- Email: [email protected]
Low temperature magnetic ordering in Bi2CuO4
ELSEVIER
Journal of Magnetism and Magnetic Materials 196-197 11999) 532-533
Journal of magnetism and magnetic materials
Low temperature magnetic ordering in Bi2CuO4 M. Baran a, Yu.P. Gaidukov b, N.P. Danilova b, A.V. Inushkin c, A. Jedrzejczak a, Yu.A. Koksharov b, V.N. Nikiforov b'*, A. Revcolevschi d, R. Szymczak a, H. S z y m c z a k a ~lnstitute ~f Physics. Polish Acaden~v ~f Seienee. 02-668, Warsaw. Pohmd hFaculo' of Physics, Low Temperature Department, M. ~ Lomonosor Moscow State UniversiO,, 119899 Moscow, Russia ~lnstitute of Molecular Physics, Russian Research Centgr "Kurchatot~" Institute" 123182, Moscow. Ruxsia %aboratoire de Chimie des Solides (CNRS) Batiment 414-91405 Otw~0 Cedex-France
Abstract
The magnetic moment and the specific heat of a single crystal and polycrystalline samples of Bi2CuO 4 have been measured at the temperatures 2-300 K and magnetic fields 0.1-5 T with the help of a SQUID magnetometer and the calorimetric relaxation technique. The possible origins of unusual increasing of the DC magnetic susceptibility below 15-20 K are discussed. We also compared our results on single crystals and polycrystalline samples. ,~" 1999 Published by Elsevier Science B.V. All rights reserved. Keywords: DC
magnetic susceptibility; Specific heat: Antiferromagnetic; Single crystal; Polycrystaltine; Lowtemperature magnetism
Our work presents the experimental data on magnetic and calorimetric properties of large ( l l 0 m g ) singlecrystal and polycrystalline samples of Bi2CuO4 at a wide range of temperatures (2-300 K) and magnetic fields 10.01-5 T). The single crystal preparation method is the same as described in Ref. [1]. Stoichiometric polycrytalline B i 2 C u O 4 samples were synthesized with the help of the standard ceramic technique by mixing Bi203 and CuO. The magnetic moment susceptibility and magnetization studies have been performed using a commercial SQUID magnetometer. The heat capacity has been measured by means of standard relaxation technique. The anisotropy of the magnetization has been investigated below 43 K. Our data confirmed the easy-plane type of A F ordering. There is a smoothed-out 'spin-flop' transition for H[la (Fig. 1). The magnetization for H[Ic is very linear at all temperatures. It is interesting that up to
* Corresponding author. E-mail: [email protected],su.
5 T the curves M(H) demonstrate sufficient anisotropy (see inset of Fig. 1). We have compared the thermal and field dependences of the magnetic moment M for the single-crystal and polycrystalline samples. To do it, the average magnetic susceptibility of single crystal have been calculated using the formula [2] L,v = (I/3)(Z, + Zb + Z,.) = (1/3)(2Z, + Z,). Fig. 2a represents Z(T) for the polycrystalline sample (curve A), Zav (curve B) and difference AZ between them (curve C). One can see that a decreasing of AT, is starting at 44 K (that is very close to TN) and vanishes at very low temperatures. The magnetization of polycrystalline sample is good in accordance with M(H) curve for Hlla (Fig. 2b). The thermal dependence of the specific heat C(Tt has a peculiarity at T~ ~ 12 K. Fig. 3 shows the curve C(T} for the single crystal below 20 K. The specific heat is proportional to T 3"2 below T~ and obeys the law T 2 6 above this temperature.
0304-8853/99/$ - see front matter :~ 1999 Published by Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 9 8 ) 0 0 8 76-2
M. Baran et al. / Journal of Magnetism and Magnetic Materials 196-197 (1999) 532-533
01 : :=',:
m 10
533
11 ~T2'6
LZ 0 ~ 0
, 10 H (kOe)
H (kOe)
I 20
10 Temperature (K)
Fig. 1. Magnetization curves for the single crystal Bi2CuO4 at 5 K and for different orientations of the magnetic field with respect to the crystallographic axis. The inset shows the magnetic moment versus magnetic field up to 50 kOe.
