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Anisotropy of magnetic properties in LaMnO3 single crystals
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 272–276 (2004) 98–99
Anisotropy of magnetic properties in LaMnO3 single crystals A.V. Korolyova,*, V.E. Arkhipova, V.S. Gavikoa, M.I. Kurkina, T.P. Lapinaa, Ya.M. Mukovskiib a
Institute of Metal Physics, Ural Branch of the Russian Academy of Sciences, S. Kovalevskaya Str. 18, Ekaterinburg, 620219, Russia b Moscow State Steel and Alloys Institute, Leninskii prosp. 4, Moscow, 119049, Russia
Abstract The magnetization M and the magnetic susceptibility w of single crystals LaMnO3 have been studied as functions of external magnetic field H (up to 50 kOe), angle f between the field direction and a crystallographic axis in the LaMnO3 lattice, and temperature T: At T ¼ 2 K the spontaneous magnetization M0 and the magnetic susceptibility along the main directions a, b, c in the orthorhombic lattice (Pnma) of LaMnO3 are 6.5 emu/g and wb Ewc E2wa D0:00013 cm3/g, respectively. The results support a canted AaFb-type magnetic structure, however the spin–flop transition at Ho50 kOe was not observed. r 2003 Elsevier B.V. All rights reserved. PACS: 75.47.Lx; 75.30.Cr; 75.30.Gw Keywords: Manganite; LaMnO3; Single crystal; Magnetic properties
LaMnO3 is the basic compound for the whole manganite family that shows various interesting physical phenomena including the colossal magnetoresistance (CMR) effect. Therefore, detailed study of this compound seems to be rather important. Formerly magnetic properties of LaMnO3 were studied in Refs. [1–3] but there are some discrepancies between the results. In order to clarify the magnetic properties of LaMnO3, in the present paper we studied the magnetization M and the magnetic susceptibility w for different directions of the single crystals. Single crystalline boule B4 mm in diameter was grown by the floating zone method with radiation heating [4]. The good-quality fragments of the single crystal with mass B0.5–1 mg were chosen for the experiments. The main crystallographic directions of the crystals in the cubic description were determined by X-ray Laue method. MðH; T; fÞ dependencies were measured using SQUID magnetometer (quantum design) in magnetic field H up to 50 kOe in wide range of *Corresponding author. Tel.: +7-3432-783643; fax: +73432-745244. E-mail address: [email protected] (A.V. Korolyov).
temperatures T: The MðfÞ dependence (f is an angle between the field direction and a chosen crystallographic axis) was measured when the sample was rotated in {1 0 0} or {1 1 0} plane around /1 0 0S or /1 1 0S axis, respectively. Two such dependencies are shown as examples in Fig. 1. Analyzing these experiments together with MðHÞ curves for main crystallographic directions (Fig. 2) and taking into account previous data on the structure and magnetic properties of LaMnO3 [1–7], we conclude that the cubic axes [0 0 1], [1 1 0] and [1 1 0] should be considered as b-, a- and c- axes in the orthorhombic Pnma description. MðHÞ isotherms in wide range of H are linear functions: I" ¼ Mr þ wH (see Fig. 2). The coercivity in all cases does not exceed B2 kOe. MðHÞ isotherm for a free rotated sample practically coincides with that measured along b-axis, i.e. b-axis is the easy magnetization direction and Mr ðHjjbÞ M0 is the spontaneous magnetization (M0 ¼ 6:5 emu/g at T ¼ 2 K). The data can be reasonably interpreted in the assumption that LaMnO3 has an AaFb type magnetic structure, in agreement with previous studies [1–3, 5–7]. Assuming that the maximum magnetic moment per formula unit Mf:u is 4 mB (92.4 emu/g) at T ¼ 2 K, we calculate the
0304-8853/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.11.042
ARTICLE IN PRESS [011] [010]
[110]
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99
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3
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A.V. Korolyov et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) 98–99
M (emu/g)
c
12
-5
(011) plane
12 10
10
a
8
8
6
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(001) plane
20
40
60
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T (K) 0
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Fig. 1. Angular dependence of magnetization MðfÞ of the LaMnO3 single crystal in the plane (0 0 1) and in the plane (0 1 1) at T ¼ 2 K and H ¼ 50 kOe.
