is satisfied in the region of 10-20 K. The slope changes to a slightly smaller value and shows a large magnetic field effect below 10 K [35]. The NQR spectrum shows similar behaviour, T~ T is constant between 10 and 20 K and there is a

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T. Suzuki et al. / Physica B 206 & 207 (1995) 771-779

rapid increase below 10 K. Below 1 K, there are two relaxation times with different temperature dependence [36]. Low-temperature specific heat measurements showed a rapid increase of C~ T below 200 mK due to quadrupole splitting of the Yb nuclear level, but still a large g value is found down to 600 mK [37]. Some unusual behaviour was observed below 1 K. A magnetic field strongly reduces C / T below about 600mK, and C / T saturates and remains constant at 3 0 m J / m o l K 2 to fields up to 4T. These phenomena are unconventional but it was necessary to clarify whether they are intrinsic or due to an impurity effect. Recently, Bonville et al. [38] proved microscopically that the rapid increase in susceptibility below 10 K is not impurity related but an intrinsic effect. Their careful Mossbauer studies down to 50 mK with a 7 T magnetic field clearly showed hyperfine splitting due to the Yb 3÷ atom. From this hyperfine splitting, the induced moments are obtained. These magnetic moment values fit well to the value of static magnetisation measurements within the error bars shown in Fig. 9. Below 2 K, the susceptibility increases according to a Curie-Weiss law with Qp = - 0 . 8 4 K a n d / z e , = 0.88p. B assuming one Yb 3÷ ion/f.u. This indicates an antiferromagnetic correlation below 2 K. Furthermore, below 2 K , for moderate applied magnetic fields

( > 2 T ) , the 'high field' magnetic susceptibility drops markedly with respect to the low field value. This corresponds closely to the rapid decrease observed in the specific heat by an applied field of 1 T and suggests the destruction of the heavy electron behaviour [37]. Now we can consider these unconventional states as intrinsic and speculate that states may be separated into two parts. One remains a heavy Fermion state and the other is a quantum spin-fluctuating state due to the magnetic correlations. The relaxation of N Q R below 2 K may be related to this. Neutron scattering experiments are useful and preliminary crystalline field splittings have been obtained at 15.4 and 28.7meV, and in addition, an anomalous q-dependent splitting of 2.6 meV by Kohgi et al. [39]. More detailed studies are needed for single crystal. Fig. 10 shows the pressure-dependent resistivity (p) and Hall effect (RH) measured by Mori et al. [40]. A clear increase in carrier concentration is observed with increasing pressure. A huge maximum, both in p and R . , also decreases with pressure. However, not shown here, p / R . at several values of the applied pressure,

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T(K) Fig. 10. Temperature dependence of the resistivity of Yb4As 3 for different values of the applied pressure; from Mori et al. [401.

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T. Suzuki et al. / Physica B 206 & 207 (1995) 771-779

demonstrates that the mobility is not affected by the pressure. Mori et al. concluded that the bands contributing to the carriers must be the most simple ones such as the p-valence band and f-band. This result also excludes the more complex band models such as that previously proposed [34}, because pressure should have affected each band in different ways, and those models can therefore not explain the simple experimental results. The model calculation of the two bands gives a good fit to the experimental data. Kasuya [41] also proposed a simple model with the f-state forming the pseudo-gap by a Kondo interaction and discussed the similarities with SmB 6 and YbB ~2-

Acknowledgements T. Suzuki would like to express his sincere thanks to Professor O. Sakai, Tohoku University for valuable discussions and is also grateful to Professor Jos A.A.J. Perenboom, University of Nijmegen for critical reading of this manuscript and valuable discussions.

References [1] T. Suzuki, Physica B 186-188 (1993) 347; Jpn. J. Appl. Phys 8 (1993) 267; T. Kasuya, H. Haga and T. Suzuki, Physica B 186 & 188 (1993) 9. [2] D.X. Li, Y. Haga, H. Shida and T. Suzuki, Solid State Commun. (in press). [3] Y. Shapira, S. Foner, N.F. Oliveira Jr and T.B. Reed, Phys. Rev. B 5 (1972) 2647. [4] F. Hulliger and H.R. Ott, Z. Phys. B 29 (1978) 47. [5] T. Suzuki, Jpn. J. Appl. Phys. 8 (1993) 44. [6] T. Matsumura, Y. Haga, Y. Nemoto, S. Nakamura, T. Goto and T. Suzuki, Physica B 206 & 207 (1995) 380. [7] Y.S. Kwon, T.S. Park, K.S. An, I.S. Jeon, S. Kimura, C.Y. Park, T. Nanba and T. Suzuki, Physica B 206 & 207 (1995) 389. [8] T. Kuroda, K. Sugiyama, Y. Haga, T. Suzuki, A. Yamagishi and M. Date, Physica B 186 & 188 (1993) 396-399. [9] M. Kohgi, T. Osakabe, K. Kakurai, T. Suzuki, Y. Haga and T. Kasuya, Phys. Rev. B 49 (1994) 7068-7071. [10] T. Kasuya, Y. Haga, T. Suzuki, T. Osakabe and M. Kohgi, J. Phys. Soc. Japan 62 (1993) 3376; T. Kasuya, T. Suzuki and Y. Haga, J. Phys. Soc. Japan 62 (1993) 2549. [11] Y. Haga, A. Uesawa, T. Terashima, S. Uji, H. Aoki, Y.S. Kwon and T. Suzuki, Physica B 206 & 207 (1995) 792.

