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Effects of applied magnetic fields on the magnetic structure of DyVO4
Solid State Communications, Vol. 17, pp. 1—3, 1975
Pergamon Press.
Printed in Great Britain
EFFECTS OF APPLIED MAGNETIC FIELDS ON THE MAGNETIC STRUCTURE OF DyVO4 W. Schafer and G. Will Mineralogisches Institut der Universität Bonn, Abteilung für Kristallstrukturlehre und Neutronenbeurgung, Germany and G. Müller-Vogt Physikalisches Institut der Universität Karisruhe, Germany. and P. Burlet Institut Max von Laue—Paul Langevin, Grenoble, France (Received 6 February 1975 by E.F. Bertaut)
The influence of a magnetic field on the magnetic structure of DyVO4 has been studied on a single crystal at 1.8 K in fields up to 15 kG. At 3.0 kG we observed a domain reorientation along the applied magnetic field. A spinflip transition to a ferromagnetic state could not be observed within our experimental range.
1. INTRODUCTION MAGNETIC, thermal, and spectroscopic measure13 as well as X-ray and neutron diffraction ments experiments45 have shown that DyVO 4 undergoes a crystallographic phase transition from tetragonal to orthorhombic symmetry (space group I4~/amd to Imma) at 13.8 K, and a magnetic phase transition to an antiferromagnetic configuration at 3.0 K. These phase transitions, without external forces, result in domains. They fields, can be asinfluenced however, for example by magnetic could been shown directly in linearly polarised light.6
We have studied by neutron diffraction the influence of a magnetic field on the magnetic structure. Neutron diffraction information the length and direction yields of thedirect individual magneticonmoment vectors, e.g. the sub-lattice behavior, in contrast to other methods which give only integral values.
2. EXPERIMENTAL The measurements donereactor on a single crystal 3 at the were high flux of the ILL of 1 x 1 x 3 mm in Grenoble at the instrument D2. A conventional magnet with a limit of 15 kOe holding a cryostat between the pole pieces was used. The Bragg angle
The spectral behavior of DyVO 4 in a magnetic 7 These field hasconclude been studied Wright and Moos.the onset of authors fromby their observations a metamagnetic transition at 2 kOe and 1.5 K to an unknown magnetic structure.
was limited to 20 = 30°.The wave was A = 0.94 A, thereby using a Cu-monochromator. Thelength crystal was mounted with its c-axis vertical, leaving the (hk0) zone for observation. The magnetic field was always perpendicular to [001] and parallel to the scattering vector. 1
2
APPLIED MAGNETIC FIELDS OF DyVO4
I
1251
Vol. 17, No. I
Weashave studied theand (100), (200), and up (400) planes as well (010), (020), (040) in fields to 10 kOe.
1 1,81<
The results are shown in Fig. I and Table 1. 3. RESULTS
100
I
~
D
Below 3 K DyVO4 exhibits an antiferromagne tic collinear spin configuration of type Ci,, or non- 3~at distinguishable A~ C,, and A~refers to a sequence of respectively (+ + —) and (+ — — +) for Dy O00,0~~ withthemomentspointing respectively along the y-axis and the x-axis. From the previously available powder experiments the two types were not distinguishable. With this structure the (100) peaks are solely magnetic, while the (200) and (400) peaks are nuclear without a magnetic contribution. One further peak of magnetic interest in the (hko).~
2
~
(0~0)
~
50
—
25
zone, the (210), is too weak to be observed. 010) 0 1
2
3
~
I
I
5
6
Magnetic field ..L. c
7
8
9
10
(1<0.]
FIG. 1.
The present experiments on a single crystal at 1.8K and in zero field yielded equal intensities for the (100) and the (010) (solely magnetic) peaks as a result of the equal distribution of two antiferromagnetic domains, corresponding to C~,= (100) peak and A~= (010) peak.