M (emu/g)
12
T = 2K
b
10 8
c
6
a
4 2 0
0
10
20
30
40
Fig. 3. Temperature dependence of magnetic susceptibility of the LaMnO3 single crystal for main orthorhombic axes (a, b, c).
200 kOe, and therefore HA must be B40–70 kOe. Such value of HA is several times lower than that given in [1–3,5], and HC value in our case is estimated to be B60–70 kOe at T ¼ 2 K. When the temperature increases, HC will decrease. Therefore we expected to observe the spin–flop transition at higher temperatures. However, we have not observed any feature, in both isotherms MðHÞ; and polytherms MðTÞ in a wide range of H and T which could confirm such spin–flop transition. The question on the spin–flop transition in LaMnO3 remains open up to now, and the high-field (>200 kOe) experiments are in progress.
50
H (kOe) Fig. 2. Magnetization curves of the LaMnO3 crystal along main orthorhombic axes (a, b, c) at T ¼ 2 K.
angle y between the sublattice magnetization vectors: cosðy=2Þ ¼ 0:07 and y ¼ 172 at H ¼ 0; the saturation field Hs ¼ 2HE þ HA ¼ 750 kOe and the Dzyaloshinski– Moriya (D–M) field HD ¼ M0 =wb ¼ 50 kOe. Finally, assuming that the canted magnetic structure arises due to the D–M interaction between Mn ions in different planes, the effective anisotropy field can be estimated as HA ¼ M02 XðMf:u: wa ÞD7 kOe and the antiferromagnetic exchange field HE ¼ 37 kOe. As the temperature increases, wb and wc changes considerably smaller than wa (Fig. 3). Nevertheless, all three temperature dependencies show a clear peak at the Neel temperature TN ¼ 136 K; which documents that the structure of the single crystal is not perfect. Both M0 and HD values decrease monotonically as temperature increases and turn to be zero at T ¼ TN : The obtained data are in qualitative agreement with the results of previous studies [1–3,5–7]; some discrepancies may arise because of a small difference in cation and oxygen stoichiometries. The present results confirm existence of canted magnetic structure AaFb type in LaMnO3. However, according to Refs. [1–3], the spin– flop transition field HC at low temperatures is about
Acknowledgements This work was supported in part by the RFBR (grants No 02-02-16425, No 02-02-16429) and by the ISTC (grant No 1859).
References [1] S. Mitsudo, K. Hirano, H. Nojiri, M. Motokawa, K. Hirota, A. Nishizawa, N. Kaneko, Y. Endoh, J. Magn. Magn. Mater. 117-181 (1998) 877. [2] Yu.F. Popov, A.M. Kadomtseva, G.P. Vorob’ev, V.Yu. Ivanov, A.A. Mukhin, A.K. Zvezdin, J. Appl. Phys. 83 (1998) 7160. [3] V. Skumryev, F. Ott, J.M.D. Coey, A. Anane, J.-P. Renard, L. Pinsard-Gaudart, A. Revcolevschi, Eur. Phys. J. B 11 (1999) 401. [4] D.A. Shulyatev, S.G. Karabashev, A.A. Arsenov, Ya.M. Mukovskii, J. Crystal Growth 198/199 (1999) 511. [5] F. Moussa, M. Hennion, J. Rodriguez-Carvajal, H. Moudden, L. Pinsard, A. Revcolevschi, Phys. Rev. B 54 (1996) 15149. [6] A.A. Mukhin, V.Yu. Ivanov, V.D. Travkin, A. Pimenov, A. Loidl, A.M. Balbashov, Europhys. Lett. 49 (2000) 514. [7] D. Ivannikov, M. Biberacher, H.-A. Krug von Nidda, A. Pimenov, A. Loidl, A.A. Mukhin, A.M. Balbashov, Phys. Rev. B 65 (2002) 214422.