[12] N. Takeda, K. Tanaka, M. Kagawa, A. Oyamada, N. Sato, S. Sakatsume, H. Aoki, T. Suzuki and T. Komatsubara, J. Phys. Soc. Japan 62 (1993) 2098. [13] K. Tanaka, N. Takeda, Y.S. Kwon, N. Sato, T. Suzuki and T. Komatsubara, Physica B 186 & 188 (1993) 150. [14] H. Kitazawa, T. Suzuki, M. Sera, I. Oguro, A. Yanase and T. Kasuya, J. Mag. Mag. Mater. 31-34 (1983) 421. [15] K. Morita, T. Goto, H. Matsui, S. Nakamura, Y. Haga, T. Suzuki and M. Kataoka, Physica B 206 & 207 (1995) 795. [16] A. Kido, S. Nimori, G. Kido, Y. Nakag'awa, Y. Haga and T. Suzuki, Physica B 186 & 188 (1993) 185-187. [17] R. Settai, T. Goto, S. Sakatsume, Y.S. Kwon, T. Suzuki and T. Kasuya Physica B 186 & 188 (1993) 176-178. [18] S. Nimori, Ph.D. Thesis, Tohoku University (1994). [19] H. Aoki, G.W. Crabtree, W. Joss and F. Huiliger, J. Magn. Magn. Mater 52 (1985) 370. [20] O. Sakai, Y. Kaneta and T. Kasuya, Jpn. J. Appl. Phys. 26-3 (1987) 477. [21] R. Settai, private communication. [22] T. Kasuya, O. Sakai, J. Tanaka, H. Kitazawa and T. Suzuki, J. Magn. Magn. Mater 63 & 64 (1987) 9. [23] H. Haga, S. Kindo, T. Shibata, T. Inoue, T. Suzuki, Y. Chiba and M. Date, Physica B 206 & 207 (1995) 792. [24] S. Kindo, T. Shibata, T. lnoue, Y. Haga, T. Suzuki, Y. Chiba and M. Date, J. Phys. Soc. Japan 62 (1993) 4190-4193. [25] N. Mori, Y. Okayama, H. Takahashi, Y. Haga and T. Suzuki, Jpn. J. Appl. Phys. 8 (1993) 182; Physica B 186 & 188 (1993) 444. [26] T. Naka, T. Matsumoto, Y. Okayama, N. Mori, Y. Haga and T. Suzuki, Proc. ICM'94 (in press). [27] Y. Okayama, Y. Ohhara, S. Mituda, H. Takahasi, H. Yoshizawa, T. Osakabe, M. Kohgi, Y. Haga, T. Suzuki and N. Mori, Physica B 186 & 188 (1993) 531-534. [28] Y. Oohara, Y. Okayama, H. Takahashi, H. Yoshizawa, N. Mori, S. Mitsuda, T. Osakabe, Y. Haga, M. Kohgi and T. Suzuki, in: Proc. 5th Int. Syrup. on Advanced Nuclear Energy Research, JAERI-M 93-228, Vol. 2 (1993) p. 203. [29] G. Busch, O. Vogt and H. Bartholin, J. de Phys. C 40 (1979) 64; J. Rossat-Mignod, P. Burlet, H. Bartholin, R. Tchapoutian, O. Vogt, C. Vettier and R. Lagnier Physica B 107 (1980) 177; K.W. Knott, G.H. Lander, M.H. Mueller and O. Vogt, Phys. Rev. B 21 (1980) 4159. [30] J. Schoenes, B. Frick and O. Vogt, Phys. Rev. B 30 (1984) 6578. [31] H. Rudigier, H.R. Ott and O. Vogt, Plays Rev. B 32 (1985) 4584. [32] R. Baptist, M. Belakhovsky, M.S.S. Brooks, R. Pinchaux, Y. Baer and O. Vogt, Physica B 102 (1980) 63. [33] A. Ochiai, E. Hotta, Y. Suzuki, T. Shikama, K. Suzuki, Y. Haga and T. Suzuki, Physica B 206 & 207 (1995) 789. [34] A. Ochiai, T. Suzuki and T. Kasuya, J. Phys. Soc. Japan 59 (1990) 4129-4141. [35] O. Nakamura, Y. Tomonaga, T. Suzuki and T. Kasuya, Physica B 171 (1991) 377-380.

T. Suzuki et al. / Physica B 206 & 207 (1995) 771-779

[36] Y. Kitaoka, M. Kyogaku, G.-q. Zheng, H. Nakamura, K. Asayama, T. Takabatake, H. Fujii and T. Suzuki, Physica B 186 & 188 (1993) 431-433. [37] U. Ahlheim, K. Fraas, P.H.P. Reinders, F. Steglich and T. Suzuki, Physica B 186 & 188 (1993) 434-436.

779

[38] P. Bonvill, A. Ochiai, T. Suzuki and E. Vincent, J. Phys. France 4 (1994) 595. [39] M. Kohgi et al. Private communication. [40] N. Mori et al., unpublished. [41] T. Kasuya, J. Phys. Soc. Japan (in press).