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Pressure effect on the magnetic properties in PrFe4P12
Journal of Magnetism and Magnetic Materials 226}230 (2001) 66}67
Pressure e!ect on the magnetic properties in PrFe P Tatsuma D. Matsuda*, Keisuke Abe, Fumihito Watanuki, Takahiro Namiki, Shanta R. Saha, Hitoshi Sugawara, Yuji Aoki, Hideyuki Sato Department of Physics, Tokyo Metropolitan University, Minami-Ohsawa 1-1, Tokyo 192-0397, Japan
Abstract The uniaxial pressure e!ect on magnetization of PrFe P single crystals has been investigated. An extremely large enhancement of magnetic susceptibility has been found at around ¹ . With increasing pressure, ¹ decreases, suggesting , , the suppression of the antiferromagnetic interaction. In the "eld dependence of magnetization, we have found an enhancement of magnetic moment with pressure at the low "eld antiferromagnetic state, suggesting that the breaking of the crystal symmetry has to be considered. 2001 Elsevier Science B.V. All rights reserved. Keywords: Filled skutterudite; PrFe P ; Uniaxial pressure; Magnetic measurement
The series of "lled skutterudite compounds RET X (RE"rare earth, actinide; T"Fe, Ru, Os; X " P, As, Sb) have attracted much attention, since the various physical properties on the systematic substitution of each element accompanied by a variety of novel phenomena, such as a metal}insulator transition [1] and intermediate valence phenomena [2,3] associated with this crystal structure have been reported. On REFe P , Torikach vili et al. have reported the "rst systematic study where they found a wide variety of interesting properties depending on RE [4]. In order to judge whether these anomalous behaviors are intrinsic, investigation on high-quality single crystals is essential. Nevertheless, reports of investigations on single crystal are few. Recently, we have succeeded in growing high-quality single crystals of REFe P and reported some anomalous behaviors in the transport and thermal properties [5,6]. PrFe P , which shows an antiferromagnetic order below ¹ &6.5 K [4], is one of the most interesting , compounds in RET P series. However, the magnetic structure of the ground state has not yet been clari"ed. At high temperatures, the resistivity shows ! log ¹ dependence and the thermoelectric power exhibits a large absolute value of !40 V/K above ¹ like the Kondo ,
* Corresponding author. Fax: #81-426-77-2487. E-mail address: [email protected] (T.D. Matsuda).
compounds. In the high "eld state above the metamagnetic transition, the value of C/¹ is extremely large(&1.4 J/Kmol), the origin of which has not been clari"ed. In this work, we report the uniaxial pressure e!ect on the magnetic properties using high-quality single crystals for the "rst time. The investigation using uniaxial pressure is a very useful method for this type of compounds which is known to be very sensitive to the substitution of elements. Especially, large distortion of lattice is expected under uniaxial pressure compared with hydrostatic pressure. The change of the symmetry is another important feature for the cubic system. Single crystal samples have been grown by the tin-#ux method [4]. Typical size of the single crystals is &4 mm. To apply a uniform uniaxial pressure on the sample, plane-shaped samples have been cut out from these crystals. The magnetic measurements were performed by using a quantum design SQUID magnetometer up to 5.5 T under uniaxial pressure in a beryllium-copper piston-cylinder-type pressure cell. The value of pressure at low temperatures has been determined by measuring the superconducting transition temperature of Pb located in the pressure cell. In these magnetic measurements, we ignore the cell contribution (below 5% at 5.5 T) in the analyses. Fig. 1 shows the temperature dependence of magnetic susceptibility () with "eld and pressure (P) along 1 0 0. At ambient pressure, exhibits a Curie}Weiss behavior down to &10 K with an e!ective magnetic moment of
0304-8853/01/$ - see front matter 2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 0 ) 0 0 6 3 0 - 2
T.D. Matsuda et al. / Journal of Magnetism and Magnetic Materials 226}230 (2001) 66}67
Fig. 1. Temperature dependence of magnetic susceptibility under the uniaxial pressure. Inset is the pressure dependence of ¹ de"ned by the peak position of the susceptibility. Broken line , is a guide to eyes.
3.6 , which is close to the value expected for a free Pr> and is consistent with the previous report [4]. A sharp peak structure in due to antiferromagnetic order is observed at ¹ "6.5 K. Below ¹ , shows a minimum , , around 3.5 K and increases with decreasing ¹, which cannot be explained either by the simple magnetic structure or by the spin wave excitation. By applying uniaxial pressure, is largely enhanced around ¹ ; i.e. the peak , value of at 1.1 kbar is more than 2 times larger than that at ambient pressure. ¹ determined by a peak position in , decreases with increasing pressures (see inset of Fig. 1), indicating the suppression of the antiferromagnetic correlation. Below ¹ , a minimum in at ambient pressure , disappears accompanied by an enhancement of by P. Above 20 K, the e!ect of the uniaxial pressure on is very small. Fig. 2 shows the "eld dependence of magnetization (M). At ambient pressure, M shows a metamagnetic transition around H "3.8 T at 2 K, which is consis + tent with the reported metamagnetic behavior in [1]. No hysteresis behavior with the metamagnetic transition is observed within the experimental accuracy. Above the metamagnetic transition, the magnetic moment &1.7 at 5.5 T is small compared to the full moment of 3.2 for Pr> ions. By applying uniaxial pressure, M is largely enhanced in the entire regions of the low "eld state, while above H , the enhancement of M is smaller than 3% at + 5.5 T. The metamagnetic transition "eld, determined by a peak in the di!erential M, does not noticeably shift with the uniaxial pressure within the experimental accuracy. At the present stage, we should consider at least three possible factors for the enhancement of M by uniaxial pressure in the low "eld state; (1) A change of the magnetic structure induced by anisotropic exchange in-
67
Fig. 2. Field dependence of magnetization under the uniaxial pressure at 2 K.
