- Email: [email protected]
Structural, χac susceptibility and high magnetic field characterization of the new hard magnetic nitrides R2Fe17Nx
Journal of Magnetism and Magnetic Materials 104-107 (1992) 211113-2005 North-Holland
Structural, Xac susceptibility and high magnetic field characterization of the new hard magnetic nitrides R2FelTN, O. Isnard ", C. Kolbeck ", S. Miraglia ", J.L. Soubeyroux ", D. Fruchart ", E. Tomey ~, C. Rillo b and M. Guillot ~ " Laboratoire de cristaihJgrap/lie du CNRS, 166,~; 3~40, Grenohle, France 1' Institut de (.Tent'ia ttt" Materiales tit' Aragon, CSI(; Unicersidad tit" Zaragoza 50009, Plaz2a Still Francisco, Zaragoztr, Spain ' Sercice National des Champs lntenses du ('NRS, 166X, 38042 Grenohh', France
Systematic investigations on the crystal and magnetic properties of the R2Fet7N , X-ray, neutron diffraction, magnetic ac susceptibility and high-field magnetization curves of some materials exhibit singularities that are not unambiguously related to anisotropy fields are evidenced even for the noneasy axis systems. Crystal data as discussed. Insertion of light elements such as H, C, N [1-3] within the metal sublattice of R2Fet7 induces largc changes in thc magnetic characteristics. The Curic temperature raises from about 300 to 700 K, simultancously the anisotropy field is found to be about some tens Tesla. Furthermore, prccisc crystal data wcre reported [4]. In this paper, results obtained by diffcrent magnetic m e a s u r e m e n t s throw light on the structural characteristics. Thc alloys wcrc p r c p a r c d by using thc cold cruciblc tecimiquc and high-frequency mclting. The purity of the starting metals was at least 3N. A n n c a l i n g of thc ingots was carricd out at a rate depending on the R clcmcnt, using thc usual proccdurc. Before and aftcr nitrogenation the matcrials wcrc chcckcd by X-ray diffraction in order to control the phase purity. Nitrogcnation was pcrformcd and controllcd by using a S E T A R A M B70 thcrnlogravimctry dcvicc. The powder was bali milled down to a mean grain sizc of 5 Ixm in order to help the s o l i d / g a s N 2 reaction, and to avoid the segregation of free iron particles. Neutron diffraction experiments allowed us to locate the interstitial e l e m e n t in a 2 R - 4 F c distordcd octahcdron [4]. Thc l',,~ expcriments havc b c e n pcrformed in the 77 to 300 K temperaturc range (H--- 1 Oe, v = 120 Hz) in a st,,.zcptomctcr dcscribcd clscwhcre [5]. The extraction tcchniquc has bccn uscd with a Bitter-coil type m a g n e t o m e t e r (0-20 T) at the Scrvicc National des C h a m p s Intcnscs in Grcnoble [6]. Both rhombohcdral typc (Th2Zn 17) a~ad hcxagonai type ~.1 t-ft.t : 2 x~,~: . . . .u~.. . . .t. u. .i. ~...'; . havc ~" . . . . . I ~ . '": , ~ l l 7 P~ of St~ t,'..~=: t a t ~ u ""~ b y "~"" t:t~. nitrides in agrccmcnt with prcviods m c a s u r c m c n t s [4]. After nitrogenation, traccs o/ some poorly crystallized iron wcrc found in all thc :ampics. This impurity is characterized by broad X-ray ol neutron diffraction peaks and never exceeds 5% of thc total quantity of the sample. From the lattice p a r a m e t e r behaviour, i: is clear that thc ccll expansion mostly conccrns the basal planc of the structurc. The cell volume incrcasc per nitrogen
nitrides have been undertaken using measurements. The ac susceptibility spin reorientation phenomena. Itigh well as the magnetic properties are
Magnet|~at~on ( P B /[.u.) 40
@
•
30
0
@@O 0
e o o o 30
@
@
0
0
@ 0 0 0 0
20
S m z F e l T I N 2.z
0
T:300K 10
i
10
20
50 e0
0@4~
@
0
O 0
@
@ 0
@@
0
0
0
0
@@ 0
¢
O
@
@
~40
0
0
00
6 0
O
¢
¢o
25 I N d 2 F e l 0 5N2.46 T--300K
0
!
i
i
5
10
15
70 !! (t~sla)
Fig. 1. Magnetization as a function of the applied field for the (a) Sm2FeI7N2. 2 and (b) NdeFe17N,.4~, compounds, q he filled squares refer to the para'.lel magr~c;.ization, open squares to th,,, perpendicular magnetization at room temperature.
