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Magnetic hyperfine fields of dilute 170Yb and 193Ir in ferromagnetic gadolinium metal
Journal of Magnetism and Magnetic Materials 0 North-Holland Publishing Company
9 (1978)
14-16
MAGNETIC HYPERFINE FIELDS OF DILUTE 17oYb AND 193Ir IN FERROMAGNETIC GADOLINIUM METAL B. PERSCHEID,
K. KRUSCH and M. FORKER
Institut fGr Strahlen- und Kernphysik
Received
der Universitiit Bonn, Nussallee 14-16,
D-5300 Bonn 1, Fed. Rep. Germany
23 March 1978
The magnetic hyperfine fields of dilute Yb and II impurities in ferromagnetic Cd metal have been determined from Miissbauer effect measurements to be: IBhf(Yb : @)I = 280(10) kG, IBhf(Ir : @)I = 624(6) kG. These hyperfine field values have been used to estimate the localized magnetic moments of 5d-impurities in Gd metal.
1. Introduction
metal at 4.2 K [3]. The hyperfine interactions are not well resolved. For comparison the Mijssbauer spectrum of dilute 17’Yb impurities in Al is shown in the upper part of fig. 1, which exhibits the experimental width of a single line. Both spectra were taken with the same Y&Al-alloy absorber. Examination of the temperature dependence of the spectrum yielded no change between 1.6 K and 40 K. so we assumed that Yb is in a 2t
Localized moments of dilute d-impurities in ferromagnetic metals can be estimated from their contribution to the magnetic hyperfine field at the impurity nucleus [ 11. The hyperfine field Bhf of d-impurities consists of three contributions: &r = &ep + B,, + Bo,
.
Beep is the contribution from the conduction electron polarization of the host. B,, is due to overlap polarization and can be neglected for d-impurities in the host Cd because the metallic radius of Cd is much larger than that of any d-impurity. The contribution B,, is caused by the core polarization of the impurity atom due to the localized moment ploC of its outer d-electrons. One finds approximately: &,
=&d/-&c
2
where R ,,d is a constant for a given d-series [2]. So one has for the host Cd: Bhf
=Bcep
+Rn&loc
.
0)
plot can be derived from Bhr if Beep and R,,d are known.
2. Mtissbauer experiment
I ,
of 17’Yb in Cd metal
-10
Fig. 1 shows the result of a Mijssbauer source experiment of dilute 17’Yb impurities (
.
Fig. 1. Miissbauer spectra Gd metal at 4.2 K.
14
0
-5 Velocity
Immlsecl
of dilute
17’Yb
5
10
impurities
in Al and
B. Perscheid et al. /Magnetic hyperfine fields in gadolinium metal
valence state in Gd metal and has no 4f-moment. Therefore we analysed the spectrum with a static hyperfine Hamiltonian. The determination of the hyperfine parameters from the unresolved spectrum is complicated by the fact that one has to expect a combined magnetic and electric interaction due to the hexagonal lattice structure of Gd metal. Least squares fits yielded two solutions: Bnr = 280(10) kG and V,, = 3.7(5)X 1017 V/cm’,&= 144(6) kG and I’,, = 9.6(7) X 1017 V/cm*. For both solutions the angle between the magnetic hyperfine field and the symmetry axis of the electric fieldgradient is approximately zero. From systematical considerations the high field solution is favoured to be the physical significant one. The values for the hyperfine field and isomer shift (0.13 mm/s) support the assumption of a 2t valence state of Yb in Gd metal.
3. Mijssbauer experiment
of 1931r in Cd metal
Fig. 2 shows the result of a Mossbauer source experiment of dilute 1931r impurities (
-lb
-4 Velocity
15
800600400200 0
I
!