teraction resulting from the symmetry breaking. (2) A change of the crystalline electronic "eld e!ect. (3) Re-alignment of the magnetic domain structure resulting from symmetry breaking by the uniaxial pressure. All these possibilities are related to each other through the symmetry breaking e!ect. To clarify the factors responsible for the enhancement M, it is important to compare the result with the hydrostatic pressure measurement. In summary, for the "rst time, we have performed magnetic measurements on single crystalline PrFe P under uniaxial pressure. In the low "eld state, we have found an enhancement of magnetic moment, suggesting that the breaking of the crystal symmetry by uniaxial pressure has to be considered. We appreciate Prof. Uwatoko for fruitful discussions on the uniaxial pressure technique. This work was supported by a Grant-in-Aid for Scienti"c Research from the Ministry of Education, Science, Sports and Culture of Japan.
References [1] C. Sekine, T. Uchiumi, I. Sirotani, T. Yagi, Phys. Rev. Lett. 79 (1997) 3218. [2] N.R. Dilley, E.J. Freeman, E.D. Bauer, M.B. Maple, Phys. Rev. B 58 (1998) 6287. [3] N. Takeda, M. Ishikawa, Physica B 259}261 (1999) 923. [4] M.S. Torikachvili, J.W. Chen, Y. Dalichaouch, R.P. Guertin, M.W. McElfresh, C. Rossel, M.B. Maple, G.P. Meisner, Phys. Rev. B 36 (1987) 8660. [5] H. Sato, Y. Abe, H. Okada, T.D. Matsuda, H. Sugawara, Y. Aoki, Physica B 281 & 282 (2000) 306. [6] T.D. Matsuda, H. Okada, H. Sugawara, Y. Aoki, H. Sato, A.V. Andreev, Y. Shiokawa, V. Sechovsky, T. Honma, E. Yamamoto, Y. O nuki, Physica B 281 & 282 (2000) 220.
Pressure e!ect on the magnetic properties in PrFe P Tatsuma D. Matsuda*, Keisuke Abe, Fumihito Watanuki, Takahiro Namiki, Shanta R. Saha, Hitoshi Sugawara, Yuji Aoki, Hideyuki Sato Department of Physics, Tokyo Metropolitan University, Minami-Ohsawa 1-1, Tokyo 192-0397, Japan
Abstract The uniaxial pressure e!ect on magnetization of PrFe P single crystals has been investigated. An extremely large enhancement of magnetic susceptibility has been found at around ¹ . With increasing pressure, ¹ decreases, suggesting , , the suppression of the antiferromagnetic interaction. In the "eld dependence of magnetization, we have found an enhancement of magnetic moment with pressure at the low "eld antiferromagnetic state, suggesting that the breaking of the crystal symmetry has to be considered. 2001 Elsevier Science B.V. All rights reserved. Keywords: Filled skutterudite; PrFe P ; Uniaxial pressure; Magnetic measurement
The series of "lled skutterudite compounds RET X (RE"rare earth, actinide; T"Fe, Ru, Os; X " P, As, Sb) have attracted much attention, since the various physical properties on the systematic substitution of each element accompanied by a variety of novel phenomena, such as a metal}insulator transition [1] and intermediate valence phenomena [2,3] associated with this crystal structure have been reported. On REFe P , Torikach vili et al. have reported the "rst systematic study where they found a wide variety of interesting properties depending on RE [4]. In order to judge whether these anomalous behaviors are intrinsic, investigation on high-quality single crystals is essential. Nevertheless, reports of investigations on single crystal are few. Recently, we have succeeded in growing high-quality single crystals of REFe P and reported some anomalous behaviors in the transport and thermal properties [5,6]. PrFe P , which shows an antiferromagnetic order below ¹ &6.5 K [4], is one of the most interesting , compounds in RET P series. However, the magnetic structure of the ground state has not yet been clari"ed. At high temperatures, the resistivity shows ! log ¹ dependence and the thermoelectric power exhibits a large absolute value of !40 V/K above ¹ like the Kondo ,
* Corresponding author. Fax: #81-426-77-2487. E-mail address: [email protected] (T.D. Matsuda).
