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Magnetic and electronic properties of DyH2 from 161Dy Mössbauer spectroscopy
Volume 67A, number 3
PHYSICS LETTERS
7 August 1978
MAGNETIC AND ELECTRONIC PROPERTIES OF DyH2 FROM 161Dy MöSSBAUER SPECTROSCOPY* G.K. SHENOY, J.M. FRIEDT‘ B.D. DUNLAP and D.G. WESTLAKE ‚
Argonne National Laboratory, Argonne, IL 60439, USA Received 12April1978
The Mössbauer study of DyH 161Dy resonance shows the presence of long- and short-range magnetic ordering below and above 3.3 K, respectively. Thethecrystal field splitting is large compared to the exchange field splitting, contrary to 2 with previous results.
Hess et al. [1] have reported the Mössbauer spectra of 161 Dy in DyH 2 and concluded from the analysis of tions were of comparable strength. This result is surtheir data that the exchange and crystal field interacprising since in ErH2 the crystal field splitting is an order of magnitude larger than that due to the ex-
0.00
—
D5H2
~~f\~(_
0.01
000 L
change field [21.Large crystal fields are also observed in PrD2 [3] and CeD2 [4J from neutron scattering
~
•
-
42K
V,
measurements. In order to clarify the reported behavior of DyH2 [1], we have remeasured the Mössbauer resonance spectra of this material using the 25.6 keV transition in 161 Dy. A sample of DyH200 ±0.01 was produced using the usual techniques of metal—hydrogen reaction. Some relevant spectra are shown in fig. 1. These differ in many respects from those reported earlier [1J. In particular, there is no spin relaxation effect present in the low temperature spectra. The origin of the discrepancy between the present results and those reported in the previous Mössbauer studies is not understood. Our primary results are the following: (1) From 300 to 6 K a single resonance line was observed, indicating no magnetic ordering down to 6 K. (2) The line width increased sharply as the temperature was lowered below 6K. At 3.5 K a magnetic hyperfine spectrum is observed with broadened hyperfine components result*
Supported by the U.S.D.O.E. On leave of absence from Centre de Recherches Nucléaires, Strasbourg, France.
o
~
0,00
38K 001 0.00
0.01
L
.85K I
I
L
-100 -80 -60 -40 -20 0 20 40 60 80 100 VELOCITY (minis) Fig. 1. Mössbauer spectra of DyH2 at various temperatures measured with a single-line source of (GdDy)F3 at 300 K.
ing from a distribution of the magnetic field. (3) Below 3.5 K the distribution vanishes, resulting in a sharp magnetic pattern. A hyperfine magnetic field of o(2400 2q~Q, f ± 50)kOe (200 ±20)and MHza quadrupole is measured interaction, at 1.8 K. e DyH 3~ions surrounded hydrogen atoms. 2 hasbya eight fluorite structure with A thecomparison Dy with the other hydrides suggests that in the cubic crys241
Volume 67A, number 3
PHYSICS LETTERS
tal field the ground state is F7 if the hydrogen atoms carry a negative charge (the hydridic model) [2]. This is confirmed from the experimental value of the hyperfine magnetic field which is nearly equal to the value of 2390 kOe calculated for this level. A F7 level produces no quadrupole interaction, even when the twofold degeneracy is removed by the exchange field. Hence the measured quadrupole interaction arises from a mixing of the crystal field levels by the exchange field. M excited crystal field level located at about 100K above the ground state when mixed into the F7 ground level by an exchange field (estimated from the antiferromagnetic ordering temperature) can in fact produce the observed quadrupole interaction and the magnetic hyperfine field. The location of the excited level is in agreement with specific heat Schottky anomaly rethe broad distribution of hyperfine SUi We ~ L interpret ~ fields observed between 6 and 3.5 K to be due to magnetic short-range ordering. This is in agreement with specific heat measurements, which show a broad hump in this temperature range [61. In addition, the specific heat data show a X-type anomaly at 3.3 K. This can be attributed to an antiferromagnetic order which is also
242
7 August 1978
observed in the Mössbauer spectra. The transition temperature obtained from both our Mössbauer results and the specific heat anomaly is slightly lower than that suggested by magnetic susceptibility investigations [7]. In conclusion, as in other rare-earth dihydrides, DyH2 falls within the hydridic model for hydrogen ions. The crystal field splittings are large compared to the exchange splittings, in agreement with observations on other rare-earth hydrides. References [1] J. [2] [3] [4] [5] [6] [7]
Hess, E.R. Bauminger, A. Mustachi, I. Nowik and S. Ofer, Phys. Lett. 37A (1971) 185. G.K. Shenoy, B.D. Dunlap, D.G. Westlake and A. Dwight, Phys. Rev. B14 (1976) 41. 42. K. Knorr and B.E. Fender, Crystal field effects in metals D.G. Hunt and D.K. Ross,(Plenum, J. Less Common Metals 45p. and alloys, ed. A. Furrer New York, 1977) (1976) 229. Z. Bieganski and J. Opyrchal, Bull. Acad. Pol. Sci. XX (1972) 775. Z. Bieganski, J. Opyrchal and M. Drulis, Phys. Stat. Sol.(a) 28 (1975) 217. Y. Kubota and W.E. Wallace, J. Chem. Phys. 39 (1963) 1285.
