Vibration damping in polycrystalline TbDy alloys was studied at cryogenic temperatures. Mechanical hysteretic losses were measured at various strains, frequencies, and loading configurations at 77 K. Some textured TbDy materials demonstrated 22.6% energy dissipation in mechanical measurements at low frequency (0.01 Hz) and a mean logarithmic decrement of 0.23 at a higher frequency (25 kHz). Ultrasonic velocities of longitudinal and shear elastic waves were measured on single and polycrystalline TbDy; little variation in ultrasonic velocities was found even for samples with large variation in crystallographic texture and magnetomechanical properties

Dooley, J.

Fultz, B.

Good, N.

English

Caltech Authors - Main

JOURNAL OF APPLIED PHYSICS VOLUME 91, NUMBER 10 15 MAY 2002Magnetomechanical damping by polycrystalline TbDy
N. Good and J. Dooley
Jet Propulsion Laboratory, 4800 Oak Grove Avenue, Pasadena, California 91109
B. Fultz
Division of Engineering and Applied Science, California Institute of Technology, Pasadena,
California 91125
Vibration damping in polycrystalline TbDy alloys was studied at cryogenic temperatures.
Mechanical hysteretic losses were measured at various strains, frequencies, and loading
configurations at 77 K. Some textured TbDy materials demonstrated 22.6% energy dissipation in
mechanical measurements at low frequency ~0.01 Hz! and a mean logarithmic decrement of 0.23 at
a higher frequency ~25 kHz!. Ultrasonic velocities of longitudinal and shear elastic waves were
measured on single and polycrystalline TbDy; little variation in ultrasonic velocities was found even
for samples with large variation in crystallographic texture and magnetomechanical properties.
© 2002 American Institute of Physics. @DOI: 10.1063/1.1452217#INTRODUCTION
Ferromagnetic TbDy alloys exhibit giant magnetostric-
tion, approaching 1% at saturation. This large coupling be-
tween mechanical energy and magnetic energy enables the
dissipation of vibration through the dynamics of magnetic
domain reorientation. These processes are subject to hyster-
etic losses and result in mechanical damping. The damping
depends on the magnetomechanical coupling factor describ-
ing the efficiency of converting elastic to magnetic energy,
the magnetic anisotropy describing the difficulty of moment
rotation, the Young’s modulus, the magnetization, the mag-
netostriction, and the crystallographic texture.1 These prop-
erties and hence the damping characteristics of the material
can be optimized through microstructural control. We expect
the damping of optimized polycrystalline TbDy to be sub-
stantial based on its large magnetostriction, magnetome-
chanical coupling factors as high as 0.75,2 and the relatively
large hysteresis measured in curves of magnetostriction ver-
sus applied field.3–5
In previous work with polycrystalline TbDy, we mea-
sured quasi-static magnetomechanical energy dissipation as
the ratio of the area of the stress–strain hysteresis loop to the
mean area under the loading and unloading curves, DE/E , at
;0.01 Hz.6 The energy lost is the product of the fractional
dissipation with the total potential energy stored in the
sample. The fraction of mechanical energy dissipated in the
material was 19.2% over a range of 0–27 MPa for commer-
cial purity TbDy textured alloys at 77 K.7820021-8979/2002/91(10)/7824/3/$19.00
Downloaded 12 Jan 2006 to 131.215.240.9. Redistribution subject toEXPERIMENT
The TbDy alloys were prepared as drop-cast, cylindrical
ingots which initially had a radial texture. The ingots were
cold-rolled by 35% in thickness and annealed at 950 °C for
1.5 h. The plane-rolling deformation is performed to reorient
the grains such that the hard c-axes lie in the direction of
applied deformation stress, and the annealing allows for
strain relief and grain growth. A second cold-rolling defor-
mation of 55% and heat treatment at 350 °C further reori-
ented the grains in the samples, which measured 938
34 mm ~commercial-grade! and 173534 mm ~high-
purity!. The well-defined c-axis grain orientation was con-
firmed by thermal expansion analysis of the textured
samples, an as-cast specimen and a single crystal TbDy con-
trol, the results of which are summarized in Table I. Speci-
mens were prepared from commercial-grade TbDy with a
typical purity of 99.7%, with the main impurities being Ta,
O, and N, and from high-purity 99.94% TbDy. Optical mi-
croscopy showed large variations of grain sizes and no clear
differences between commercial and high-purity samples.
