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Magnetic properties of 3d — Transition metal and rare earth fluoride glasses
TC 5
Physica 108B (1981) 1291-1292 North-Holland Publishing Company
MAGNETIC PROPERTIES
OF 3d - TRANSITION METAL AND RARE EARTH FLUORIDE GLASSES
J.P. Renard, C. Dupas, E. V@lu, C. Jacoboni (a), G. Fonteneau (b) and J. Lucas (b).
Institut d'Electronique Fondamentale, LA 22, B~timent 220, Universit@ Paris-Sud, 91405, Orsay Cedex, France
The ac susceptibility of fluoride glasses in the ternary systems PbF~-MnF2-FeF2, ThF4-BaF2-MnF2, ZnF2-BaFp-RF~(R=Dy-Ho) has been studied down to 0.3 K. The sus~eptibllity of rare earth glasses exhibits a broad maximum strongly dependent on the measuring frequency v while a spin glass transition with a sharp susceptibility cusp nearly independent on v is observed in 3d - transition metal glasses. Magnetic after effects are observed below the spin freezing temperature.
1. INTRODUCTION. Magnetic amorphous insulators with predominant antiferromagnetic interactions are frustrated systems (I) because of the topological disorder. They may have a spin glass (SG) transition at low temperature. Indeed, it has been recently shown that manganese and cobalt aluminosilicate glasses (2) exhibit a SG phase at a few Kelvins. We have investigated the magnetic properties of a series of fluoride g l a s s ~ b y ac susceptibility measurements using a mutual inductance bridge in1~he temperature range 0.3 77 K. In addition ~F nuclear magnetic resonance and remanent magnetization measurements were performed on some of these glasses. 2. EXPERIMENTAL
RESULTS.
2.1. 3d-transition
susceptibilities exhibit a very sharp cusp which is frequency independent in the range 7-1300 Hz (3). The remanent magnetization of amorphous PbMnFeF 7 was measured in the temperature range 1.2-4.2 K as a function of time and magnetic field up to 4 Teslas (4). The isothermal remanent magnetization (IRM) and thermoremanent magnetization (TRM) have the typical field behavior observed previously in metallic SG (5). It decreases slowly with time t following a io~ t law. In presence of remanent magnetization o , the ac susceptibility is anisotropic (4), the one perpendicular to ~ x~,being higher tha~ X~. The difference X~- X~ zs proportional to o in agreement with th~ model of a macroscopic anisotropy field of o proposed by H. Alloul (6) in Cu-Mm SG.
metal glasses.
A common characteristics of the Mn 2+ and Fe 3+ glasses is : i- the existence of large mean antiferromagnetic interactions evidenced by negative Curie-Weiss temperatures @ (tableI), ii - a progressive change from a Curie-Weiss to Curie behavior of the susceptibility when lowering temperature well below l@l, iii - the occurrence of a cusp of the ac susceptibility which is very sharp in the magnetically concentrated glasses and less pronounced in the less concentrated ones. The cusp is drastically rounded in small applied dc fields of about 100 Oe and the temperature of the cusp T^ has a very small dependence on the measurxng frequency as in the metallic SG Cu-Mn or Au-Fe. •
PbF -MnF -FeF glasses : 2 . . We ~ave e s p e c i a l l y i n v e s t i g a t e d the g l a s s e s with composition PbMnFeF 7 and Pb2MnFeF 9. Their ac
The effect of dilution by diamagnetic atoms of the glass Pb MnFeF has been investigated by replacing Mn b~ Zn a~d Fe by Ga (7). As shown in table I, the spin freezing temperature Tf is strongly depressed by dilution and the ratio Tf/IO I . . also decreases. At the same concentratlon, the magnetic properties are more affected on dilution by Ga than by Zn. For strong Ga dilution, the magnetic susceptibility does not exhibit any cusp but only a change of its thermal variation. The 19F NMR study of these glasses is consistent with the model of a glassy network of chains of corner sharing MF~ octahedra (M=Fe, Mn) with Pb 2+ in interstitial position. Tbsspin freezing is evidenced by an abrupt increase of the NMR linewidth at a temperature lower than Tf. B a F - T h F -MnF glasses : 2 4 2 . They may be consldered as amorphous
diluted MnF 2.
