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Low-temperature phase transition in EuMn2O5 induced by a strong magnetic field
Physica B 284}288 (2000) 1402}1403
Low-temperature phase transition in EuMn O induced by a strong magnetic "eld Y.F. Popov *, A.M. Kadomtseva , G.P. Vorob'ev , V.A. Sanina , A.K. Zvezdin, M.M. Tehranchi Department of Physics, KOKEF, Moscow State University, Leninskie gory, 119899 Moscow, Russia Institute of General Physics, 117942 Moscow, Russia
Abstract The magnetostriction, magnetoelectric e!ect and phase transitions induced by a strong magnetic "eld in EuMn O single crystal have been investigated. It is known that EuMn O compounds show structural and magnetic phase transitions and incommensurate magnetic structure around 40 K. New phase transitions from a modulated spin structure to a homogeneous structure in EuMn O at 26 K accompanied by a signi"cant change of electrical polarization induced by a high magnetic "eld have been studied. 2000 Published by Elsevier Science B.V. All rights reserved. Keywords: Incommensurate magnetic structure; Magnetoelectric e!ect
1. Introduction
2. Results and discussion
EuMn O compound has been the subject of a num ber of investigations because of the simultaneous electric and magnetic ordering of manganese ions at a temperature near 40 K [1,2]. Another phase transition has been observed near 20 K, and the character of such a transition is not well understood [1}3]. Neutron investigations show [4] that the magnetic structures of ions Mn> and Mn> are space-modulated structures. The symmetry of EuMn O (P ) allows the existence of a linear magnetoelectric e!ect. However, we think that the linear magnetoelectric e!ect can be realized only in high magnetic "elds, which are able to destroy the modulated spin structure. In this work the magnetoelectric e!ect and the magnetostriction have been investigated in magnetic "elds up to 250 kOe for the "rst time. A phase transition has been induced by these "elds, from the modulated spin structure and to a structure that may be homogeneous.
Electrical polarization and magnetostriction of EuMn O crystals along a-, b-, c-axis induced by a mag netic "eld have been investigated from 5 to 50 K. Fig. 1 shows a sign change of electric susceptibility near 29 K related to the existence of a spontaneous transition between various magnetic structures. A sharp growth of polarization at low temperatures up to 26 K in a "eld of 100 kOe is observed. Most likely, this growth is connected with a reorganization of a modulated structure. Negative jumps of electric polarization at H +150 kOe are observed between 26 and 32 K. Lin ear dependence of electrical polarization P (H ) at higher ? A H is detected. It can be connected with the destruction of a modulated structure. Above 40 K the crystal is in a paramagnetic state and the magnetoelectric e!ect disappears. The electrical polarization measured along the b-axis for H""c behaves similarly to P (H ). The transition from ? A the modulated structure to the homogeneous antiferromagnetic state was accompanied by a hysteresis in the P (H ) curves. ? @ A Measurements of the longitudinal magnetoelectric e!ect in P (H ) and P (H ) have shown that for a A A @ @ homogeneous antiferromagnetic state the component of
* Corresponding author. Tel.: #7-095-939-1142; fax: #7095-939-5907. E-mail address: [email protected] (Y.F. Popov)
0921-4526/00/$ - see front matter 2000 Published by Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 9 9 ) 0 2 5 6 5 - X
Y.F. Popov et al. / Physica B 284}288 (2000) 1402}1403
Fig. 1. Electrical polarization P (H ) of EuMn O crystal ver? A sus a magnetic "eld in the c-direction, at several temperatures.
a diagonal susceptibility a "a "0. The destruction AA @@ of a modulated structure in "elds of 140}150 kOe was accompanied by magnetostriction deformations. The electric polarization P (H ) (Fig. 2) was negative ? ? and had no signi"cant anomalies at temperatures 10 and 16 K. There was a positive sharp peak of polarization at a temperature of 23 K. An order of magnitude increase in polarization was observed. At 29 K, there was a two-step phase transition near 175 and 220 kOe. Thus, diagonal magnetoelectric e!ect is equal to zero at these "elds (a "0). Dependence of longitudinal magnetostriction ?? j corresponded to the P (H ) curve and it has ?? ? ? anomalies at temperatures close to the phase transition points.
1403
Fig. 2. Electrical polarization dependence P (H ) of EuMn O ? ? crystal. Field H is along the a-axis. ?
Acknowledgements This work was supported by RFBR (Nos. 96-02-96429 and 98-02-16848).
References [1] [2] [3] [4]
V.A. Sanina et al., Phys. Solid State 30 (1988) 3015. T. Doi, K. Kohn, Phase Transition 38 (1988) 3015. Ya. Kayata et al., J. Phys. Soc. Japan 65 (1996) 1383. G. Buisson, Phys. Stat. Sol. A 17 (1973) 191.