The processed samples exhibited magnetostrictive strains of
up to 56% of single crystal values.3–5
Ultrasonic measurements were made by affixing a piezo-
electric transducer to the specimen, introducing a series of
elastic pulses at 5 MHz, and measuring the round-trip sound
wave propagation time with an oscilloscope. A screw-driven
Instron load frame was operated in stroke control to apply
compressive stresses to a prismatic bar of TbDy instru-TABLE I. Thermal expansion analysis summary of polycrystalline and single crystal TbDy.
Sample
x-axis
expansion
1026/K
y-axis
expansion
1026/K
z-axis
expansion
1026/K
x1y /
2z
Tb60Dy40 , single crystal 3.3 3.3 14.7 0.22
Tb76Dy24 , as-cast, 99.7% purity 5.4 7.1 8.1 0.77
Tb76Dy24 , textured, 99.94% purity 6.2 5.2 10.7 0.53
Tb76Dy24 , textured, 99.7% purity 4.2 5.3 12.1 0.394 © 2002 American Institute of Physics
 AIP license or copyright, see http://jap.aip.org/jap/copyright.jsp
7825J. Appl. Phys., Vol. 91, No. 10, 15 May 2002 Good, Dooley, and Fultz
Downloaded 12 JTABLE II. Fractional dissipation and Young’s modulus of TbDy for various applied stress as at 77 K.
Sample
Applied stress
range ~MPa!
Strain range
~ppm!
Fractional
energy
dissipation
Young’s
modulus
~GPa!
Tb76Dy24 , 0–36 0–2150 13.8% 17.2a
polycrystalline 0–14 0–900 16.7% 15.6
99.94% purity 14–28 1100–1750 12.9% 21.5
Tb76Dy24 , 0–27 0–2700 19.2%a 10.0a
polycrystalline 99.7% 0–10 0–900 22.6% 10.5
purity 10–20 1250–2100 16.5% 13.3
aPreviously reported values ~Ref. 6!.mented with electrical resistance strain gauges. Measure-
ments were performed at room temperature and with the
sample immersed in liquid nitrogen (LN2). The stress–strain
data showed magnetomechanical hysteresis when the sample
was at 77 K. High-frequency dynamic magnetomechanical
damping measurements were made for comparison with the
quasi-static results. The sample rested on an aluminum plate
within a solenoid while immersed in LN2 . A mechanical
impulse was imparted to the sample and the induced current
in the solenoid was measured.
RESULTS
Further analysis of the previously reported quasi-static
minor loop stress-strain curves6 shows a number of interest-
ing relationships summarized in Table II, with a typical
TbDy stress-strain curve at 77 K and 300 K, shown in Fig. 1.
The commercial-grade specimen consistently showed larger
strain amplitudes for the same applied stresses as compared
to high-purity specimens. For the ranges measured, a 27%–
35% larger fractional energy dissipation was measured on
commercial-grade specimens, with the highest ratio seen for
the minor loops at low amplitudes. At low frequencies,
DE/E of the minor loops varies inversely with the applied
stress; for example, the commercial purity specimen shows a
DE/E522.6% over a range of 0–900 ppm, compared to
DE/E516.5% over a range of 1250–2100 ppm—a differ-an 2006 to 131.215.240.9. Redistribution subject toence of 37%. In general, minor loops at lower applied
stresses exhibited lower Young’s moduli as measured by the
slopes of the stress–strain curves.
Measurements of ultrasonic velocities of shear and lon-
gitudinal waves in single crystal and textured TbDy samples
at room temperature are summarized in Table III. While
fairly large differences in magnetostrictive and magnetostric-
tive damping performance were seen between commercial-
grade and high-purity samples of polycrystalline TbDy, the
ultrasonic measurements revealed only small differences.
