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Substitution effect on magnetic properties of CePt3Si
ARTICLE IN PRESS
Physica B 359–361 (2005) 187–189 www.elsevier.com/locate/physb
Substitution effect on magnetic properties of CePt3Si Gaku Motoyama, Suguru Yamamoto, Yasukage Oda, Koh-ichi Ueda, Takao Kohara Graduate School of Material Science, Himeji Institute of Technology, University of Hyogo, Kamigori-cho, Ako-gun, Hyogo 678-1297, Japan
Abstract In order to investigate a substitution effect and a heat treatment effect, we have prepared polycrystalline samples of CePt3d Si1þd ðd ¼ 0:05 0:15Þ: We have carried out the DC and AC magnetic susceptibility on this system. It is found that the magnetic susceptibility at low temperatures is enhanced with increasing Pt concentration, and the magnetic susceptibility of quenched CePt3 Si samples has two anomalies at T ¼ 2:2 and 3 K. These anomalies are sensitive to the heat treatment and the substitution. r 2005 Elsevier B.V. All rights reserved. Keywords: Heavy fermion superconductor; Antiferromagnetism; Non-centrosymmetric; CePt3 Si
Recently, E. Bauer et al. [1] discovered a new heavy-fermion compound CePt3 Si which undergoes an antiferromagnetic (AFM) order at T N ¼ 2.2 K and a superconducting (SC) order at T c ¼ 0:75 K: In UPd2 Al3 ; it is commonly recognized that AFM and SC coexists [2]. But, the coexistence of AFM and SC of URu2 Si2 and the coexistence of ferromagnetism (FM) and SC of UGe2 have been reconsidered [3,4]. It is unique that CePt3 Si has no centrosymmetry in the crystal structure. CePt3 Si crystallizes with the (CePt3 B)-type. The lack of inversion symmetry Corresponding
author. Tel.: +81 791 580 134; fax: +81 791 580 132. E-mail address: [email protected] (K.-i. Ueda).
in this system comes mainly from the two 1a positions occupied by Pt and Si. The occupying of the 1a positions may be made random by the substitution and the heat treatment. We have prepared polycrystalline samples of CePt3d Si1þd : It was synthesized by melting a stoichiometric amount of constituent elements, each of which has the purity of 99.9%, 99.95% and 99.9999% for cerium, platinum and silicon. We heat-treated by two ways: (1) We kept a sample at 950 C in the high vacuum quartz tube for a week and cooled down over 3 days to room temperature. (2) We did at 950 C for a week and cooled down steeply to room temperature. Non heat-treated, heat-treated by (1)-way and by (2)way samples were named ‘‘as cast’’, ‘‘950a’’ and
0921-4526/$ - see front matter r 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2005.01.031
ARTICLE IN PRESS G. Motoyama et al. / Physica B 359– 361 (2005) 187–189
188
‘‘950q’’. And then, we called the sample which was heat-treated by the (1)-way and additionally did by the (2)-way ‘‘950a&950q’’. We had carried out Xray scattering measurements. There is no unexpected peak, therefore the prepared samples are almost composed of CePt3 Si: In addition, the specific heat result (not shown here) which has a jump around 0.7 K and a kink anomaly at 2.2 K is consistent with the previous result [1]. To investigate the heat treatment effect, we repeated the measurements and the heat treatments using a unique sample. The DC magnetic susceptibility measurements were carried out using a SQUID magnetometer. Fig. 1 shows the temperature dependence of the DC magnetic susceptibility wðTÞ: wðTÞ was measured with increasing temperature in the external magnetic field of 10 Oe after it was cooled down to the lowest temperature in the zero-field (ZFC), and was measured with decreasing temperature in the external magnetic field (FC). wðTÞ of the ‘‘as cast’’ sample indicated a characteristic behavior in the FC and ZFC measurements below 3 K. wðTÞ of the FC increased suddenly at 3 K, suggesting a FM order. On the other hand, wðTÞ of the ZFC showed a sharp peak at 3 K, indicating that the magnetic moments are freezed below this temperature. We note that wðTÞ of the FC has a peak at 2.2 K, showing the AFM order. Whereas, in the wðTÞ both of the FC and ZFC of the sample ‘‘950a’’, the anomaly at 3 K almost disappeared, although the