Table 1. Relative change of the measured peak intensities (in percentage of the zero-field values) in outside magnetic fields directed along the scattering vector in the basal plane. The field direction was rotated by 90°between the (hOO) and the (OkO) measurements H [kOe] (100) or (010) 0 1.0 2.0 2.5 2.75 3.0 3.25 3.5 5.0 l0.~
(200) (020)
Intensity % (400) (040)
100 98 98 87 78 51 32
100 95 95 95 93 90 88
100 93 93 91 90 90 90
5 0
86 86
88 89
The pertinent experiments as a function of field were done at T = 1.8 K. In order to overcome nonreproducible effects and to ensure an equilibrium distribution of the domains we have first subjected the specimen to 15 kG for several minutes at 4.2 K.
(010) (100)
(020) (200)
100 97 91 49
100 96 95 97
22
96
9 0 0
97 94 94
Non-distinguishable
If we now apply a magnetic field, for example along the y-axis,we enforce an orientation of the domains into the configuration A~(Fig. 1). The critical field is 3.0 kOe. The domain reorientation begins at 2.5 kOe at 1.8 K and above 3.5 kOe we have one single
Vol. 17, No. 1
APPLIED MAGNETIC FIELDS OF DyVO4
domain. During the experiment H is parallel to the scattering vector = [010]. The experhnental setup does not allow to check for the (100) peak without turningH into that direction. We have therefore switched the field off and then looked for (100), finding an enhancement of 100 per cent. Ten minutes after the field had been switched off, the (100) intensity had still a 75 per cent higher value than in the original statistical distribution, and after four hours it was still at 40 per cent. In a similar experiment withH parallel to = [100] we observe now the C~,domains, while the A~ domains disappear. The (100) peak disappears however in a somewhat weaker magnetic field between 2.0 and 3.0 kOe, with a mean value of 3.5 kOe (Table 1). This implies that the As-domains are slightly more stable than the C~, -domains, an observation which is in agreement with experiments by Leask et al.6 in polarised light, Further experiments in fields up to 15 kOe revealed no further changes in the magnetic behavior. It was not possible to observe a spin—flip to a ferromagnetic state as claimed by Cooke et al. from magnetisation measurements. A ferromagnetic state must show up in an increase of intensity at the (200) and (400) nuclear peak position and in the disappearance of all (100),
1.
3
(010) and (001) antiferromagnetic peaks. We are going to do further neutron measurements with different diffraction geometries so that the scatteringvector of the observed peak is not parallel or nearly parallel to the outside magnetic field. 4 DISCUSSION Our neutron diffraction experiments 6 in linearlycorroborate polarized the observation by Leask et aL light, that a single domain distribution is enforced by an outside magnetic field. A spin—flip transition to a ferromagnetic state, as claimed by Wright and Moos from optical measurements7 could not be observed. It is noteworthy however, that the magnetic moment vector changes its position under the influence of an applied magnetic field into a direction parallel to that field. Normally one would expect an orientation perpendicular to an applied field. We will try further experiments with H perpendicular to the scattering vector, in order to study the whole zone in a field. The shift of the critical field by 0.5 kOe is in accordance with the observed anisotropy in the basal plane.
REFERENCES COOKE A.H., ELLIS C.J., GEHRING K.A., LEASK M.J.M., MARTIN D.M., WANKLYN B.M., WELLS M.R. and WHITE R.L., Solid State Commun. 8,689(1970).
2.
COOKE A.H., MARTIN D.M. and WELLS M.R., Solid State Commun. 9, 519 (1971).
3.
HARLEY R.T., HAYES W. and SMITH S.R.P., Solid State Commun. 9,515 (1971); BECKER P.J. and LAUGHSCH J.,Phys. Status Solidi B44, Kl09 (1971). GOBEL H. and WILL G.,Phys. Status Sojidi (b) 50. 147 (1972); SAYETAT F., BOUCHERLE J.X., BELAKHOVSKYM., KALLELA.,TCHEOU F., and FUESS H.,Phys. Lett. 34A, 7,361(1971). WILLG. and SCHAFER W.,J. Phys. C: Solid State Phys. 4,811(1971).
4. 5. 6. 7.
LEASK M.J.M., MAXWELL K.J., TYTE R.N., BECKER P.J., KASTEN A. and WOCHNER W., Solid State Commun. 13, 693 (1973). WRIGHT J.C. and MOOS H.W., Phys. Rev. B4, 163 (1971).