Journal of Magnetism and Magnetic Materials 272–276 (2004) 98–99
Anisotropy of magnetic properties in LaMnO3 single crystals A.V. Korolyova,*, V.E. Arkhipova, V.S. Gavikoa, M.I. Kurkina, T.P. Lapinaa, Ya.M. Mukovskiib a
Institute of Metal Physics, Ural Branch of the Russian Academy of Sciences, S. Kovalevskaya Str. 18, Ekaterinburg, 620219, Russia b Moscow State Steel and Alloys Institute, Leninskii prosp. 4, Moscow, 119049, Russia
Abstract The magnetization M and the magnetic susceptibility w of single crystals LaMnO3 have been studied as functions of external magnetic field H (up to 50 kOe), angle f between the field direction and a crystallographic axis in the LaMnO3 lattice, and temperature T: At T ¼ 2 K the spontaneous magnetization M0 and the magnetic susceptibility along the main directions a, b, c in the orthorhombic lattice (Pnma) of LaMnO3 are 6.5 emu/g and wb Ewc E2wa D0:00013 cm3/g, respectively. The results support a canted AaFb-type magnetic structure, however the spin–flop transition at Ho50 kOe was not observed. r 2003 Elsevier B.V. All rights reserved. PACS: 75.47.Lx; 75.30.Cr; 75.30.Gw Keywords: Manganite; LaMnO3; Single crystal; Magnetic properties
LaMnO3 is the basic compound for the whole manganite family that shows various interesting physical phenomena including the colossal magnetoresistance (CMR) effect. Therefore, detailed study of this compound seems to be rather important. Formerly magnetic properties of LaMnO3 were studied in Refs. [1–3] but there are some discrepancies between the results. In order to clarify the magnetic properties of LaMnO3, in the present paper we studied the magnetization M and the magnetic susceptibility w for different directions of the single crystals. Single crystalline boule B4 mm in diameter was grown by the floating zone method with radiation heating [4]. The good-quality fragments of the single crystal with mass B0.5–1 mg were chosen for the experiments. The main crystallographic directions of the crystals in the cubic description were determined by X-ray Laue method. MðH; T; fÞ dependencies were measured using SQUID magnetometer (quantum design) in magnetic field H up to 50 kOe in wide range of *Corresponding author. Tel.: +7-3432-783643; fax: +73432-745244. E-mail address: [email protected] (A.V. Korolyov).
temperatures T: The MðfÞ dependence (f is an angle between the field direction and a chosen crystallographic axis) was measured when the sample was rotated in {1 0 0} or {1 1 0} plane around /1 0 0S or /1 1 0S axis, respectively. Two such dependencies are shown as examples in Fig. 1. Analyzing these experiments together with MðHÞ curves for main crystallographic directions (Fig. 2) and taking into account previous data on the structure and magnetic properties of LaMnO3 [1–7], we conclude that the cubic axes [0 0 1], [1 1 0] and [1 1 0] should be considered as b-, a- and c- axes in the orthorhombic Pnma description. MðHÞ isotherms in wide range of H are linear functions: I" ¼ Mr þ wH (see Fig. 2). The coercivity in all cases does not exceed B2 kOe. MðHÞ isotherm for a free rotated sample practically coincides with that measured along b-axis, i.e. b-axis is the easy magnetization direction and Mr ðHjjbÞ M0 is the spontaneous magnetization (M0 ¼ 6:5 emu/g at T ¼ 2 K). The data can be reasonably interpreted in the assumption that LaMnO3 has an AaFb type magnetic structure, in agreement with previous studies [1–3, 5–7]. Assuming that the maximum magnetic moment per formula unit Mf:u is 4 mB (92.4 emu/g) at T ¼ 2 K, we calculate the
0304-8853/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.11.042
ARTICLE IN PRESS [011] [010]
[110]
[00-1] [-100]
[-110]
14
99
b
3
[001](011) [100](001)
χ ,10 (cm /g)
A.V. Korolyov et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) 98–99
M (emu/g)
c
12
-5
(011) plane
12 10
10
a
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80
100
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90
120
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Fig. 1. Angular dependence of magnetization MðfÞ of the LaMnO3 single crystal in the plane (0 0 1) and in the plane (0 1 1) at T ¼ 2 K and H ¼ 50 kOe.