0312-8853/92/$05.00 © 1992 - Elsevier Science Publishers B.V. All rights reserved
2004
O. ism~rd et al. / Characterization
of R, Fe17N, S m2Fe 17N2.2
S m2Fe 1 7
4 ,~2 ,
= E
,~
o
Z '
':/.
, ,, 'I¸ ~,/,
1
L, ¸'
, ,
' ",'(GL", '
,.
..:
,.-2 v
"
'" ' '" "'"' ":':'"" """ '""":'i','
;', .,': ",,:'.:,,:,. v,"v'::";':... • .......
,,,,,
Z " '102
0
iO'
100'
150'
~'00 ' : : ; 5 0 ' ' 3 0 0 T (K)
0 50
350
100
150
200 250 T (K)
300
350
Fig. 2. ~t',,c susceptibility measurements of (a) Sm2Fe17 and (b) Sm2Fet7N2.2 as a function of temperature. The upper and lower curves refer to the in-phme and out-of plane signals, respectively.
atom is found to be almost constant ( A V / N = 6 ,,~'a/N) along the R series, cxcept for the R = Ce case which exhibits a largcr ccU cxpansion. Such behaviour has been observed in the corresponding 2:17 hydrides and has been attributed to some changes in the 4f states of the rare earth. The location of nitrogen has been determined b:,, using neutron diffraction on the rhombohcdral type ot structure. Nitrogen occupics a distorted 2R-4Fc octahcdron. Tiffs occupicd intcrstitia! site makcs thc atom dcnsity largcr in the basal planc and induces an anisotropic ccll expansiom Thc final coordination numbcr of R (in thc planc) is 3Fc ---*3Fc + 3N, thus modifying thc local dcnsity of the valence clcctrons, thcn changing the crystal ficld paramctcrs. Thc dumbbcll Fc-Fc distance incrcascs markcdly morc than all thc other metal-metal distances. A systematic study of the magnetization behaviour has bcen performcd under fields as high as 20 T, at 4.2,
7
a
100, 200 and 300 K. Thc samples wcrc polycrystallinc ori~,uted fine powders and the magnetic field was applied parallel and perpendicular to the alignment direction. This allows to distinguish between the planar and the easy axis types of materials. The anisotropy fields are higher than for the pure alloys and they remain higher than 20 T for Nd2Fet6.sNz46 even at room tempetaturc ffig. la). For SmaFelTNz2 a crossover o[ thc II and _L curves appears close to RT (fig. 1O), thus indicating a morc complcx bchaviour, i.c. a changc of thc casy axis that is ncithcr along the II nor along the _L alignment direction. Thc ac susceptibility measurements here again characterizc the diffcrcnt types of materials. For the nonmagnetic or m~gnctic R clcmcnts, having a'j < 0 (second-order Stcvcns cocfficicnt), no singularity was detected both on thc II and _L curves for X' and X" (X = X ' - Jx") and on the pure and nitrided materials. The Xll signal is about twicc the X'~ one, monotoni-
7
Er2Fel 7
6
Er2Fe 17N2.45
6
.---5
---,5
Z .
Z '
E
o3 .....
c2
"-'2
1
Z " "10
0 5O
150
, , Z "'102
1 ....
100
-,,
200 T (K)
i
0
250
300
350
-1 5O
100
150
~1~
200 250 T (K)
300
350
Fig. 3. :t,~ susceptibility measurements of (a) Er, Fe17 and (b) EreFel7Ne.zs as a function of temperature. The upper and lower curves refer to the in-plane and out-of-plane signals, respectively.
