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Experimental study of magnetic and crystallographic transitions in DyVO4
PHYSICS
Volume 34A, number 7
EXPERIMENTAL
19 April 1971
LETTERS
STUDY OF MAGNETIC TRANSITIONS IN
AND CRYSTALLOGRAPHIC DyV04
F. SAYETAT, J. X. BOUCHERLE CNRS, Chemin des Martyrs, Grenoble, France M. BELAKHOVSKY,
A. KALLEL,
F. TCHEOU and H. FUESS *
CENG, Chemin des Martyrs,
Grenoble,
France
Received 13 March 1971
Low temperatures X-rays, Mbssbauer and neutron diffraction measurements ha.ve been performed on a powder DyVO4 sample; evidence for a crystallographic distorsion in the paramagnetic region is definitevely established, and the temperature dependence of its magnitude is given; the magnetic structure below TN = 3.1 K is discussed.
Recently [l] the compound DyV04 has been shown to reveal interesting features, not exhibited in other compounds of the vanadate series, mainly the presence of a Jahn Teller distorsion at 14 K. There still remained some controversy or uncertainty about the actual existence of this distorsion, and about the magnetic structure of DyVO4. We have performed low temperature X-rays, M6ssbauer and neutron diffraction studies in order to elucidate these points. Neutrons diffraction measurements indicate TN = 3.1 f 0.1 K by following the thermal variation of the strong (100) magnetic line (fig. 1). Spin configurations were worked out by applying the representation theory [e.g. 21. The possible modes are found to be Cy or Ax (fig. 1). These configurations correspond to the switching of a and b axes, this result allows us to decide between the two possible models (I and II) given
J
15.6K
.’
r!
* Present address: A.E.A., Harwell,
Materials Physics Divisions, Didcot, Berks, England.
U.K.
1.5K I
-20
I
-lo
I
I
I
lo
20
Fig. 2. M6ssbauer spectra of 161 Dy nucleus in DyV04 Fig. 1. Temperature dependence of the (100) magnetic line, and the spin configurations A, or Cy.
at 1.5 K, 12 K and 15.5 K, exhibiting the broadening and the sharp collapse of the hyperfine splitting.
361
Volume 34A, number
7
PHYSICS
19 April 1971
LETTERS Table 1 Tetragonal T =29K
a = 7.1395
Orthorhombic 2.6 ,cT=S 7K a = 7.1515 b =
c = 6.2899
7.1275
c = 6.2899
plausible assumption of an orthorhombic distorsion, we have estimated its maximum value to be: a, b (orthorhombic) I
10
I
20
1
30
TM
Fig. 3. Temperature dependence of the dlstorsion a - 6 = E. The splitting of the (600) line into the (600) and (060) lines below 12 K is shown.
by Cooke and coworkers
[l]: we can rule out model I. The magnetic moment at 1.5 K has been found to be (8.6 f 0.5)~~~ and (9.1 f 0.2)C(B by neutron and MBssbauer experiments respectively. One may fist mention that no crystallographic change has been found across the magnetic transition at 3.1 K, either by Mijssbauer or X-rays
measurements. It is hard to say whether spin-lattice relaxation effects in the Miissbauer spectra (fig. 2) around 14 K are connected to the distorsion, if any. Direct evidence of the distorsion is given by the X-rays experiment (fig. 3). According to the *****
362
= Q (tetragonal
*
f c
2’
with E: 0.024 b. The parameter c does not change and the resulting parameters are displayed in table 1. No variation was observed for the unit cell volume, within a relative accuracy of 10m4, and no hysteresis has shown up. We thank Professor E. F. Bertaut, F. de Bergevin and J. Chappert for helpful discussions and comments.
References [l] A. H. Cooke, C. J. Ellis, K. A. G&ring,
M. J. M. Leaak, D.M. Martin. B.M. Wanklyn. M. R. Wells and R. L. White, Solid State Corn& s (1970) 689. Complementary papers have been presented at the Intern. Cod on Magnetism (1970), Grenoble, J. de P.hya., to be published. 121E. F. Bertaut, Magnetism III, eds. Rado and Suhl (Acad. Press, 1953) p. 150.
