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A new magnetoelectric compound: DyCoO3
Solid State Communications,Vol. 17, pp. 237—239, 1975.
Pergainon Press.
Printed in Great Britain
A NEW MAGNETOELECTRIC COMPOUND: DyCoO3 G. Velleaud and M. Mercier Institut Universitaire de Technologie, 03107 Montlucon, France (Received 24 February 1975; in revised form 21 March 1975 by E.F. Bertaut)
A first order magnetoelectric effect with a = 10_2 is measured on a powder sample of DyCoO3, due to the Dy~ions. The metamagnetic behaviour is demonstrated.
H II [O1~ ~ Yp b~ 3\ /1 3 ~ I /1 \ /~9:6O~ \ / / \ x,a / xa 2/ \4 2/ 4 GA C F F P X Y X Y, “~ Yb \/ H/Jpbo] / \ X~ 2/ \. F C FL I P X Y’
ORTHOCOBALTITES of rare earths have a perovskite structure with orthorhombic distortion and show two weakly coupled magnetic nets. The space group is Pbnm with four molecules in the cell. The cobalt atoms are on the 4b sites and the four rare earth atoms on the
y b.
—
4c sites I(x,y, 1/4), II(~,y,3/4),111(1/2 +x, 1/2 —y, 3/4), IV(1/2 —x, 1/2 +y, 1/4). The parameters of the cellarea=5.162,b=5.400andc=7398.’
\ /
3~ to the high value of the crystal field, ions Due are diamagnetic. The Ned temperature ofthe the Co ordered state of the Dy3~ions is 3.6 ±0.05 K2 and the saturation moment, at OK, is 9!.LB and 8.SI.ZB at 1.5 K. The magnetic cell is identical to the chemical cell and the magnetic group is Pb n m The modes are G~(+ + —) and A~(+ — +) with an angle 0 = 60° .
—
_____
—
FIG. 1. Magnetic structure of DyCoO
—
3 (G~A~) and possible effect of a magnetic field.
between the moment I and the binary a or x axis (Fig. I). 3~ions is 6H The ground state of theenergy Dy is not minimal 1512. Due to the fact that the dipolar for DyCoO 3 with 0 = 60°,that the exchange forces are probably weak and, a fortiori, their anisotropic contribution, 0 is fixed by the crystal fieldstate and is 3 The ground is indepentherefore dent of the temperature. split by the crystal field into a series of eight Kramer’s doublets and only the lower doublet is occupied at low temperatures and that doublet has an Ising-like character.
4Thus an alternating electric field, applied alonga~2. the x binary axis, may induce a magnetization
~.,
5
proportional to the field along the same axis = a~~E~/4ir in Gauss units. The same is true for the other y or z Another condition for the is existence of directions. the first order magnetoelectric effect that the magnetic atoms are not on symmetry centers because the EH product must remain unchanged under the symmetry operations. The 4c sites of Dy~ions are not centers of symmetry but mirrors. The 4b sites are centers of symmetry and a first order magnetoelectric effect is forbidden but not the second order effect f3 = (4ir5 )/E2 (if Co3~was magnetic) (Table 1).
Within the point group m’m’m’ a first order magnetoelectric effect is allowed whose coefficients are ~ 237
A NEW MAGNETOELECTRIC COMPOUND: DyCoO3
238
Vol. 17, No.2
Table 1. Nature ofthe magnetoelectric coefficients for the magnetic point groups of Pbnm for the perovskite compounds ABO3 where B is a metal and A a rare earth. XYZ are the three orthogonal binary axes of the cell, respectively along the a, b, c parameters 3~ A3~ Magnetic point ofNature the m.e. Directions of the effect 4bBsites 4c sites group coefficients m’ m m’ m
m’ m m m’
m’ m’ m m
m
m
m
m’ m
m’ m’ m
m m’ m’
a a a a
(3
(3
XX XY YZ XZ
YY YX ZY ZX
ZZ
xYz
XZY ~
ZXY
~
ZZZ XXX YYY
XXZ~3~ ZZX~3~ XXY~3~
G~ A~
A~ G~ G~
A,,
G~
C~
yy~~3~ G~ yy~(3) F~
A~
F~
C,,
G~
F~
C~,
ZZY~
F~
A~
C~
F~
C~
C~ F~
~.1O
3
c~JO
8
5 4~
6 3
4 2
1
2
HkOe
a
FIG. 3. Metamagnetic behaviour demonstrated by mag-
FiG. 2. Curye of a(j) for a powder sample of DyCoO
with annealing static fields FL -—
=
3.3 kV/cm and
3
e.
