- Email: [email protected]
Magnetoresistivity properties of some ternary stannides based on cerium and nickel
Physica B 259—261 (1999) 44—45
Magnetoresistivity properties of some ternary stannides based on cerium and nickel B. Chevalier *, J. Garcı´ a Soldevilla, J.I. Espeso, J. Rodrı´ guez Ferna´ndez, J.C. Go´mez Sal, J. Etourneau Institut de Chimie de la Matie` re Condense´ e de Bordeaux, Avenue du Dr. A. Schweitzer, 33608 Pessac Cedex, France Universidad de Cantabria, Facultad de Ciencias, Avda. de los Castros, s/n 39005 Santander, Spain
Abstract The stannides CeNi Sn (intermediate valence), CeNi Sn (antiferromagnet), CeNiSn (antiferromagnet then ferromag net) and Ce Ni Sn (Kondo antiferromagnet) were investigated by magnetoresistivity (MR) measurements. Various behaviours were detected: (i) MR is always positive and weak ( 4.8% at 2 K and 9 T) for CeNi Sn as expected for a non-magnetic metal; (ii) for CeNi Sn the positive MR increases strongly ( 35% at 2 K) below ¹ "11 K; (iii) a large , negative MR is observed at 9 T in the paramagnetic state of Ce Ni Sn ( !18% at 6 K) and CeNiSn ( !7% at 5 K) suggesting the influence of the Kondo effect. 1999 Elsevier Science B.V. All rights reserved. Keywords: Cerium stannide; Magnetoresistivity; Kondo effect
The ternary stannides existing in the Ce—Ni—Sn system, exhibit various interesting magnetic properties. Ce Ni Sn is an intermediate valence compound. CeNi Sn and CeNi Sn order antiferromagnetically respectively below ¹ "11 and 1.8 K. Two magnetic transitions ap, pear at 3.9 and 2.6 K for CeNiSn . Finally, Ce Ni Sn and CeNiSn are considered respectively as a Kondo antiferromagnet (¹ "4.7 K) and a Kondo insulator. The mag, netoresistivity (MR) measurements are of interest in order to study the influence of Kondo effect on the physical properties of cerium-based compounds. Nowadays, only CeNi Sn and CeNiSn were investigated by MR experi ments [1,2]. We present our study concerning CeNi Sn, CeNi Sn , CeNiSn and Ce Ni Sn. All the samples were prepared by direct melting of the constituting elements using an induction levitation furnace. Then, the ingots were annealed under vacuum at 800°C for three weeks. Their examination by microprobe analysis and X-ray powder diffraction confirms both their single-phase character and structural properties as
* Corresponding author. Tel.: 33-(0)5-56-84-63-36; fax: 33(0)5-56-84-27-61; e-mail: [email protected].
described previously [3]. MR measurements were performed down to 2 K for magnetic fields 0 T)B)9 T using a PPMS quantum design system. For CeNi Sn, MR, defined by (o(B)!o(0 ¹))/o(0 ¹), is always positive and follows at all temperatures the law MR"aB (Fig. 1): the constant value a is respectively equal to 1.64;10\% T\ at 50 K and 6.96; 10\% T\ at 2 K and for 0 T)B)6 T. This behaviour characterizes a non-magnetic metal; MR being due to the Lorentz force on the conduction electrons. Also, MR is practically temperature independent between 2 and 9 K. These results are similar to those corresponding to CeNi characterized as an intermediate valence compound, confirming the same character of CeNi Sn having a high ¹ 500 K spin fluctuation temperature [3]. In the temperature range 2 K)¹)50 K, MR of CeNi Sn is always positive but exhibits various behav iours (Fig. 2). In the paramagnetic state, i.e. at 50 and 25 K, MR increases normally with B respectively below 5 and 2 T. This result suggests that the Kondo interaction is rather small or non-existent in this stannide. Below ¹ "11 K, MR increases strongly with B and , passes through a maximum near 5 T; two anomalies are
0921-4526/99/$ — see front matter 1999 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 9 8 ) 0 0 9 4 7 - 8
B. Chevalier et al. / Physica B 259—261 (1999) 44—45
Fig. 1. Magnetoresistance for CeNi Sn (solid lines present fits with aB law for 50 and 2 K).