Low-temperature phase transition in EuMn O induced by a strong magnetic "eld Y.F. Popov *, A.M. Kadomtseva , G.P. Vorob'ev , V.A. Sanina , A.K. Zvezdin, M.M. Tehranchi Department of Physics, KOKEF, Moscow State University, Leninskie gory, 119899 Moscow, Russia Institute of General Physics, 117942 Moscow, Russia
Abstract The magnetostriction, magnetoelectric e!ect and phase transitions induced by a strong magnetic "eld in EuMn O single crystal have been investigated. It is known that EuMn O compounds show structural and magnetic phase transitions and incommensurate magnetic structure around 40 K. New phase transitions from a modulated spin structure to a homogeneous structure in EuMn O at 26 K accompanied by a signi"cant change of electrical polarization induced by a high magnetic "eld have been studied. 2000 Published by Elsevier Science B.V. All rights reserved. Keywords: Incommensurate magnetic structure; Magnetoelectric e!ect
1. Introduction
2. Results and discussion
EuMn O compound has been the subject of a num ber of investigations because of the simultaneous electric and magnetic ordering of manganese ions at a temperature near 40 K [1,2]. Another phase transition has been observed near 20 K, and the character of such a transition is not well understood [1}3]. Neutron investigations show [4] that the magnetic structures of ions Mn> and Mn> are space-modulated structures. The symmetry of EuMn O (P ) allows the existence of a linear magnetoelectric e!ect. However, we think that the linear magnetoelectric e!ect can be realized only in high magnetic "elds, which are able to destroy the modulated spin structure. In this work the magnetoelectric e!ect and the magnetostriction have been investigated in magnetic "elds up to 250 kOe for the "rst time. A phase transition has been induced by these "elds, from the modulated spin structure and to a structure that may be homogeneous.
Electrical polarization and magnetostriction of EuMn O crystals along a-, b-, c-axis induced by a mag netic "eld have been investigated from 5 to 50 K. Fig. 1 shows a sign change of electric susceptibility near 29 K related to the existence of a spontaneous transition between various magnetic structures. A sharp growth of polarization at low temperatures up to 26 K in a "eld of 100 kOe is observed. Most likely, this growth is connected with a reorganization of a modulated structure. Negative jumps of electric polarization at H +150 kOe are observed between 26 and 32 K. Lin ear dependence of electrical polarization P (H ) at higher ? A H is detected. It can be connected with the destruction of a modulated structure. Above 40 K the crystal is in a paramagnetic state and the magnetoelectric e!ect disappears. The electrical polarization measured along the b-axis for H""c behaves similarly to P (H ). The transition from ? A the modulated structure to the homogeneous antiferromagnetic state was accompanied by a hysteresis in the P (H ) curves. ? @ A Measurements of the longitudinal magnetoelectric e!ect in P (H ) and P (H ) have shown that for a A A @ @ homogeneous antiferromagnetic state the component of
* Corresponding author. Tel.: #7-095-939-1142; fax: #7095-939-5907. E-mail address: [email protected] (Y.F. Popov)
0921-4526/00/$ - see front matter 2000 Published by Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 9 9 ) 0 2 5 6 5 - X
Y.F. Popov et al. / Physica B 284}288 (2000) 1402}1403
Fig. 1. Electrical polarization P (H ) of EuMn O crystal ver? A sus a magnetic "eld in the c-direction, at several temperatures.
a diagonal susceptibility a "a "0. The destruction AA @@ of a modulated structure in "elds of 140}150 kOe was accompanied by magnetostriction deformations. The electric polarization P (H ) (Fig. 2) was negative ? ? and had no signi"cant anomalies at temperatures 10 and 16 K. There was a positive sharp peak of polarization at a temperature of 23 K. An order of magnitude increase in polarization was observed. At 29 K, there was a two-step phase transition near 175 and 220 kOe. Thus, diagonal magnetoelectric e!ect is equal to zero at these "elds (a "0). Dependence of longitudinal magnetostriction ?? j corresponded to the P (H ) curve and it has ?? ? ? anomalies at temperatures close to the phase transition points.
1403
Fig. 2. Electrical polarization dependence P (H ) of EuMn O ? ? crystal. Field H is along the a-axis. ?
Acknowledgements This work was supported by RFBR (Nos. 96-02-96429 and 98-02-16848).
References [1] [2] [3] [4]
V.A. Sanina et al., Phys. Solid State 30 (1988) 3015. T. Doi, K. Kohn, Phase Transition 38 (1988) 3015. Ya. Kayata et al., J. Phys. Soc. Japan 65 (1996) 1383. G. Buisson, Phys. Stat. Sol. A 17 (1973) 191.