Powder samples of DyCoO3 were prepared by the Neutron Diffraction Laboratory of the Nuclear 2. The Center measureof Grenoble and pressed at 4 x iO~ kg/cm ment of the magnetoelectric effect was made at 1 kHz with the apparatus already described.5 The sample was annealed through the Ned temperature with static parallel fields H. = 2.000 Oe and E_ = 3.3 kY/cm applied in the direction of the alternating field E~
netoelectric effect on a powder sample of DyCoO3 at T = TN e, with annealing static fields E. = 3.3 ky/cm andH...=20000e. —
5
which induces the magnetization The measured magnetoelectric coefficient a is function of the three values ~ a,~,~ The Ned temperature of the Dy3~ordering was extrapolated from the temperature at which the effect disappears and measured as 3.57K (Fig. 2). For the lowest temperature obtained 1.7 K, the value of a is 10-2 (without dimension in the system of Gauss units). The value ofa is bound to the values _.
Vol. 17, No.2
ANEW MAGNETOELECTRIC COMPOUND: DyCoO3
and to the relative sign of the annealing fields and 10-2 is the highest value we obtained. It is of7the same order DyA1O 79 ofmagnitude as for crystals TbAIO3, 3 and TbPO,’°which have theofhighest values of a found up to now.~~12 The magnetoelectric effect exists in two other compounds of Dy ions, DyAIO 7°and 3 DyPO 23’14 4. The metamagnetism was observed by magnetic measurements and a saturation moment of only 51.LB was obtained.~Due to the fact that the anisotropy 3 the field is much larger than theby ordering field metamagnetisin is obtained spin flip, i.e. the moments are reversed but remain in the local
anisotropy directions. Thus the saturation moment observed is inferior of to the moments theoreticalon value only the projection the because direction of the magnetic field is measured. The metamagnetic behaviour due to the appearance of the modes F~C~ or F~C~ which do not allow a first order effect (Table 1) is also apparentfrom the magnetoelectric effect: a decreases down to zero when an increasing magnetic field is applied (Fig. 3). This phenomenon was previously observed on TbA1O 7 DyPO 14 and 3, 4 DyAlO 3.Th Acknowledgement We thank Mr Paquin for excellent technical assistance. —
REFERENCES 1. 2. 3.
KAPPATSCH A., QUEZEL-AMBRUNAZ S. and SIVARDIERE J.,J. Phys. 31,369 (1970). KAPPATSCH A., These, University of Grenoble (1969). SIVARDIERE J., These, University of Grenoble (1970); TCHEOU F. and ROSSAT-MIGNOD J.,J. Phys. 33,423 (1972). 4. BIRSS R.R., Symmetry andMagnetism p. 146. North-Holland, Amsterdam (1966). 5. BERTAUT E.F. and MERCIER M.,Mat. Res. Bull. 6,907 (1971). 6. HORNREICH R.M.,J. AppL Phys. 41,950(1970). 7.
MERCIERM. and BAUER P., Colloque LesEléments de TerresRares, C.N.RS. Paris No. 180, Vol. 2, 377 (1970). 8. HOLMES L.M.,VANUITERT L.G. and HULL G.W.,Solid State Commun. 9,1373(1971). 9. HOLMES L.M. and VAN UITERT L.G., Phys. Rev. B 5, 147 (1972). 10. RADOG.T.and FERRARI J.M.,AIPConf Proc. 10,1417(1972). 11. 12. 13. 14.
COXD.E.,Int.J.Magn. 6, 67 (1974). SCHMID H.,Int. I. Magn. 4,337 (1973).
15.
HOLMES L.M.,Jnt.J.Magn. 6,111(1974).
RADO G.T.,Phys. Rev. Lett. 23,644(1969). RADOG.T.,SolidStateCommun. 8, 1349 (1970).