(a)Laboratoire des fluorures et oxyfluorures ioniques,ERA609, Universit@ du Maine, Route de Laval, ( ~ 7 2 0 1 7 - L e Mans-C$dex, France. ~JLaboratoire de Chimie Min@rale D, LA 245, Universit@ de Rennes Beaulieu, Av. du G@n@ral Leclerc, 35042-Rennes-C@dex, France.
0378-4363/81/0000-0000/$02.50
© North-Holland Publishing Company
1291
1292
Their T (Table I) slightly depend on the measu• f rlng frequency v • The correspondlng data can he fitted by a linear relation between T~ I and In v. This relation is indeed expected on the basis of independent clusters with a relaxation time ~= ~ exp(E/kT),but T and E have clearly unphysica~ values, o For example, z
in Bao.o5Tho
8h$~n0.55F2. _
we obtain
different for Gd 3+ which is in an S state than for Dy 3+ and Ho 3+. In glasses with Gd3 , a cusp or a kink at a well definite temperature is observed, while the susceptibility of glasses with Ho 3+ has a rather broad maxlmum. It can be concluded that the SG transition of these insulating glasses is drastically affected by local crystal field effects.
= 1.5x10-51s and E/k = 150K. O
REFERENCES. TABLE I : Curie-Weiss and freezing temperature of some 3d-transition metal fluoride glasses at v = 75 Hz.
i
-o(K)
Tf
Toulouse
2)
Verhelst R.A., Kline K.W., De Graaf A.M. and Hooper H.O., phys. Rev. B11 (1975) 4427
190
11.77
0.062
IPb2MnFeF 9 ~
135
5.26
0.039
"8Ga0 "2F9 6Ga0 LF9
123
3.96
0.032
100
2.82
0.028
iPb2MnFe 0 4Ga 0 6F9
76
1.65
0.02]
IPb2MnFe0"2Ga0"sF 9
67
0.95
0.014
iPb2MnGaF 9
36
0.35
0.010
iPb2FeMn 0. 6Zn0.4£9
128
3.20
0.025
i!Pb2FeMn0.2Zn0.8F9
110
1.55
0.0]4
Ba0.05Th0.4Mn0.55F2.8
~30
].37
~0.0~5
!Ba0. iTh0.35~0.55F2.7
~30
1.32
~0.045
G., Comm. Phys. 2 (1977)
115
Ferr6 J., Pommier J., Renard J.P. and Knorr K., J. Phys. C 13 (1980) 3697.
Tf/IoI
PbMnFeF 7
iPb2MnFe IPb2MnFe
1)
B) Renard J.P., Miranday J.P. and Varret F., Solid State Commun.
35 (]980)•
41
4) V61u E., Renard J.P. and Miranday J.P., J. de Phys. Lett., to be published.
5) Tholence J.L. and Tournier R., J. de Phys. 35 (1974) C4-229
6) Alloul H. and Hippert F., J. de Phys. Lett. 41 (1980) 201
7) Dupas C., Le Dang K., Renard J.P. Veillet
i
i.
2.2. Pare earth glasses. The ac susceptibility
of the amorphous
fluorides
Ba0. 2 Zn0.35 DY0.45 F2.45 and Ba0. 2 Zn0.45 Ho 0 ~ F o ~q exhibits a broad maximum at a temperaZ~re~T~which strongly depends on v. At v= 80 Hz, ~he respective T~ values ar~ 0.77 and 0.42 K. A linear relation ~etween Tf- and in v is observed in the range 9-480 Hz and the corresponding ~ and E have quite reasonable values : ~ = ~.6 x ]0-10s and E = 13.5 K for the Dy glass~ This behavior is similar to that of the previously studied amorphous holmium alaminosilicate (8) which is well interpreted by the model of independent clusters. The drastic dlfference with 3d-transition metal glasses can be due to : i" - the relatively small magnetic ion concentration. ii - the effects of the large local crystal field. As to clear up this point, rare earth ~ons were introduced in the BaF -ThF--MnF~ glasses The 2 a effect on the magnetic susceptibility is rather
P., Miranday J.P. and Jacoboni Phys. to be published.
8)
C., J. de
Chappert C., Beauvillain P., Renard J.P. and Knorr M., J. Mag. Mag. Mater., 15-18 (1980) 117.