Fig. 2. Magnetoresistance for CeNi Sn (dashed lines presents fits with aB law for 50 and 25 K).
clearly observed around 4 and 6 T at 2 K shifting to lower fields with increasing temperatures. This behaviour agrees with the antiferromagnetic state of CeNi Sn ; since the application of B induces an enhancement of effective scattering mechanism (MR'0) caused by the instability of moments oriented antiparallel to B. The occurrence below ¹ of anomalies in the MR"f (B) , curve coincides with the metamagnetic transitions observed from magnetization measurements. Certainly, the magnetic phase diagram (B, ¹) of CeNi Sn is complex. As the temperature is lowered below 50 K, negative MR is measured for Ce Ni Sn taking a large value of — 18% at 6 K, then MR changes sign at low fields below ¹ "4.7 K (Fig. 3). These results indicate: (i) the ,
45
Fig. 3. Magnetoresistance for Ce Ni Sn.
presence of Kondo interaction in the paramagnetic range; MR(0 is due to the quenching of the spin fluctuations. In fact the field dependence of MR observed at 50, 25 and 12 K agrees in the full B range with the MR model considering Kondo interactions used for CeNi Sn [1]; (ii) the occurrence of antiferromagnetic ordering at lowtemperature since MR'0; the broad peaks appearing at high fields (8, 7 and 4 T at 2, 3 and 4 K, respectively) on the MR"f (B) curves agree with the existence of metamagnetic transition. However, the strong influence of Kondo interaction is clearly observed in the low field behaviour of these curves which reflect the competition between Kondo (MR(0) and antiferromagnetic ordering (MR'0) below ¹ . , MR of CeNiSn is always negative down to 2 K. In the paramagnetic range (even at 25 K) the negative curvature could reflect the existence of Kondo interactions. For ¹(8 K, a change of regime appears reminiscent of the onset of ferromagnetic ordering. This behaviour is an evidence that the antiferromagnetic structure found between 2.6 and 3.9 K became easily ferromagnetic with low applied fields. In conclusion, our study demonstrates that Kondo interaction influences the physical properties of Ce Ni Sn and CeNiSn but is ineffective for CeNi Sn . References [1] V.V. Gridin, S.A. Sergeenkov, A.M. Strydom, P.de V. du Plessis, Phys Rev. B 50 (1994) 12995. [2] K. Sugiyama, M. Fujita, K. Kindo, G. Nakamoto, K. Kobayashi, T. Takabatake, H. Fujii, Physica B 230-232 (1997) 683. [3] F. Fourgeot, Thesis, Univ. Bordeaux I, no. 1576, 1996.
Magnetoresistivity properties of some ternary stannides based on cerium and nickel B. Chevalier *, J. Garcı´ a Soldevilla, J.I. Espeso, J. Rodrı´ guez Ferna´ndez, J.C. Go´mez Sal, J. Etourneau Institut de Chimie de la Matie` re Condense´ e de Bordeaux, Avenue du Dr. A. Schweitzer, 33608 Pessac Cedex, France Universidad de Cantabria, Facultad de Ciencias, Avda. de los Castros, s/n 39005 Santander, Spain
Abstract The stannides CeNi Sn (intermediate valence), CeNi Sn (antiferromagnet), CeNiSn (antiferromagnet then ferromag net) and Ce Ni Sn (Kondo antiferromagnet) were investigated by magnetoresistivity (MR) measurements. Various behaviours were detected: (i) MR is always positive and weak ( 4.8% at 2 K and 9 T) for CeNi Sn as expected for a non-magnetic metal; (ii) for CeNi Sn the positive MR increases strongly ( 35% at 2 K) below ¹ "11 K; (iii) a large , negative MR is observed at 9 T in the paramagnetic state of Ce Ni Sn ( !18% at 6 K) and CeNiSn ( !7% at 5 K) suggesting the influence of the Kondo effect. 1999 Elsevier Science B.V. All rights reserved. Keywords: Cerium stannide; Magnetoresistivity; Kondo effect
The ternary stannides existing in the Ce—Ni—Sn system, exhibit various interesting magnetic properties. Ce Ni Sn is an intermediate valence compound. CeNi Sn and CeNi Sn order antiferromagnetically respectively below ¹ "11 and 1.8 K. Two magnetic transitions ap, pear at 3.9 and 2.6 K for CeNiSn . Finally, Ce Ni Sn and CeNiSn are considered respectively as a Kondo antiferromagnet (¹ "4.7 K) and a Kondo insulator. The mag, netoresistivity (MR) measurements are of interest in order to study the influence of Kondo effect on the physical properties of cerium-based compounds. Nowadays, only CeNi Sn and CeNiSn were investigated by MR experi ments [1,2]. We present our study concerning CeNi Sn, CeNi Sn , CeNiSn and Ce Ni Sn. All the samples were prepared by direct melting of the constituting elements using an induction levitation furnace. Then, the ingots were annealed under vacuum at 800°C for three weeks. Their examination by microprobe analysis and X-ray powder diffraction confirms both their single-phase character and structural properties as
* Corresponding author. Tel.: 33-(0)5-56-84-63-36; fax: 33(0)5-56-84-27-61; e-mail: [email protected].