239
Pergainon Press.
Printed in Great Britain
A NEW MAGNETOELECTRIC COMPOUND: DyCoO3 G. Velleaud and M. Mercier Institut Universitaire de Technologie, 03107 Montlucon, France (Received 24 February 1975; in revised form 21 March 1975 by E.F. Bertaut)
A first order magnetoelectric effect with a = 10_2 is measured on a powder sample of DyCoO3, due to the Dy~ions. The metamagnetic behaviour is demonstrated.
H II [O1~ ~ Yp b~ 3\ /1 3 ~ I /1 \ /~9:6O~ \ / / \ x,a / xa 2/ \4 2/ 4 GA C F F P X Y X Y, “~ Yb \/ H/Jpbo] / \ X~ 2/ \. F C FL I P X Y’
ORTHOCOBALTITES of rare earths have a perovskite structure with orthorhombic distortion and show two weakly coupled magnetic nets. The space group is Pbnm with four molecules in the cell. The cobalt atoms are on the 4b sites and the four rare earth atoms on the
y b.
—
4c sites I(x,y, 1/4), II(~,y,3/4),111(1/2 +x, 1/2 —y, 3/4), IV(1/2 —x, 1/2 +y, 1/4). The parameters of the cellarea=5.162,b=5.400andc=7398.’
\ /
3~ to the high value of the crystal field, ions Due are diamagnetic. The Ned temperature ofthe the Co ordered state of the Dy3~ions is 3.6 ±0.05 K2 and the saturation moment, at OK, is 9!.LB and 8.SI.ZB at 1.5 K. The magnetic cell is identical to the chemical cell and the magnetic group is Pb n m The modes are G~(+ + —) and A~(+ — +) with an angle 0 = 60° .
—
_____
—
FIG. 1. Magnetic structure of DyCoO
—
3 (G~A~) and possible effect of a magnetic field.
between the moment I and the binary a or x axis (Fig. I). 3~ions is 6H The ground state of theenergy Dy is not minimal 1512. Due to the fact that the dipolar for DyCoO 3 with 0 = 60°,that the exchange forces are probably weak and, a fortiori, their anisotropic contribution, 0 is fixed by the crystal fieldstate and is 3 The ground is indepentherefore dent of the temperature. split by the crystal field into a series of eight Kramer’s doublets and only the lower doublet is occupied at low temperatures and that doublet has an Ising-like character.
4Thus an alternating electric field, applied alonga~2. the x binary axis, may induce a magnetization
~.,
5
proportional to the field along the same axis = a~~E~/4ir in Gauss units. The same is true for the other y or z Another condition for the is existence of directions. the first order magnetoelectric effect that the magnetic atoms are not on symmetry centers because the EH product must remain unchanged under the symmetry operations. The 4c sites of Dy~ions are not centers of symmetry but mirrors. The 4b sites are centers of symmetry and a first order magnetoelectric effect is forbidden but not the second order effect f3 = (4ir5 )/E2 (if Co3~was magnetic) (Table 1).
Within the point group m’m’m’ a first order magnetoelectric effect is allowed whose coefficients are ~ 237
A NEW MAGNETOELECTRIC COMPOUND: DyCoO3
238
Vol. 17, No.2
Table 1. Nature ofthe magnetoelectric coefficients for the magnetic point groups of Pbnm for the perovskite compounds ABO3 where B is a metal and A a rare earth. XYZ are the three orthogonal binary axes of the cell, respectively along the a, b, c parameters 3~ A3~ Magnetic point ofNature the m.e. Directions of the effect 4bBsites 4c sites group coefficients m’ m m’ m
m’ m m m’
m’ m’ m m
m
m
m
m’ m
m’ m’ m
m m’ m’
a a a a
(3
(3
XX XY YZ XZ
YY YX ZY ZX
ZZ
xYz
XZY ~
ZXY
~
ZZZ XXX YYY
XXZ~3~ ZZX~3~ XXY~3~
G~ A~
A~ G~ G~
A,,
G~
C~
yy~~3~ G~ yy~(3) F~
A~
F~
C,,
G~
F~
C~,
ZZY~
F~
A~
C~
F~
C~
C~ F~
~.1O
3
c~JO
8
5 4~
6 3
4 2
1
2
HkOe
a
FIG. 3. Metamagnetic behaviour demonstrated by mag-
FiG. 2. Curye of a(j) for a powder sample of DyCoO
with annealing static fields FL -—
=
3.3 kV/cm and
3
e.