Volume 34A, number 7
EXPERIMENTAL
19 April 1971
LETTERS
STUDY OF MAGNETIC TRANSITIONS IN
AND CRYSTALLOGRAPHIC DyV04
F. SAYETAT, J. X. BOUCHERLE CNRS, Chemin des Martyrs, Grenoble, France M. BELAKHOVSKY,
A. KALLEL,
F. TCHEOU and H. FUESS *
CENG, Chemin des Martyrs,
Grenoble,
France
Received 13 March 1971
Low temperatures X-rays, Mbssbauer and neutron diffraction measurements ha.ve been performed on a powder DyVO4 sample; evidence for a crystallographic distorsion in the paramagnetic region is definitevely established, and the temperature dependence of its magnitude is given; the magnetic structure below TN = 3.1 K is discussed.
Recently [l] the compound DyV04 has been shown to reveal interesting features, not exhibited in other compounds of the vanadate series, mainly the presence of a Jahn Teller distorsion at 14 K. There still remained some controversy or uncertainty about the actual existence of this distorsion, and about the magnetic structure of DyVO4. We have performed low temperature X-rays, M6ssbauer and neutron diffraction studies in order to elucidate these points. Neutrons diffraction measurements indicate TN = 3.1 f 0.1 K by following the thermal variation of the strong (100) magnetic line (fig. 1). Spin configurations were worked out by applying the representation theory [e.g. 21. The possible modes are found to be Cy or Ax (fig. 1). These configurations correspond to the switching of a and b axes, this result allows us to decide between the two possible models (I and II) given
J
15.6K
.’
r!
* Present address: A.E.A., Harwell,
Materials Physics Divisions, Didcot, Berks, England.
U.K.
1.5K I
-20
I
-lo
I
I
I
lo
20
Fig. 2. M6ssbauer spectra of 161 Dy nucleus in DyV04 Fig. 1. Temperature dependence of the (100) magnetic line, and the spin configurations A, or Cy.
at 1.5 K, 12 K and 15.5 K, exhibiting the broadening and the sharp collapse of the hyperfine splitting.
361
Volume 34A, number
7
PHYSICS
19 April 1971
LETTERS Table 1 Tetragonal T =29K
a = 7.1395
Orthorhombic 2.6 ,cT=S 7K a = 7.1515 b =
c = 6.2899
7.1275
c = 6.2899
plausible assumption of an orthorhombic distorsion, we have estimated its maximum value to be: a, b (orthorhombic) I
10
I
20
1
30
TM
Fig. 3. Temperature dependence of the dlstorsion a - 6 = E. The splitting of the (600) line into the (600) and (060) lines below 12 K is shown.
by Cooke and coworkers
[l]: we can rule out model I. The magnetic moment at 1.5 K has been found to be (8.6 f 0.5)~~~ and (9.1 f 0.2)C(B by neutron and MBssbauer experiments respectively. One may fist mention that no crystallographic change has been found across the magnetic transition at 3.1 K, either by Mijssbauer or X-rays
measurements. It is hard to say whether spin-lattice relaxation effects in the Miissbauer spectra (fig. 2) around 14 K are connected to the distorsion, if any. Direct evidence of the distorsion is given by the X-rays experiment (fig. 3). According to the *****
362
= Q (tetragonal
*
f c
2’
with E: 0.024 b. The parameter c does not change and the resulting parameters are displayed in table 1. No variation was observed for the unit cell volume, within a relative accuracy of 10m4, and no hysteresis has shown up. We thank Professor E. F. Bertaut, F. de Bergevin and J. Chappert for helpful discussions and comments.
References [l] A. H. Cooke, C. J. Ellis, K. A. G&ring,
M. J. M. Leaak, D.M. Martin. B.M. Wanklyn. M. R. Wells and R. L. White, Solid State Corn& s (1970) 689. Complementary papers have been presented at the Intern. Cod on Magnetism (1970), Grenoble, J. de P.hya., to be published. 121E. F. Bertaut, Magnetism III, eds. Rado and Suhl (Acad. Press, 1953) p. 150.