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The magnetic structure of plastically deformed chromium
TECHNICAL
The tendency for covalent bonding of the ~OXZS of the first transition series is much higher than in the rare earths elements. As a cunsequence, in the Mn(I1) salts the kinetic exchange is dominant. In the Fe(D) salts one observes an increase in s-electron density at the iron nucleus on going from the oxide to the telluride compound, Here the covalency between the magnetic 3d-electrons and the diamagnetic ions is not able to overcome the effects of the partial occupation of the 4s orbitals of Fe(II), This is consistent with the current ~te~retation of the isomer shift in iron compoun~~15‘16)
1, 2. 3. 4. 5.
a. 7.
8. 9. IO. 11. 12. 13. 14. 15. 16.
1955
NOTES f. Fhys. Chem. St&d~
Vol. 27, PP. 19554957.
structure of pIasticM deformed chromium
The magnetic
{Received 1 June 1956) SEVERAL investigators have shown by neutron diffraction measurements that pure chromium can
exist ss two magnetic phases with a transition temperature of 120°K. In the high temperature phase each (100) reciprocal lattice point is surrounded by six satellites, while in the low tempemture phase the two satellites lying on the line joining the origin to the ~lQ0) point have vanished. There is no departure from cubic symmetry in either phase and na evidence of a two-phase region. From these observations SHXRANEand T~lf~r(lf have proposed a model in which the magnetic moment density varies sinusoidally with a periodicity of 27 unit cells at room temperature. The wave References vector of the modulation is in the (lOO> direction; MCGUZRET. R. and SCHAFERM, W., J. A&. Pfz~s. in the high temperature phase the magnetic 35,984 (1964). moment is perpendicular to this direction whiIe SoM. W., J. A@ Phys. 36,1145 (1965). C~WP S. H. and Ram E. L.. P&s. fiew. 133. in the low temperature phase it is parallel. A811 (1964). The present experiments were carried out to ARGYLEIl. E.; SUSTS3. C. and FREISERM, J., Phys. determine the magnetic structure of heavily cold Reo. Z&t. 15.822 11965). &XCH G., JU&oo p. anh VOLT Q., R@x&? deS worked chromium in the hope that some informaProp&%& Electroniques des ~~ocka~~o~~~~re~ tion could be obtained about the weIl-known disd’Europium. Colloque Internatianal sur les crepancy between the value of the N&e1 temperaD&iv& Semi-MBtaIIiques, Orsay (1965). ture determined from single crystal and from polyBRIX P., HUGER S., KXENLEP. and QUIT~N D., crystalline material. BACON(~) has already shown Phys. Lett. 13, 140 (1964). that specimen purity is not the cause of this WICKS H. H., NOWK I., WERNICKJ. H., SHIRLJIYD. A. and FRANKELR. B., ayperfine discrepancy. P’ietis and fsome~ Sh&s in ~ag~e#~~~y Ordered The crystat used was part of a tensile test &rq&m Compounds. To be published. specimen of high purity chromium (nitrogen FRSA. J. and WATSONR. E., ~~~e~~s~ O*O~lS~*, oxygen 0.024~~) obtained from Mr. (Editors Rado G. T. and Suhl II.), Vol. IIA, p. 214. Academic Press, New York (1965). C. W. Weaver of the Defence Standards LaboraYAN HOUTEN S., Phys. Lett. 2, 21s (1962). tories, Melbourne, Victoria. The axis of the ONOK., ITOA. and Hrr+~m E..I Phvs. ” Sac. .&&am specimen was within a few degrees of [I IO] and the 17, 1615 (1962). specimen had been strained 8% in tension at room PICM~ S. J. and ALPERIN I% A., ButE. Ant. Pkys. Six. IO, 32 (1965). temperature (to fracture). It was mounted on a DE GRA~FA. M. and XAVIERR. M., Phys. Lett. 18, neutron diffractometer equipped with a three 225 (1965). circle goniometer. The neutron wavelength was ibDl%RSONP. W., Pkys. Rev. 11&2 (1959). 