Nevertheless, we expect a correlation between the measured
ultrasonic velocities and the magnetization arising from an
elastic wave traveling through the material. In addition, we
include in Table III values of Young’s modulus calculated
from the ultrasonic velocities of the polycrystalline samples
determined from the formula Y5rVl
2(12n)/(11n)(1
22n), with Poisson’s ratio n5(Vl2/Vt222)/2(Vl2/Vt221)
with Vl and Vt being the longitudinal and shear velocities,
respectively.7 These results agree well with our measured
room temperature Young’s moduli in Table II.
Several aspects of the magnetoelastic behavior of the
samples are apparent from the dynamical damping data. A
typical result is shown in Fig. 2, with the induced voltage of
the solenoid ~proportional to current! plotted versus time.
Since the magnetic sample is excited mechanically by an
impact force, the decay of the inductive pickup can be attrib-
uted to the dissipation of vibrational energy within theTABLE III. Ultrasonic velocities of shear and longitudinal waves in single crystal and polycrystalline TbDy at
room temperature. Room temperature Young’s moduli as measured by the slope of the stress–strain curve and
derived from ultrasonic velocity measurements.
Sample
Ultrasonic velocity ~km/s!
Measured
Young’s
modulus
~GPa!
Derived
Young’s
modulus
~GPa!Shear Longitudinal
Tb, single crystal
c-axis
1.70 3.23
Dy, single crystal,
c-axis
1.71 3.09
Tb60Dy40 , single crystal,
b-axis
1.64 2.89
Tb76Dy24 , polycrystalline
99.7% purity
1.60 3.05 49.6 54.1
Tb76Dy24 , polycrystalline
99.94% purity
1.60 3.00 57.2 55.2 AIP license or copyright, see http://jap.aip.org/jap/copyright.jsp
7826 J. Appl. Phys., Vol. 91, No. 10, 15 May 2002 Good, Dooley, and Fultzsample. The approximately 35–40 ms period corresponds to
sound velocities of 1.6–1.8 km/s across a specimen of 32.4
mm. These are similar to measured sound velocities in poly-
crystalline TbDy of 1.7 km/s and 2.9 km/s for ultrasonic
shear and longitudinal waves, respectively.
The corresponding mean logarithmic decrement d
5DE/2E5ln(An /An11) is often used to describe the damping
capacity of materials, with An corresponding to the vibra-
tional amplitude of the nth oscillation of a vibrating element.
By fitting the peaks of the oscillations in Fig. 2 to decaying
exponential curves, we observe a decay in the amplitude of
the signal peaks corresponding to d50.23. This is within a
FIG. 1. Quasi-static magnetoelastic damping of Tb76Dy24 ~99.7% purity! at
77 K and 300 K.
FIG. 2. Dynamic magnetoelastic damping signal from polycrystalline
Tb60Dy40 at 77 K.Downloaded 12 Jan 2006 to 131.215.240.9. Redistribution subject tofactor of 2 of our measured low-stress quasi-static damping
capacities of TbDy alloys shown in Table II. This variation is
not unexpected owing to the slightly different composition
and a number of additional damping sources in the test sys-
tem, for example, the interface of the specimen with the coil
and the presence of external noise sources. Nevertheless,
from these data the high-frequency damping capacity of
TbDy is apparent.
DISCUSSION
At lower stresses, the magnetization proceeds by rear-
rangement of domain morphology, which is subject to losses
associated with microstructural features. Perhaps the impuri-
ties in the commercial-grade material could be responsible
for additional dissipation. Higher stresses can cause the mag-
netization to orient out of the basal plane along higher-
energy directions, causing an effective stiffening of the ma-
terial and a higher elastic modulus as shown in Table I.