PHYSICS LETTERS
7 August 1978
MAGNETIC AND ELECTRONIC PROPERTIES OF DyH2 FROM 161Dy MöSSBAUER SPECTROSCOPY* G.K. SHENOY, J.M. FRIEDT‘ B.D. DUNLAP and D.G. WESTLAKE ‚
Argonne National Laboratory, Argonne, IL 60439, USA Received 12April1978
The Mössbauer study of DyH 161Dy resonance shows the presence of long- and short-range magnetic ordering below and above 3.3 K, respectively. Thethecrystal field splitting is large compared to the exchange field splitting, contrary to 2 with previous results.
Hess et al. [1] have reported the Mössbauer spectra of 161 Dy in DyH 2 and concluded from the analysis of tions were of comparable strength. This result is surtheir data that the exchange and crystal field interacprising since in ErH2 the crystal field splitting is an order of magnitude larger than that due to the ex-
0.00
—
D5H2
~~f\~(_
0.01
000 L
change field [21.Large crystal fields are also observed in PrD2 [3] and CeD2 [4J from neutron scattering
~
•
-
42K
V,
measurements. In order to clarify the reported behavior of DyH2 [1], we have remeasured the Mössbauer resonance spectra of this material using the 25.6 keV transition in 161 Dy. A sample of DyH200 ±0.01 was produced using the usual techniques of metal—hydrogen reaction. Some relevant spectra are shown in fig. 1. These differ in many respects from those reported earlier [1J. In particular, there is no spin relaxation effect present in the low temperature spectra. The origin of the discrepancy between the present results and those reported in the previous Mössbauer studies is not understood. Our primary results are the following: (1) From 300 to 6 K a single resonance line was observed, indicating no magnetic ordering down to 6 K. (2) The line width increased sharply as the temperature was lowered below 6K. At 3.5 K a magnetic hyperfine spectrum is observed with broadened hyperfine components result*
Supported by the U.S.D.O.E. On leave of absence from Centre de Recherches Nucléaires, Strasbourg, France.
o
~
0,00
38K 001 0.00
0.01
L
.85K I
I
L
-100 -80 -60 -40 -20 0 20 40 60 80 100 VELOCITY (minis) Fig. 1. Mössbauer spectra of DyH2 at various temperatures measured with a single-line source of (GdDy)F3 at 300 K.
ing from a distribution of the magnetic field. (3) Below 3.5 K the distribution vanishes, resulting in a sharp magnetic pattern. A hyperfine magnetic field of o(2400 2q~Q, f ± 50)kOe (200 ±20)and MHza quadrupole is measured interaction, at 1.8 K. e DyH 3~ions surrounded hydrogen atoms. 2 hasbya eight fluorite structure with A thecomparison Dy with the other hydrides suggests that in the cubic crys241
Volume 67A, number 3
PHYSICS LETTERS
tal field the ground state is F7 if the hydrogen atoms carry a negative charge (the hydridic model) [2]. This is confirmed from the experimental value of the hyperfine magnetic field which is nearly equal to the value of 2390 kOe calculated for this level. A F7 level produces no quadrupole interaction, even when the twofold degeneracy is removed by the exchange field. Hence the measured quadrupole interaction arises from a mixing of the crystal field levels by the exchange field. M excited crystal field level located at about 100K above the ground state when mixed into the F7 ground level by an exchange field (estimated from the antiferromagnetic ordering temperature) can in fact produce the observed quadrupole interaction and the magnetic hyperfine field. The location of the excited level is in agreement with specific heat Schottky anomaly rethe broad distribution of hyperfine SUi We ~ L interpret ~ fields observed between 6 and 3.5 K to be due to magnetic short-range ordering. This is in agreement with specific heat measurements, which show a broad hump in this temperature range [61. In addition, the specific heat data show a X-type anomaly at 3.3 K. This can be attributed to an antiferromagnetic order which is also
242
7 August 1978
observed in the Mössbauer spectra. The transition temperature obtained from both our Mössbauer results and the specific heat anomaly is slightly lower than that suggested by magnetic susceptibility investigations [7]. In conclusion, as in other rare-earth dihydrides, DyH2 falls within the hydridic model for hydrogen ions. The crystal field splittings are large compared to the exchange splittings, in agreement with observations on other rare-earth hydrides. References [1] J. [2] [3] [4] [5] [6] [7]
Hess, E.R. Bauminger, A. Mustachi, I. Nowik and S. Ofer, Phys. Lett. 37A (1971) 185. G.K. Shenoy, B.D. Dunlap, D.G. Westlake and A. Dwight, Phys. Rev. B14 (1976) 41. 42. K. Knorr and B.E. Fender, Crystal field effects in metals D.G. Hunt and D.K. Ross,(Plenum, J. Less Common Metals 45p. and alloys, ed. A. Furrer New York, 1977) (1976) 229. Z. Bieganski and J. Opyrchal, Bull. Acad. Pol. Sci. XX (1972) 775. Z. Bieganski, J. Opyrchal and M. Drulis, Phys. Stat. Sol.(a) 28 (1975) 217. Y. Kubota and W.E. Wallace, J. Chem. Phys. 39 (1963) 1285.