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Magnetic, dielectric and magnetoelectric properties of new family of orthorhombic multiferroic Eu1−xYxMNO3 manganites
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 300 (2006) e130–e133 www.elsevier.com/locate/jmmm
Magnetic, dielectric and magnetoelectric properties of new family of orthorhombic multiferroic Eu1xYxMNO3 manganites V.Yu. Ivanova, A.A. Mukhina,, V.D. Travkina, A.S. Prokhorova, A.M. Kadomtsevab, Yu.F. Popovb, G.P. Vorob’evb, K.I. Kamilovb, A.M. Balbashovc a
General Physics Institute of the Russian Academy of Science, 38 Vavilov Street, 119991 Moscow, Russia b Moscow State University, Leninskie Gori, 119899 Moscow, Russia c Moscow Power Engineering Institute, 14 Krasnokazarmennaya Street, 105835 Moscow, Russia Available online 17 November 2005
Abstract Multiferroic ground states with a spatially modulated antiferromagnetic structure and electric polarization have been revealed in Eu1xYxMnO3 (0:2pxp0:5) single crystals. While the slightly substituted (xp0:1) compounds exhibited a transition from the incommensurate (IC) to the canted antiferromagnetic (CAF) state at T CA oT N , the transitions from IC to commensurate ferroelectric (C/FE) phase were observed at T lock oT N for x40:2. Various phase transitions were observed in the magnetic fields up to 250 kOe along a, b, c axes by magnetization, magnetostriction and electric polarization measurements which show an existence of a spontaneous electric polarization below Tlock. r 2005 Elsevier B.V. All rights reserved. PACS: 77.22.Ch; 77.22.Ej; 77.84.Bw; 75.50.Ee; 75.30.Kz Keywords: Multiferroic; Incommensurate magnetic structure; Electric polarization; Manganites; Field-induced transition
1. Introduction Recently new interesting properties of rare-earth orthorhombic manganites RMnO3 were revealed which are related to a change of their magnetic structure from a canted antiferromagnetic (CAF) layer ordering (AyFz) to a modulated antiferromagnetic (sinusoidal) one for R ¼ Eu, Gd, Tb, Dy due to frustration of exchange interactions upon decreasing of R-ionic radii rR [1–5]. It results in appearance of electric polarization below incommensurate–commensurate (IC–C) transition at temperature T lock oT N ¼ 45250 K and unusual magnetic-field-induced transitions accompanied by reorientation or suppression of electric polarization for R ¼ Tb, Dy [1,2] and Gd [6]. We have realized multiferroic states in the substituted Eu1xYxMnO3, where an average rR and parameters of Mn–O–Mn bonds are continuously adjusted by a content Corresponding author. Tel.: +7 095 132 8175; fax: +7 095 135 3003.
E-mail address: [email protected] (A.A. Mukhin). 0304-8853/$ - see front matter r 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2005.10.165
of Y with a smaller ionic radii thus permitting a gradual control of magnetic and electric ground states.
2. Experimental The single Eu1xYxMnO3 (0pxp0:5) crystals were grown by a floating zone method. Powder X-ray-phase analysis showed that the crystals were single phase and exhibited an orthorhombic crystal structure of the Pbnm type. Magnetization and susceptibility were measured in the steady magnetic field H up to 14 kOe and pulsed field up to 250 kOe using the vibrating sample magnetometer and inductance method, respectively. Dielectric permittivity of oriented plane-parallel wafers was measured by LCR-meter at a frequency 1 MGz. Field-induced change of electric polarization DP(H) ¼ P(Hmax)P(H)) and magnetostriction l(H) was measured in the pulsed magnetic fields by the method described elsewhere [6]. The DP measurements were performed after the poling of samples
ARTICLE IN PRESS V.Y. Ivanov et al. / Journal of Magnetism and Magnetic Materials 300 (2006) e130–e133
3. Results and discussion Temperature dependence of spontaneous magnetization, DC susceptibility (Fig. 1) and dielectric permittivity (Fig. 2) show that the slightly substituted (xp0:1) compounds exhibit a transition from the IC to the CAF state at TCA accompanied by a weak decrease of the dielectric constant. No spontaneous ferromagnetic moment was observed between TN and TCA; however, it was induced by magnetic fields (1–5 T) which is shown by the open symbols in Fig. 1a. For x ¼ 0:2 a dielectric anomaly observed at Tlock ¼ 30 K was ascribed to the IC–C phase transition (similar to TbMnO3 and DyMnO3 [1,2]), followed by the transition to the CAF phase at TCA22 K which was accompanied by the peak of wc. The latter transition shows a significant temperature hysteresis
6 x=0
σc, emu/g
0.1
c-a xis
(a)
4
resulting in retaining of C phase up to lowest T in zerofield-cooled regime. For xX0:3 only the IC–C transitions were found while the CAF phase disappeared at all. The observed anisotropy of the magnetic susceptibility (wb owa;c ) indicates on a spin (sinusoidal) ordering along b axis below TN. An interesting feature of wa(T) behavior is its bend at Tlock and further decreasing in the C phase 1.1 x=0 1.0
x=0.2
1.1
x=0.2
a-axis 1.0 1.2
(a)
(b)
a-axis
1.1
0.2
2
x=0
[110]
Dielectric constant, ε (T) / ε (5 K)
in the electric field up to 5 kV/cm while cooling from a temperature above TN.