54-
~ T
40 35 ooi
--,~ Hlla ...... H[Ic / d' E' ~ / /
30 [] =49[]K u ° ° °m° ° i
o o
o
T = 20 K
%
umo
T=,~K
polyctys[al
~ 25 ,,:
2o
o
7
~ t5
32
10
1-
i~i!/i
l C
5. a)
0
b) 00
T(K)
0.2
0 4
0.6
08
H(T)
Fig. 2. (a) Comparison between the thermal dependence of the magnetic susceptibility of Bi2CuO4 in polycrystalline sample and single crystal. Curve A: polycrystalline sample (H = 5 kOe); curve B: average susceptibility, calculated from data for the single crystal (H = 1 kOe); curve C: difference between curve A and B. (b) Comparison between the magnetization curves for polycrystalline sample and single crystal of BizCuO4. Squares correspond to the polycrystalline sample. The temperature is equal to 20 K.
Fig. 3. The thermal dependence of the specific heat of the single crystal BizCuO4 from 4 up to 20 K. variation of magnetocrystalline anisotropy parameters (MAP) KIL and K~. A F resonance data [6] show a strong temperature dependence of the resonance parameters below 20 K [7] and predict a decreasing of the parameter KII by a factor 3 on cooling from 20 down to 10 K. It was suggested [-2] that the M A P play important role in the variation of the magnetic susceptibility in AF state. Hence, if the M A P decrease significantly below 15-20 K, it can result to increasing of Z± and ZiP Our results of specific heat studies on the single-crystal and the polycrystalline samples [8] indicate some magnetic or structural transition at the specific temperature TI (Fig. 3). There is some evidence that this low-temperature transition may be concerned with the change of a mobility of A F domain walls in (ab) plane [6]. The latter effect could be due to the decreasing of K± below T1. In conclusion, the magnetic anomaly in Bi2CuO4 below 20 K is similar as in poly- as in single crystal and, probably, do not result from the impurities presence in the sample. We suppose that increasing of magnetic susceptibility at low temperatures is due to the decreasing of MAP.
References
The anomalous increasing of the DC magnetic susceptibility below 1 5 - 2 0 K was initially attributed to exchange-coupling chains of Cu 2+ I-3] or paramagnetic impurities/oxygen vacancies [4]. The first possibility is unlikely because of the 3D character of the interactions in BizCuO4. In order to examine the effect of the oxygen deficiencies the annealed polycrystalline samples have been studied but no difference between annealed and as-grown samples was found [4]. Assuming the paramagnetic impurities we should accept that in all samples (polycrystalline and single crystals) these are identical. There is a little likelihood of it. The other reason of increasing Z below 15 K may be due to the spin-wave behaviour [5]. But the slope of the curve z(T) rejects this possibility. Probably, the temperature variation of the magnetic susceptibility below 20 K is determined by the
[1] G. Dhalenne, A. Revcolevschi, M. Ain, B. Hennion, G. Andre, Cryst. Prop. Prep. 36-38 (1991) 11. [2] J.B. Goodenough, Magnetism and the Chemical Bond, Interscience Publishers, Wiley, New York, London, 1963. [3] K. Sreedhar, P, Ganguly, S. Ramasesha, J. Phys. C 21 (1988) 1129. [4] K. Yamada, K. Takada, S. Hosoya, Y. Watanbe, Y. Endoh, N. Tomonaga, T. Suzuki, T. Ishigaki, T. Kamiyama, H. Asano, F. Izumi, J. Phys. Soc. Japan 60 (7) (1991) 2406. [5] F. Keffer, in: S.N.Y. Flugge (Ed.), Handbuch der Physik, Vol. 18/2, Springer, Berlin, 1966. [6] L.E. Svistov, V.A. Chubarenko, A.Ya. Shapiro, A.V. Zalesski, G.A. Petrakovski, J. Exp. Theoret. Phys. 86 (1998) 1228. [7] G.A. Petrakovskii, K.A. Sablina, A.I. Pankrats, V.M. Vorotinov, A. Furrer, B. Roessli, P. Fischer, J. Magn. Magn. Mater. 140-144 (1995) 1991. [8] Yu.P. Gaidukov, V.N. Nikiforov, N.N. Samarin, Low Temp. Phys. 22 (1996) 705.
