LT 21

Proceeding s of the 21st International Conference on Low Temperature PhysicsPrague, August 8-14, 1996
Part $4 - LT Properties of Solids 1: Amorphous solids

Transport and Thermal Properties of Amorphous Mn-Y Alloys
Manabu Ikebea, Hiroyuki Fujishiro a, Yoshihisa Obib, Hiroyasu Fujimori b and Koshichi Noto aa Faculty of Engineering, lwate University, 4-3-5, Ueda, Morioka 020, Japanb Institute for Materials Research, Tohoku University, Aoba-ku, Sendal 980, JapanThe thermal conductivity t:, thermal diffusivity r and electrical resistivity p were measured between 15K and 150K for
Mnl00.xY X binary amorphous alloys which were prepared by high rate de sputtering, ct was measured quasisimultaneously with ~: by an arbitrary heating method. No anomaly associated with spin glass transition was observedin transport properties. The specific heat C was estinmted from the relation C=tz/ct, which indicated the Debye
temperature O0,~250K for Mn52Y48.
1. I N T R O D U C T I O NMagnetic properties of Mn atoms in amorphousalloys strongly depend on their mutual distance andenvironment. As a result, Mn based binary anmrphousalloys exhibit various interesting properties from theviewpoint of the magnetism [1-4]. Magnetic propertiesof amorphous Mnl00.xY X alloys were previously
investigated by the present authors [3]. The acsusceptibility measurement suggested a monotonic
decrease of the spin glass transition temperature T o withincreasing Y concentration X. This paper reports theresults of the thermal and the electrical transportmeasurement on Mn-Y amorphous system. The electron
and phonon contributions to the thermal conductivity ~:were separated by use of the Wiedemann-Franz law. Thespecific heat C was estimated from the ratio of theconductivity and diffusivity. Studies on the thermaltransport in metallic amorphous systems are scarce andaccumulation of the data seems to be necessary.
2. EXPERIMENTAL
Amorphous Mn-Y alloys were prepared in bulk
forms by a high rate de-sputtering technique. All thesamples were conftrmed to have an amorphous structureby X-ray diffraction and compositions were determinedby chemical analyses. Typical sample dimensions were~ 3 x 0.3 x 12ram 3 with a total weight ~50rag. The
electrical resistivity p was measured by a standard fourterminal method and the thermal conductivity ~ wasmeasured by a steady state heat flow method [5].
AuFe(0.07at.%)-chromel thermocouples were used asthermometers. For a typical sample (Mn52Y48) thethermal diffusivity r was also measured by an arbitrary
heating method developed by the present authors [6,7].
For all the measurements, a Gifford-MeMahon cycle He
refrigerator was used as a cryostat.

Czechoslovak Journal of Physics, Vol. 46 (1996), Suppl. $4

3. RESULTS AND DISCUSSION
Fig. 1 shows p vs. temperature T for Mn57Y43,Mn52Y48 and Mn37Y63. The observed p values areabout 3001a~2cm at 15K and about 2601xf~cm at 280K
for all the samples. Relatively large values of p with anegative temperature coefficient are considered to comefrom the amorphous structure of the present Mn-Yalloys. According to our previous report, T~ values ofMn57Y43, Mn52Y48 and Mn37Y63 were estimated to
be about 40K, 35K and 25K, respectively. No anomaly
was observed in tile p vs. T curves associated with thespin glass transition.
Fig. 2 shows K vs. T curves for the corresponding
samples. The r values of Mn-Y are also very small fora metallic system, which may also be regarded as acharacteristic of an amorphous structure. No anomalous
behavior of ~: was observed around T o either.
In Fig. 3 we devided ~ of Mn52Y48 into theelectronic component Ke and the phonon component Kph"
0.4. . . .

i. . . .

iE 0,35. . . .

~MnszY~ |-"MnsTY43 I

0.3
r0 "2 0.

.

.

.