e131
x=0.5
x=0.5 1.0
0
0
(b)
1.5
20
40
60
0
20
40
60
Temperature, K
a
Fig. 2. Temperature dependence of dielectric constant perpendicular to the c (a) and along c axis (b) for Eu1xYxMnO3 single crystals. e(5 K)E15–25.
c 1.0
x=0.1 b
1.5
(c) P
a
1.0
x=0.2
40
b 0.5 (d)
1.5
c
Temperature, K
-4
3
χ dc , 1 0 cm /g.
c
IC
CAF
20
a 1.0
0
C / FE
x=0.3
b 20
40
60
Temperature, K Fig. 1. Temperature dependence of the spontaneous and field-induced magnetization along c axis (filled and open symbols, respectively) (a) and DC susceptibility along three crystallographic axes (b)–(d) of some Eu1xYxMnO3 single crystals. Double, down and up arrows indicate the TN, TCA and Tlock, respectively.
0
0.0
0.1
0.2 0.3 Concentration, x
0.4
0.5
Fig. 3. Phase T2x diagram of Eu1xYxMnO3, where P denotes paramagnetic phase, CAF—canted antiferromagnetic, IC incommensurate antiferromagnetic, C/FE: commensurate ferroelectric. Lines—guide for eyes.
ARTICLE IN PRESS V.Y. Ivanov et al. / Journal of Magnetism and Magnetic Materials 300 (2006) e130–e133
e132
which indicates a change of magnetic (and electric) structure. The observed phase transformations were mapped in the T–x phase diagram shown in Fig. 3. Various phase transitions were revealed in the magnetic fields along a, b, c axes. The transitions from C (IC) to CAF phase were observed for HJc below Tlock (TN) as jumps in the Mc(Hc), lc(Hc) and DPc,a(Hc) curves at threshold fields from few kOe (x ¼ 0, 0.1) up to 200 kOe (x ¼ 0.2, 0.3). These data are illustrated in Fig. 4 for x ¼ 0:2. A remarkable feature of the DPc,a(Hc) curves is a polarization sign dependence on a sign of poling field along corresponding axes (Fig. 4d). The effect (as well as nonzero DP) is observed only when ToT lock indicating an existence of a spontaneous electric polarization below 20
σ c,emu/g
15
Tlock, that enables us to identify the C phase as well as ferroelectric one (commensurate ferroelectric, C/FE) (see Fig. 3). Amplitude of field-induced change of the DPc,a(Hc) at the transition depends also on a value of the poling field and exhibit a strong anisotropy |DPa|b|DPc| (Fig. 4c and d). Another interesting feature of the observed transition for HJc is its significant hysteresis: for a zero-field cooled regime the antiferromagnetic C/FE phase retains up to the lowest temperatures (To4 K), while it is suppressed by Hkc and is transformed to the CAF state which holds even when H ¼ 0. The onset of the field-induced transition occurs at HcE50 kOe with sharp jumps of the sc, lc and DPa,c, which, however, finishes at Hc110–130 kOe according to a smooth part of the DPa,c(H) curves (Fig. 4). It may indicate a two-stage character of the C/FE–CAF transition with an appearance of some intermediate phase possessing both a weak ferromagnetic moment and electric polarization. Perhaps this phase remains after removing the
10 5
(a) 10
σa, emu/g
0
λc,10-6
100
5
(a)
50 0 20
(b) 0
H || a
E = 4.3 kV/cm λa, 10-6
∆Pc, µC / m2
50
E = 2.1 kV/cm
10
(b)
0 (c) 0
800 E = 0.97 kV/cm 600
E = 1 kV/cm ∆Pa, µC / m2
∆Pa, µC / m2
500
0
0.65 400 0.16 200
E = -1 kV/cm
(c)
(d)
-500 0
50
100
150
Magnetic field, kOe Fig. 4. Magnetic field dependence of magnetization (a), magnetostriction (b), and changes of polarization along c (c) and a axis (d) in Eu0.8Y0.2MnO3 for Hkc at T ¼ 4.5 K. DP(H) curves were obtained after cooling in electric field from T4TN.
