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HAL Id: jpa-00214035

https://hal.archives-ouvertes.fr/jpa-00214035

Submitted on 1 Jan 1971

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HYPERFINE FIELDS ON MANGANESE IN IRON-MANGANESE ALLOYS

P. Costa-Ribeiro, P. Radhakrishna, D. Thoulouze, Y. Ishikawa

To cite this version:

P. Costa-Ribeiro, P. Radhakrishna, D. Thoulouze, Y. Ishikawa. HYPERFINE FIELDS ON MAN- GANESE IN IRON-MANGANESE ALLOYS. Journal de Physique Colloques, 1971, 32 (C1), pp.C1- 76-C1-77. �10.1051/jphyscol:1971121�. �jpa-00214035�

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JOURNAL DE PHYSlQUE Colloque C I, suppl6ment au no 2-3, Tome 32, Fe'vrier-Mars 1971, page C I - 76

HYPERFINE FIELDS ON MANGANESE IN IRON-MANGANESE ALLOYS

P. COSTA-RIBEIRO, P. RADHAKRISHNA, D. THOULOUZE Centre de Recherches sur les Tr&s Basses TempCratures,

C . N. R. S . , 38, Grenoble-Gare, France and Y. ISHIKAWA

Department of Physics, Tohoku University, Sendai, Japan

R6sum6. - Des etudes prkcedentes sur les alliages de y Fe-Mn ont prevu que le moment magnetique du manganese doit varier rapidement d'environ 1 .UB pour 50 % de Mn k 4 GB pour 30 % de Mn. Des mesures de chaleur spkcifique ont kt6 effectuees de 0,04 OK a environ 0,s OKpour dkterrniner le champ hyperfin sur les noyaux de manganese. Le moment magnetique qu'on peut en dkduire varie d'environ 2 PB a 3,5 ,YB pour cette meme variation de concentration. On discute ces rksultats en fonction des donnbs prkkdemment obtenues pour ces alliages.

Abstract. - Previous studies of gamma Fe-Mn alloys have shown that the magnetic moment of the manganese is expected to change rapidly with concentration, varying from about 1 .UB for 50 % Mn to 4 C(B for 30 %. Specific heat measurements from about 0.04 O K to 0.5 OKhave been carried out to determine the hyperfine field on the manganese nuclei. The magnetic moment deduced varies from about 2 PB to 3.5 .UB for these concentrations, respectively. These results are discussed in the light of other data.

Several studies of the properties of gamma Fe-Mn 1000 alloys have been carried out in an attempt to find a

suitable model for the magnetic behaviour. In the course of such measurements, Ishikawa and Endoh [I]

predicted a striking dependence of the magnetic moment of the manganese on the concentration. In this context, we have studied the hyperfine field on the

manganese by the nuclear specific heat method in an 100 attempt to follow the variation of the magnetic moment

with concentration. -5'

- @I n

Experimental technique. Two samples of about a

tenth of a mole containing respectively 28.6 at % of Mn 3

and 47.57 at %were prepared by melting the consti- tuents together in an induction furnace and annealing in sealed quartz tubes, filled with 1 atm of argon, for

three days at 1 100 OC. LL u

The specific heat measurements, from about 30 m OK i

to 0.3 OK, were carried out in the double demagne- cr, tization apparatus previously described [2].

+ . k-Mn 285%

. . ....

Fe-Mn 4757%

Results. - Expressing the specific heat of the alloys in the form :

c, = A I T ~ + YT

we find a value of A = 1 760 ergs-deg per mole with a y of 6.60 mJ per degree per mole for the 71.4 %

Fe-28.6 % Mn alloy and A = 1 000 ergs. deg per mole with a y of 6.1 mJ per degree per mole for the 52.43 %

Fe-47.57 % Mn alloy. The contribution to the nuclear specific heat of 2.19 % of 55Fe in the iron is negligible.

The specific heat results are indicated in figure 1.

With a value of 3.46 p, for the nuclear moment of manganese, these values give a hyperfine field of 99.4 kOe for the 28.6 % Mn alloy and 58.15 kOe for the one containing 47.57 % Mn.

