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Short Notes phys. stat. sol. (a)

K2 1 K21 (1975)

27,

Subject classification: 18.2: 21.1; 21.1.1 Solid State Physics Institute, Academy of Sciences of the USSR, Chernogolovka The Effect of Pressure on the Curie Points of Fe-Ni-Cu and Fe-Ni-Mn Alloys BY V.E. ANTONOV, G.T. DUBOVKA, and E.G. PONYATOVSKII There is a series of papers on the effect of pressure on the Curie points T of
C

Fe alloys with other transition elements. For the Fe-Ni system it is stated (1to 4)

that in the Invar concentration range T greatly depends on pressure P, the magnitude dTc/dP

I

I

C

increases with decreasing T

C

.

However, in binary alloys T is
C

strongly related to the concentration of both components. In ternary alloys one can vary T keeping the concentration of one of the components constant.
C

The preseht paper deals with the elucidation of the question whether the magnitude dT /dP in alloys is basically determined by the value of T or by the Fe conC C

centration. For this purpose three groups of ternary alloys Fe Fe66(Nil-xCux)34, and Fe

(Ni Cu ) 61 1-x x 39 concentrations were changed and the iron content remained constant. The alloys were prepared from electrolytic Ni, Cu, and Mn and carbonyl Fe by melting in

66(Ni 1-xMnx)34' were investigated. The Ni-Mn and Ni-Cu

argon atmosphere in an induction furnace. The melts were subjected to homogeneous annealing at T = 1100 C for 6 h and subsequent quenching in water. All the samples excepting the alloy No. 12 (Table 1) were investlgated at hydrostatic pressures up to 15 kbar. The pressure was measured by a manganin wire gauge with an accuracy of +200 bar, the temperature by a chromel-alumel thermocouple with an accuracy of +1.5 deg. Alloy No. 12 was investigated using AgCl as the pressure transmitting
0

medium. In this case the pressure up to 20 kbar was determined with an accuracy of +1kbar. The Curie points were determined by the differential transformer method (3) using the temperature dependence of the initial magnetic permeability with an accuracy of +3 deg. The alloys Fe-Ni-Cu as well as Fe-Ni-Mn had a disordered f.c.c. structure. The obtained magnitudes of T and dT /dP are summarised in Table 1.
C C

The Curie points of all the investigated alloys decrease when substituting Ni by Mn or Cu. The dependence of the Curie points on pressure is linear. For more convenient comparison of our data with recently published.results, dT /dP of alloys
C


K22

fiysica status solidi (a) 27 Table 1

(Fig. 1, 2) is given as a function of T shown by a dashed line.

C'

-

a similar dependence for Fe-Ni alloys (4) is

It is seen from Fig. 1 that dTc/dP of Fe66(Nil-xMnx)34 alloys increases slightly at the beginning when Ni is substituted by Mn; at further increasing of the

Mn content one can observe a small drop of this value. For the investigated
Fe66(Nil-xCux)34 and Fe
(Ni Cu ) alloys (Fig. 2) dT /dP is nearly independent 61 1-x x 34 C

of Tc.
Let us pay attention to the following point of interest. In contrast to Fe-Ni binary alloys (4), where the Curie point is varied at the expense of changing the concentration of both components, in ternary Fe-Ni-Cu and Fe-Ni-Mn alloys it is changed at the expense of the alloying component ratio, the Fe concentration being constant.


Short Notes

K23

300

400

500

TC

(OK)

600

Fig. 1 Fig. 1. Dependence of dT /dP on Tc of Fe
C

Fig. 2

alloys. The dashed line Mn 66 (Ni 1-x x) 34 shows a similar dependence for Fe-Ni alloys (4)
C

Fig. 2. Dependence of dT /dP on T of Fe-Ni-Cu alloys; 0 Fe66(Nil-xCux)94,
C

0

Fe61(Nil-xCux)39.

The dashed line is for Fe-Ni alloys (4)

As it is seen in Fig. 1 and 2 in this case dT /dP either is nearly independent of
C

T

C

(Fe-Ni-Cu alloys) or weakly depends on Tc (Fe-Ni-Mn alloys). Thus, it is stated
C

experimentally that the value of dT /dP depends basically on the iron concentration. From the viewpoint of a collective electron ferromagnetism the Curie point and magnetization are determined by a sum curve of the electron density of states and by the value of the exchange interaction shifting sub-bands with spin directions (+) and (-). The fact that the displacement of T with pressure is principally controlled
'C

by the Fe concentration allows to suppose that from the summary density of states of our alloys the part concerning Fe may be separated. It is rather sensitive to the volume, depends very weakly on the Fe environment by other ions and gives rise to the observed high pressure effects. The authors would like to express their thanks to I. Y. Georgieva and V .G. Glebovskii who melted the samples investigated in this work and to A.K. Gapeev for chemical analysis of the samples. References
(1) L, PATRICK, Phys. Rev.

93,

384 (1954).


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physica status solidi (a) 27

(2)R.C. WAYNE and L.C. BARTEL, Phys. Letters A 28, 196 (1968).
(3) G. T. DUBOVKA and E. G. PONYATOVSIUI, Fiz. Metallov i Metallovedenie 33,

640 (1972).
(4) G.T. DUBOVKA and E.G. PONYATUVSKII, Dokl. Akad. Nauk SSSR

206,

83

(1972).
(Received November 21, 1974)