0
0
50
100
150
Magnetic field, kOe Fig. 5. Magnetic field dependence of magnetization (a), longitudinal magnetostriction (b), and changes of polarization along a axis (c) in Eu0.8Y0.2MnO3 for Hka at T ¼ 4.5 K. DP(H) curves were obtained after cooling in electric field from T4TN.
ARTICLE IN PRESS V.Y. Ivanov et al. / Journal of Magnetism and Magnetic Materials 300 (2006) e130–e133
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4. Conclusion δ Paa
δ P cc
+ 60
δ Paa, µC / m2
600 δ P cc
400
-
40
20
200
0 0
δPcc, µC / m2
800
1
2 3 E, kV/cm
4
5
0
Fig. 6. Dependence of change of the electric polaization induced by Hkc and Hka axes DPcc,aa ¼ DPc,a(0)—DPc,a(Hmax c,a ) versus the poling electric field Ec,a in Eu0.8Y0.2MnO3 at T ¼ 4.5 K; DP7 cc corresponds to up and down magnetic field in Fig. 4c.
The substituted Eu1xYxMnO3 (0:2pxp0:5) manganites exhibit the remarkable multiferroic states with a modulated antiferromagnetic structure and electric polarization upon decreasing of the average rare-earth ionic radii with increasing Y concentration. These states are observed below the IC–C transition at Tlock accompanied by anomalies in the dielectric constant. Various phase transitions were observed in the magnetic fields up to 250 kOe along a, b, c axes by magnetization, magnetostriction and electric polarization measurements which indicate close interrelations of the electric polarizaion with the magnetic structure. The observed ferroelectricity has an improper character and could be attributed to spin-lattice interaction in the modulated off-center symmetry magnetic structure. Acknowledgements
magnetic field and corresponds to a double dashed region at the x–T diagram in Fig. 3. For Hkb and a axes, another field-induced transitions were revealed. For Hkb, a spin–flop transition was observed at Hb200 kOe accompanied by jumps of the magnetization, magnetostriction and electric polarization. Unusual phase transitions were also found for Hka at Ha50–100 kOe and ToT lock (Fig. 5) which was accompanied by a huge change of polarization DPa. The value of the induced polarization DPa as well as its sign (not shown) depend on poling field (Fig. 5c). The extracted fieldinduced changes of the polarization DPa,c for Hka and c axes versus the poling field are shown in Fig. 6 for x ¼ 0:2. They exhibit a tendency for a saturation but are far to achieve it. The maximum value of the induced polarization DPaa800 mC/m2 is comparable to TbMnO3 and DyMnO3 corresponding data [1,2].
This work was supported by Russian Foundation for Basic Research (Project nos. 04-02-16592, 03-02-16445, 0302-16759, 04-02-81046-Bel2004). References [1] T. Kimura, T. Goto, H. Shintani, K. Ishizaka, T. Arima, Y. Tokura, Nature 426 (2003) 55. [2] T. Goto, T. Kimura, G. Lawes, A.P. Ramirez, Y. Tokura, Phys. Rev. Lett. 92 (2004) 257201. [3] T. Kimura, S. Ishihara, H. Shintani, T. Arima, K.T. Takahashi, K. Ishizaka, Y. Tokura, Phys. Rev. B 68 (2003) 060403. [4] J. Hemberger, S. Lobina, H.-A. Krug von Nidda, N. Tristan, V.Yu. Ivanov, A.A. Mukhin, A.M. Balbashov, A. Loidl, Phys. Rev. B 70 (2004) 024414. [5] A.A. Mukhin, V.Yu. Ivanov, V.D. Travkin, A.S. Prokhorov, A.M. Balbashov, J. Magn. Magn. Mater. 272–276 (2004) 96. [6] A.M. Kadomtseva, Yu.F. Popov, G.P. Vorob’ev, K.I. Kamilov, A.P. Pyatakov, V.Yu. Ivanov, A.A. Mukhin, A.M. Balbashov, JETP Lett. 81 (2005) 19.