I

''

100
TemperatureII

200
(K)

'!

''300Fig. 1. Temperature dependence of the electricalresistivity of Mn~0o.xYx.

2241

4..

g,Mn,oo.xYx. . . .

i ..... '20,, ,,

^6u4

A

Mn,rY=Mn~.Y,m
9 Mn67Y(3i. . . .

I0,,,I,

50
TemperatureEa=. . . .

1.2.~
230K

OD=250K ~'T".%>-.2Q.

,,,~,3o''''|)')

'

1''',

50

thermal'gO

K o eo~Oo9IC~)hO0 0o O0(0o8a o O e@~e00000000
0 00050
Temperature. - -K e100
(K)

150

Ke was estimated from the Wiedemann-Franz law,(1)

where 1_4)(=2.45 x 10-8 Watt ohm cm/deg) is the Lorentz
number, The values of Ke(T) were almost the same forthe present three MaY amorphous alloys because ofalmost the same p values in Fig. 1. Kph (=K-Ke)
slightly surpassed Ke at high temperatures above 100K.
Kph, however, became overwhelmingly dominant in thelow temperature region below 50K.
In Fig. 4, we show the thermal diffusivity ct ofMn52Y48 which was measured quasi-simultaneouslywith r under an identical experimental setup [6,7]. Thespecifie heat C (per unit volume) can be estimated fromthe relation C=rda. The molar specific heat C M ofMn52Y48 was determined by use of the measured

224200,L~LXLX.A.A.~LXLX,~A LxLXL~LXLX..~., 0.4 ,,,,I"o0.2 O
J . . . .

,. . . .

5010050Temperature (K)Fig. 4. The thermal diffusivity and the estimated specificheat of Mn52Y48 as a function of temperature. Thevalue of the specific heat is normalized by the measured
one at 150K (~27J/molK). Debye specific heat curves
are shown for comparison.
density d=5.0g/cm3. The result is plotted also in Fig. 4.
The behavior of C M corresponds to Debye temperature
OD~250K, though the estimation of the absolute valueof C M is not very accurate due to possible •error inevery K, ct and d determination.

o.. -''"

Fig. 3. Total Jr the electronic contribution Kc and thephonon contribution Kph of Mn52Y48.

Kc(T)=LoT/P(T),~(I)

Mns2Y4a20OEI-100(K)Fig. 2. Temperature dependence of theconductivity.

~~". . . .

"0b-,**!t'*'mttt,~6.6,"'~
9r,

iMns2Y4aE

I0i,,.
0,. . . .

4. S U M M A R Y
The transport and the thermal properties of anamorphous spin glass system Mnl0o.xYx were studied.
No anomaly accompanied with the spin glass transition
was confwmed in the transport properties. The absenceof anomaly near TG in the phonon thermal conductivity
may indicate that the phonon-spin coupling is not sostrong in amorphous Mn-Y system. Quasi-simultaneous
measurement of K and a enabled us to determine thespecific heat of the sputtered amorphous alloy withweight of only about 50rag. The Debye temperature ofMn52Y48 is estimated to be 250K from the specific heat.
The authors wish to thank T. Naito of Tohoku
University for his important contribution.

REFERENCES[1] Y. Endo: Solid State Phys. 5 (1970) 245.
[2] J.J. Hauser et at.: Phys. Rev. B20 (1979) 3391.
[3] Y. Obi et at.: J. Phys. Sac. Jpn. 56 (1987) 1623.
[4] Y. Obi el at.: J. de Phys. C8 (1988) 1097.
[5] N. Hobara et al.: Cryogenic Engineering 28 (1993)
688 (in Japanese).
[6] H. Fujishiro et at.: Cryogenic Engineering 28(1993) 533 (in Japanese).
[7] M. Ikebe el at.: J. Phys. Sac. Jpn. 63 (1994) 3107.

Czech. J. Phys. 46 (1996), Suppl. $4