MAGNETOCALORIC EFFECT AND CRITICAL PHENOMENA OF IRON, COBALT AND NICKEL NEAR THE CURIE TEMPERATURE

(1)

HAL Id: jpa-00214052

https://hal.archives-ouvertes.fr/jpa-00214052

Submitted on 1 Jan 1971

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

MAGNETOCALORIC EFFECT AND CRITICAL PHENOMENA OF IRON, COBALT AND NICKEL

NEAR THE CURIE TEMPERATURE

W. Rocker, R. Kohlhaas, H. Schöpgens

To cite this version:

W. Rocker, R. Kohlhaas, H. Schöpgens. MAGNETOCALORIC EFFECT AND CRITICAL PHE-

NOMENA OF IRON, COBALT AND NICKEL NEAR THE CURIE TEMPERATURE. Journal de

Physique Colloques, 1971, 32 (C1), pp.C1-652-C1-653. �10.1051/jphyscol:19711225�. �jpa-00214052�

(2)

JOURNAL DE PHYSIQUE

Colloque C I, ~upplkment au no 2-3, Tome 32, Fkvrier-Mars 1971, page C 1 - ⁶⁵²

MAGNETOCALORIC EFFECT AND CRITICAL PHENOMENA OF IRON, COBALT AND NICKEL NEAR THE CURIE TEMPERATURE

by W. ROCKER, R. KOHLHAAS and H. W. SCH~PGENS

Max-Planck-Institut fur Eisenforschung, Diisseldorf and Abt. Metallphysik im 1I.Physikalischen Institut der Universjtat Koln

Rdsumk. -

Les propriktts magnetiques de Fe, Co et Ni et I'effet magnCtocalorique ont

6te

CtudiCs dans les environs du point de Curie. L'aimantation spontanke et I'inverse de

la

susceptibilite initiale ant

C t t

calculkes. Les exposants

j?, y, 6

et

TC

ont Bte donnts.

Abstract.

- The magnetic properties of Fe, Co and Ni have been measured together with the magnetocaloric effect

in

the neighbourhood of the Curie temperature. Spontaneous magnetization and reciprocal initial susceptibility have been computed. The critical indices 8,

7, 6

and

n

are given.

Till now there have been given uniform exponents

b and

y

concerning the magnetization-field-tempera- ture behaviour of a ferromagnetic in a great tempera- ture range about the critical point. These critical indices were combinable with scaling laws and they allowed to calculate the exponents 6 of the magneti- zation and

n

of the magnetocaloric effect at T,.

Following theoretical discussions of Kadanoff [I]

two values for /? were to be expected according to the distance from the critical point.

This supposition was confirmed by exact measure- ments of Arajs [2] on nickel from which /? was calcu- lated

:

b

=

0.50 for

^E=

I 1 - TIT, I

=

4

x

...

⁵^x

B

⁼

0.34 for

E =

I ¹ - TIT,

( =

5

x

... 3

x

1 0 - I . We have studied with a modified Faraday force technique the magnetization behaviour of Fe, Co and Ni spheres together with the magnetocaloric effect in a wide temperature range about the Curie point with external fields from 100 to 25 000 Oe. The appa- ratus and the measuring procedure have been des- cribed by Lange [3]. Fig. 1 shows some of these magnetization curves of Fe, Co and Ni as a function of temperature with the external field as a parameter.

In fig. 2 there are plotted some curves of the magne-

tocaloric effect as a function of temperature without field.

FIG. 2.

- Magnetocaloric effect of Fe,

Co

and Ni plotted

vs

temperature

^TO

without

field.

The numerous automatically measured points were given into a PDP-10 digital computer to calculate according to Kouvel [4] with a parabolic extrapola- tion process [3] the temperature dependence of the spontaneous magnetization

so

and the reciprocal initial susceptibility 1 / ~ , . In fig. 3 there are plotted the square of spontaneous magnetization and the reciprocal initial susceptibility versus temperature.

The temperature dependence of both quantities is not linear in the whole temperature range.

Fra. 1.

