MAGNETOSTRICTION AND THERMAL EXPANSION OF CHROMIUM

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MAGNETOSTRICTION AND THERMAL EXPANSION OF CHROMIUM

E. Kondorsky, T. Kostina, L. Ekonomova

To cite this version:

E. Kondorsky, T. Kostina, L. Ekonomova. MAGNETOSTRICTION AND THERMAL EX- PANSION OF CHROMIUM. Journal de Physique Colloques, 1971, 32 (C1), pp.C1-417-C1-418.

�10.1051/jphyscol:19711147�. �jpa-00213966�

JOURNAL DE PHYSIQUE

Collogue C 1, supplement au n° 2-3, Tome 32, Fevrier-Mars 1971, page C 1 - 417

MAGNETOSTRICTION AND THERMAL EXPANSION OF CHROMIUM

E. I. KONDORSKY, T. I. KOSTINA, L. N. EKONOMOVA Moscow, State University, U. S. S. R.

Abstract. — The thermal expansion coefficient a = f(T) and longitudinal and transversal magnetostriction X^ and X

of chromium were measured between 77-340 °K. It has been shown that transitions through the temperatures and spin-flip are accompanied by isotropic change of the volume. Anomalous thermal contraction of chromium occurs between 77-90 °K.

Résumé. — On a mesuré le coefficient d'expansion thermique a = f(T) ainsi que les magnétostrictions longiduti- nale X^ et perpendiculaire A

du chrome entre 77 et 340 °K. On a montré que des transitions et des renversements de spins s'accompagnent d'une variation isotrope de volume. Il se produit une concentration thermique du chrome anormale entre 77 et 90 °K.

In paper [1] the results of measurements of electrical resistivity, magnetoresistance and magnetic suscepti- bility of chromium were presented. The present paper contents the results obtained for thermal expansion and magnetostriction of the same polycrystalline chro- mium. Thermal expansion and magnetostriction have been investigated in the temperature range 77-350 °K.

Measurements were performed using the conventional strain-gauge method with a compensation pickup. The compensation pickup was used to eliminate galvano- metric and temperature effects.

Figure 1 shows the dependence of longitudinal and x.io

l +10 + 5 0 - 5 -10

+ 5 0 - 5 -10

— —

A

V 11

7? ^{+** &}

Hx=13ki>

HM=13kOe

90 130

J

J

r

i

\

^

2 9 0 3 3 0

— ^ T°K FIG. 1. — Dependence of longitudinal and transverse magneto- strictions on temperature taken at T

— 311 °K and Tip = 122 K,

H = 13 kOe.

transverse magnetostrictions on temperature measured at H = 13 kOe in the range of the Neel temperature r

and the spin-flip temperature X

. Figure 2 corres- ponding dependence of magnetoresistance. Figure 3 shows the temperature dependence at the thermal

/ A/

expansion coefficient a = — -j . It is seen from these figures that magnetic ordering which appears at

I

\

V

H = 13 kOe

FIG. 2. —• Dependence of the magnetoresistance AR./U on tem- perature.

/ A

r\

\

f

s _r-°

FIG. 3. — Dependence of linear expansion coefficient a on temperature.

T

= 311 °K and the change in chromium magnetic structure at T

= 122 °K [2, 3] characterized by phase transitions of the first kind [4] are accompanied by the picks on the curves of magnetostriction and the linear expansion coefficient a. It follows from compa- rison of the curves a, c, b and d in figure 1 that transi- tions through the temperatures T

and r

are accom- panied by isotropic change of the volume.

The influence of the heating speed on the linear thermal expansion has been also investigated. When a sample is rapidly heated from 77 to 85 °K compression of the sample takes place up to A/// ~ 1.2 x 1 0

, and then it again begins to expand. The depth of the

29

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19711147

c l - 4 1 8 E. I. KONDORSKY, T. I. KOSTINA, L. N. EKONOMOVA

minimum is linearly dependent on the heating speed

and it is higher the higher is the speed. When cooling the sample the reverse is true, viz. it expands with cooling. For the first time such anomalous behaviour was described in paper

When the process of heating is very slow (200 over 3 h) this anomaly is absent.

Such anomaly of chromium may be related to

<<

over-heating

of a sample. In this case the increase

of energy which appears due to retarding of transition of one kind would be compensated by decreasing exchange energy by spontaneous compression.

Discussion. - The increase of the longitudinal magnetostriction All and magnetoresistance AR/R was found when the temperature decreased below 120

It is seen from figures I and 2 that the values of All and AR/R are bigger in the phase AF, than in the

phase AF,. The possible explanation is that there are different processes of magnetization in phases AF, and AF,. Let us assume that the shifts of domains' boun- daries (Bloch's walls) take place in chromium after magnetic field was applied. Then, as it follows from domain's picture suggested in papers [2, 3, 61, the shift of boundaries which divide domains in phase AF, takes place either with or without the change of wave vector's Q direction. On the contrary, the shift of the domain's boundaries in phase AF, should always be accompanied by change of Q directions. It is much probably that the deformation which arises due to change of Q direction is greater than one which appears due to change of vector

direction (y is polarisation vector). In both cases the shift of Bloch's walls may be either reversible or irreversible as in ferromagnetic substances. Irreversible shift of Bloch's walls in chromium should lead to magnetic hysteresis.

References

[l] KOSTINA

KOSLOVA

KONDORSKY

(A.), WERNER (S. A.), RENDRICK

J . E . T . F . , 1 9 6 3 , U . S . S . R . 4 5 .

Rev.

1965,

K21 ARCO (A.

MARCUS

A.),

(W. A.),

[5]

1921,

Rev.,

1968,

2. [6] LOMER

(London), 1962, [31 WERNER (S. A.), ARROTT (A.), RENDRICK

489

1964,

Rev.,

1967,