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Magnetic characterization of Ba(Fe0.9Co0.1)2As2
Physica C 470 (2010) S397–S398
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Physica C journal homepage: www.elsevier.com/locate/physc
Magnetic characterization of BaðFe0:9 Co0:1 Þ2 As2 S. Gaudio a,*, G. de Marzi a, A. Angrisani Armenio a, G. Celentano a, L. Morici a, A. della Corte a, U. Gambardella b, J. Jiang c, E.E. Hellstrom c, J.D. Weiss c, D.C. Larbalestier c a
ENEA Frascati Research Centre, Frascati 00044, Italy CNR-INFM, SuperMat Regional Laboratory, 84081 Baronissi, Italy c NHMFL, Florida State University, Tallahassee, FL 32310, USA b
a r t i c l e
i n f o
Article history: Accepted 27 October 2009 Available online 31 October 2009 Keywords: Iron based superconductors Pnictides Dc magnetic properties
a b s t r a c t We performed a magnetic characterization of BaðFe1x Cox Þ2 As2 polycrystal. We show the hysteretic behavior as a function of the magnetic field, the AC susceptibility and the magnetization as a function of temperature. When compared with single crystals, our Jc values are lower whereas the Hirr ones are higher, probably due to intergrain weak links and different critical temperatures. Ó 2009 Elsevier B.V. All rights reserved.
We report on the magnetic characterization of BaðFe1x Cox Þ2 As2 (x = 0.10) polycrystalline sample. Cobalt-doped sample have been synthesized at the NHFML labs, and its dimensions are 0:1 0:3 0:5 mm3 . Magnetization measurements have been carried out by means of a Vibrating Sample Magnetometer (VSM, Oxford Instruments), operating with magnetic fields up to 12 T, and at variable temperatures through a controlled helium gas flow. In Fig. 1 we show the magnetization (M) vs. temperature (T) measured in zero-field-cooling (ZFC) and field-cooling (FC) conditions at an applied field of 100 Oe. Since M varies linearly with fields up to 100 Oe at 4.2 K, the ZFC M shows that the system is still fully shielded for temperatures up to 15 K, with a rather broad transition to the normal state with T c 24 K; this is higher than the one in the single crystal [2] with same nominal doping. The FC signal is strongly reduced, indicative of the high-efficiency of pinning. The ac susceptibility at H ¼ 103 Oe between 30 and 200 K (inset of Fig. 1) shows a different temperature dependence and a larger value in comparison with the single crystal [1], likely due to magnetic impurities. Fig. 2 shows magnetization hysteresis loops which exhibit a small fish-tail hump at 5–10 T, similar to that of single crystals [2]. However, when compared with the single crystals [2], M in the polycrystalline sample is found to be one order of magnitude lower. The critical current density J c should scale accordingly, hence the expected J c should be of the order of 104 A=cm2 at T = 4.2 K. On the other hand, the Hirr derived from the closure point * Corresponding author. Tel.: +39 06 94005827. E-mail address: [email protected] (S. Gaudio). 0921-4534/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2009.10.136
of the hysteresis loops results considerably higher than the single crystal one. In fact, at 15 K, we get Hirr > 12 T (at 20 K Hirr 10 T), whereas for the single crystal this is Hirr 12 T ðHirr 3 TÞ [2]. As it can be seen in the inset of Fig. 2, the sample presents a magnetic state above T c , comprised a paramagnetic state and a hysteretic contribution at lower field. The hysteresis decreases as the temperature is raised.
Fig. 1. M (T) in ZFC and FC at 100 Oe. Inset: vðTÞ above T c in a background field of 103 Oe.
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S. Gaudio et al. / Physica C 470 (2010) S397–S398
In conclusion, when compared with single crystals, the polycrystalline sample has: (a) lower J c and (b) higher Hirr down to 15 K, probably due to weak links at the grain boundaries, as in [3], and the difference in T c . References [1] A.S. Sefat et al., Phys. Rev. B 77 (2008) 174503. [2] A. Yamamoto et al., Appl. Phys. Lett. 94 (2009) 062511. [3] S. Lee, J. Jiang, et al., arXiv: cond-mat/0907.3741, 2009.