Polycrystalline TbDy alloys with crystallographic tex-
ture were prepared, and their mechanical hysteresis was mea-
sured. An approximately 30% larger fractional energy dissi-
pation was found for commercial-grade materials than for
high-purity materials. At 25 kHz, a d50.23 was measured
for TbDy at 77 K, comparable to the largest measured quasi-
static fractional energy dissipation of 22.6%. The high mag-
netomechanical damping capacities of textured TbDy poly-
crystalline alloys at low frequencies in quasi-static loadings
and at higher frequencies in cyclic loading demonstrate the
potential use of this material in cryogenic vibration damping
applications.
ACKNOWLEDGMENTS
The authors thank Dr. A. E. Clark for stimulating discus-
sions, Dr. M. Wun-Fogle for the use of several single crystal
specimens, and Dr. T. Lograsso for preparing the ingots. The
authors acknowledge support from NASA’s Microgravity Di-
vision. The Jet Propulsion Laboratory is operated by the
California Institute of Technology under contract with
NASA.
1 J. P. Teter, K. B. Hathaway, and A. E. Clark, J. Appl. Phys. 79, 6213
~1996!.
2 A. E. Clark, M. Wun-Fogle, J. B. Restorff, and J. F. Lindberg, IEEE Trans.
Magn. 29, 3511 ~1993!.
3 J. A. Dooley, C. A. Lindensmith, R. G. Chave, N. Good, J. Graetz, and
B. Fultz, J. Appl. Phys. 85, 6256 ~1999!.
4 R. Chave, C. Lindensmith, J. Dooley, B. Fultz, and M. Birsan, NASA
Tech Briefs 23, 44 ~1999!.
5 J. Dooley, N. Good, J. Graetz, R. Chave, and B. Fultz, Adv. Cryog. Eng.
46, 383 ~1999!.
6 J. Graetz, N. Good, J. Dooley, R. Chave, and B. Fultz, J. Appl. Phys. 87,
5795 ~2000!.
7 R. E. Green. Treatise on Materials Science and Technology, Vol. 3 ~Aca-
demic, New York, 1973!, p. 53. AIP license or copyright, see http://jap.aip.org/jap/copyright.jsp


Magnetomechanical damping by polycrystalline TbDy

JOURNAL OF APPLIED PHYSICS VOLUME 91, NUMBER 10 15 MAY 2002Magnetomechanical damping by polycrystalline TbDy
N. Good and J. Dooley
Jet Propulsion Laboratory, 4800 Oak Grove Avenue, Pasadena, California 91109
B. Fultz
Division of Engineering and Applied Science, California Institute of Technology, Pasadena,
California 91125
Vibration damping in polycrystalline TbDy alloys was studied at cryogenic temperatures.
Mechanical hysteretic losses were measured at various strains, frequencies, and loading
configurations at 77 K. Some textured TbDy materials demonstrated 22.6% energy dissipation in
mechanical measurements at low frequency~0.01 Hz! and a mean logarithmic decrement of 0.23 at
a higher frequency~25 kHz!. Ultrasonic velocities of longitudinal and shear elastic waves were
measured on single and polycrystalline TbDy; little variation in ultrasonic velocities was found even
for samples with large variation in crystallographic texture and magnetomechanical properties.
© 2002 American Institute of Physics.@DOI: 10.1063/1.1452217#ic
be
tic
st
in
cr
gy
n
ag
er
ec
b-
m
ve
-
n
t
al
he
th
e
cal
re
for
nt
for
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ri-
-
ed
con-
ci-
a
,
i-
lear
les.
