The magnetization of powdered samples of Dy2O3 has been measured at temperatures between 1.45 deg and 4.2 K, in applied magnetic fields ranging to 7 Teslas. A linear dependence of magnetization on applied field is observable in high field region, the slope of which is independent of temperature over the range investigated. The extrapolated saturation magnetic moment is 2.77 + or - 0.08 Bohr magnetons per ion

Flood, D. J.

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-iG5E ICt OF Dy20 3 (AS) L 20 BCncls
$4.0C G3/ 2 3 38112
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HIGH-FIELD MAGNETIZATION OF Dy20 3
by Dennis J. Flood
Lewis Research Center
Cleveland, Ohio
April 1974
https://ntrs.nasa.gov/search.jsp?R=19740015112 2020-03-23T10:05:42+00:00Z
HIGH-FIELD MAGNETIZATION OF Dy20 3
by Dennis J. Flood
Lewis Research Center
SUMMARY
The magnetization of powdered samples of Dy20 3 has been measured
at temperatures between 1.450 and 4.20 K, in applied magnetic fields
ranging to 7 Teslas. A linear dependence of magnetization on applied
field is observable in the high-field region, the slope of which is
independent of temperature over the range investigated. The extrapolated
saturation magnetic moment is 2.77+0.08 Bohr magnetons per ion.
INTRODUCTION
The magnetization of a simple paramagnetic material is given by
M = NgB J B\ kT + a(H) (1)
N is the number of magnetic ions per cubic centimeter, g is the spectro-
scopic splitting factor, J is ground state total angular momentum quantum
number, and pB is the Bohr magneton. The function BJ(Jg1BH/kT) is the
Brillouin function, and a(H) is a term which arises when the ground state
magnetic energy levels have been perturbed by the presence of nearby
upper energy levels (ref. 1). The contribution to M from the second
term a(H) is independent of temperature if the separation between the
ground state and the nearest excited state is large compared to kT.
This contribution to the magnetization is known as van Vleck paramag-
netism. A standard perturbation calculation yields (ibid).
a(H) 2NJJ )12  (2)
H AE
where J' refers to an excited state of the system, po is the magnetic
moment operator, and AE is the separation between the ground state and
excited energy levels. Van Vleck paramagnetism is usually small, and
can be difficult to observe in the low field region. At magnetic
saturation, however,
M = NgB J + a(H) = const + a(H) (3)
and observation of a(H) can become relatively easy.
2EXPERIMENTAL METHODS
The compound was obtained from a commercial supplier in powder form.
A portion of the sample was tightly packed into one of two hollow phenolic
cylinders which were wound with nearly identical 750 turn pick-up coils.
The pick-up coils were connected in series opposition to one another,
and the difference voltage was applied to the input of an integrator.
This arrangement automatically eliminated the large background emf caused
by the changing magnetic field itself. The measurements were made by
suspending the cylinders side-by-side in a helium bath at the center of
a 10 centimeter (4") diameter bore, water-cooled solenoid capable of
producing magnetic fields in excess of 7 Tesla. A schematic diagram of
the experiment is shown in figure 1. The sample was 0.8 cm in diameter
3
and 5.2 cm in length with a density of 3.32 grh/cm..
RESULTS AND DISCUSSION
The magnetization of Dy203 (Neel temp - 1.20 K (ref. 2)) as a function
of applied magnetic field is shown for several temperatures in figure 2.
The high field data indicate a contribution to the magnetization which is
linear with a slope independent of temperature. From figure 2, a(H) =
0.133x105 H (H in Tesla). Westrum and Justice (ref. 3) found from specific
heat data that the separation between the ground state magnetic energy
level, which is a Kramer's doublet, and the first excited level, also a
-l
Kramer's doublet, is 75 cm-1. Using this value in equation (2) yields
(J'iIolJ) = 3.04x10 - 2 0 ergs/gauss. (N = 10.7x1021 ions/cm
3 for the sample
used.) This rather large value for the off-diagonal term indicates ap-
preciable mixing of the states of the system.
The number of Bohr magnetons per ion peff at saturation is given by
Peff = gJ = M(H) - a(H) (4)
eff N11 BNuB
and from the data, pff = 2.77±0.08. (Hund's rules predict Pff = 10
+++
for the free Dy ion.) In the case of extreme anisotropy, such that
g = 0 and g = 2 g L (Jz) , where gL is the free-ion Lande splitting
factor, the effective moment for a powdered solid is given by
gl ' (5)
Peff 2
where J' = 1/2 is the effective ground-state spin, and (Jz) is the
original aximuthal quantum number of the ground state doublet. In this
3case, g = 5.54±0.2, so that (Jz) = 4.15±0.15. Since (JZ) must have
half-integer values, the result indicates only that g1l is probably
greater than g , but that g cannot be neglected entirely. Studies
of single crystal samples (which are difficult to prepare) will be
necessary to completely characterize the magnetic anisotropy of the
compound.
SUMMARY OF RESULTS
Saturation magnetization measurements of powdered samples of Dy203
yield a value of 2.77+0.08 Bohr magnetons per ion. The saturation region
has a positive, temperature-independent slope equal to 0.133x105 (for H
in Tesla). The compound appears to be anisotropic, but may not be strong-
ly so.
REFERENCES
1. Van Vleck, John H.: The Theory of Electric and Magnetic Suscepti-
bilities. The Clarendon Press, 1932.
2. Bonrath, H.; Hellwege, K. H.; Micolay, K.; and Weber, G.: Antiferro-
magnetic Transitions of Dy20 3 , Er2O 3 , and Yb203  in the Temperature
Range of 1.1 to 4.20 K. I. Experimental Portion. Physik Konden-
sierten Materie, vol. 4, no. 5, 1966, pp. 382-390.
3. Westrum, Edgar F. Jr.; and Justice, Bruce H.: Thermophysical Proper-
ties of the Lanthanide Oxides. III. Heat Capacities, Thermodynamic
Properties, and Some Energy Levels of Dysprosium (III), Holmium (III),
and Ebium (III) Oxides. J. Phys. Chem., vol. 67, Mar. 1963, pp. 659-
665.
X-Y PLOTTER
INTEGRATOR
PHENOLIC
CYLINDERS
MAGNET
LpICKUP COILS CS-65785
Figure 1. - Schematic diagram of magnetization measure-
ment technique.
4. Ox1 5  -
Dy20 3
3.60 -
Slope = O 133x10 5
3.20 -
2.80
S 2.40
E
.2 2.00
a 1. 60
o =4.2K
S=2. 7K
1.20 - = 1.92K
o= 1.45K
. 80
.40
0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0
Applied field H (Tesla)
Figure 2 - Magnetization of powdered samples of Dy20 3.


High-field magnetization of Dy2O3

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