described previously [3]. MR measurements were performed down to 2 K for magnetic fields 0 T)B)9 T using a PPMS quantum design system. For CeNi Sn, MR, defined by (o(B)!o(0 ¹))/o(0 ¹), is always positive and follows at all temperatures the law MR"aB (Fig. 1): the constant value a is respectively equal to 1.64;10\% T\ at 50 K and 6.96; 10\% T\ at 2 K and for 0 T)B)6 T. This behaviour characterizes a non-magnetic metal; MR being due to the Lorentz force on the conduction electrons. Also, MR is practically temperature independent between 2 and 9 K. These results are similar to those corresponding to CeNi characterized as an intermediate valence compound, confirming the same character of CeNi Sn having a high ¹ 500 K spin fluctuation temperature [3]. In the temperature range 2 K)¹)50 K, MR of CeNi Sn is always positive but exhibits various behav iours (Fig. 2). In the paramagnetic state, i.e. at 50 and 25 K, MR increases normally with B respectively below 5 and 2 T. This result suggests that the Kondo interaction is rather small or non-existent in this stannide. Below ¹ "11 K, MR increases strongly with B and , passes through a maximum near 5 T; two anomalies are
0921-4526/99/$ — see front matter 1999 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 9 8 ) 0 0 9 4 7 - 8
B. Chevalier et al. / Physica B 259—261 (1999) 44—45
Fig. 1. Magnetoresistance for CeNi Sn (solid lines present fits with aB law for 50 and 2 K).
Fig. 2. Magnetoresistance for CeNi Sn (dashed lines presents fits with aB law for 50 and 25 K).
clearly observed around 4 and 6 T at 2 K shifting to lower fields with increasing temperatures. This behaviour agrees with the antiferromagnetic state of CeNi Sn ; since the application of B induces an enhancement of effective scattering mechanism (MR'0) caused by the instability of moments oriented antiparallel to B. The occurrence below ¹ of anomalies in the MR"f (B) , curve coincides with the metamagnetic transitions observed from magnetization measurements. Certainly, the magnetic phase diagram (B, ¹) of CeNi Sn is complex. As the temperature is lowered below 50 K, negative MR is measured for Ce Ni Sn taking a large value of — 18% at 6 K, then MR changes sign at low fields below ¹ "4.7 K (Fig. 3). These results indicate: (i) the ,
45
Fig. 3. Magnetoresistance for Ce Ni Sn.
presence of Kondo interaction in the paramagnetic range; MR(0 is due to the quenching of the spin fluctuations. In fact the field dependence of MR observed at 50, 25 and 12 K agrees in the full B range with the MR model considering Kondo interactions used for CeNi Sn [1]; (ii) the occurrence of antiferromagnetic ordering at lowtemperature since MR'0; the broad peaks appearing at high fields (8, 7 and 4 T at 2, 3 and 4 K, respectively) on the MR"f (B) curves agree with the existence of metamagnetic transition. However, the strong influence of Kondo interaction is clearly observed in the low field behaviour of these curves which reflect the competition between Kondo (MR(0) and antiferromagnetic ordering (MR'0) below ¹ . , MR of CeNiSn is always negative down to 2 K. In the paramagnetic range (even at 25 K) the negative curvature could reflect the existence of Kondo interactions. For ¹(8 K, a change of regime appears reminiscent of the onset of ferromagnetic ordering. This behaviour is an evidence that the antiferromagnetic structure found between 2.6 and 3.9 K became easily ferromagnetic with low applied fields. In conclusion, our study demonstrates that Kondo interaction influences the physical properties of Ce Ni Sn and CeNiSn but is ineffective for CeNi Sn . References [1] V.V. Gridin, S.A. Sergeenkov, A.M. Strydom, P.de V. du Plessis, Phys Rev. B 50 (1994) 12995. [2] K. Sugiyama, M. Fujita, K. Kindo, G. Nakamoto, K. Kobayashi, T. Takabatake, H. Fujii, Physica B 230-232 (1997) 683. [3] F. Fourgeot, Thesis, Univ. Bordeaux I, no. 1576, 1996.