s of
zo-
s of
und
en
ply
tru-INTRODUCTION
Ferromagnetic TbDy alloys exhibit giant magnetostr
tion, approaching 1% at saturation. This large coupling
tween mechanical energy and magnetic energy enables
dissipation of vibration through the dynamics of magne
domain reorientation. These processes are subject to hy
etic losses and result in mechanical damping. The damp
depends on the magnetomechanical coupling factor des
ing the efficiency of converting elastic to magnetic ener
the magnetic anisotropy describing the difficulty of mome
rotation, the Young’s modulus, the magnetization, the m
netostriction, and the crystallographic texture.1 These prop-
erties and hence the damping characteristics of the mat
can be optimized through microstructural control. We exp
the damping of optimized polycrystalline TbDy to be su
stantial based on its large magnetostriction, magneto
chanical coupling factors as high as 0.75,2 and the relatively
large hysteresis measured in curves of magnetostriction
sus applied field.3–5
In previous work with polycrystalline TbDy, we mea
sured quasi-static magnetomechanical energy dissipatio
the ratio of the area of the stress–strain hysteresis loop to
mean area under the loading and unloading curves,DE/E, at
;0.01 Hz.6 The energy lost is the product of the fraction
dissipation with the total potential energy stored in t
sample. The fraction of mechanical energy dissipated in
material was 19.2% over a range of 0–27 MPa for comm
cial purity TbDy textured alloys at 77 K.7820021-8979/2002/91(10)/7824/3/$19.00
Downloaded 12 Jan 2006 to 131.215.240.9. Redistribution subject to AIP-
-
the
er-
g
ib-
,
t
-
ial
t
e-
r-
as
he
e
r-
EXPERIMENT
The TbDy alloys were prepared as drop-cast, cylindri
ingots which initially had a radial texture. The ingots we
cold-rolled by 35% in thickness and annealed at 950 °C
1.5 h. The plane-rolling deformation is performed to reorie
the grains such that the hardc-axes lie in the direction of
applied deformation stress, and the annealing allows
strain relief and grain growth. A second cold-rolling defo
mation of 55% and heat treatment at 350 °C further reo
ented the grains in the samples, which measured 938
34 mm ~commercial-grade! and 173534 mm ~high-
purity!. The well-definedc-axis grain orientation was con
firmed by thermal expansion analysis of the textur
samples, an as-cast specimen and a single crystal TbDy
trol, the results of which are summarized in Table I. Spe
mens were prepared from commercial-grade TbDy with
typical purity of 99.7%, with the main impurities being Ta
O, and N, and from high-purity 99.94% TbDy. Optical m
croscopy showed large variations of grain sizes and no c
differences between commercial and high-purity samp
The processed samples exhibited magnetostrictive strain
up to 56% of single crystal values.3–5
Ultrasonic measurements were made by affixing a pie
electric transducer to the specimen, introducing a serie
elastic pulses at 5 MHz, and measuring the round-trip so
wave propagation time with an oscilloscope. A screw-driv
Instron load frame was operated in stroke control to ap
compressive stresses to a prismatic bar of TbDy insTABLE I. Thermal expansion analysis summary of polycrystalline and single crystal TbDy.
Sample
x-axis
expansion
1026/K
y-axis
expansion
1026/K
z-axis
expansion
1026/K
x1y/
2z
Tb60Dy40 , single crystal 3.3 3.3 14.7 0.22
Tb76Dy24 , as-cast, 99.7% purity 5.4 7.1 8.1 0.77
Tb76Dy24 , textured, 99.94% purity 6.2 5.2 10.7 0.53
Tb76Dy24 , textured, 99.7% purity 4.2 5.3 12.1 0.394 © 2002 American Institute of Physics
 license or copyright, see http://jap.aip.org/jap/copyright.jsp
7825J. Appl. Phys., Vol. 91, No. 10, 15 May 2002 Good, Dooley, and Fultz
Downloaded 12 JaTABLE II. Fractional dissipation and Young’s modulus of TbDy for various applied stress as at 77 K.
Sample
Applied stress
range~MPa!
Strain range
~ppm!
Fractional
energy
dissipation
Young’s
modulus
~GPa!
Tb76Dy24 , 0–36 0–2150 13.8% 17.2
a
polycrystalline 0–14 0–900 16.7% 15.6
99.94% purity 14–28 1100–1750 12.9% 21.5
Tb76Dy24 , 0–27 0–2700 19.2%
a 10.0a
polycrystalline 99.7% 0–10 0–900 22.6% 10.5
purity 10–20 1250–2100 16.5% 13.3
aPreviously reported values~Ref. 6!.ur
th
m
ic
t
la
re
ti
t-
al
. 1
rg
a
%
o
f
s
d
s
t
r
ed
the
on-
les
ile
ric-
cial-
he
es.
ured
an
we
d
les
s,
ed
the
a. A
of
an
ib-
e
mented with electrical resistance strain gauges. Meas
ments were performed at room temperature and with
sample immersed in liquid nitrogen (LN2). The stress–strain
data showed magnetomechanical hysteresis when the sa
was at 77 K. High-frequency dynamic magnetomechan
damping measurements were made for comparison with
quasi-static results. The sample rested on an aluminum p
within a solenoid while immersed in LN2. A mechanical
impulse was imparted to the sample and the induced cur
in the solenoid was measured.