Pergamon Press.
Printed in Great Britain
EFFECTS OF APPLIED MAGNETIC FIELDS ON THE MAGNETIC STRUCTURE OF DyVO4 W. Schafer and G. Will Mineralogisches Institut der Universität Bonn, Abteilung für Kristallstrukturlehre und Neutronenbeurgung, Germany and G. Müller-Vogt Physikalisches Institut der Universität Karisruhe, Germany. and P. Burlet Institut Max von Laue—Paul Langevin, Grenoble, France (Received 6 February 1975 by E.F. Bertaut)
The influence of a magnetic field on the magnetic structure of DyVO4 has been studied on a single crystal at 1.8 K in fields up to 15 kG. At 3.0 kG we observed a domain reorientation along the applied magnetic field. A spinflip transition to a ferromagnetic state could not be observed within our experimental range.
1. INTRODUCTION MAGNETIC, thermal, and spectroscopic measure13 as well as X-ray and neutron diffraction ments experiments45 have shown that DyVO 4 undergoes a crystallographic phase transition from tetragonal to orthorhombic symmetry (space group I4~/amd to Imma) at 13.8 K, and a magnetic phase transition to an antiferromagnetic configuration at 3.0 K. These phase transitions, without external forces, result in domains. They fields, can be asinfluenced however, for example by magnetic could been shown directly in linearly polarised light.6
We have studied by neutron diffraction the influence of a magnetic field on the magnetic structure. Neutron diffraction information the length and direction yields of thedirect individual magneticonmoment vectors, e.g. the sub-lattice behavior, in contrast to other methods which give only integral values.
2. EXPERIMENTAL The measurements donereactor on a single crystal 3 at the were high flux of the ILL of 1 x 1 x 3 mm in Grenoble at the instrument D2. A conventional magnet with a limit of 15 kOe holding a cryostat between the pole pieces was used. The Bragg angle
The spectral behavior of DyVO 4 in a magnetic 7 These field hasconclude been studied Wright and Moos.the onset of authors fromby their observations a metamagnetic transition at 2 kOe and 1.5 K to an unknown magnetic structure.
was limited to 20 = 30°.The wave was A = 0.94 A, thereby using a Cu-monochromator. Thelength crystal was mounted with its c-axis vertical, leaving the (hk0) zone for observation. The magnetic field was always perpendicular to [001] and parallel to the scattering vector. 1
2
APPLIED MAGNETIC FIELDS OF DyVO4
I
1251
Vol. 17, No. I
Weashave studied theand (100), (200), and up (400) planes as well (010), (020), (040) in fields to 10 kOe.
1 1,81<
The results are shown in Fig. I and Table 1. 3. RESULTS
100
I
~
D
Below 3 K DyVO4 exhibits an antiferromagne tic collinear spin configuration of type Ci,, or non- 3~at distinguishable A~ C,, and A~refers to a sequence of respectively (+ + —) and (+ — — +) for Dy O00,0~~ withthemomentspointing respectively along the y-axis and the x-axis. From the previously available powder experiments the two types were not distinguishable. With this structure the (100) peaks are solely magnetic, while the (200) and (400) peaks are nuclear without a magnetic contribution. One further peak of magnetic interest in the (hko).~
2
~
(0~0)
~
50
—
25
zone, the (210), is too weak to be observed. 010) 0 1
2
3
~
I
I
5
6
Magnetic field ..L. c
7
8
9
10
(1<0.]
FIG. 1.
The present experiments on a single crystal at 1.8K and in zero field yielded equal intensities for the (100) and the (010) (solely magnetic) peaks as a result of the equal distribution of two antiferromagnetic domains, corresponding to C~,= (100) peak and A~= (010) peak.
