i
.
•
**
.
.
.
.
•
.
2
.
.
.
-
.
[
-
:-
TOFI
ORNL P
1735
-
.
1
.
...
1
-..
.
...
.
.
.... .. .
.
.
. .-.- .-..
.
...
?
.
-
11:25 | 1.4 1.6
***
VA
MICROCOPY RESOLUTION TEST CHART
NATIONAL BUREAU OF STANDARDS - 1963
2
.
-
.
.
24
.,..
.
.
ORNZ -p-1736
Conf-65/106-2
-
s
NOV 18 18:55
65-97
NOTE:
This is a draft of a paper which is being submitted for
publication. Contents of this paper should neither be
quoted nor referred to without permission of the authors.
LEGAL NOTICE
T96 report was prepared as an account of Government sponsored work. Neither the United
Slates, oor the Commiosion, nor any person acting on behalf of the Commission:
A. Makes any warranty or representation, expressed or implied, with respect to the accu-
racy, completeness, or usefulness of the information contained in this report, or that the use
of any information, apparatus, method, or process disclosed in this report may not infringe
privately owned rigbio; or
B. Assumes any liabilities with respect to the use of, or for damagco rebulung from the
use of any information, apparatue, method, or process disclosed in this report,
Ao usod in the above, "person acting on behalf of the Commission" includes any em-
plcyoe or contractor of the Commission, or employee of such contractor, to the extent that
such employee or contractor of the Commission, or employee of such contractor prepares,
dlaseminates, or provides access is, any information pursuant to his employment or contract
with the Commission, or his employment with such contractor.
Magnetic Structure Properties of Tb-Sc Alloys
\H. R. Child and W. C. Koehler