Physica 108B (1981) 1291-1292 North-Holland Publishing Company
MAGNETIC PROPERTIES
OF 3d - TRANSITION METAL AND RARE EARTH FLUORIDE GLASSES
J.P. Renard, C. Dupas, E. V@lu, C. Jacoboni (a), G. Fonteneau (b) and J. Lucas (b).
Institut d'Electronique Fondamentale, LA 22, B~timent 220, Universit@ Paris-Sud, 91405, Orsay Cedex, France
The ac susceptibility of fluoride glasses in the ternary systems PbF~-MnF2-FeF2, ThF4-BaF2-MnF2, ZnF2-BaFp-RF~(R=Dy-Ho) has been studied down to 0.3 K. The sus~eptibllity of rare earth glasses exhibits a broad maximum strongly dependent on the measuring frequency v while a spin glass transition with a sharp susceptibility cusp nearly independent on v is observed in 3d - transition metal glasses. Magnetic after effects are observed below the spin freezing temperature.
1. INTRODUCTION. Magnetic amorphous insulators with predominant antiferromagnetic interactions are frustrated systems (I) because of the topological disorder. They may have a spin glass (SG) transition at low temperature. Indeed, it has been recently shown that manganese and cobalt aluminosilicate glasses (2) exhibit a SG phase at a few Kelvins. We have investigated the magnetic properties of a series of fluoride g l a s s ~ b y ac susceptibility measurements using a mutual inductance bridge in1~he temperature range 0.3 77 K. In addition ~F nuclear magnetic resonance and remanent magnetization measurements were performed on some of these glasses. 2. EXPERIMENTAL
RESULTS.
2.1. 3d-transition
susceptibilities exhibit a very sharp cusp which is frequency independent in the range 7-1300 Hz (3). The remanent magnetization of amorphous PbMnFeF 7 was measured in the temperature range 1.2-4.2 K as a function of time and magnetic field up to 4 Teslas (4). The isothermal remanent magnetization (IRM) and thermoremanent magnetization (TRM) have the typical field behavior observed previously in metallic SG (5). It decreases slowly with time t following a io~ t law. In presence of remanent magnetization o , the ac susceptibility is anisotropic (4), the one perpendicular to ~ x~,being higher tha~ X~. The difference X~- X~ zs proportional to o in agreement with th~ model of a macroscopic anisotropy field of o proposed by H. Alloul (6) in Cu-Mm SG.
metal glasses.
A common characteristics of the Mn 2+ and Fe 3+ glasses is : i- the existence of large mean antiferromagnetic interactions evidenced by negative Curie-Weiss temperatures @ (tableI), ii - a progressive change from a Curie-Weiss to Curie behavior of the susceptibility when lowering temperature well below l@l, iii - the occurrence of a cusp of the ac susceptibility which is very sharp in the magnetically concentrated glasses and less pronounced in the less concentrated ones. The cusp is drastically rounded in small applied dc fields of about 100 Oe and the temperature of the cusp T^ has a very small dependence on the measurxng frequency as in the metallic SG Cu-Mn or Au-Fe. •
PbF -MnF -FeF glasses : 2 . . We ~ave e s p e c i a l l y i n v e s t i g a t e d the g l a s s e s with composition PbMnFeF 7 and Pb2MnFeF 9. Their ac
The effect of dilution by diamagnetic atoms of the glass Pb MnFeF has been investigated by replacing Mn b~ Zn a~d Fe by Ga (7). As shown in table I, the spin freezing temperature Tf is strongly depressed by dilution and the ratio Tf/IO I . . also decreases. At the same concentratlon, the magnetic properties are more affected on dilution by Ga than by Zn. For strong Ga dilution, the magnetic susceptibility does not exhibit any cusp but only a change of its thermal variation. The 19F NMR study of these glasses is consistent with the model of a glassy network of chains of corner sharing MF~ octahedra (M=Fe, Mn) with Pb 2+ in interstitial position. Tbsspin freezing is evidenced by an abrupt increase of the NMR linewidth at a temperature lower than Tf. B a F - T h F -MnF glasses : 2 4 2 . They may be consldered as amorphous
diluted MnF 2.