I
I
I
I,
Yb Lu Hf To W ReOsIr
I
I,
Pt Au
Sd” 5d’ 5d2 5d35d4 5d5 5d6 5d’ 5d3 5d”
Fig. 3. Systematics of the magnetic hyperfine fields of Sdimpurities in Gd metal. The dashed line connects the experimental values and the solid line represents an estimate of the conduction electron contribution to the hyperfine field.
been used. The spectrum exhibits a well resolved hyper fine interaction and a least squares fit yielded the parameters: Bnf = 624(6) kG and I’,, = 19.5(5.0) X 1017 V/cm*. The excellent resolution even allowed the determination of an axial asymmetry of the electric fieldgradient.
d
5
C mmlsecl
Fig. 2. Mossbauer spectrum of dilute 1931r impurities in Gd metal at 4.2 K. Solid and dashed lines are least squares fits with axial asymmetric and symmetric electric fieldgradients respectively.
16
B. Perscheid et al. /Magnetic
hyperfine fields in gadolinium metal
4. Discussion In fig. 3 the Bhr- values of Yb and Ir are incorporated into the systematics of magnetic hyperfine fields of Sdimpurities in Cd metal. The experimental values [5] have been connected by the dashed line. A rough estimate of the contribution Beep to the hyperfine field is given by the solid line, which was obtained by interpolating between the values of the fields of the closed shell impurities Yb and Au [6] at both ends of the 5dseries. The difference between the solid line and the experimental values is attributed to the contribution B,, to the hyperfine field. From these differences the localized moments of the 5d-impurities in Cd can be estimated using eq. (1) and the constant R 5d= - lOOO(200) kG/pn [2], All Sd-impurities in Gd metal
have negative moments reaching a maximum value of -0.5 pn at Re and OS. Ir has, if at all, only a small localized moment of approximately -0.05 pg. This is quite striking because Ir has a rather large moment in other host metals, e.g. Fe and Ni.
References [l] [2] [3] [4] [S] [6]
D.A. Shirley, S.S. Rosenblum and E. Matthias, Phys. Rev. 170 (1968) 363. LA. Campbell, J. Phys. C2 (1969) 1338. B. Perscheid, K. Krusch and M. Forker (to be published). B. Perscheid and M. Forker, Z. Physik (in press). G.N. Rao, At. Data Nucl. Data Tables 15 (1975) 553. B. Perscheid, H. Biichsler and M. Forker, Phys. Rev. B14 (1976) 4803.
9 (1978)
14-16
MAGNETIC HYPERFINE FIELDS OF DILUTE 17oYb AND 193Ir IN FERROMAGNETIC GADOLINIUM METAL B. PERSCHEID,
K. KRUSCH and M. FORKER
Institut fGr Strahlen- und Kernphysik
Received
der Universitiit Bonn, Nussallee 14-16,
D-5300 Bonn 1, Fed. Rep. Germany
23 March 1978
The magnetic hyperfine fields of dilute Yb and II impurities in ferromagnetic Cd metal have been determined from Miissbauer effect measurements to be: IBhf(Yb : @)I = 280(10) kG, IBhf(Ir : @)I = 624(6) kG. These hyperfine field values have been used to estimate the localized magnetic moments of 5d-impurities in Gd metal.
1. Introduction
metal at 4.2 K [3]. The hyperfine interactions are not well resolved. For comparison the Mijssbauer spectrum of dilute 17’Yb impurities in Al is shown in the upper part of fig. 1, which exhibits the experimental width of a single line. Both spectra were taken with the same Y&Al-alloy absorber. Examination of the temperature dependence of the spectrum yielded no change between 1.6 K and 40 K. so we assumed that Yb is in a 2t
Localized moments of dilute d-impurities in ferromagnetic metals can be estimated from their contribution to the magnetic hyperfine field at the impurity nucleus [ 11. The hyperfine field Bhf of d-impurities consists of three contributions: &r = &ep + B,, + Bo,
.
Beep is the contribution from the conduction electron polarization of the host. B,, is due to overlap polarization and can be neglected for d-impurities in the host Cd because the metallic radius of Cd is much larger than that of any d-impurity. The contribution B,, is caused by the core polarization of the impurity atom due to the localized moment ploC of its outer d-electrons. One finds approximately: &,
=&d/-&c
2
where R ,,d is a constant for a given d-series [2]. So one has for the host Cd: Bhf
=Bcep
+Rn&loc
.