- Specific magnetization of Fe, Co and Ni plotted

vs RG. 3.

- Square

of

spontaneous magnetization and reciprocal temperature with external field as a parameter initial susceptibility vs temperature.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19711225

(3)

MAGNETOCALORIC EFFECT AND CRITICAL PHENOMENA O F IRON, COBALT AND NICKEL C 1

-

⁶⁵³

A log-log plot of a. vs

E =

I 1 - TITc I respecti- vely of 1/x0 vs

E

shown in fig. 4 allows the deter-

FIG.

5. -

Log-log plot of magnetization vs internal field and magnetocaloric effect vs magnetization at

Te.

FIG. 4.

- Log-log plot of spontaneous magnetization and reciprocal initial susceptibility vs

E =

I

1 - TITc[.

mination of the exponents p and

y.

There is no uni- form value for p and y in the whole investigated tem- perature range. Fig. 5 shows the log-log plot of the magnetization a t Tc vs internal field and of the magne- tocaloric effect vs magnetization to determine the critical indices 6 and

n.

In the table there are given the exact values of the determined exponents P, y, 6 and n and the ranges of their validity. The mean deviation of these values is about

f

3 %. Moreover the values for 6 and

^a

cal- culated with the scaling laws

6

⁼

1 + y/Pand

n

=

2 + ^(y ^- 1)/p (according to Wohlfarth

[ 5 ] )

by using the experimental values for and

y

are noticed in parenthesis. The agreement between the calculated and the experimental values for 6 and n is not very satisfactory.

To conclude there is to remark that the exact behaviour of a ferromagnetic transition metal at the critical point seems to be more complicated than it was first assumed. Here is the behaviour near T, not exactly to be described by the scaling laws.

Acknowledgements.

-

We thank Prof. Arajs for sending us the preprint [2].

Experimental values of the exponents

P, y, 6

and

n

and range of validity.

In

parenthesis : values for

6

and

a

calculated b y using the scaling laws and the experimental values for

P

^and

y .

Range

~ = 4

x ...

& = 4 x

... ^{H i =} 1 ... 25 kOe Tc

8

x

...

4 x

6

x

... 4 x lo-'

Exponent 0 Y 6

n OK

References

[I]

KADANOFF (L. P.), GOTZE

(W.),

HAMBLEN

(D.), [3]

LANGE (H.), KOHLHAAS (R.) and ROCKER

(W.), Fors-

HECHT (R.), LEWIS

(E.

A.

S.),

PALCIAUSKAS

(V. chungsbericht des Landes Nordrhein-Westfalen,

V.), RAYL

( M . ) ,

SWIFT (J.), ASPNES

(D.)

and 1969,

^1992.

KANE (J.),

Rev. Mod. Phys.,

1967,

39,

395.

[4]

KOUVEL (J.

S.),

General Electric Research Labora-

[2]

ARAB (S.), TEHAN

(B. L.),

ANDERSON

(E.

E.) and

tory

Report No. 57-RL-1799, 1957.

STELMACH (A.

A.),

to

be

published. [5] MATHON (J.) and WOHLFARTH

(E.

P.),

J. Phys. C,

1969,

2,

MAGNETOCALORIC EFFECT AND CRITICAL PHENOMENA OF IRON, COBALT AND NICKEL NEAR THE CURIE TEMPERATURE

HAL Id: jpa-00214052

https://hal.archives-ouvertes.fr/jpa-00214052

Submitted on 1 Jan 1971

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

MAGNETOCALORIC EFFECT AND CRITICAL PHENOMENA OF IRON, COBALT AND NICKEL

NEAR THE CURIE TEMPERATURE

W. Rocker, R. Kohlhaas, H. Schöpgens

To cite this version:

W. Rocker, R. Kohlhaas, H. Schöpgens. MAGNETOCALORIC EFFECT AND CRITICAL PHE-

NOMENA OF IRON, COBALT AND NICKEL NEAR THE CURIE TEMPERATURE. Journal de

Physique Colloques, 1971, 32 (C1), pp.C1-652-C1-653. �10.1051/jphyscol:19711225�. �jpa-00214052�

