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Anomalous temperature dependence of resistance in hyperfine enhanced nuclear antiferromagnet PrIn3 at mK-temperatures
Physica B 284}288 (2000) 1690}1691
Anomalous temperature dependence of resistance in hyper"ne enhanced nuclear antiferromagnet PrIn at mK-temperatures Yoshitomo Karaki *, Minoru Kubota , Hidehiko Ishimoto , Yoshichika O nuki Institute for Solid State Physics, University of Tokyo, 7-22-1 Roppongi, Minato-ku, Tokyo 106-8666, Japan Department of Physics, Osaka University, Toyonaka, Osaka, 560-0043, Japan
Abstract We have measured electrical resistance in a single crystal of PrIn down to temperatures below 0.1 mK. A minimum of the resistance is observed at 3 mK, below which the resistance increases gradually as temperature decreases. No remarkable change in the resistance is found at a nuclear antiferromagnetic ordering temperature of ¹ "0.14 mK. 2000 Elsevier Science B.V. All rights reserved. , Keywords: Electrical resistance; Nuclear quadrupole moment; Van Vleck paramagnet
Nuclear spins usually interact weakly with conduction electrons. However, those in a Van Vleck paramagnet such as Pr inter-metallic compounds have strong coupling with the conduction electrons because of the large hyper"ne interaction and the s}f interaction. This is the origin of hyper"ne enhanced nuclear magnetism. The interaction between nuclear spins is strongly enhanced and the ordering temperature becomes of the order of mK. Temperature dependence of resistance near the nuclear ferromagnetic ordering in a Van Vleck paramagnet has been studied by two groups so far [1,2]. Miki et al. observed a resistance decrease at the ferromagnetic transition of PrCu . However, for antiferromagnetic or dering there are no studies until now. PrIn is one of the few Van Vleck paramagnets which show antiferromagnetic nuclear ordering [3]; ¹ is 0.14 mK. A remarkable , feature of PrIn is a large nuclear quadrupole interaction (eqQ/h"#228 MHz) at the indium site [4]. Because of the large quadrupole interaction, the ordering of the In quadrupole moment begins at &10 mK and is almost accomplished below 0.2 mK. We have studied the
* Corresponding author. E-mail address: [email protected] (Y. Karaki)
resistance of PrIn from following viewpoints: One is the observation of resistance anomaly at ¹ . The other is the , e!ect of the nuclear quadrupole moment on conduction electrons. Sample was a single crystal of PrIn grown by the Czochralski pulling method. Crystal structure is of the cubic Cu Au type. The residual resistivity ratio (RRR) of the sample is about 160. This value is considerably large among Pr intermetallic compounds and gives evidence for high quality of the sample. It was cut into a thin plate of 2;0.5;15 mm. The sample was glued to a silver sample holder with silver epoxy. The holder was mounted on the second stage of the two-stage nuclear demagnetization refrigerator which was used in the previous speci"c heat measurments [4]. Temperature of the sample was measured by a platinum NMR thermometer on the second stage below 15 mK and by a resistance thermometer above 15 mK. These were calibrated against a He-MC thermometer on the "rst stage. Resistance of the sample was measured with an AC impedance bridge method where a SQUID was used as a null detector. The AC excitation current of 16 Hz and 50 lA (peak to peak) was aligned along [1 1 1]. The heat dissipation due to the current was on the order of 10\ W which causes a negligible temperature di!erence between the sample and the thermometer.
0921-4526/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 9 9 ) 0 2 9 1 9 - 1
Y. Karaki et al. / Physica B 284}288 (2000) 1690}1691
Fig. 1. The resistance of PrIn at B"0.
1691
the Van Vleck paramagnet shows a resistance anomaly only in the vicinity of the transition temperature [5]. It could be possible to observe the anomaly for the other current directions than [1 1 1]. Secondly, a minimum in the resistance is seen at about 3 mK, below which the resistance increases gradually and approaches a saturation value below 0.2 mK. A resistance minimum is a well known feature of the Kondo e!ect. In fact, the sample contained 3d magnetic impurities of Fe(10 ppm) and Mn(3 ppm). However, the magnetization measurement at 3 mT showed free spin behavior of impurities, followed by saturation below 3 mK [3]. Hence, the impurity spins are fully polarized below 10 mK at 10 mT and no serious in#uence is expected for the conduction electrons. Nevertheless, the temperature dependence at 10 mT in Fig. 2 is similar to that in zero "eld, in contradiction to the Kondo e!ect. Therefore, a possible cause of the resistance anomaly observed below 10 mK might be the interaction between the conduction electrons and the quadrupole moment which shows ordering below 10 mK. Theoretical studies on the e!ect would be highly desirable.
References
Fig. 2. The resistance of PrIn at B"10 mT.
The resistance of PrIn below 50 mK at B"0 is shown in Fig. 1. First, no remarkable resistance change was observed at ¹ of 0.14 mK, although the mean "eld , calculation predicts that the nuclear magnetic ordering of
[1] J. Kiely, T. Manley, W. Weyhmann, J. Low Temp. Phys. 67 (1987) 291. [2] T. Miki, M. Yanaka, M. Nakagawa, D. Kim, O. Ishikawa, T. Hata, H. Ishii, T. Kodama, Phys. Rev. Lett. 69 (1992) 375. [3] Y. Karaki, M. Kubota, H. Ishimoto, Y. O nuki, Phys. Rev. B, in preparation. [4] Y. Karaki, Y. Koike, M. Kubota, H. Ishimoto, Y. O nuki, Czech. J. Phys. 46 (Suppl. S4) (1996) 2209. [5] H. Ishii, J. Magn. Magn. Mater. 76&77 (1988) 247.