1 7- (K)

0 0.1 1

FIG. 1. - Specific heat of gamma Fe-Mn alloys as a function of temperature.

this range of concentration, as was shown by Ishikawa and Endoh [I].

The magnetic moment of the Mn atoms in these alloys can be estimated by assuming that the hyperfine field is proportional to the magnetic moment on the atom, an assumption which is not unreasonable for antiferromagnetic metals. A hyperfine field of 65 kOe has been obtained for y-Mn in which the magnetic moment of the manganese atom is 2.3 + 0.1 p, [3]

and hence the estimated moments of the Mn are Discussion. - These results show that the internal 2.06 + 0.1 p, for the 47.57 % Mn and 3.52 + 0.2 p~

field on the Mn nucleus increases as the concentration for the 28.6 % Mn alloy respectively. This increase of of manganese decreases in the alloys. This behaviour the magnetic moment of the manganese on decreasing is in sharp contrast with the fact that the hyperfine its concentration is in qualitative agreement with the field on the iron nucleus remains almost constant in suggestion of Ishikawa and Endoh [I]. Their results

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1971121

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HYPERFINE FIELDS ON MANGANESE I N IRON-MANGANESE ALLOYS C 1 - 7 7

show that the average magnetic moment of y-Fe-Mn increases from 1 pB to 1.9 pB as the manganese concen- tration decreases from 50 % to 30 %. This increase in the average moment is presumably due mainly to the increase of the magnetic moment of the manganese with decreasing concentration. They estimate this magnetic moment at 4.05 p, for 30 % Mn and 1.15 pB for 50 % Mn. They have also measured the diffe- rence I p,,-p,, / by magnetic diffuse scattering from single crystals [4], and obtain magnetic moments of 4.4

,

0.4 p, (at 0 OK) for the manganese in the 30 %

alloy and 1.2 _f 0.2 p, (at 0 O K ) in the 50 % alloy.

The difference between our values is less than their conjecture, but this discrepancy could possibly be par- tially explained by a lack of proportionality between the hyperfine field and the magnetic moment.

The reason for this behaviour is to be sought for in an appropriate model for the magnetic properties of the gamma Fe-Mn alloys. At present, no single model seems to be completely satisfactory. The bulk of the evidence, based on susceptibility, specific heat and ther- moelectric power, seems to favour a non-localized

model [5], although studies of diffuse neutron scatter- ing have shown that at least some of the magnetization of antiferromagnetic 50 % Fe-Mn is due to localized moments 161. The spin density wave model is also apparently not applicable [5].

A qualitative discussion of our results is probably permissible in terms of a band model. In such a model, the main reason for the increase in the magnetic moment of the manganese as its concentration decrea- ses would be a narrowing of its d-band on adding iron atoms. The moment of manganese is apparently quite sensitive to the Mn-Mn distance and also to the presence of other atoms, modifying the d-band.

In this context, it is known that the addition of a metal, like palladium, leads to an increase of the moment of manganese from about 2.3 .f 0.05 p, for pure gamma-manganese, to about 3.0 f 0.1 pB for 21 % Pd, as shown by Hicks and Pepper [7]. A detailed investigation of the band structure of an fcc alloy system could further clarify the processes involved.

We wish to thank Dr Y. Endoh for preparation of the samples and Dr. R. Tournier for useful discussions.

References

[I] I~HIKAWA (Y.), ENDOH (Y.), J. Phys. Soc. Jap., 1967, [5] HASHIMOTO (T.), ISHIKAWA (Y.), J. Phys. Soc. Jap.,

23, 205. 1967, 23, 213.

[2] KEYSTON (J. R. G,), LACAZE (A.), and THOULOUZE (D.), [6] VANCE (E. R.), DAVIS (R. L.), J. Phys. Soc. Jap.,

Cryogenics, 1969, 8, 295. 1968,25,367.

[3] Ho (J. C.), PHILLIPS (N. E.), Phys. Lett., 1964, 10, 34. [7] HICKS (T. J.), PEPPER (A. R.), and SMITH (J. H.), [41 ISHIKAWA (Y.), ENDOH (Y.), J. App. Phys., 1968, 39, J. Phys. (C.), 1968, 1, 1683.

1318.

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