1.10 A. BLOEMERRGENN. and ROWLAND T. J,, Phys. Rev. 97, The magnetic structure at room temperature 1679 (1955). WALKER L. R., WERTHE~M G. K. and JACCARXNO V., was examined by scanning around each (100) P&S. Rev. Lett. 6,QS (1961). reciprocal lattice point in turn. In this material, in ~.woN J., Applications of the M&sbauer E&t in contrast with annealed chromium, the surChemistry and Solid State Physics, Technical of each point were no longer identical Repart Series NO. SO, International Atomic rounding Energy Agency, Vienna (1966). and only the satellite reflections indexing as I
<
1956
TECHNICAL
(60, 12 6); (0, 1, + 6); (1, 0, rt8) (in the terminology of Shirane and Takei) were found. Thus plastic deformation, or the residual elastic strains, had restrained the magnetic moment density modulation vector to be along [OOl]. This structure is identical with that found for field-cooled chromium by BASTOW and STREET.(~)
900
NOTES
far more about [OOl] than about [OTO]. If the stresses associated with these tilt boundaries are along [ITO] the growth of domains whose orientation is closest to the stress direction, i.e. [loo], [OlO], will be inhibited, in agreement with the work of Bastow and Street on elastically stressed chromium.
1
.90
-20
200-
rod
0
WTEGRATED
x
HALF
lNTENS4TY
WIDTH
-
- 10
0 0
30
60
90
I 120
0 160
la0
y
FIG. 1. Variation in integrated intensity and full width at half maximum intensity of the (110) reflection with azimuthal angle.
During the experiments it became obvious that the mosaic block distribution was highly anisotropic, and, in an attempt to relate this anisotropy to the magnetic structure, the integrated intensity and full width at half maximum intensity as a function of azimuthal angle about the scattering vector were measured for the (110) reflection. The results, uncorrected for instrumental or strain broadening, are shown in Fig. 1. The zero position on this curve corresponds to the [OOl] normal to the plane of the incident and diffracted beams. An interpretation in terms of mosaic block misorientation shows that the mosaic blocks are tilted
Ol9
20
II
21
2
FIG. 2. The
23
7.4
5
e IbEGcaEER
(0, 0, l-6) and (0, 0,1+6) reflections 77°K and 298°K temperature.
at
The crystal was then mounted successively in a cryostat and in a furnace, and the low and high temperature transition examined. Results of scans over the (0,0, 1 & 6) reflections at 298°K and 77°K are shown in Fig. 2. Remnants of the high temperature phase remain at 77°K. The period of the magnetic structure is 27 unit cells at 298°K and 21 unit cells at 77”K, which is
TECHNICAL
1957
NOTES
401
3
2Of
8
i g F
20
0
RUNI
0
RUN 2
I E
10
FIG. 3 (a, b). The variation of the peak intensity of the (0, 0, l-6)
identical to that of annealed chromium. In Figs. 3(a), 3(b), the variation in temperature of the (0, 0,1 - 6) reflection is plotted. The low temperature transformation is not complete until 150°K [Fig. 3(a)] but neither the temperature nor the sharpness of the Neel temperature transition is affected [Fig. 3(b)]. It can be concluded that plastic deformation modifies the magnetic structure of chromium but does not affect the NCel point transition.
reflection with temperature.
Materials Division, AAEC ResearchEstablishment Lucas Heights N. 5’.W, , Australia
T. M. SABINE G. W. Cox
References 1. SHIRANBG. and TAKEIW. J., J. Phys. Sot. Japan 17,
Suppl. BIII, 35 (1962). 2. BACON G. E., Acta Crystallogr. 14,823 (1961). 3. BASTOW T. J. and STREETR., PYOC.Phys. Sot. Land. 86, 1142 (1965).