RAUDA SIOD FOR ANNOUNCEMENT
IN MUCISBAR SCIENCE ABSTRACTS
SOLID STATE DIVISION
OAK RIDGE NATIONAL LABORATORY
Operated by
UNION CARBIDE CORPORATION
for the
U. S. Atomic Energy Commission
Oak Ridge, Tennessee, U.S.A.
October, 1965
Magnetic Structure Properties of Tb-Sc Alloys
H. R. Child and W. C. Koehler
Solid State Division, Oak Ridge National Laboratory
Oak Ridge, Tennessee
ABSTRACT
The results of a neutron diffraction study of the magnetic
structure properties of the Th-Sc alloy system are reported. Five
binary alloys with Tb content from 90 atomic percent to 25 atomic
percent have been exanined by powder techniques from 3000K down to
liquid helium temperatures to determine the magnetic ordering tem-
peratures and the magnetic structures. The dilution by Sc causes
-
-
-
-
the spiral magnetic phase of Tb to remain stable over a temperature
interval larger than in the pure metal. This effect is the same
general behavior as that found in the Tb-Y system previously reported.
However, the Néel points of the Tb-Sc alloy's fall well below those
found for To-Y and the initial turn angles are smaller in this
system. In falls more rapidly for Th-Sc alloys than for Tb-Y alloys
as a function of the effective spin variable x = c(8 - 1) J(J + 1),
Where c is the atomic percent of Tb, and reaches 0°K at x about 2.5,
The 25% Tb alloy shows no visible magnetic order down to 1.3°K in
contrast to the Tb-Y system where magnetic order was observed with
as little as 5 at.% Tb. The universal curve of Ty vs. x previously
9
:
found for rare earth alloys is not obeyed in the Tb-Sc system.
**
Research sponsored by the U. S. Atomic Energy Commission under
contract with the Union Carbide Corporation.
-2-
INTRODUCTION
Recently a number of experiments have been conducted to de-
termine the effect of dilution by a non-magnetic element on the mag-
netic structures of the heavy rare earth metals. The rare earth-
yttrium systems have been extensively studied and the results
showed that dilution by Y tended to stabilize the spiral or modulated
antiferromagretic structure of the rare earth at the expense of the
ferromagnetic phase. Furthermore, to a good approximation, the Neel
temperatures and the initial turn angles for all the rare earth
metals and rare earth-Y alloys were universal functions of the
effective spin parameter x = c(8 - 1)?J(J + 1) in which c is the
atomic concentration of rare earth with total quantum number J and
Lande factor g. The factor (8 - 1)?J(J + 1) is the square of the
projection of the spin on the total angular momentum for the rare
earth. On the other hand, in rare earth-lanthanum? and thorium
alloys, the ferromagnetic structures were found to be stabilized
by dilution and no correlation with x was observed. Attempts to ex-
plain these results on the basis of the Ruderman-Kittel-Kasuya-
Yosida (RKKY) theory“ met with only limited success.
The present paper describes an investigation extending these
experiments to terbium-Scandium alloys. The magnetization of the
gadoliniun-scandium system was studied by Nigh et al.' who found
marked differences with the Gd-Y system. Hence, a series of Tb-Sc
solid solutions were prepared and examined by neutron diffraction
to compare their magnetic behavior with the Tb-Y and Tb-La systems.
Neutron diffraction patterns were taien from room temperature down
to 1.3°K from rods of the alloys. Certain specimens were then filed
and annealed at about 700°c and re-examined. The transition ten-
peratures were measured by following the magnetic intensity as
function of temperature and the turn angles of the spiral structures
were determined from the separation of the magnetic satellites from
their respective nuclear positions.
RESULTS
Table I lists the five alloys exami.ned and gives the significant
parameters obtained.
The dilution of To by Sc tends to stabilize
the spiral structure. Although this is the same general effect as
that observed in the alloys of Y with Tb, there are quantitative
differences. In Figure 1, the solid points show Tv and T, versus x
for these five alloys and they fall well below the equivalent curves
for the Y alloys shown by the solid lines. Furthermore, I goes to
zero for x + 2.5 since the 25 at % To alloy shows no visible magnetic
order down to 1.3°K. This is in sharp contrast to the Y case where
magnetic order was observed for alloys with as little as 5 at.% TO
at an x of 0.53.
A spiral magnetic structure can be cunveniently characterized by
the value of the angle between the moments in adjacent layers, the
interlayer turn angle w, which is in general temperature dependent.
The value of this angle just below the transition temperature, wyo
and its value at low temperature wpr (or we', the value just above
the transition to ferromagnetism) are plotted versus x in Figure 2
for the Tbo.Sc alloys and the values for Tb-Y alloys are shown by the
solid lines for comparison.
The limiting value of w, as x decreases
appears to be about 10 degrees lower for Sc than for Y alloys al-
though the lack of magnetic order for the low concentration alloy
makes this value somewhat uncertain. The temperature variation of
the turn angle decreases with decreasing Tb concentration to a
greater extent than in the Tb-Y system. Concentrations <70 at.% To
have a temperature independeat turn angle, about 20 at.% higher than
the concentration at which the temperature dependence of w disappear-
ed for Tb-Y alloys.
The magnetic intensities from the three filed and annealed
alloys were measured and calibrated with a standard Ni sample. The
products ut per atom were obtained from the magnetic intensities
by assuming a spiral configuration for the 71% and 51% Tb alloys and
a ferromagnetic arrangement for the 90% alloy and assuming in all
cases that the moment direction is in the base plane. The moment
per Tb atom was obtained from the u?p? values by correcting for the
co..centration and assuming the form factor obtained from an earlier
study of TbN.° An average value of 8.6 + 0.4 Mo per To atom was ob-
tained from the three alloys.
DISCUSSION
The curve of T, versus x, Figure 1, for Tb-Y alloys was follow-
ed fairly well by alloys of other heavy rare earths with Y, and with
each other, and by the system Tb Lu. 'That the hexagonal close-pack-
ed alloys in the systems Tb-LA and To-Th do not follow this same
general behavior is not too surprising because of the differences
in electronic structure of the latter elements from those of the
heavy rare earths and yttrium. As for Sc, the outer electron
configuration, 34–4s?, is similar to that of Y, 4a 58, and of the
hee.vy rare earths, 5a+682, but its size is appreciably smaller than
that of the other elements. An indication that the limiting value
of the interlayer turn angle may depend on the average separation of
atoms is illustrated by the slightly lower value, 46° per layer,
found ir Tb-Lu, as compared to 51° per layer in Tb-Y. More surpris-
ing, however, is the comp).ete disappearance of long range magnetic
order in fairly concentrated alloys.
This result implies that the
interaction must be a very short range one, whereas the existence
in Tb, and in the very concentrated alloys, of a spiral structure
implies a long range one. We have as yet no satisfactory explana.
tion of this result. The moment value of 8,6 + 0.44 Me for the three
alloys indicates no excess above the expected value of 9.0 Mg per
Tb atom in contrast to results obtained from magnetization measure-
ments on specimens in the Gd-Sc system.
ACKNOWLEDGMENT
The authors wish to express their gratitude to R. B. Quin y
and D. E. Lavalle and to the Arc Melting Section of the Metals and
Ceramics Division for their aid in sample preparation.
RMTERENCES
1. H. R. Child, W. C. Koehler, E. O. Wollan, and J. W. Cable, Phys.
Rev. 138, A1655 (1965).
2. W. C. Koehler, J. Appl. Phys. 36, 1078 (1965).
3. W. C. Koehler, H. R. Child, and J. W. Cable, Proc. 5th Rare Earth
Conference, Ames, Iowa, September, 1965.
4. K. Yosida, Prog. In Low-Temperature Physics, edited by C. J. Gorter
(North-Holland Publishing Company, Amsterdam, 1964) Vol. IV,
Cap. V.
5. H. E. Nigh, s. Legvold, F. H. Spedding, and B. J. Beaudry,
J. Chem. Phys. 41, 3799 (1964).
H. R. Child, M. K. Wilkinson, J. W. Cable, W. C. Koehler, and
E. O. Wollan, Phys. Rev. 131, 922 (1963). Recently Steinsvoll
et al. (Proc. of the Fifth Rare Earth Conference, Ames, Iowa,
September, 1965) have measured a form factor for metallic terbium,
Over the region of overlap, the two sets of data agree within ex-
perimental error.
TABLE CAPTION
Table I - Magnetic Structure Parameters of To-Sc Alloys.
FIGURE CAPTIONS
Fig. 1 - Magnetic Transition Temperatures of Tb-Sc Alloys vs. X
Compared to Tb-Y Alloys.
Fig. 2 - Interlayer Turn Angles of Tb-Sc Alloys vs. x Compared to
Tb~Y Alloys.
ORNL DWG. 65-10585
24
27
TABLE I
MAGNETIC STRUCTURE PARAMETERS OF Tb-Sc ALLOYS
Alloy
TvK) TCK) W(deg.) Wr(deg.)
90% Tb 10% SC 9.45 200 159
80% Tb 20% Sc 8.40 174 <15
71% Tb 29% Sc 7.56 153
51% Tb 49% Sc 5,36 104
25% Tb 75% SC 2.63 <1.3
34
ORNL-DWG 65-10277
250

MAGNETIC TRANSITION TEMPERATURE (OK)
Tb-Y
TN
Tb-Sc
Tb-ylic Tb-sc
12
6
8
x=c19-112 J1J+1)
FIG. 1

ORNL-DWG 65-10276
Tь-Y
Tb-Sc
INTERLAYER TURN ANGLE ( deg/layer)
Wf
4
6
x=c19-112 11 1+1)
8
10
FIG. 2
END
DATE FILMED
12/ 7 / 65