Ν
Ν
Ν
(a)
weak AFM signal at 2.2 K can be observed (at the arrowed point). But, these anomalies reappeared clearly to the sample ‘‘950a&950q’’. We think that these anomalies are intrinsic properties of CePt3 Si: We speculate that there are ordered Pt(1a) and Si(1a) atom and random phases. The ‘‘as cast’’ sample has both of them. In the ‘‘950a’’, the ordered phase is dominant. And both the phases exist in the ‘‘950a&950q’’. The random phase seems to cause the anomaly at 3 K. Fig. 2 shows the temperature dependence of the real and imaginary parts of the AC magnetic susceptibility, which are referred to as w0 and w00 ; respectively. These measurements were carried out by applying an AC magnetic field H with a frequency of 85 Hz. Compared w0 of the ‘‘950a’’ with one of the ‘‘as cast’’ (‘‘950a&950q’’), the T c of ‘‘950a’’ is 0:1 K higher and the width of the transition temperatures are narrow. Superconductivity is dominant in the ordered phase which does not indicate the anomaly at 3 K. Fig. 3 shows the temperature dependence of the DC magnetic susceptibility for the CePt3d Si1þd which were prepared by only melting. The magnitude of w at low temperatures enhances with decreasing x compared with the x ¼ 0: This enhancement started around 100 K and became marked around 10 K: When the x increases from x ¼ 0; the magnitude of w at low temperatures seems to become slightly smaller. By increasing Pt concentration, both 1a positions are occupied by
(b)
(c)
Fig. 1. Temperature dependence of the DC magnetic susceptibility of CePt3 Si was measured by applying an external magnetic field of H ¼ 10 Oe: (a) For the sample ‘‘as cast’’, (b) for the sample ‘‘950a’’ and (c) for the sample ‘‘950a&950q’’.
χ
χ
χ
χ
χ
χ
(a)
(b)
(c)
Fig. 2. Temperature dependence of the AC magnetic susceptibility of the CePt3 Si around a superconducting transition temperature. (a) For the sample ‘‘as cast’’, (b) for the sample ‘‘950a’’ and (c) for the sample ‘‘950a&950q’’.
ARTICLE IN PRESS G. Motoyama et al. / Physica B 359– 361 (2005) 187–189
δ
δ
δ δ δ δ δ
Fig. 3. Temperature dependence of the DC magnetic susceptibility of the CePt3d Si1þd by applying an external magnetic field H ¼ 1000 Oe:
Pt atoms, partially. These Pt-chains cause the enhancement of magnetic susceptibility. In addition, the randomness of 1a position gives the Ptchain, too. Therefore, Pt-chain seems to cause the anomaly indicated at Fig. 1. Here is no space for
189
figure, but, the anomaly at 3 K becomes marked on Pt-rich samples. We cannot deny that these anomalies indicated at Fig. 1 come from some extraphases. But it is difficult to attribute these anomalies to any impurity atoms, because they vanish and reappear with the heat treatment. This system is found to be sensitive to the substitution and the heat treatment. The coexistence of SC and AFM of CePt3 Si seems to be complicated and must be studied carefully. We thank N.K. Sato for both his experimental supports and useful discussions. This work was supported by the Grant-in-Aid for Young Scientists (B)(15740222). References [1] [2] [3] [4]
E. Bauer, et al., Phys. Rev. Lett. 92 (2004) 027003. N.K. Sato, et al., Nature (London) 410 (2001) 340. K. Matsuda, et al., Phys. Rev. Lett. 87 (2001) 087203. G. Motoyama, et al., Phys. Rev. B 65 (2001) 020510.