Journal of Magnetism and Magnetic Materials 196-197 11999) 532-533
Journal of magnetism and magnetic materials
Low temperature magnetic ordering in Bi2CuO4 M. Baran a, Yu.P. Gaidukov b, N.P. Danilova b, A.V. Inushkin c, A. Jedrzejczak a, Yu.A. Koksharov b, V.N. Nikiforov b'*, A. Revcolevschi d, R. Szymczak a, H. S z y m c z a k a ~lnstitute ~f Physics. Polish Acaden~v ~f Seienee. 02-668, Warsaw. Pohmd hFaculo' of Physics, Low Temperature Department, M. ~ Lomonosor Moscow State UniversiO,, 119899 Moscow, Russia ~lnstitute of Molecular Physics, Russian Research Centgr "Kurchatot~" Institute" 123182, Moscow. Ruxsia %aboratoire de Chimie des Solides (CNRS) Batiment 414-91405 Otw~0 Cedex-France
Abstract
The magnetic moment and the specific heat of a single crystal and polycrystalline samples of Bi2CuO 4 have been measured at the temperatures 2-300 K and magnetic fields 0.1-5 T with the help of a SQUID magnetometer and the calorimetric relaxation technique. The possible origins of unusual increasing of the DC magnetic susceptibility below 15-20 K are discussed. We also compared our results on single crystals and polycrystalline samples. ,~" 1999 Published by Elsevier Science B.V. All rights reserved. Keywords: DC
magnetic susceptibility; Specific heat: Antiferromagnetic; Single crystal; Polycrystaltine; Lowtemperature magnetism
Our work presents the experimental data on magnetic and calorimetric properties of large ( l l 0 m g ) singlecrystal and polycrystalline samples of Bi2CuO4 at a wide range of temperatures (2-300 K) and magnetic fields 10.01-5 T). The single crystal preparation method is the same as described in Ref. [1]. Stoichiometric polycrytalline B i 2 C u O 4 samples were synthesized with the help of the standard ceramic technique by mixing Bi203 and CuO. The magnetic moment susceptibility and magnetization studies have been performed using a commercial SQUID magnetometer. The heat capacity has been measured by means of standard relaxation technique. The anisotropy of the magnetization has been investigated below 43 K. Our data confirmed the easy-plane type of A F ordering. There is a smoothed-out 'spin-flop' transition for H[la (Fig. 1). The magnetization for H[Ic is very linear at all temperatures. It is interesting that up to
* Corresponding author. E-mail: [email protected],su.
5 T the curves M(H) demonstrate sufficient anisotropy (see inset of Fig. 1). We have compared the thermal and field dependences of the magnetic moment M for the single-crystal and polycrystalline samples. To do it, the average magnetic susceptibility of single crystal have been calculated using the formula [2] L,v = (I/3)(Z, + Zb + Z,.) = (1/3)(2Z, + Z,). Fig. 2a represents Z(T) for the polycrystalline sample (curve A), Zav (curve B) and difference AZ between them (curve C). One can see that a decreasing of AT, is starting at 44 K (that is very close to TN) and vanishes at very low temperatures. The magnetization of polycrystalline sample is good in accordance with M(H) curve for Hlla (Fig. 2b). The thermal dependence of the specific heat C(Tt has a peculiarity at T~ ~ 12 K. Fig. 3 shows the curve C(T} for the single crystal below 20 K. The specific heat is proportional to T 3"2 below T~ and obeys the law T 2 6 above this temperature.
0304-8853/99/$ - see front matter :~ 1999 Published by Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 9 8 ) 0 0 8 76-2
M. Baran et al. / Journal of Magnetism and Magnetic Materials 196-197 (1999) 532-533
01 : :=',:
m 10
533
11 ~T2'6
LZ 0 ~ 0
, 10 H (kOe)
H (kOe)
I 20
10 Temperature (K)
Fig. 1. Magnetization curves for the single crystal Bi2CuO4 at 5 K and for different orientations of the magnetic field with respect to the crystallographic axis. The inset shows the magnetic moment versus magnetic field up to 50 kOe.