O. lsnard etal. / Characterization of R e Fe t7 N~
cally increasing with temperature. For two pure 2:17 alloys having R ( a j > 0), Er and Sm, kinks are detected on the X' and X" curves at 130 and 240 K, respectively (figs. 2a, 3a). These anomalies are almost smoothed out for the corresponding nitride rcsults. For both series (R = Sm, Er), the ratio )¢ '/)¢" is markedly magnified after nitrogenation (figs. 2b, 3b), in agreement with the magnetic hardening. Nitrogenation of the R2Fet7 series dramatically increases the Curie temperature and the anisotropy field. Both effects are strictly correlated to the particular location of the interstitial element. It relaxes the metal lattice and allows the stressed F e - F e dumbbell," to share more positivc exchange interactions. Moreover, this changes the local valence electron density of the nearest neighbourhood of the R site, thus reinforcing the crystal field strength. High-field as well as ac susceptibility measurements allow to point out the easy plane or the easy axis behaviour. The latter technique reveals anomalies for some of the materials that cannot
2(}115
be understood in terms of a simple spin rcoricntation phenomenon. References
[1] J.M.D. Coey and Hong Sun, J. Magn. Magn. Mater. 87 (1990) L251. [2] O. lsnard, S. Miraglia, J.L. Soubeyroux, D. Fruchart and A. Stergiou, J. Less-Common Met. 102 (1990) 273. [3] K.H.J. Buschow, T.H. Jacobs and W. Coene, IEEE Trans. Magn. 26 (1990) 1364. [4] S. Miraglia, J.L. Soubeyroux, C. Kolbeck, O. lsnard, D. Fruchart and M. CJt,illot, J. Less-Common Met. (1991) in press. [5] C. RiUo, F. Lera, J. Barr,lomg and A.J. van Duyneveldt, Workshop on Magnetic Sasceptibility of Superconductors and Other Spin Systems, Coolfont, Washington (May 1991) in press. [6] J.C. Picoche, M. Guillot and A. Marchand, Physica B 155 (1989) 407.
Structural, Xac susceptibility and high magnetic field characterization of the new hard magnetic nitrides R2FelTN, O. Isnard ", C. Kolbeck ", S. Miraglia ", J.L. Soubeyroux ", D. Fruchart ", E. Tomey ~, C. Rillo b and M. Guillot ~ " Laboratoire de cristaihJgrap/lie du CNRS, 166,~; 3~40, Grenohle, France 1' Institut de (.Tent'ia ttt" Materiales tit' Aragon, CSI(; Unicersidad tit" Zaragoza 50009, Plaz2a Still Francisco, Zaragoztr, Spain ' Sercice National des Champs lntenses du ('NRS, 166X, 38042 Grenohh', France
Systematic investigations on the crystal and magnetic properties of the R2Fet7N , X-ray, neutron diffraction, magnetic ac susceptibility and high-field magnetization curves of some materials exhibit singularities that are not unambiguously related to anisotropy fields are evidenced even for the noneasy axis systems. Crystal data as discussed. Insertion of light elements such as H, C, N [1-3] within the metal sublattice of R2Fet7 induces largc changes in thc magnetic characteristics. The Curic temperature raises from about 300 to 700 K, simultancously the anisotropy field is found to be about some tens Tesla. Furthermore, prccisc crystal data wcre reported [4]. In this paper, results obtained by diffcrent magnetic m