Journal of Magnetism and Magnetic Materials 300 (2006) e130–e133 www.elsevier.com/locate/jmmm
Magnetic, dielectric and magnetoelectric properties of new family of orthorhombic multiferroic Eu1xYxMNO3 manganites V.Yu. Ivanova, A.A. Mukhina,, V.D. Travkina, A.S. Prokhorova, A.M. Kadomtsevab, Yu.F. Popovb, G.P. Vorob’evb, K.I. Kamilovb, A.M. Balbashovc a
General Physics Institute of the Russian Academy of Science, 38 Vavilov Street, 119991 Moscow, Russia b Moscow State University, Leninskie Gori, 119899 Moscow, Russia c Moscow Power Engineering Institute, 14 Krasnokazarmennaya Street, 105835 Moscow, Russia Available online 17 November 2005
Abstract Multiferroic ground states with a spatially modulated antiferromagnetic structure and electric polarization have been revealed in Eu1xYxMnO3 (0:2pxp0:5) single crystals. While the slightly substituted (xp0:1) compounds exhibited a transition from the incommensurate (IC) to the canted antiferromagnetic (CAF) state at T CA oT N , the transitions from IC to commensurate ferroelectric (C/FE) phase were observed at T lock oT N for x40:2. Various phase transitions were observed in the magnetic fields up to 250 kOe along a, b, c axes by magnetization, magnetostriction and electric polarization measurements which show an existence of a spontaneous electric polarization below Tlock. r 2005 Elsevier B.V. All rights reserved. PACS: 77.22.Ch; 77.22.Ej; 77.84.Bw; 75.50.Ee; 75.30.Kz Keywords: Multiferroic; Incommensurate magnetic structure; Electric polarization; Manganites; Field-induced transition
1. Introduction Recently new interesting properties of rare-earth orthorhombic manganites RMnO3 were revealed which are related to a change of their magnetic structure from a canted antiferromagnetic (CAF) layer ordering (AyFz) to a modulated antiferromagnetic (sinusoidal) one for R ¼ Eu, Gd, Tb, Dy due to frustration of exchange interactions upon decreasing of R-ionic radii rR [1–5]. It results in appearance of electric polarization below incommensurate–commensurate (IC–C) transition at temperature T lock oT N ¼ 45250 K and unusual magnetic-field-induced transitions accompanied by reorientation or suppression of electric polarization for R ¼ Tb, Dy [1,2] and Gd [6]. We have realized multiferroic states in the substituted Eu1xYxMnO3, where an average rR and parameters of Mn–O–Mn bonds are continuously adjusted by a content Corresponding author. Tel.: +7 095 132 8175; fax: +7 095 135 3003.
E-mail address: [email protected] (A.A. Mukhin). 0304-8853/$ - see front matter r 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2005.10.165
of Y with a smaller ionic radii thus permitting a gradual control of magnetic and electric ground states.
2. Experimental The single Eu1xYxMnO3 (0pxp0:5) crystals were grown by a floating zone method. Powder X-ray-phase analysis showed that the crystals were single phase and exhibited an orthorhombic crystal structure of the Pbnm type. Magnetization and susceptibility were measured in the steady magnetic field H up to 14 kOe and pulsed field up to 250 kOe using the vibrating sample magnetometer and inductance method, respectively. Dielectric permittivity of oriented plane-parallel wafers was measured by LCR-meter at a frequency 1 MGz. Field-induced change of electric polarization DP(H) ¼ P(Hmax)P(H)) and magnetostriction l(H) was measured in the pulsed magnetic fields by the method described elsewhere [6]. The DP measurements were performed after the poling of samples
ARTICLE IN PRESS V.Y. Ivanov et al. / Journal of Magnetism and Magnetic Materials 300 (2006) e130–e133
3. Results and discussion Temperature dependence of spontaneous magnetization, DC susceptibility (Fig. 1) and dielectric permittivity (Fig. 2) show that the slightly substituted (xp0:1) compounds exhibit a transition from the IC to the CAF state at TCA accompanied by a weak decrease of the dielectric constant. No spontaneous ferromagnetic moment was observed between TN and TCA; however, it was induced by magnetic fields (1–5 T) which is shown by the open symbols in Fig. 1a. For x ¼ 0:2 a dielectric anomaly observed at Tlock ¼ 30 K was ascribed to the IC–C phase transition (similar to TbMnO3 and DyMnO3 [1,2]), followed by the transition to the CAF phase at TCA22 K which was accompanied by the peak of wc. The latter transition shows a significant temperature hysteresis
6 x=0
σc, emu/g
0.1
c-a xis
(a)
4
resulting in retaining of C phase up to lowest T in zerofield-cooled regime. For xX0:3 only the IC–C transitions were found while the CAF phase disappeared at all. The observed anisotropy of the magnetic susceptibility (wb owa;c ) indicates on a spin (sinusoidal) ordering along b axis below TN. An interesting feature of wa(T) behavior is its bend at Tlock and further decreasing in the C phase 1.1 x=0 1.0
x=0.2
1.1
x=0.2
a-axis 1.0 1.2
(a)
(b)
a-axis
1.1
0.2
2
x=0
[110]
Dielectric constant, ε (T) / ε (5 K)
in the electric field up to 5 kV/cm while cooling from a temperature above TN.