54-
~ T
40 35 ooi
--,~ Hlla ...... H[Ic / d' E' ~ / /
30 [] =49[]K u ° ° °m° ° i
o o
o
T = 20 K
%
umo
T=,~K
polyctys[al
~ 25 ,,:
2o
o
7
~ t5
32
10
1-
i~i!/i
l C
5. a)
0
b) 00
T(K)
0.2
0 4
0.6
08
H(T)
Fig. 2. (a) Comparison between the thermal dependence of the magnetic susceptibility of Bi2CuO4 in polycrystalline sample and single crystal. Curve A: polycrystalline sample (H = 5 kOe); curve B: average susceptibility, calculated from data for the single crystal (H = 1 kOe); curve C: difference between curve A and B. (b) Comparison between the magnetization curves for polycrystalline sample and single crystal of BizCuO4. Squares correspond to the polycrystalline sample. The temperature is equal to 20 K.
Fig. 3. The thermal dependence of the specific heat of the single crystal BizCuO4 from 4 up to 20 K. variation of magnetocrystalline anisotropy parameters (MAP) KIL and K~. A F resonance data [6] show a strong temperature dependence of the resonance parameters below 20 K [7] and predict a decreasing of the parameter KII by a factor 3 on cooling from 20 down to 10 K. It was suggested [-2] that the M A P play important role in the variation of the magnetic susceptibility in AF state. Hence, if the M A P decrease significantly below 15-20 K, it can result to increasing of Z± and ZiP Our results of specific heat studies on the single-crystal and the polycrystalline samples [8] indicate some magnetic or structural transition at the specific temperature TI (Fig. 3). There is some evidence that this low-temperature transition may be concerned with the change of a mobility of A F domain walls in (ab) plane [6]. The latter effect could be due to the decreasing of K± below T1. In conclusion, the magnetic anomaly in Bi2CuO4 below 20 K is similar as in poly- as in single crystal and, probably, do not result from the impurities presence in the sample. We suppose that increasing of magnetic susceptibility at low temperatures is due to the decreasing of MAP.
References
The anomalous increasing of the DC magnetic susceptibility below 1 5 - 2 0 K was initially attributed to exchange-coupling chains of Cu 2+ I-3] or paramagnetic impurities/oxygen vacancies [4]. The first possibility is unlikely because of the 3D character of the interactions in BizCuO4. In order to examine the effect of the oxygen deficiencies the annealed polycrystalline samples have been studied but no difference between annealed and as-grown samples was found [4]. Assuming the paramagnetic impurities we should accept that in all samples (polycrystalline and single crystals) these are identical. There is a little likelihood of it. The other reason of increasing Z below 15 K may be due to the spin-wave behaviour [5]. But the slope of the curve z(T) rejects this possibility. Probably, the temperature variation of the magnetic susceptibility below 20 K is determined by the
[1] G. Dhalenne, A. Revcolevschi, M. Ain, B. Hennion, G. Andre, Cryst. Prop. Prep. 36-38 (1991) 11. [2] J.B. Goodenough, Magnetism and the Chemical Bond, Interscience Publishers, Wiley, New York, London, 1963. [3] K. Sreedhar, P, Ganguly, S. Ramasesha, J. Phys. C 21 (1988) 1129. [4] K. Yamada, K. Takada, S. Hosoya, Y. Watanbe, Y. Endoh, N. Tomonaga, T. Suzuki, T. Ishigaki, T. Kamiyama, H. Asano, F. Izumi, J. Phys. Soc. Japan 60 (7) (1991) 2406. [5] F. Keffer, in: S.N.Y. Flugge (Ed.), Handbuch der Physik, Vol. 18/2, Springer, Berlin, 1966. [6] L.E. Svistov, V.A. Chubarenko, A.Ya. Shapiro, A.V. Zalesski, G.A. Petrakovski, J. Exp. Theoret. Phys. 86 (1998) 1228. [7] G.A. Petrakovskii, K.A. Sablina, A.I. Pankrats, V.M. Vorotinov, A. Furrer, B. Roessli, P. Fischer, J. Magn. Magn. Mater. 140-144 (1995) 1991. [8] Yu.P. Gaidukov, V.N. Nikiforov, N.N. Samarin, Low Temp. Phys. 22 (1996) 705.