M (emu/g)
12
T = 2K
b
10 8
c
6
a
4 2 0
0
10
20
30
40
Fig. 3. Temperature dependence of magnetic susceptibility of the LaMnO3 single crystal for main orthorhombic axes (a, b, c).
200 kOe, and therefore HA must be B40–70 kOe. Such value of HA is several times lower than that given in [1–3,5], and HC value in our case is estimated to be B60–70 kOe at T ¼ 2 K. When the temperature increases, HC will decrease. Therefore we expected to observe the spin–flop transition at higher temperatures. However, we have not observed any feature, in both isotherms MðHÞ; and polytherms MðTÞ in a wide range of H and T which could confirm such spin–flop transition. The question on the spin–flop transition in LaMnO3 remains open up to now, and the high-field (>200 kOe) experiments are in progress.
50
H (kOe) Fig. 2. Magnetization curves of the LaMnO3 crystal along main orthorhombic axes (a, b, c) at T ¼ 2 K.
angle y between the sublattice magnetization vectors: cosðy=2Þ ¼ 0:07 and y ¼ 172 at H ¼ 0; the saturation field Hs ¼ 2HE þ HA ¼ 750 kOe and the Dzyaloshinski– Moriya (D–M) field HD ¼ M0 =wb ¼ 50 kOe. Finally, assuming that the canted magnetic structure arises due to the D–M interaction between Mn ions in different planes, the effective anisotropy field can be estimated as HA ¼ M02 XðMf:u: wa ÞD7 kOe and the antiferromagnetic exchange field HE ¼ 37 kOe. As the temperature increases, wb and wc changes considerably smaller than wa (Fig. 3). Nevertheless, all three temperature dependencies show a clear peak at the Neel temperature TN ¼ 136 K; which documents that the structure of the single crystal is not perfect. Both M0 and HD values decrease monotonically as temperature increases and turn to be zero at T ¼ TN : The obtained data are in qualitative agreement with the results of previous studies [1–3,5–7]; some discrepancies may arise because of a small difference in cation and oxygen stoichiometries. The present results confirm existence of canted magnetic structure AaFb type in LaMnO3. However, according to Refs. [1–3], the spin– flop transition field HC at low temperatures is about
Acknowledgements This work was supported in part by the RFBR (grants No 02-02-16425, No 02-02-16429) and by the ISTC (grant No 1859).
References [1] S. Mitsudo, K. Hirano, H. Nojiri, M. Motokawa, K. Hirota, A. Nishizawa, N. Kaneko, Y. Endoh, J. Magn. Magn. Mater. 117-181 (1998) 877. [2] Yu.F. Popov, A.M. Kadomtseva, G.P. Vorob’ev, V.Yu. Ivanov, A.A. Mukhin, A.K. Zvezdin, J. Appl. Phys. 83 (1998) 7160. [3] V. Skumryev, F. Ott, J.M.D. Coey, A. Anane, J.-P. Renard, L. Pinsard-Gaudart, A. Revcolevschi, Eur. Phys. J. B 11 (1999) 401. [4] D.A. Shulyatev, S.G. Karabashev, A.A. Arsenov, Ya.M. Mukovskii, J. Crystal Growth 198/199 (1999) 511. [5] F. Moussa, M. Hennion, J. Rodriguez-Carvajal, H. Moudden, L. Pinsard, A. Revcolevschi, Phys. Rev. B 54 (1996) 15149. [6] A.A. Mukhin, V.Yu. Ivanov, V.D. Travkin, A. Pimenov, A. Loidl, A.M. Balbashov, Europhys. Lett. 49 (2000) 514. [7] D. Ivannikov, M. Biberacher, H.-A. Krug von Nidda, A. Pimenov, A. Loidl, A.A. Mukhin, A.M. Balbashov, Phys. Rev. B 65 (2002) 214422.