e a s u r e m e n t s throw light on the structural characteristics. Thc alloys wcrc p r c p a r c d by using thc cold cruciblc tecimiquc and high-frequency mclting. The purity of the starting metals was at least 3N. A n n c a l i n g of thc ingots was carricd out at a rate depending on the R clcmcnt, using thc usual proccdurc. Before and aftcr nitrogenation the matcrials wcrc chcckcd by X-ray diffraction in order to control the phase purity. Nitrogcnation was pcrformcd and controllcd by using a S E T A R A M B70 thcrnlogravimctry dcvicc. The powder was bali milled down to a mean grain sizc of 5 Ixm in order to help the s o l i d / g a s N 2 reaction, and to avoid the segregation of free iron particles. Neutron diffraction experiments allowed us to locate the interstitial e l e m e n t in a 2 R - 4 F c distordcd octahcdron [4]. Thc l',,~ expcriments havc b c e n pcrformed in the 77 to 300 K temperaturc range (H--- 1 Oe, v = 120 Hz) in a st,,.zcptomctcr dcscribcd clscwhcre [5]. The extraction tcchniquc has bccn uscd with a Bitter-coil type m a g n e t o m e t e r (0-20 T) at the Scrvicc National des C h a m p s Intcnscs in Grcnoble [6]. Both rhombohcdral typc (Th2Zn 17) a~ad hcxagonai type ~.1 t-ft.t : 2 x~,~: . . . .u~.. . . .t. u. .i. ~...'; . havc ~" . . . . . I ~ . '": , ~ l l 7 P~ of St~ t,'..~=: t a t ~ u ""~ b y "~"" t:t~. nitrides in agrccmcnt with prcviods m c a s u r c m c n t s [4]. After nitrogenation, traccs o/ some poorly crystallized iron wcrc found in all thc :ampics. This impurity is characterized by broad X-ray ol neutron diffraction peaks and never exceeds 5% of thc total quantity of the sample. From the lattice p a r a m e t e r behaviour, i: is clear that thc ccll expansion mostly conccrns the basal planc of the structurc. The cell volume incrcasc per nitrogen
nitrides have been undertaken using measurements. The ac susceptibility spin reorientation phenomena. Itigh well as the magnetic properties are
Magnet|~at~on ( P B /[.u.) 40
@
•
30
0
@@O 0
e o o o 30
@
@
0
0
@ 0 0 0 0
20
S m z F e l T I N 2.z
0
T:300K 10
i
10
20
50 e0
0@4~
@
0
O 0
@
@ 0
@@
0
0
0
0
@@ 0
¢
O
@
@
~40
0
0
00
6 0
O
¢
¢o
25 I N d 2 F e l 0 5N2.46 T--300K
0
!
i
i
5
10
15
70 !! (t~sla)
Fig. 1. Magnetization as a function of the applied field for the (a) Sm2FeI7N2. 2 and (b) NdeFe17N,.4~, compounds, q he filled squares refer to the para'.lel magr~c;.ization, open squares to th,,, perpendicular magnetization at room temperature.
0312-8853/92/$05.00 © 1992 - Elsevier Science Publishers B.V. All rights reserved
2004
O. ism~rd et al. / Characterization
of R, Fe17N, S m2Fe 17N2.2
S m2Fe 1 7
4 ,~2 ,
= E
,~
o
Z '
':/.
, ,, 'I¸ ~,/,
1
L, ¸'
, ,
' ",'(GL", '
,.
..:
,.-2 v
"
'" ' '" "'"' ":':'"" """ '""":'i','
;', .,': ",,:'.:,,:,. v,"v'::";':... • .......
,,,,,
Z " '102
0
iO'
100'
150'
~'00 ' : : ; 5 0 ' ' 3 0 0 T (K)
0 50
350
100
150
200 250 T (K)
300
350
Fig. 2. ~t',,c susceptibility measurements of (a) Sm2Fe17 and (b) Sm2Fet7N2.2 as a function of temperature. The upper and lower curves refer to the in-phme and out-of plane signals, respectively.