(a)Laboratoire des fluorures et oxyfluorures ioniques,ERA609, Universit@ du Maine, Route de Laval, ( ~ 7 2 0 1 7 - L e Mans-C$dex, France. ~JLaboratoire de Chimie Min@rale D, LA 245, Universit@ de Rennes Beaulieu, Av. du G@n@ral Leclerc, 35042-Rennes-C@dex, France.
0378-4363/81/0000-0000/$02.50
© North-Holland Publishing Company
1291
1292
Their T (Table I) slightly depend on the measu• f rlng frequency v • The correspondlng data can he fitted by a linear relation between T~ I and In v. This relation is indeed expected on the basis of independent clusters with a relaxation time ~= ~ exp(E/kT),but T and E have clearly unphysica~ values, o For example, z
in Bao.o5Tho
8h$~n0.55F2. _
we obtain
different for Gd 3+ which is in an S state than for Dy 3+ and Ho 3+. In glasses with Gd3 , a cusp or a kink at a well definite temperature is observed, while the susceptibility of glasses with Ho 3+ has a rather broad maxlmum. It can be concluded that the SG transition of these insulating glasses is drastically affected by local crystal field effects.
= 1.5x10-51s and E/k = 150K. O
REFERENCES. TABLE I : Curie-Weiss and freezing temperature of some 3d-transition metal fluoride glasses at v = 75 Hz.
i
-o(K)
Tf
Toulouse
2)
Verhelst R.A., Kline K.W., De Graaf A.M. and Hooper H.O., phys. Rev. B11 (1975) 4427
190
11.77
0.062
IPb2MnFeF 9 ~
135
5.26
0.039
"8Ga0 "2F9 6Ga0 LF9
123
3.96
0.032
100
2.82
0.028
iPb2MnFe 0 4Ga 0 6F9
76
1.65
0.02]
IPb2MnFe0"2Ga0"sF 9
67
0.95
0.014
iPb2MnGaF 9
36
0.35
0.010
iPb2FeMn 0. 6Zn0.4£9
128
3.20
0.025
i!Pb2FeMn0.2Zn0.8F9
110
1.55
0.0]4
Ba0.05Th0.4Mn0.55F2.8
~30
].37
~0.0~5
!Ba0. iTh0.35~0.55F2.7
~30
1.32
~0.045
G., Comm. Phys. 2 (1977)
115
Ferr6 J., Pommier J., Renard J.P. and Knorr K., J. Phys. C 13 (1980) 3697.
Tf/IoI
PbMnFeF 7
iPb2MnFe IPb2MnFe
1)
B) Renard J.P., Miranday J.P. and Varret F., Solid State Commun.
35 (]980)•
41
4) V61u E., Renard J.P. and Miranday J.P., J. de Phys. Lett., to be published.
5) Tholence J.L. and Tournier R., J. de Phys. 35 (1974) C4-229
6) Alloul H. and Hippert F., J. de Phys. Lett. 41 (1980) 201
7) Dupas C., Le Dang K., Renard J.P. Veillet
i
i.
2.2. Pare earth glasses. The ac susceptibility
of the amorphous
fluorides
Ba0. 2 Zn0.35 DY0.45 F2.45 and Ba0. 2 Zn0.45 Ho 0 ~ F o ~q exhibits a broad maximum at a temperaZ~re~T~which strongly depends on v. At v= 80 Hz, ~he respective T~ values ar~ 0.77 and 0.42 K. A linear relation ~etween Tf- and in v is observed in the range 9-480 Hz and the corresponding ~ and E have quite reasonable values : ~ = ~.6 x ]0-10s and E = 13.5 K for the Dy glass~ This behavior is similar to that of the previously studied amorphous holmium alaminosilicate (8) which is well interpreted by the model of independent clusters. The drastic dlfference with 3d-transition metal glasses can be due to : i" - the relatively small magnetic ion concentration. ii - the effects of the large local crystal field. As to clear up this point, rare earth ~ons were introduced in the BaF -ThF--MnF~ glasses The 2 a effect on the magnetic susceptibility is rather
P., Miranday J.P. and Jacoboni Phys. to be published.
8)
C., J. de
Chappert C., Beauvillain P., Renard J.P. and Knorr M., J. Mag. Mag. Mater., 15-18 (1980) 117.