0)
plot can be derived from Bhr if Beep and R,,d are known.
2. Mtissbauer experiment
I ,
of 17’Yb in Cd metal
-10
Fig. 1 shows the result of a Mijssbauer source experiment of dilute 17’Yb impurities (
.
Fig. 1. Miissbauer spectra Gd metal at 4.2 K.
14
0
-5 Velocity
Immlsecl
of dilute
17’Yb
5
10
impurities
in Al and
B. Perscheid et al. /Magnetic hyperfine fields in gadolinium metal
valence state in Gd metal and has no 4f-moment. Therefore we analysed the spectrum with a static hyperfine Hamiltonian. The determination of the hyperfine parameters from the unresolved spectrum is complicated by the fact that one has to expect a combined magnetic and electric interaction due to the hexagonal lattice structure of Gd metal. Least squares fits yielded two solutions: Bnr = 280(10) kG and V,, = 3.7(5)X 1017 V/cm’,&= 144(6) kG and I’,, = 9.6(7) X 1017 V/cm*. For both solutions the angle between the magnetic hyperfine field and the symmetry axis of the electric fieldgradient is approximately zero. From systematical considerations the high field solution is favoured to be the physical significant one. The values for the hyperfine field and isomer shift (0.13 mm/s) support the assumption of a 2t valence state of Yb in Gd metal.
3. Mijssbauer experiment
of 1931r in Cd metal
Fig. 2 shows the result of a Mossbauer source experiment of dilute 1931r impurities (
-lb
-4 Velocity
15
800600400200 0
I
!
I
I
I
I,
Yb Lu Hf To W ReOsIr
I
I,
Pt Au
Sd” 5d’ 5d2 5d35d4 5d5 5d6 5d’ 5d3 5d”
Fig. 3. Systematics of the magnetic hyperfine fields of Sdimpurities in Gd metal. The dashed line connects the experimental values and the solid line represents an estimate of the conduction electron contribution to the hyperfine field.
been used. The spectrum exhibits a well resolved hyper fine interaction and a least squares fit yielded the parameters: Bnf = 624(6) kG and I’,, = 19.5(5.0) X 1017 V/cm*. The excellent resolution even allowed the determination of an axial asymmetry of the electric fieldgradient.
d
5
C mmlsecl
Fig. 2. Mossbauer spectrum of dilute 1931r impurities in Gd metal at 4.2 K. Solid and dashed lines are least squares fits with axial asymmetric and symmetric electric fieldgradients respectively.
16
B. Perscheid et al. /Magnetic
hyperfine fields in gadolinium metal
4. Discussion In fig. 3 the Bhr- values of Yb and Ir are incorporated into the systematics of magnetic hyperfine fields of Sdimpurities in Cd metal. The experimental values [5] have been connected by the dashed line. A rough estimate of the contribution Beep to the hyperfine field is given by the solid line, which was obtained by interpolating between the values of the fields of the closed shell impurities Yb and Au [6] at both ends of the 5dseries. The difference between the solid line and the experimental values is attributed to the contribution B,, to the hyperfine field. From these differences the localized moments of the 5d-impurities in Cd can be estimated using eq. (1) and the constant R 5d= - lOOO(200) kG/pn [2], All Sd-impurities in Gd metal
have negative moments reaching a maximum value of -0.5 pn at Re and OS. Ir has, if at all, only a small localized moment of approximately -0.05 pg. This is quite striking because Ir has a rather large moment in other host metals, e.g. Fe and Ni.
References [l] [2] [3] [4] [S] [6]
D.A. Shirley, S.S. Rosenblum and E. Matthias, Phys. Rev. 170 (1968) 363. LA. Campbell, J. Phys. C2 (1969) 1338. B. Perscheid, K. Krusch and M. Forker (to be published). B. Perscheid and M. Forker, Z. Physik (in press). G.N. Rao, At. Data Nucl. Data Tables 15 (1975) 553. B. Perscheid, H. Biichsler and M. Forker, Phys. Rev. B14 (1976) 4803.