Physica B 359–361 (2005) 187–189 www.elsevier.com/locate/physb
Substitution effect on magnetic properties of CePt3Si Gaku Motoyama, Suguru Yamamoto, Yasukage Oda, Koh-ichi Ueda, Takao Kohara Graduate School of Material Science, Himeji Institute of Technology, University of Hyogo, Kamigori-cho, Ako-gun, Hyogo 678-1297, Japan
Abstract In order to investigate a substitution effect and a heat treatment effect, we have prepared polycrystalline samples of CePt3d Si1þd ðd ¼ 0:05 0:15Þ: We have carried out the DC and AC magnetic susceptibility on this system. It is found that the magnetic susceptibility at low temperatures is enhanced with increasing Pt concentration, and the magnetic susceptibility of quenched CePt3 Si samples has two anomalies at T ¼ 2:2 and 3 K. These anomalies are sensitive to the heat treatment and the substitution. r 2005 Elsevier B.V. All rights reserved. Keywords: Heavy fermion superconductor; Antiferromagnetism; Non-centrosymmetric; CePt3 Si
Recently, E. Bauer et al. [1] discovered a new heavy-fermion compound CePt3 Si which undergoes an antiferromagnetic (AFM) order at T N ¼ 2.2 K and a superconducting (SC) order at T c ¼ 0:75 K: In UPd2 Al3 ; it is commonly recognized that AFM and SC coexists [2]. But, the coexistence of AFM and SC of URu2 Si2 and the coexistence of ferromagnetism (FM) and SC of UGe2 have been reconsidered [3,4]. It is unique that CePt3 Si has no centrosymmetry in the crystal structure. CePt3 Si crystallizes with the (CePt3 B)-type. The lack of inversion symmetry Corresponding
author. Tel.: +81 791 580 134; fax: +81 791 580 132. E-mail address: [email protected] (K.-i. Ueda).
in this system comes mainly from the two 1a positions occupied by Pt and Si. The occupying of the 1a positions may be made random by the substitution and the heat treatment. We have prepared polycrystalline samples of CePt3d Si1þd : It was synthesized by melting a stoichiometric amount of constituent elements, each of which has the purity of 99.9%, 99.95% and 99.9999% for cerium, platinum and silicon. We heat-treated by two ways: (1) We kept a sample at 950 C in the high vacuum quartz tube for a week and cooled down over 3 days to room temperature. (2) We did at 950 C for a week and cooled down steeply to room temperature. Non heat-treated, heat-treated by (1)-way and by (2)way samples were named ‘‘as cast’’, ‘‘950a’’ and
0921-4526/$ - see front matter r 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2005.01.031
ARTICLE IN PRESS G. Motoyama et al. / Physica B 359– 361 (2005) 187–189
188
‘‘950q’’. And then, we called the sample which was heat-treated by the (1)-way and additionally did by the (2)-way ‘‘950a&950q’’. We had carried out Xray scattering measurements. There is no unexpected peak, therefore the prepared samples are almost composed of CePt3 Si: In addition, the specific heat result (not shown here) which has a jump around 0.7 K and a kink anomaly at 2.2 K is consistent with the previous result [1]. To investigate the heat treatment effect, we repeated the measurements and the heat treatments using a unique sample. The DC magnetic susceptibility measurements were carried out using a SQUID magnetometer. Fig. 1 shows the temperature dependence of the DC magnetic susceptibility wðTÞ: wðTÞ was measured with increasing temperature in the external magnetic field of 10 Oe after it was cooled down to the lowest temperature in the zero-field (ZFC), and was measured with decreasing temperature in the external magnetic field (FC). wðTÞ of the ‘‘as cast’’ sample indicated a characteristic behavior in the FC and ZFC measurements below 3 K. wðTÞ of the FC increased suddenly at 3 K, suggesting a FM order. On the other hand, wðTÞ of the ZFC showed a sharp peak at 3 K, indicating that the magnetic moments are freezed below this temperature. We note that wðTÞ of the FC has a peak at 2.2 K, showing the AFM order. Whereas, in the wðTÞ both of the FC and ZFC of the sample ‘‘950a’’, the anomaly at 3 K almost disappeared, although the
