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Volume 31A. number 9 PHYSICS LETTERS 4 May 1970 THE CONCENTRATION DEPENDENCE OF THE Ni HYPERFINE FIELD IN NiPd ALLOYS U. ERICH, J.&RING, S. HUFNER * and E. KANKELEIT Institut ftiv Technische Kernphysik, Technische Hochschule, Darmstadt Received 17 March 1970 The hyperfine field at the Ni site in NiPd alloys is measured by the Mossbauer effect in 61Ni. The concentration dependence of the hyperfine field can be fitted for this alloy as well as for FePd and CoPd alloys under the assumption that a positive field contribution is proportional to the polarization of the Pd matrix. The concentration dependence of the hf field at the 61Ni nuclei in the Ni,Pdl_.alloy series (0.1 SK G 1) by using the MSssbauer-effect in 6lNi has been measured; the experimental details have been described by Erich [l]. No structures which could be attributed to a spread of hf fields were found and therefore the spectra were analyzed under the assumption of a single hf field acting on all Ni nuclei. The figure shows the concentration dependence * * of the 6lNi hf field; also shown are the data for the hf fields at the Fe and Co nuclei in the corresponding alloy series [2-51. For the interpretation of the measured concen- tration dependence it is assumed that the hf field is made up of two contributions. One which is due to the constant local moment at the metal site and one which is due to the polarization of the matrix; therefore the following equation can be set up, which has been used to calculate the curves in the figure H eff ‘HM + bM(i- PM) where HM is the hf field in pure Fe, Co or Ni, i the average moment per Fe, Co or Ni atom in the Pd alloy, p M the magnetic moment of Fe(2.8 PH), Co(1.7 PH) or Ni(0.6 PH) and bM an adjustable parameter different for every alloy series. The values of ,ii have been taken from refs.[6]-[9]. The VaheS for hM which give the best agreement with the measured hf fields are 5 kOe/E.cH, 70 kOe,‘pB and 125 kOe/pB for FeXPdl_X, * IV. Physikalisches Institut, Freie Universitlt, Berlin. ** We have determined the sign of the hf field in the alloy Pdo 7Ni0 3 as positive by making an experi- ment in an external field. 492 CoXPdl_r and NiXPdl_X respectively. The very different values for bM in the FePd and the NiPd system may suggest a larger range of the polar- ization in FePd as compared to NiPd as indicated also by the different Curie temperatures of these alloys [7]. 0 Fe,, Pdl_, 0 co, Pdl_x l Nix Pdl_x Fig.1. Hyperfine fields (He& at the M sites in M$dI_r(Oc xG1) with M = Fe, Co, Ni. The Fe values are taken from ref. [3], those for Co from refs. [5] and [6]. The curves have been calculated from Heff = HM + b~(/i - /.LM) with values for p from refs. [6]-[9]. Values for bM are 5 kOe/)LB, ‘70 kOe/lJB and 125 kOe/pB for M = Fe, Co, Ni respectively.

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Page 1: The concentration dependence of the Ni hyperfine field in NiPd alloys

Volume 31A. number 9 PHYSICS LETTERS 4 May 1970

THE CONCENTRATION DEPENDENCE OF THE Ni HYPERFINE FIELD IN NiPd ALLOYS

U. ERICH, J.&RING, S. HUFNER * and E. KANKELEIT Institut ftiv Technische Kernphysik, Technische Hochschule, Darmstadt

Received 17 March 1970

The hyperfine field at the Ni site in NiPd alloys is measured by the Mossbauer effect in 61Ni. The concentration dependence of the hyperfine field can be fitted for this alloy as well as for FePd and CoPd alloys under the assumption that a positive field contribution is proportional to the polarization of the Pd matrix.

The concentration dependence of the hf field at the 61Ni nuclei in the Ni,Pdl_.alloy series (0.1 SK G 1) by using the MSssbauer-effect in 6lNi

has been measured; the experimental details have been described by Erich [l]. No structures which could be attributed to a spread of hf fields were found and therefore the spectra were analyzed under the assumption of a single hf field acting on all Ni nuclei. The figure shows the concentration dependence * * of the 6lNi hf field; also shown are the data for the hf fields at the Fe and Co nuclei in the corresponding alloy series [2-51.

For the interpretation of the measured concen- tration dependence it is assumed that the hf field is made up of two contributions. One which is due to the constant local moment at the metal site and one which is due to the polarization of the matrix; therefore the following equation can be set up, which has been used to calculate the curves in the figure

H eff ‘HM + bM(i- PM)

where HM is the hf field in pure Fe, Co or Ni, i the average moment per Fe, Co or Ni atom in the Pd alloy, p M the magnetic moment of Fe(2.8 PH), Co(1.7 PH) or Ni(0.6 PH) and bM an adjustable parameter different for every alloy series. The values of ,ii have been taken from refs.[6]-[9]. The VaheS for hM which give the best agreement with the measured hf fields are 5 kOe/E.cH, 70 kOe,‘pB and 125 kOe/pB for FeXPdl_X,

* IV. Physikalisches Institut, Freie Universitlt, Berlin. ** We have determined the sign of the hf field in the

alloy Pdo 7Ni0 3 as positive by making an experi- ment in an external field.