RESULTS
Further analysis of the previously reported quasi-sta
minor loop stress-strain curves6 hows a number of interes
ing relationships summarized in Table II, with a typic
TbDy stress-strain curve at 77 K and 300 K, shown in Fig
The commercial-grade specimen consistently showed la
strain amplitudes for the same applied stresses as comp
to high-purity specimens. For the ranges measured, a 27
35% larger fractional energy dissipation was measured
commercial-grade specimens, with the highest ratio seen
the minor loops at low amplitudes. At low frequencie
DE/E of the minor loops varies inversely with the applie
stress; for example, the commercial purity specimen show
DE/E522.6% over a range of 0–900 ppm, compared
DE/E516.5% over a range of 1250–2100 ppm—a diffen 2006 to 131.215.240.9. Redistribution subject to AIPe-
e
ple
al
he
te
nt
c
.
er
red
–
n
or
,
a
o
-
ence of 37%. In general, minor loops at lower appli
stresses exhibited lower Young’s moduli as measured by
slopes of the stress–strain curves.
Measurements of ultrasonic velocities of shear and l
gitudinal waves in single crystal and textured TbDy samp
at room temperature are summarized in Table III. Wh
fairly large differences in magnetostrictive and magnetost
tive damping performance were seen between commer
grade and high-purity samples of polycrystalline TbDy, t
ultrasonic measurements revealed only small differenc
Nevertheless, we expect a correlation between the meas
ultrasonic velocities and the magnetization arising from
elastic wave traveling through the material. In addition,
include in Table III values of Young’s modulus calculate
from the ultrasonic velocities of the polycrystalline samp
determined from the formulaY5rVl
2(12n)/(11n)(1
22n), with Poisson’s ration5(Vl
2/Vt
222)/2(Vl
2/Vt
221)
with Vl and Vt being the longitudinal and shear velocitie
respectively.7 These results agree well with our measur
room temperature Young’s moduli in Table II.
Several aspects of the magnetoelastic behavior of
samples are apparent from the dynamical damping dat
typical result is shown in Fig. 2, with the induced voltage
the solenoid~proportional to current! plotted versus time.
Since the magnetic sample is excited mechanically by
impact force, the decay of the inductive pickup can be attr
uted to the dissipation of vibrational energy within thy at
urve andTABLE III. Ultrasonic velocities of shear and longitudinal waves in single crystal and polycrystalline TbD
room temperature. Room temperature Young’s moduli as measured by the slope of the stress–strain c
derived from ultrasonic velocity measurements.
Sample
Ultrasonic velocity~km/s!
Measured
Young’s
modulus
~GPa!
Derived
Young’s
modulus
~GPa!Shear Longitudinal
Tb, single crystal
c-axis
1.70 3.23
Dy, single crystal,
c-axis
1.71 3.09
Tb60Dy40 , single crystal,
b-axis
1.64 2.89
Tb76Dy24 , polycrystalline
99.7% purity
1.60 3.05 49.6 54.1
Tb76Dy24 , polycrystalline
99.94% purity
1.60 3.00 57.2 55.2 license or copyright, see http://jap.aip.org/jap/copyright.jsp
s
2
ol
ic
g
-
.
ng
e
ing
is
on
sys-
oil
less,
of
ear-
ses
uri-
ible
ag-
er-
a-
-
ea-
si-
for
asi-
g-
ly-
gs
the
ng
s-
tal
The
i-
the
th
ns.
nd
A
ng.
ine
7826 J. Appl. Phys., Vol. 91, No. 10, 15 May 2002 Good, Dooley, and Fultzsample. The approximately 35–40 ms period correspond
sound velocities of 1.6–1.8 km/s across a specimen of 3
mm. These are similar to measured sound velocities in p
crystalline TbDy of 1.7 km/s and 2.9 km/s for ultrason
shear and longitudinal waves, respectively.