Ν
Ν
Ν
(a)
weak AFM signal at 2.2 K can be observed (at the arrowed point). But, these anomalies reappeared clearly to the sample ‘‘950a&950q’’. We think that these anomalies are intrinsic properties of CePt3 Si: We speculate that there are ordered Pt(1a) and Si(1a) atom and random phases. The ‘‘as cast’’ sample has both of them. In the ‘‘950a’’, the ordered phase is dominant. And both the phases exist in the ‘‘950a&950q’’. The random phase seems to cause the anomaly at 3 K. Fig. 2 shows the temperature dependence of the real and imaginary parts of the AC magnetic susceptibility, which are referred to as w0 and w00 ; respectively. These measurements were carried out by applying an AC magnetic field H with a frequency of 85 Hz. Compared w0 of the ‘‘950a’’ with one of the ‘‘as cast’’ (‘‘950a&950q’’), the T c of ‘‘950a’’ is 0:1 K higher and the width of the transition temperatures are narrow. Superconductivity is dominant in the ordered phase which does not indicate the anomaly at 3 K. Fig. 3 shows the temperature dependence of the DC magnetic susceptibility for the CePt3d Si1þd which were prepared by only melting. The magnitude of w at low temperatures enhances with decreasing x compared with the x ¼ 0: This enhancement started around 100 K and became marked around 10 K: When the x increases from x ¼ 0; the magnitude of w at low temperatures seems to become slightly smaller. By increasing Pt concentration, both 1a positions are occupied by
(b)
(c)
Fig. 1. Temperature dependence of the DC magnetic susceptibility of CePt3 Si was measured by applying an external magnetic field of H ¼ 10 Oe: (a) For the sample ‘‘as cast’’, (b) for the sample ‘‘950a’’ and (c) for the sample ‘‘950a&950q’’.
χ
χ
χ
χ
χ
χ
(a)
(b)
(c)
Fig. 2. Temperature dependence of the AC magnetic susceptibility of the CePt3 Si around a superconducting transition temperature. (a) For the sample ‘‘as cast’’, (b) for the sample ‘‘950a’’ and (c) for the sample ‘‘950a&950q’’.
ARTICLE IN PRESS G. Motoyama et al. / Physica B 359– 361 (2005) 187–189
δ
δ
δ δ δ δ δ
Fig. 3. Temperature dependence of the DC magnetic susceptibility of the CePt3d Si1þd by applying an external magnetic field H ¼ 1000 Oe:
Pt atoms, partially. These Pt-chains cause the enhancement of magnetic susceptibility. In addition, the randomness of 1a position gives the Ptchain, too. Therefore, Pt-chain seems to cause the anomaly indicated at Fig. 1. Here is no space for
189
figure, but, the anomaly at 3 K becomes marked on Pt-rich samples. We cannot deny that these anomalies indicated at Fig. 1 come from some extraphases. But it is difficult to attribute these anomalies to any impurity atoms, because they vanish and reappear with the heat treatment. This system is found to be sensitive to the substitution and the heat treatment. The coexistence of SC and AFM of CePt3 Si seems to be complicated and must be studied carefully. We thank N.K. Sato for both his experimental supports and useful discussions. This work was supported by the Grant-in-Aid for Young Scientists (B)(15740222). References [1] [2] [3] [4]
E. Bauer, et al., Phys. Rev. Lett. 92 (2004) 027003. N.K. Sato, et al., Nature (London) 410 (2001) 340. K. Matsuda, et al., Phys. Rev. Lett. 87 (2001) 087203. G. Motoyama, et al., Phys. Rev. B 65 (2001) 020510.