The tendency for covalent bonding of the ~OXZS of the first transition series is much higher than in the rare earths elements. As a cunsequence, in the Mn(I1) salts the kinetic exchange is dominant. In the Fe(D) salts one observes an increase in s-electron density at the iron nucleus on going from the oxide to the telluride compound, Here the covalency between the magnetic 3d-electrons and the diamagnetic ions is not able to overcome the effects of the partial occupation of the 4s orbitals of Fe(II), This is consistent with the current ~te~retation of the isomer shift in iron compoun~~15‘16)
1, 2. 3. 4. 5.
a. 7.
8. 9. IO. 11. 12. 13. 14. 15. 16.
1955
NOTES f. Fhys. Chem. St&d~
Vol. 27, PP. 19554957.
structure of pIasticM deformed chromium
The magnetic
{Received 1 June 1956) SEVERAL investigators have shown by neutron diffraction measurements that pure chromium can
exist ss two magnetic phases with a transition temperature of 120°K. In the high temperature phase each (100) reciprocal lattice point is surrounded by six satellites, while in the low tempemture phase the two satellites lying on the line joining the origin to the ~lQ0) point have vanished. There is no departure from cubic symmetry in either phase and na evidence of a two-phase region. From these observations SHXRANEand T~lf~r(lf have proposed a model in which the magnetic moment density varies sinusoidally with a periodicity of 27 unit cells at room temperature. The wave References vector of the modulation is in the (lOO> direction; MCGUZRET. R. and SCHAFERM, W., J. A&. Pfz~s. in the high temperature phase the magnetic 35,984 (1964). moment is perpendicular to this direction whiIe SoM. W., J. A@ Phys. 36,1145 (1965). C~WP S. H. and Ram E. L.. P&s. fiew. 133. in the low temperature phase it is parallel. A811 (1964). The present experiments were carried out to ARGYLEIl. E.; SUSTS3. C. and FREISERM, J., Phys. determine the magnetic structure of heavily cold Reo. Z&t. 15.822 11965). &XCH G., JU&oo p. anh VOLT Q., R@x&? deS worked chromium in the hope that some informaProp&%& Electroniques des ~~ocka~~o~~~~re~ tion could be obtained about the weIl-known disd’Europium. Colloque Internatianal sur les crepancy between the value of the N&e1 temperaD&iv& Semi-MBtaIIiques, Orsay (1965). ture determined from single crystal and from polyBRIX P., HUGER S., KXENLEP. and QUIT~N D., crystalline material. BACON(~) has already shown Phys. Lett. 13, 140 (1964). that specimen purity is not the cause of this WICKS H. H., NOWK I., WERNICKJ. H., SHIRLJIYD. A. and FRANKELR. B., ayperfine discrepancy. P’ietis and fsome~ Sh&s in ~ag~e#~~~y Ordered The crystat used was part of a tensile test &rq&m Compounds. To be published. specimen of high purity chromium (nitrogen FRSA. J. and WATSONR. E., ~~~e~~s~ O*O~lS~*, oxygen 0.024~~) obtained from Mr. (Editors Rado G. T. and Suhl II.), Vol. IIA, p. 214. Academic Press, New York (1965). C. W. Weaver of the Defence Standards LaboraYAN HOUTEN S., Phys. Lett. 2, 21s (1962). tories, Melbourne, Victoria. The axis of the ONOK., ITOA. and Hrr+~m E..I Phvs. ” Sac. .&&am specimen was within a few degrees of [I IO] and the 17, 1615 (1962). specimen had been strained 8% in tension at room PICM~ S. J. and ALPERIN I% A., ButE. Ant. Pkys. Six. IO, 32 (1965). temperature (to fracture). It was mounted on a DE GRA~FA. M. and XAVIERR. M., Phys. Lett. 18, neutron diffractometer equipped with a three 225 (1965). circle goniometer. The neutron wavelength was ibDl%RSONP. W., Pkys. Rev. 11&2 (1959). 