Fig. 2. Magnetic hysteresis loops collected at different temperatures.
Contents lists available at ScienceDirect
Physica C journal homepage: www.elsevier.com/locate/physc
Magnetic characterization of BaðFe0:9 Co0:1 Þ2 As2 S. Gaudio a,*, G. de Marzi a, A. Angrisani Armenio a, G. Celentano a, L. Morici a, A. della Corte a, U. Gambardella b, J. Jiang c, E.E. Hellstrom c, J.D. Weiss c, D.C. Larbalestier c a
ENEA Frascati Research Centre, Frascati 00044, Italy CNR-INFM, SuperMat Regional Laboratory, 84081 Baronissi, Italy c NHMFL, Florida State University, Tallahassee, FL 32310, USA b
a r t i c l e
i n f o
Article history: Accepted 27 October 2009 Available online 31 October 2009 Keywords: Iron based superconductors Pnictides Dc magnetic properties
a b s t r a c t We performed a magnetic characterization of BaðFe1x Cox Þ2 As2 polycrystal. We show the hysteretic behavior as a function of the magnetic field, the AC susceptibility and the magnetization as a function of temperature. When compared with single crystals, our Jc values are lower whereas the Hirr ones are higher, probably due to intergrain weak links and different critical temperatures. Ó 2009 Elsevier B.V. All rights reserved.
We report on the magnetic characterization of BaðFe1x Cox Þ2 As2 (x = 0.10) polycrystalline sample. Cobalt-doped sample have been synthesized at the NHFML labs, and its dimensions are 0:1 0:3 0:5 mm3 . Magnetization measurements have been carried out by means of a Vibrating Sample Magnetometer (VSM, Oxford Instruments), operating with magnetic fields up to 12 T, and at variable temperatures through a controlled helium gas flow. In Fig. 1 we show the magnetization (M) vs. temperature (T) measured in zero-field-cooling (ZFC) and field-cooling (FC) conditions at an applied field of 100 Oe. Since M varies linearly with fields up to 100 Oe at 4.2 K, the ZFC M shows that the system is still fully shielded for temperatures up to 15 K, with a rather broad transition to the normal state with T c 24 K; this is higher than the one in the single crystal [2] with same nominal doping. The FC signal is strongly reduced, indicative of the high-efficiency of pinning. The ac susceptibility at H ¼ 103 Oe between 30 and 200 K (inset of Fig. 1) shows a different temperature dependence and a larger value in comparison with the single crystal [1], likely due to magnetic impurities. Fig. 2 shows magnetization hysteresis loops which exhibit a small fish-tail hump at 5–10 T, similar to that of single crystals [2]. However, when compared with the single crystals [2], M in the polycrystalline sample is found to be one order of magnitude lower. The critical current density J c should scale accordingly, hence the expected J c should be of the order of 104 A=cm2 at T = 4.2 K. On the other hand, the Hirr derived from the closure point * Corresponding author. Tel.: +39 06 94005827. E-mail address: [email protected] (S. Gaudio). 0921-4534/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2009.10.136
of the hysteresis loops results considerably higher than the single crystal one. In fact, at 15 K, we get Hirr > 12 T (at 20 K Hirr 10 T), whereas for the single crystal this is Hirr 12 T ðHirr 3 TÞ [2]. As it can be seen in the inset of Fig. 2, the sample presents a magnetic state above T c , comprised a paramagnetic state and a hysteretic contribution at lower field. The hysteresis decreases as the temperature is raised.
Fig. 1. M (T) in ZFC and FC at 100 Oe. Inset: vðTÞ above T c in a background field of 103 Oe.
S398
S. Gaudio et al. / Physica C 470 (2010) S397–S398
In conclusion, when compared with single crystals, the polycrystalline sample has: (a) lower J c and (b) higher Hirr down to 15 K, probably due to weak links at the grain boundaries, as in [3], and the difference in T c . References [1] A.S. Sefat et al., Phys. Rev. B 77 (2008) 174503. [2] A. Yamamoto et al., Appl. Phys. Lett. 94 (2009) 062511. [3] S. Lee, J. Jiang, et al., arXiv: cond-mat/0907.3741, 2009.
Fig. 2. Magnetic hysteresis loops collected at different temperatures.