492

CoXPdl_r and NiXPdl_X respectively. The very different values for bM in the FePd and the NiPd system may suggest a larger range of the polar- ization in FePd as compared to NiPd as indicated also by the different Curie temperatures of these alloys [7].

0 Fe,, Pdl_,

0 co, Pdl_x

l Nix Pdl_x

Fig.1. Hyperfine fields (He& at the M sites in M$dI_r(Oc xG1) with M = Fe, Co, Ni. The Fe values are taken from ref. [3], those for Co from refs. [5] and [6]. The curves have been calculated from Heff = HM + b~(/i - /.LM) with values for p from refs. [6]-[9]. Values for bM are 5 kOe/)LB, ‘70 kOe/lJB and

125 kOe/pB for M = Fe, Co, Ni respectively.

Page 2: The concentration dependence of the Ni hyperfine field in NiPd alloys

Volume 31A, number 9 PHYSICS LETTERS

Table 1. Hyperfine fields (in kCe) of Ni, Co, Fe, Pd in the same

References 1.

4 May 1970

materials as hosts [2-51.

Host

-. 2.

Ni

Ni co Fe Pd 3. - 78 -189 -234 +178*

U. Erich, Z. Physik 227 (1969) 25. D. A. Shirley in Hyperfine structure and nuclear radiation, eds. E. Matthias and D. A. Shireley, (North Holland, Amsterdam), p. 979. P. P. Craig, B. Mozer and R. Segnan, Phys. Rev. Letters 14 (1965) 896.

Impurity co -120 -216 -288 +270 4. Fe -283 -323 -337 -295 Pd -194 -400 -594 0

*for the alloy PdO.gNiO.1 5. 6.

We gratefully acknowledge discussions with Prof. B. Elschner. This work was supported by the Bundesministerium fiir Bildung und Wissen- schaft.

7. 8.

9.

A. Balahanov, N. Delyagin, A. Erzinkyan, V. Parfenova and V. Shpinel, Proc. , 11th Intern. Conf. on Low temperature physics. St. Andrews, Scotland (1968), p. 527. P. Reivari, Phys. Rev. Letters 22 (1969) 167. J. Crangle, Phil. Mag. 5 (1960) 335. J. Crangle and W. R. Scott, J. Appl. Phys. 36 (1965) 921. R. M. Bozorth, P. A. Wolff, D. D. Davis, V. B. Compton and J. H. Wernick. Phys. Rev. 122 (1961) 1157. G. Fischer, A.Herr and A. J. P. Meyer,‘J. Appl. Phys. 39 (1968) 545.

*****

PARAMAGNETISM IN Ni-Cu ALLOYS

S. MISHR4, H. CLAUS and P. A. BECK University of Illinois, Urbana, IIE. 61801, USA

Received 2 February 1970

The paramagnetic properties of virtually iron-free N~O.~CUO.~ are consistent with the moment assign- ments for various local atomic environments, based on ferromagnetic data.

The decrease in the ferromagnetic moment in Ni-Cu solid solution alloys with increasing Cu content was recently interpreted [l] in terms of a dependence of the Ni-moment on local atomic environment, i.e., on the number n of Ni nearest neighbors (NN) and on the number m of Ni sec- ond-nearest neighbors (2NN). In the present note we examine the question whether or not this con- cept, and the moments assigned to the various configurations, are consistent with the magnetic properties of the paramagnetic alloys.

Fig. 1 shows that, within the experimental accuracy, the magnetization at 4.2oK for alloy NiO.3 CuO.7 (homogenized at 105oOC and quenched) is proportional to the applied field. From this we estimate that p < 3. For compari- son, fig. 1 also shows a Brillouin curve with p = gS = 8.9. As seen in fig. 2, the susceptibility x (in emu/g) includes a temperature-independent term

P as well as a Curie-Weiss type term:

x = cp /8M(T- 0) + x0, where M is the mol. weight (in g) and c is the concentration (in at. fractions) of the magnetic dipoles with effective

H/T (kOe/*K)

Fig. 1. Temperature-dependent magnetization at 4.20K for Ni6.3 Cu6.7 is proportional to applied field; cluster dipOh moment is less than 3c(B. Dashed line:

Brillouin curve for 8.0 @B/dipole.

moment ppB/dipOle. The data fit the uation with parameter values: cp2 = 2.62 x lo- “g

x0 = 1.03~10-6 (emu/g) and 8 = -90K. /atom,

For an alloy with x at. fraction Ni the concen- tration c,,~ of Ni atoms with environment char- acterized byn and m (see above) is

493