Anomalous temperature dependence of resistance in hyper"ne enhanced nuclear antiferromagnet PrIn at mK-temperatures Yoshitomo Karaki *, Minoru Kubota , Hidehiko Ishimoto , Yoshichika O nuki Institute for Solid State Physics, University of Tokyo, 7-22-1 Roppongi, Minato-ku, Tokyo 106-8666, Japan Department of Physics, Osaka University, Toyonaka, Osaka, 560-0043, Japan
Abstract We have measured electrical resistance in a single crystal of PrIn down to temperatures below 0.1 mK. A minimum of the resistance is observed at 3 mK, below which the resistance increases gradually as temperature decreases. No remarkable change in the resistance is found at a nuclear antiferromagnetic ordering temperature of ¹ "0.14 mK. 2000 Elsevier Science B.V. All rights reserved. , Keywords: Electrical resistance; Nuclear quadrupole moment; Van Vleck paramagnet
Nuclear spins usually interact weakly with conduction electrons. However, those in a Van Vleck paramagnet such as Pr inter-metallic compounds have strong coupling with the conduction electrons because of the large hyper"ne interaction and the s}f interaction. This is the origin of hyper"ne enhanced nuclear magnetism. The interaction between nuclear spins is strongly enhanced and the ordering temperature becomes of the order of mK. Temperature dependence of resistance near the nuclear ferromagnetic ordering in a Van Vleck paramagnet has been studied by two groups so far [1,2]. Miki et al. observed a resistance decrease at the ferromagnetic transition of PrCu . However, for antiferromagnetic or dering there are no studies until now. PrIn is one of the few Van Vleck paramagnets which show antiferromagnetic nuclear ordering [3]; ¹ is 0.14 mK. A remarkable , feature of PrIn is a large nuclear quadrupole interaction (eqQ/h"#228 MHz) at the indium site [4]. Because of the large quadrupole interaction, the ordering of the In quadrupole moment begins at &10 mK and is almost accomplished below 0.2 mK. We have studied the
* Corresponding author. E-mail address: [email protected] (Y. Karaki)
resistance of PrIn from following viewpoints: One is the observation of resistance anomaly at ¹ . The other is the , e!ect of the nuclear quadrupole moment on conduction electrons. Sample was a single crystal of PrIn grown by the Czochralski pulling method. Crystal structure is of the cubic Cu Au type. The residual resistivity ratio (RRR) of the sample is about 160. This value is considerably large among Pr intermetallic compounds and gives evidence for high quality of the sample. It was cut into a thin plate of 2;0.5;15 mm. The sample was glued to a silver sample holder with silver epoxy. The holder was mounted on the second stage of the two-stage nuclear demagnetization refrigerator which was used in the previous speci"c heat measurments [4]. Temperature of the sample was measured by a platinum NMR thermometer on the second stage below 15 mK and by a resistance thermometer above 15 mK. These were calibrated against a He-MC thermometer on the "rst stage. Resistance of the sample was measured with an AC impedance bridge method where a SQUID was used as a null detector. The AC excitation current of 16 Hz and 50 lA (peak to peak) was aligned along [1 1 1]. The heat dissipation due to the current was on the order of 10\ W which causes a negligible temperature di!erence between the sample and the thermometer.
0921-4526/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 9 9 ) 0 2 9 1 9 - 1
Y. Karaki et al. / Physica B 284}288 (2000) 1690}1691
Fig. 1. The resistance of PrIn at B"0.
1691
the Van Vleck paramagnet shows a resistance anomaly only in the vicinity of the transition temperature [5]. It could be possible to observe the anomaly for the other current directions than [1 1 1]. Secondly, a minimum in the resistance is seen at about 3 mK, below which the resistance increases gradually and approaches a saturation value below 0.2 mK. A resistance minimum is a well known feature of the Kondo e!ect. In fact, the sample contained 3d magnetic impurities of Fe(10 ppm) and Mn(3 ppm). However, the magnetization measurement at 3 mT showed free spin behavior of impurities, followed by saturation below 3 mK [3]. Hence, the impurity spins are fully polarized below 10 mK at 10 mT and no serious in#uence is expected for the conduction electrons. Nevertheless, the temperature dependence at 10 mT in Fig. 2 is similar to that in zero "eld, in contradiction to the Kondo e!ect. Therefore, a possible cause of the resistance anomaly observed below 10 mK might be the interaction between the conduction electrons and the quadrupole moment which shows ordering below 10 mK. Theoretical studies on the e!ect would be highly desirable.
References
Fig. 2. The resistance of PrIn at B"10 mT.
The resistance of PrIn below 50 mK at B"0 is shown in Fig. 1. First, no remarkable resistance change was observed at ¹ of 0.14 mK, although the mean "eld , calculation predicts that the nuclear magnetic ordering of
[1] J. Kiely, T. Manley, W. Weyhmann, J. Low Temp. Phys. 67 (1987) 291. [2] T. Miki, M. Yanaka, M. Nakagawa, D. Kim, O. Ishikawa, T. Hata, H. Ishii, T. Kodama, Phys. Rev. Lett. 69 (1992) 375. [3] Y. Karaki, M. Kubota, H. Ishimoto, Y. O nuki, Phys. Rev. B, in preparation. [4] Y. Karaki, Y. Koike, M. Kubota, H. Ishimoto, Y. O nuki, Czech. J. Phys. 46 (Suppl. S4) (1996) 2209. [5] H. Ishii, J. Magn. Magn. Mater. 76&77 (1988) 247.