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MAGNETIC ORDERING IN THE
SUPERCONDUCTING STATE OF (La1-XSrX)2CuO4
DETECTED BY µSR
H. Kitazawa, K. Katsumata, E. Torikai, K. Nagamine
To cite this version:
JOURNAL DE PHYSIQUE
Colloque C8, Suppl6ment au no 12, Tome 49, decembre 1988
MAGNETIC ORDERING IN THE SUPERCONDUCTING STATE OF
( ~ a ~ -CuOq DETECTED BY pSR
~ ~ r ~ )H. Kitazawa ( I ) , K. Katsumata (I), E. Torikai (2)1 and K. Nagamine ( 3 )
( I ) T h e Institute of Physical and Chemical Reseach (RIKEN), Wako, Saitama 351-01, Japan
(2) T h e Doctoral Research Course in Human Culture, Ochanomizu University, Bunkyo-ku, Tokyo 112, Japan (3) Meson Science Laboratory, Faculty of Science, University of Tokyo ( U T - M S L ) , Bunkyo-ku, Tokyo 118, Japan Abstract.
-
The positive muon spin relaxation method has been applied to investigate single crystals of the oxide superconductor (Lal-xSrx)2 Cu04. It is concluded that a magnetic ordering coexsists with the superconductivity for the X = 0.04 sample from the temperature dependences of the initial polarization and the relaxation rate.Several models based on magnetic interactions t o produce electron pairing have been proposed for the origin of high transition temperature superconductiv- ity (Tc) [I-31. However there has been no direct ex- perimental proofs for these models yet. Recently, the existence of a new magnetic phase in the low Sr con- centration region between the antiferromagnetic (AF)
and superconducting (SC) phase of the high Tc ox- ide superconductors, (Lal-x Arx), Cu04-6 (A = Ca, Sr, Ba) has been revealed by means of the NQR mea- surements [4, 51. It seems that this phase diagram is suggestive for the importance of the magnetic in- teraction. We have performed positive muon spin relaxation ( ~ t + SR) measurements on single crystals of (Lal-xSrx), CuOr-6 (LSCO) with the concentra- tion from the AF phase (X = 0) t o the SC phase ( X = 0.04). Recently we have reported [6] that the magnetically ordered phase coexists with the super- conducting one in the case of X = 0.04. In this paper we studied the magnetic ordering in the SC state of LSCO using the microscopic magnetic probe, p+.
Four kinds of single crystals of LSCO (X = 0, 0.01, 0.02, 0.04) as large as 15 x 15 x 3 mm3 were grown using CuO as a flux. The hSR measurements were carried out at the Booster Meson Facility of the Me- son Science Laboratory, University of Tokyo located at KEK, Tsukuba, Japan. We deduce the time spectrum of A (0) Gz ( t ) from the measurement of the positron intensity emitted from the muons. Here A (0) is the ini- tial asymmetry of the p+ spin polarization and G z ( t )
is the longitudinal relaxation function in the case when the external field is applied a l o ~ g the p+ spin direc- tion. The single crystals were placed with the c-axis parallel t o the direction of the initial spin polariza- tion. Each time spectrum was analyzed by assuming that Gz (t) has the Gaussian or exponential functional
form.
Figures la, l b show the temperature dependences of the relaxation rate (A) and the reduced initial as-
0 1
' " 1 ' " ' 1 I " ''
' ' 1
1 '5 10 50 100 500
T ( K )
Fig. 1. - The temperature dependences of the re- laxation rate and the reduced initial asymmetry in (Lal-xSrx) CuOc-6 obtained from the present analysis.
(e) and (A); Gaussian, (o), (A), ( a ) and (V); Exponan- tial.
symetry (A ( 0 ) /A,,,,), where A,,,, corresponds to the initial asymmetry a t the paramagnetic phase. The time spectra of the X = 0.02 and 0.04 samples were measured in zero field. It is found that in high temper- ature region (T
>
7 K) the zero field time spectrum is well fitted with the Gaussian form. This suggests that the muon spin relaxation is caused by the static ran- dom field originated from nuclear dipole moments [7].On the other hand, the time spectrum is fitted with an exponential form better than the Gaussian one below 7 K, reflecting the dynamical effect such as exchange narrowing. For the X = 0.04 sample, which has the
'Present address: Faculty of Engineering, Yamanashi University, Kofu, Yamanashi 400, Japan.