atom is found to be almost constant ( A V / N = 6 ,,~'a/N) along the R series, cxcept for the R = Ce case which exhibits a largcr ccU cxpansion. Such behaviour has been observed in the corresponding 2:17 hydrides and has been attributed to some changes in the 4f states of the rare earth. The location of nitrogen has been determined b:,, using neutron diffraction on the rhombohcdral type ot structure. Nitrogen occupics a distorted 2R-4Fc octahcdron. Tiffs occupicd intcrstitia! site makcs thc atom dcnsity largcr in the basal planc and induces an anisotropic ccll expansiom Thc final coordination numbcr of R (in thc planc) is 3Fc ---*3Fc + 3N, thus modifying thc local dcnsity of the valence clcctrons, thcn changing the crystal ficld paramctcrs. Thc dumbbcll Fc-Fc distance incrcascs markcdly morc than all thc other metal-metal distances. A systematic study of the magnetization behaviour has bcen performcd under fields as high as 20 T, at 4.2,
7
a
100, 200 and 300 K. Thc samples wcrc polycrystallinc ori~,uted fine powders and the magnetic field was applied parallel and perpendicular to the alignment direction. This allows to distinguish between the planar and the easy axis types of materials. The anisotropy fields are higher than for the pure alloys and they remain higher than 20 T for Nd2Fet6.sNz46 even at room tempetaturc ffig. la). For SmaFelTNz2 a crossover o[ thc II and _L curves appears close to RT (fig. 1O), thus indicating a morc complcx bchaviour, i.c. a changc of thc casy axis that is ncithcr along the II nor along the _L alignment direction. Thc ac susceptibility measurements here again characterizc the diffcrcnt types of materials. For the nonmagnetic or m~gnctic R clcmcnts, having a'j < 0 (second-order Stcvcns cocfficicnt), no singularity was detected both on thc II and _L curves for X' and X" (X = X ' - Jx") and on the pure and nitrided materials. The Xll signal is about twicc the X'~ one, monotoni-
7
Er2Fel 7
6
Er2Fe 17N2.45
6
.---5
---,5
Z .
Z '
E
o3 .....
c2
"-'2
1
Z " "10
0 5O
150
, , Z "'102
1 ....
100
-,,
200 T (K)
i
0
250
300
350
-1 5O
100
150
~1~
200 250 T (K)
300
350
Fig. 3. :t,~ susceptibility measurements of (a) Er, Fe17 and (b) EreFel7Ne.zs as a function of temperature. The upper and lower curves refer to the in-plane and out-of-plane signals, respectively.
O. lsnard etal. / Characterization of R e Fe t7 N~
cally increasing with temperature. For two pure 2:17 alloys having R ( a j > 0), Er and Sm, kinks are detected on the X' and X" curves at 130 and 240 K, respectively (figs. 2a, 3a). These anomalies are almost smoothed out for the corresponding nitride rcsults. For both series (R = Sm, Er), the ratio )¢ '/)¢" is markedly magnified after nitrogenation (figs. 2b, 3b), in agreement with the magnetic hardening. Nitrogenation of the R2Fet7 series dramatically increases the Curie temperature and the anisotropy field. Both effects are strictly correlated to the particular location of the interstitial element. It relaxes the metal lattice and allows the stressed F e - F e dumbbell," to share more positivc exchange interactions. Moreover, this changes the local valence electron density of the nearest neighbourhood of the R site, thus reinforcing the crystal field strength. High-field as well as ac susceptibility measurements allow to point out the easy plane or the easy axis behaviour. The latter technique reveals anomalies for some of the materials that cannot
2(}115
be understood in terms of a simple spin rcoricntation phenomenon. References
[1] J.M.D. Coey and Hong Sun, J. Magn. Magn. Mater. 87 (1990) L251. [2] O. lsnard, S. Miraglia, J.L. Soubeyroux, D. Fruchart and A. Stergiou, J. Less-Common Met. 102 (1990) 273. [3] K.H.J. Buschow, T.H. Jacobs and W. Coene, IEEE Trans. Magn. 26 (1990) 1364. [4] S. Miraglia, J.L. Soubeyroux, C. Kolbeck, O. lsnard, D. Fruchart and M. CJt,illot, J. Less-Common Met. (1991) in press. [5] C. RiUo, F. Lera, J. Barr,lomg and A.J. van Duyneveldt, Workshop on Magnetic Sasceptibility of Superconductors and Other Spin Systems, Coolfont, Washington (May 1991) in press. [6] J.C. Picoche, M. Guillot and A. Marchand, Physica B 155 (1989) 407.