Table 1. Relative change of the measured peak intensities (in percentage of the zero-field values) in outside magnetic fields directed along the scattering vector in the basal plane. The field direction was rotated by 90°between the (hOO) and the (OkO) measurements H [kOe] (100) or (010) 0 1.0 2.0 2.5 2.75 3.0 3.25 3.5 5.0 l0.~
(200) (020)
Intensity % (400) (040)
100 98 98 87 78 51 32
100 95 95 95 93 90 88
100 93 93 91 90 90 90
5 0
86 86
88 89
The pertinent experiments as a function of field were done at T = 1.8 K. In order to overcome nonreproducible effects and to ensure an equilibrium distribution of the domains we have first subjected the specimen to 15 kG for several minutes at 4.2 K.
(010) (100)
(020) (200)
100 97 91 49
100 96 95 97
22
96
9 0 0
97 94 94
Non-distinguishable
If we now apply a magnetic field, for example along the y-axis,we enforce an orientation of the domains into the configuration A~(Fig. 1). The critical field is 3.0 kOe. The domain reorientation begins at 2.5 kOe at 1.8 K and above 3.5 kOe we have one single
Vol. 17, No. 1
APPLIED MAGNETIC FIELDS OF DyVO4
domain. During the experiment H is parallel to the scattering vector = [010]. The experhnental setup does not allow to check for the (100) peak without turningH into that direction. We have therefore switched the field off and then looked for (100), finding an enhancement of 100 per cent. Ten minutes after the field had been switched off, the (100) intensity had still a 75 per cent higher value than in the original statistical distribution, and after four hours it was still at 40 per cent. In a similar experiment withH parallel to = [100] we observe now the C~,domains, while the A~ domains disappear. The (100) peak disappears however in a somewhat weaker magnetic field between 2.0 and 3.0 kOe, with a mean value of 3.5 kOe (Table 1). This implies that the As-domains are slightly more stable than the C~, -domains, an observation which is in agreement with experiments by Leask et al.6 in polarised light, Further experiments in fields up to 15 kOe revealed no further changes in the magnetic behavior. It was not possible to observe a spin—flip to a ferromagnetic state as claimed by Cooke et al. from magnetisation measurements. A ferromagnetic state must show up in an increase of intensity at the (200) and (400) nuclear peak position and in the disappearance of all (100),
1.
3
(010) and (001) antiferromagnetic peaks. We are going to do further neutron measurements with different diffraction geometries so that the scatteringvector of the observed peak is not parallel or nearly parallel to the outside magnetic field. 4 DISCUSSION Our neutron diffraction experiments 6 in linearlycorroborate polarized the observation by Leask et aL light, that a single domain distribution is enforced by an outside magnetic field. A spin—flip transition to a ferromagnetic state, as claimed by Wright and Moos from optical measurements7 could not be observed. It is noteworthy however, that the magnetic moment vector changes its position under the influence of an applied magnetic field into a direction parallel to that field. Normally one would expect an orientation perpendicular to an applied field. We will try further experiments with H perpendicular to the scattering vector, in order to study the whole zone in a field. The shift of the critical field by 0.5 kOe is in accordance with the observed anisotropy in the basal plane.
REFERENCES COOKE A.H., ELLIS C.J., GEHRING K.A., LEASK M.J.M., MARTIN D.M., WANKLYN B.M., WELLS M.R. and WHITE R.L., Solid State Commun. 8,689(1970).
2.
COOKE A.H., MARTIN D.M. and WELLS M.R., Solid State Commun. 9, 519 (1971).
3.
HARLEY R.T., HAYES W. and SMITH S.R.P., Solid State Commun. 9,515 (1971); BECKER P.J. and LAUGHSCH J.,Phys. Status Solidi B44, Kl09 (1971). GOBEL H. and WILL G.,Phys. Status Sojidi (b) 50. 147 (1972); SAYETAT F., BOUCHERLE J.X., BELAKHOVSKYM., KALLELA.,TCHEOU F., and FUESS H.,Phys. Lett. 34A, 7,361(1971). WILLG. and SCHAFER W.,J. Phys. C: Solid State Phys. 4,811(1971).
4. 5. 6. 7.
LEASK M.J.M., MAXWELL K.J., TYTE R.N., BECKER P.J., KASTEN A. and WOCHNER W., Solid State Commun. 13, 693 (1973). WRIGHT J.C. and MOOS H.W., Phys. Rev. B4, 163 (1971).