Colloque C I, ~upplkment au no 2-3, Tome 32, Fkvrier-Mars 1971, page C 1 - 652

MAGNETOCALORIC EFFECT AND CRITICAL PHENOMENA OF IRON, COBALT AND NICKEL NEAR THE CURIE TEMPERATURE

by W. ROCKER, R. KOHLHAAS and H. W. SCH~PGENS

Max-Planck-Institut fur Eisenforschung, Diisseldorf and Abt. Metallphysik im 1I.Physikalischen Institut der Universjtat Koln

Les propriktts magnetiques de Fe, Co et Ni et I'effet magnCtocalorique ont

CtudiCs dans les environs du point de Curie. L'aimantation spontanke et I'inverse de

susceptibilite initiale ant

calculkes. Les exposants

et

ont Bte donnts.

- The magnetic properties of Fe, Co and Ni have been measured together with the magnetocaloric effect

the neighbourhood of the Curie temperature. Spontaneous magnetization and reciprocal initial susceptibility have been computed. The critical indices 8,

and

are given.

Till now there have been given uniform exponents

b and

concerning the magnetization-field-tempera- ture behaviour of a ferromagnetic in a great tempera- ture range about the critical point. These critical indices were combinable with scaling laws and they allowed to calculate the exponents 6 of the magneti- zation and

of the magnetocaloric effect at T,.

Following theoretical discussions of Kadanoff [I]

two values for /? were to be expected according to the distance from the critical point.

This supposition was confirmed by exact measure- ments of Arajs [2] on nickel from which /? was calcu- lated

b

0.50 for

I 1 - TIT, I

4

...

B

0.34 for

I 1 - TIT,

5

... 3

In fig. 2 there are plotted some curves of the magne-

tocaloric effect as a function of temperature without field.

- Magnetocaloric effect of Fe,

and Ni plotted

temperature

without

The numerous automatically measured points were given into a PDP-10 digital computer to calculate according to Kouvel [4] with a parabolic extrapola- tion process [3] the temperature dependence of the spontaneous magnetization

and the reciprocal initial susceptibility 1 / ~ , . In fig. 3 there are plotted the square of spontaneous magnetization and the reciprocal initial susceptibility versus temperature.

The temperature dependence of both quantities is not linear in the whole temperature range.

- Specific magnetization of Fe, Co and Ni plotted

- Square

spontaneous magnetization and reciprocal temperature with external field as a parameter initial susceptibility vs temperature.

-

A log-log plot of a. vs

I 1 - TITc I respecti- vely of 1/x0 vs

shown in fig. 4 allows the deter-

FIG.

Log-log plot of magnetization vs internal field and magnetocaloric effect vs magnetization at

- Log-log plot of spontaneous magnetization and reciprocal initial susceptibility vs

I

mination of the exponents p and

There is no uni- form value for p and y in the whole investigated tem- perature range. Fig. 5 shows the log-log plot of the magnetization a t Tc vs internal field and of the magne- tocaloric effect vs magnetization to determine the critical indices 6 and

In the table there are given the exact values of the determined exponents P, y, 6 and n and the ranges of their validity. The mean deviation of these values is about

3 %. Moreover the values for 6 and

cal- culated with the scaling laws

6

1 + y/Pand

n

2 + (y - 1)/p (according to Wohlfarth

by using the experimental values for and

are noticed in parenthesis. The agreement between the calculated and the experimental values for 6 and n is not very satisfactory.

To conclude there is to remark that the exact behaviour of a ferromagnetic transition metal at the critical point seems to be more complicated than it was first assumed. Here is the behaviour near T, not exactly to be described by the scaling laws.

Acknowledgements.

We thank Prof. Arajs for sending us the preprint [2].

P, y, 6

n

Colloque C I, ~upplkment au no 2-3, Tome 32, Fkvrier-Mars 1971, page C 1 - ⁶⁵²

I ¹ - TIT,

2 + ^(y ^- 1)/p (according to Wohlfarth

... ^{H i =} 1 ... 25 kOe Tc