compounds. In the high "eld state above the metamagnetic transition, the value of C/¹ is extremely large(&1.4 J/Kmol), the origin of which has not been clari"ed. In this work, we report the uniaxial pressure e!ect on the magnetic properties using high-quality single crystals for the "rst time. The investigation using uniaxial pressure is a very useful method for this type of compounds which is known to be very sensitive to the substitution of elements. Especially, large distortion of lattice is expected under uniaxial pressure compared with hydrostatic pressure. The change of the symmetry is another important feature for the cubic system. Single crystal samples have been grown by the tin-#ux method [4]. Typical size of the single crystals is &4 mm. To apply a uniform uniaxial pressure on the sample, plane-shaped samples have been cut out from these crystals. The magnetic measurements were performed by using a quantum design SQUID magnetometer up to 5.5 T under uniaxial pressure in a beryllium-copper piston-cylinder-type pressure cell. The value of pressure at low temperatures has been determined by measuring the superconducting transition temperature of Pb located in the pressure cell. In these magnetic measurements, we ignore the cell contribution (below 5% at 5.5 T) in the analyses. Fig. 1 shows the temperature dependence of magnetic susceptibility () with "eld and pressure (P) along 1 0 0. At ambient pressure, exhibits a Curie}Weiss behavior down to &10 K with an e!ective magnetic moment of
0304-8853/01/$ - see front matter 2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 0 ) 0 0 6 3 0 - 2
T.D. Matsuda et al. / Journal of Magnetism and Magnetic Materials 226}230 (2001) 66}67
Fig. 1. Temperature dependence of magnetic susceptibility under the uniaxial pressure. Inset is the pressure dependence of ¹ de"ned by the peak position of the susceptibility. Broken line , is a guide to eyes.
3.6 , which is close to the value expected for a free Pr> and is consistent with the previous report [4]. A sharp peak structure in due to antiferromagnetic order is observed at ¹ "6.5 K. Below ¹ , shows a minimum , , around 3.5 K and increases with decreasing ¹, which cannot be explained either by the simple magnetic structure or by the spin wave excitation. By applying uniaxial pressure, is largely enhanced around ¹ ; i.e. the peak , value of at 1.1 kbar is more than 2 times larger than that at ambient pressure. ¹ determined by a peak position in , decreases with increasing pressures (see inset of Fig. 1), indicating the suppression of the antiferromagnetic correlation. Below ¹ , a minimum in at ambient pressure , disappears accompanied by an enhancement of by P. Above 20 K, the e!ect of the uniaxial pressure on is very small. Fig. 2 shows the "eld dependence of magnetization (M). At ambient pressure, M shows a metamagnetic transition around H "3.8 T at 2 K, which is consis + tent with the reported metamagnetic behavior in [1]. No hysteresis behavior with the metamagnetic transition is observed within the experimental accuracy. Above the metamagnetic transition, the magnetic moment &1.7 at 5.5 T is small compared to the full moment of 3.2 for Pr> ions. By applying uniaxial pressure, M is largely enhanced in the entire regions of the low "eld state, while above H , the enhancement of M is smaller than 3% at + 5.5 T. The metamagnetic transition "eld, determined by a peak in the di!erential M, does not noticeably shift with the uniaxial pressure within the experimental accuracy. At the present stage, we should consider at least three possible factors for the enhancement of M by uniaxial pressure in the low "eld state; (1) A change of the magnetic structure induced by anisotropic exchange in-
67
Fig. 2. Field dependence of magnetization under the uniaxial pressure at 2 K.
teraction resulting from the symmetry breaking. (2) A change of the crystalline electronic "eld e!ect. (3) Re-alignment of the magnetic domain structure resulting from symmetry breaking by the uniaxial pressure. All these possibilities are related to each other through the symmetry breaking e!ect. To clarify the factors responsible for the enhancement M, it is important to compare the result with the hydrostatic pressure measurement. In summary, for the "rst time, we have performed magnetic measurements on single crystalline PrFe P under uniaxial pressure. In the low "eld state, we have found an enhancement of magnetic moment, suggesting that the breaking of the crystal symmetry by uniaxial pressure has to be considered. We appreciate Prof. Uwatoko for fruitful discussions on the uniaxial pressure technique. This work was supported by a Grant-in-Aid for Scienti"c Research from the Ministry of Education, Science, Sports and Culture of Japan.
References [1] C. Sekine, T. Uchiumi, I. Sirotani, T. Yagi, Phys. Rev. Lett. 79 (1997) 3218. [2] N.R. Dilley, E.J. Freeman, E.D. Bauer, M.B. Maple, Phys. Rev. B 58 (1998) 6287. [3] N. Takeda, M. Ishikawa, Physica B 259}261 (1999) 923. [4] M.S. Torikachvili, J.W. Chen, Y. Dalichaouch, R.P. Guertin, M.W. McElfresh, C. Rossel, M.B. Maple, G.P. Meisner, Phys. Rev. B 36 (1987) 8660. [5] H. Sato, Y. Abe, H. Okada, T.D. Matsuda, H. Sugawara, Y. Aoki, Physica B 281 & 282 (2000) 306. [6] T.D. Matsuda, H. Okada, H. Sugawara, Y. Aoki, H. Sato, A.V. Andreev, Y. Shiokawa, V. Sechovsky, T. Honma, E. Yamamoto, Y. O nuki, Physica B 281 & 282 (2000) 220.