C8 - 2150 JOURNAL DE PHYSIQUE
superconducting transition temperature a t 11 K, both the A (0) and X show no anomaly a t around Tc. On the other hand, A (0) suddenly decreases a t around 5 K. At the same time, X has a steep maximum a t around 5 K. The X = 0.02 sample which is in the normal state down t o 2.8 K, show anomalies in the asymmetry and the relaxation rate a t around 5 K.
The time spectra of the X = 0 and 0.01 samples were measured under the longitudinal field of 30 Oe. The longitudinal field was applied to reduce the ef- fect of the nuclear dipolar field. It is found that un- der the longitudinal field the time spectra can be fit- ted with the exponential form in all the temperature
range. For the X = 0 sample, A (0) decreases very steeply a t around the antiferromagnetic ordering tem- perature TN (250 K). For the X = 0.01 sample, the temperature dependences of the relaxation rate and
A (0) behave similarly t o the X = 0.02 sample. This means that the X = 0.01 sample undergoes the same magnetic ordering as the X = 0.02 one. The mag- netic susceptibility for the X = 0.04 sample is almost independent on temperature at least above 77 K and shows 66 % of the ideal value of the Meissner effect at 4.2 K [6]. It is concluded that the X = 0.04 sample undergoes a magnetic phase transition at 5 K in the superconductivity state.
Figure 2 shows the concentration
-
temperature phase diagram obtained from the result of pSR and electrical resistivity measurements [6, 81. The NBel temperature suddenly decreases with increase of Sr.But TN does not show such a large concentration
dependence above about X = 0.01. Our result is consistent with that of NQR for (Lal-xBrx), Cu04 (LBCO) by Kitaoka et al. [5]. Our new finding is the
coexistence of the magnetism witb the superconduc- tivity a t X = 0.04. Watanabe et al. have found the
existence of a new r>hase for LBCO between the antifer- romagnetic phase and superconducting phase 141. Re-
cently Aharony et al. have predicted that a spin-glass
(SG) phase appears in the concentrations between the A F and SC phase [9]. Niedermayer et al. have re- ported that the X = 0.02 sample is antiferromagnetic from the pSR experiment (101. As for the magnetic phase X = 0.04, we need further experimental studies t o identify whether it is the AF phase or the spin-glass phase.
Why the magnetic ordering state can coexist with the superconductivity in the case of the X = 0.04 sam- ple? The LSCO system is different from Chevrel com- pounds, such as REMoS8, in which the magnetic order- ing is reported t o coexist with the superconductivity. In this case the rare earth atoms and Mo 5d-electrons cause the magnetic ordering and the superconducting current, separately [ll]. In LSCO, we have only one kind of atom (Cu) which is supposed t o be responsible for both the magnetism and superconductivity.
Fig. 2. - The magnetic transition temperature
(a)
o b tained from the present study. The superconducting (+[a]
and I3[6]) transition temperatures are also shown. AF; an- tiferromagnetic phase, SC; superconducting phase, M; mag- netic phase, N; normal (paramagnetic) phase.Acknowledgements
This work was partially supported by a Research Fund from RIKEN and by Grant-in-Aid for Special Project Research on Meson Science of Ministry of Ed- ucation, Science and Culture of Japan.
[I] Anderson, P. ,W., Science 235 (1987) 1196. [2] Aoki, H. and Kamimura, H., Solid State Commun.
63 (1987) 665.
[3] Emery, V. J., Phys. Rev. Lett. 58 (1987) 2794.
[4] Watanabe, I., Kumagai, K., Nakamura, Y., Kimura, T., Nakamichi, Y. and Nakajima, H., J.
Phys. Soc. Jpn 56 (1987) 3028.
[5] Kitaoka, Y., Tshida, K., Hiramatsu, S. and Asayama, K., J. Pkys. Soc. J p n 57 (1987) 734. [6] Kitazawa, H., Katsumata, K., Torikai, E. and
Nagamine, K., Solid State Commun. 67 (1988) 1191.
[7] Kubo, R. and Toyabe, T., Magnetic Resonance and Relaxation (Ed. R. Blinc, North-Holland, Amsterdam) 1967.
[8] Uchida, S., Takagi, H., Kitazawa, K. and Tanaka,
S., Jpn J. Appl. Pkys. Lett. 26 (1987) L1.
[9] Aharony, A., Birgeneau, R. J., Coniglio, A., Kast-
ner, M. A. and Stanley, H. E., Phys. Rev. Lett. 60 (1985) 1330.
[lo] Niedermayer, Ch., Budnick, J. I., Chamberland, B., Golinik, A., Recknagel, E., Rossmanith, M., Weidinger, A. and Yang, D. P., in press.
[ l l ] Ishikawa, M. and Fischer,