1.10 A. BLOEMERRGENN. and ROWLAND T. J,, Phys. Rev. 97, The magnetic structure at room temperature 1679 (1955). WALKER L. R., WERTHE~M G. K. and JACCARXNO V., was examined by scanning around each (100) P&S. Rev. Lett. 6,QS (1961). reciprocal lattice point in turn. In this material, in ~.woN J., Applications of the M&sbauer E&t in contrast with annealed chromium, the surChemistry and Solid State Physics, Technical of each point were no longer identical Repart Series NO. SO, International Atomic rounding Energy Agency, Vienna (1966). and only the satellite reflections indexing as I
<
1956
TECHNICAL
(60, 12 6); (0, 1, + 6); (1, 0, rt8) (in the terminology of Shirane and Takei) were found. Thus plastic deformation, or the residual elastic strains, had restrained the magnetic moment density modulation vector to be along [OOl]. This structure is identical with that found for field-cooled chromium by BASTOW and STREET.(~)
900
NOTES
far more about [OOl] than about [OTO]. If the stresses associated with these tilt boundaries are along [ITO] the growth of domains whose orientation is closest to the stress direction, i.e. [loo], [OlO], will be inhibited, in agreement with the work of Bastow and Street on elastically stressed chromium.
1
.90
-20
200-
rod
0
WTEGRATED
x
HALF
lNTENS4TY
WIDTH
-
- 10
0 0
30
60
90
I 120
0 160
la0
y
FIG. 1. Variation in integrated intensity and full width at half maximum intensity of the (110) reflection with azimuthal angle.
During the experiments it became obvious that the mosaic block distribution was highly anisotropic, and, in an attempt to relate this anisotropy to the magnetic structure, the integrated intensity and full width at half maximum intensity as a function of azimuthal angle about the scattering vector were measured for the (110) reflection. The results, uncorrected for instrumental or strain broadening, are shown in Fig. 1. The zero position on this curve corresponds to the [OOl] normal to the plane of the incident and diffracted beams. An interpretation in terms of mosaic block misorientation shows that the mosaic blocks are tilted
Ol9
20
II
21
2
FIG. 2. The
23
7.4
5
e IbEGcaEER
(0, 0, l-6) and (0, 0,1+6) reflections 77°K and 298°K temperature.
at
The crystal was then mounted successively in a cryostat and in a furnace, and the low and high temperature transition examined. Results of scans over the (0,0, 1 & 6) reflections at 298°K and 77°K are shown in Fig. 2. Remnants of the high temperature phase remain at 77°K. The period of the magnetic structure is 27 unit cells at 298°K and 21 unit cells at 77”K, which is
TECHNICAL
1957
NOTES
401
3
2Of
8
i g F
20
0
RUNI
0
RUN 2
I E
10
FIG. 3 (a, b). The variation of the peak intensity of the (0, 0, l-6)
identical to that of annealed chromium. In Figs. 3(a), 3(b), the variation in temperature of the (0, 0,1 - 6) reflection is plotted. The low temperature transformation is not complete until 150°K [Fig. 3(a)] but neither the temperature nor the sharpness of the Neel temperature transition is affected [Fig. 3(b)]. It can be concluded that plastic deformation modifies the magnetic structure of chromium but does not affect the NCel point transition.
reflection with temperature.
Materials Division, AAEC ResearchEstablishment Lucas Heights N. 5’.W, , Australia
T. M. SABINE G. W. Cox
References 1. SHIRANBG. and TAKEIW. J., J. Phys. Sot. Japan 17,
Suppl. BIII, 35 (1962). 2. BACON G. E., Acta Crystallogr. 14,823 (1961). 3. BASTOW T. J. and STREETR., PYOC.Phys. Sot. Land. 86, 1142 (1965).