The corresponding mean logarithmic decrementd
5DE/2E5 ln(An /An11) is often used to describe the dampin
capacity of materials, withAn corresponding to the vibra
tional amplitude of thenth oscillation of a vibrating element
By fitting the peaks of the oscillations in Fig. 2 to decayi
exponential curves, we observe a decay in the amplitud
the signal peaks corresponding tod50.23. This is within a
FIG. 1. Quasi-static magnetoelastic damping of Tb76Dy24 ~99.7% purity! at
77 K and 300 K.
FIG. 2. Dynamic magnetoelastic damping signal from polycrystall
Tb60Dy40 at 77 K.Downloaded 12 Jan 2006 to 131.215.240.9. Redistribution subject to AIPto
.4
y-
of
factor of 2 of our measured low-stress quasi-static damp
capacities of TbDy alloys shown in Table II. This variation
not unexpected owing to the slightly different compositi
and a number of additional damping sources in the test
tem, for example, the interface of the specimen with the c
and the presence of external noise sources. Neverthe
from these data the high-frequency damping capacity
TbDy is apparent.
DISCUSSION
At lower stresses, the magnetization proceeds by r
rangement of domain morphology, which is subject to los
associated with microstructural features. Perhaps the imp
ties in the commercial-grade material could be respons
for additional dissipation. Higher stresses can cause the m
netization to orient out of the basal plane along high
energy directions, causing an effective stiffening of the m
terial and a higher elastic modulus as shown in Table I.
Polycrystalline TbDy alloys with crystallographic tex
ture were prepared, and their mechanical hysteresis was m
sured. An approximately 30% larger fractional energy dis
pation was found for commercial-grade materials than
high-purity materials. At 25 kHz, ad50.23 was measured
for TbDy at 77 K, comparable to the largest measured qu
static fractional energy dissipation of 22.6%. The high ma
netomechanical damping capacities of textured TbDy po
crystalline alloys at low frequencies in quasi-static loadin
and at higher frequencies in cyclic loading demonstrate
potential use of this material in cryogenic vibration dampi
applications.
ACKNOWLEDGMENTS
The authors thank Dr. A. E. Clark for stimulating discu
sions, Dr. M. Wun-Fogle for the use of several single crys
specimens, and Dr. T. Lograsso for preparing the ingots.
authors acknowledge support from NASA’s Microgravity D
vision. The Jet Propulsion Laboratory is operated by
California Institute of Technology under contract wi
NASA.
1J. P. Teter, K. B. Hathaway, and A. E. Clark, J. Appl. Phys.79, 6213
~1996!.
2A. E. Clark, M. Wun-Fogle, J. B. Restorff, and J. F. Lindberg, IEEE Tra
Magn.29, 3511~1993!.
3J. A. Dooley, C. A. Lindensmith, R. G. Chave, N. Good, J. Graetz, a
B. Fultz, J. Appl. Phys.85, 6256~1999!.
4R. Chave, C. Lindensmith, J. Dooley, B. Fultz, and M. Birsan, NAS
Tech Briefs23, 44 ~1999!.
5J. Dooley, N. Good, J. Graetz, R. Chave, and B. Fultz, Adv. Cryog. E
46, 383 ~1999!.
6J. Graetz, N. Good, J. Dooley, R. Chave, and B. Fultz, J. Appl. Phys.87,
5795 ~2000!.
7R. E. Green.Treatise on Materials Science and Technology, Vol. 3 ~Aca-
demic, New York, 1973!, p. 53. license or copyright, see http://jap.aip.org/jap/copyright.jsp


http://authors.library.caltech.edu/4216/1/GOOjap02.pdf

Magnetomechanical damping by polycrystalline TbDy

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