e131
x=0.5
x=0.5 1.0
0
0
(b)
1.5
20
40
60
0
20
40
60
Temperature, K
a
Fig. 2. Temperature dependence of dielectric constant perpendicular to the c (a) and along c axis (b) for Eu1xYxMnO3 single crystals. e(5 K)E15–25.
c 1.0
x=0.1 b
1.5
(c) P
a
1.0
x=0.2
40
b 0.5 (d)
1.5
c
Temperature, K
-4
3
χ dc , 1 0 cm /g.
c
IC
CAF
20
a 1.0
0
C / FE
x=0.3
b 20
40
60
Temperature, K Fig. 1. Temperature dependence of the spontaneous and field-induced magnetization along c axis (filled and open symbols, respectively) (a) and DC susceptibility along three crystallographic axes (b)–(d) of some Eu1xYxMnO3 single crystals. Double, down and up arrows indicate the TN, TCA and Tlock, respectively.
0
0.0
0.1
0.2 0.3 Concentration, x
0.4
0.5
Fig. 3. Phase T2x diagram of Eu1xYxMnO3, where P denotes paramagnetic phase, CAF—canted antiferromagnetic, IC incommensurate antiferromagnetic, C/FE: commensurate ferroelectric. Lines—guide for eyes.
ARTICLE IN PRESS V.Y. Ivanov et al. / Journal of Magnetism and Magnetic Materials 300 (2006) e130–e133
e132
which indicates a change of magnetic (and electric) structure. The observed phase transformations were mapped in the T–x phase diagram shown in Fig. 3. Various phase transitions were revealed in the magnetic fields along a, b, c axes. The transitions from C (IC) to CAF phase were observed for HJc below Tlock (TN) as jumps in the Mc(Hc), lc(Hc) and DPc,a(Hc) curves at threshold fields from few kOe (x ¼ 0, 0.1) up to 200 kOe (x ¼ 0.2, 0.3). These data are illustrated in Fig. 4 for x ¼ 0:2. A remarkable feature of the DPc,a(Hc) curves is a polarization sign dependence on a sign of poling field along corresponding axes (Fig. 4d). The effect (as well as nonzero DP) is observed only when ToT lock indicating an existence of a spontaneous electric polarization below 20
σ c,emu/g
15
Tlock, that enables us to identify the C phase as well as ferroelectric one (commensurate ferroelectric, C/FE) (see Fig. 3). Amplitude of field-induced change of the DPc,a(Hc) at the transition depends also on a value of the poling field and exhibit a strong anisotropy |DPa|b|DPc| (Fig. 4c and d). Another interesting feature of the observed transition for HJc is its significant hysteresis: for a zero-field cooled regime the antiferromagnetic C/FE phase retains up to the lowest temperatures (To4 K), while it is suppressed by Hkc and is transformed to the CAF state which holds even when H ¼ 0. The onset of the field-induced transition occurs at HcE50 kOe with sharp jumps of the sc, lc and DPa,c, which, however, finishes at Hc110–130 kOe according to a smooth part of the DPa,c(H) curves (Fig. 4). It may indicate a two-stage character of the C/FE–CAF transition with an appearance of some intermediate phase possessing both a weak ferromagnetic moment and electric polarization. Perhaps this phase remains after removing the
10 5
(a) 10
σa, emu/g
0
λc,10-6
100
5
(a)
50 0 20
(b) 0
H || a
E = 4.3 kV/cm λa, 10-6
∆Pc, µC / m2
50
E = 2.1 kV/cm
10
(b)
0 (c) 0
800 E = 0.97 kV/cm 600
E = 1 kV/cm ∆Pa, µC / m2
∆Pa, µC / m2
500
0
0.65 400 0.16 200
E = -1 kV/cm
(c)
(d)
-500 0
50
100
150
Magnetic field, kOe Fig. 4. Magnetic field dependence of magnetization (a), magnetostriction (b), and changes of polarization along c (c) and a axis (d) in Eu0.8Y0.2MnO3 for Hkc at T ¼ 4.5 K. DP(H) curves were obtained after cooling in electric field from T4TN.