Powder samples of DyCoO3 were prepared by the Neutron Diffraction Laboratory of the Nuclear 2. The Center measureof Grenoble and pressed at 4 x iO~ kg/cm ment of the magnetoelectric effect was made at 1 kHz with the apparatus already described.5 The sample was annealed through the Ned temperature with static parallel fields H. = 2.000 Oe and E_ = 3.3 kY/cm applied in the direction of the alternating field E~
netoelectric effect on a powder sample of DyCoO3 at T = TN e, with annealing static fields E. = 3.3 ky/cm andH...=20000e. —
5
which induces the magnetization The measured magnetoelectric coefficient a is function of the three values ~ a,~,~ The Ned temperature of the Dy3~ordering was extrapolated from the temperature at which the effect disappears and measured as 3.57K (Fig. 2). For the lowest temperature obtained 1.7 K, the value of a is 10-2 (without dimension in the system of Gauss units). The value ofa is bound to the values _.
Vol. 17, No.2
ANEW MAGNETOELECTRIC COMPOUND: DyCoO3
and to the relative sign of the annealing fields and 10-2 is the highest value we obtained. It is of7the same order DyA1O 79 ofmagnitude as for crystals TbAIO3, 3 and TbPO,’°which have theofhighest values of a found up to now.~~12 The magnetoelectric effect exists in two other compounds of Dy ions, DyAIO 7°and 3 DyPO 23’14 4. The metamagnetism was observed by magnetic measurements and a saturation moment of only 51.LB was obtained.~Due to the fact that the anisotropy 3 the field is much larger than theby ordering field metamagnetisin is obtained spin flip, i.e. the moments are reversed but remain in the local
anisotropy directions. Thus the saturation moment observed is inferior of to the moments theoreticalon value only the projection the because direction of the magnetic field is measured. The metamagnetic behaviour due to the appearance of the modes F~C~ or F~C~ which do not allow a first order effect (Table 1) is also apparentfrom the magnetoelectric effect: a decreases down to zero when an increasing magnetic field is applied (Fig. 3). This phenomenon was previously observed on TbA1O 7 DyPO 14 and 3, 4 DyAlO 3.Th Acknowledgement We thank Mr Paquin for excellent technical assistance. —
REFERENCES 1. 2. 3.
KAPPATSCH A., QUEZEL-AMBRUNAZ S. and SIVARDIERE J.,J. Phys. 31,369 (1970). KAPPATSCH A., These, University of Grenoble (1969). SIVARDIERE J., These, University of Grenoble (1970); TCHEOU F. and ROSSAT-MIGNOD J.,J. Phys. 33,423 (1972). 4. BIRSS R.R., Symmetry andMagnetism p. 146. North-Holland, Amsterdam (1966). 5. BERTAUT E.F. and MERCIER M.,Mat. Res. Bull. 6,907 (1971). 6. HORNREICH R.M.,J. AppL Phys. 41,950(1970). 7.
MERCIERM. and BAUER P., Colloque LesEléments de TerresRares, C.N.RS. Paris No. 180, Vol. 2, 377 (1970). 8. HOLMES L.M.,VANUITERT L.G. and HULL G.W.,Solid State Commun. 9,1373(1971). 9. HOLMES L.M. and VAN UITERT L.G., Phys. Rev. B 5, 147 (1972). 10. RADOG.T.and FERRARI J.M.,AIPConf Proc. 10,1417(1972). 11. 12. 13. 14.
COXD.E.,Int.J.Magn. 6, 67 (1974). SCHMID H.,Int. I. Magn. 4,337 (1973).
15.
HOLMES L.M.,Jnt.J.Magn. 6,111(1974).
RADO G.T.,Phys. Rev. Lett. 23,644(1969). RADOG.T.,SolidStateCommun. 8, 1349 (1970).
239