0
0
50
100
150
Magnetic field, kOe Fig. 5. Magnetic field dependence of magnetization (a), longitudinal magnetostriction (b), and changes of polarization along a axis (c) in Eu0.8Y0.2MnO3 for Hka at T ¼ 4.5 K. DP(H) curves were obtained after cooling in electric field from T4TN.
ARTICLE IN PRESS V.Y. Ivanov et al. / Journal of Magnetism and Magnetic Materials 300 (2006) e130–e133
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4. Conclusion δ Paa
δ P cc
+ 60
δ Paa, µC / m2
600 δ P cc
400
-
40
20
200
0 0
δPcc, µC / m2
800
1
2 3 E, kV/cm
4
5
0
Fig. 6. Dependence of change of the electric polaization induced by Hkc and Hka axes DPcc,aa ¼ DPc,a(0)—DPc,a(Hmax c,a ) versus the poling electric field Ec,a in Eu0.8Y0.2MnO3 at T ¼ 4.5 K; DP7 cc corresponds to up and down magnetic field in Fig. 4c.
The substituted Eu1xYxMnO3 (0:2pxp0:5) manganites exhibit the remarkable multiferroic states with a modulated antiferromagnetic structure and electric polarization upon decreasing of the average rare-earth ionic radii with increasing Y concentration. These states are observed below the IC–C transition at Tlock accompanied by anomalies in the dielectric constant. Various phase transitions were observed in the magnetic fields up to 250 kOe along a, b, c axes by magnetization, magnetostriction and electric polarization measurements which indicate close interrelations of the electric polarizaion with the magnetic structure. The observed ferroelectricity has an improper character and could be attributed to spin-lattice interaction in the modulated off-center symmetry magnetic structure. Acknowledgements
magnetic field and corresponds to a double dashed region at the x–T diagram in Fig. 3. For Hkb and a axes, another field-induced transitions were revealed. For Hkb, a spin–flop transition was observed at Hb200 kOe accompanied by jumps of the magnetization, magnetostriction and electric polarization. Unusual phase transitions were also found for Hka at Ha50–100 kOe and ToT lock (Fig. 5) which was accompanied by a huge change of polarization DPa. The value of the induced polarization DPa as well as its sign (not shown) depend on poling field (Fig. 5c). The extracted fieldinduced changes of the polarization DPa,c for Hka and c axes versus the poling field are shown in Fig. 6 for x ¼ 0:2. They exhibit a tendency for a saturation but are far to achieve it. The maximum value of the induced polarization DPaa800 mC/m2 is comparable to TbMnO3 and DyMnO3 corresponding data [1,2].
This work was supported by Russian Foundation for Basic Research (Project nos. 04-02-16592, 03-02-16445, 0302-16759, 04-02-81046-Bel2004). References [1] T. Kimura, T. Goto, H. Shintani, K. Ishizaka, T. Arima, Y. Tokura, Nature 426 (2003) 55. [2] T. Goto, T. Kimura, G. Lawes, A.P. Ramirez, Y. Tokura, Phys. Rev. Lett. 92 (2004) 257201. [3] T. Kimura, S. Ishihara, H. Shintani, T. Arima, K.T. Takahashi, K. Ishizaka, Y. Tokura, Phys. Rev. B 68 (2003) 060403. [4] J. Hemberger, S. Lobina, H.-A. Krug von Nidda, N. Tristan, V.Yu. Ivanov, A.A. Mukhin, A.M. Balbashov, A. Loidl, Phys. Rev. B 70 (2004) 024414. [5] A.A. Mukhin, V.Yu. Ivanov, V.D. Travkin, A.S. Prokhorov, A.M. Balbashov, J. Magn. Magn. Mater. 272–276 (2004) 96. [6] A.M. Kadomtseva, Yu.F. Popov, G.P. Vorob’ev, K.I. Kamilov, A.P. Pyatakov, V.Yu. Ivanov, A.A. Mukhin, A.M. Balbashov, JETP Lett. 81 (2005) 19.