Superconductivity in FeZr, NiZr and CuZr amorphous metal alloys: Analysis of low temperature specific heat

Solid State Communications, Printed

in Great

Vol. 47, No. 6,

479-483,

pp.

0038-1098/83

1983.

S3.00 + .OO

Pergamon

Britain.

SUPERCONDUCTIVITY

IN Fe-Zr,

ANALYSIS

Ni-Zr

AND

Cu-Zr

AMORPHOUS

OF LOW TEMPERATURE

SPECIFIC

METAL

Press Ltd.

ALLOYS:

HEAT

D.G. Onn and L.Q. Wang Department

of Physics.

University

of Delaware,

Newark,

DE 19711,

U.S.A.

and K. Fukamichi The Research

Institute

for Iron,

Steel and Other

(Received

30 March

Metals.

Tohoku

1983 by A.C.

University,

Sendai-980,

Japan

Chynoweth)

Fe,,,,,_xZrx amorphous alloys are shown to be superconducting for x ; 68 + 2. Comparison of low temperature specific heat measurements for Fe-Zr with previous results for Ni-Zr and Cu-Zr show that the composition trends ofN,(E,) are consistent with recent theoretical models and photoemission results. Furthermore, the factor v = No(EF)(/‘) is composition independent and the same for all superconductors in these three alloy series. From these results we conclude that T, of pure amorphous Zr will be 5.1 K, compared with 0.55 K for crystalline Zr.

BY MEASURING specific show

the low temperature

heat C, of the Fe-Zr that

they

the C, results

supcrconduct establishes

and NO(KF), OD(T)

density

the composition

trends

ing constant

and hence

Delaware

O,(O)

of the electron

Figure

I shows

Comparison results where

of these new results

results

for Ni--Zr

to the decrease

for Cu-Zr

alloys

(I*)

alloys

only

to C,

these alloys

the Debye

apparently

studies

temperature

T, for

before

the onset

here only

related and will

present

results

a more

forx

in

complete

in a future

attributable

in

versally

analysis

In the text

[Zrj

amorphous

one of us (KF)

presents

and were

Zr concentration alloys

l-2

in alloys.

were melt-spun

mm wide

and

2(a)J.

479

in and

concentration

for the

amorphous

= 68 + 3 [see Fig. 2(a)]. (K/atomic

of 0.09

forx

of an up-turn

in the Fe-Zr

For

For

percentage)

(K/atomic

alloys

percent-

which

supcrconduct

the Cu-Zr

5 30 2 5 with

alloys dT,/dx

super01.0.07

a “linear”

phonon

contribution

(UT),

systems

(TLS)

uni-

materials

= 0.05 mJ mol-’

found

[6, 7) by using the averK-*

obtained

measurements

of Cu-Zr

contribution

never exceeds

one percent

alloys

from

low

[2). This

of our C,

in the

state.

In Fig. 2(c), and in Tables

IS to 20pm

in the

no such up-turn

temperature

normal

by

C,

to the two-level

in amorphous

age value ofa

publication

of C’p due

percentage).

We estimated

131. The Fe-Zr

dT,/dx

amorphous

occurs

data for

0.5 K.

the critical

is 0.25

5 37 f 2. [Fig.

(K/atomic

of the

decrease

shows at -

is [ZrJ

dT,/dx

with

conductivity

to

of superconductivity

C, and x measurements

alloys

alloys

age) for Ni-Zr

out

of superconduc-

summary

to the onset

superconducts that

C,

vs T*. The rise in

contribution

to Cp in the form

ofsuperconductivity

Fe-Zr

alloys

ferromagnetism

(CM)

(melt-spun)

and is indepen-

for the magnetic

from

of

one gram in

Cp/T vs T* data for Fe,sZr,,. [Sj sIlow evidence of a magnetic

state.

We conclude onset

CJT

of

as is the rapid

Cp/T. The data for FcJOZr,

of the

we have carried

at University

superconducting

form

in the electronic

and Fe,%r10

compared

measurements

a trend

behavior

We present

of both

while

We can then estimate

susceptibility

this series showing

parameters

FeMZr,, contribution

Zr as 5.1 f 0.2 K.

In addition

tivity.

our

is the

of all three

on Zr concentration

pure amorphous

spin-glass

element,

concentrations

of the 3d element.

with

that 17 = NO(EF)(/*).

matrix

series studied

is dependent

magnetic

shows

is the electron-ion

same for all zirconium 3d-Zr

[2]

for f’c--Zr

[ 11 and published

alloys

standard

typical

in the standard

superconducting

previous

by the

C’, was measured

were all about

sarnplcs

T, is apparent

C’, at

arc

found.

dent

technique

141. C,

f%25Zr,s

coupl-

factors

technique.

mass.

and

equation,

--phonon

its contributing

to be amorphous

X-ray

using a heat-pulse

of

of the

of states Iv,(ly~)

temperature

T,. From the McMillan

to

h,,

trends

All were confirmed

Dcbye-Schcrrer

we

for x 5 68 + 2. Analysis

and of the Dcbyc

in addition

thin.

to 40K)

alloys

the composition

and bare electronic

crlhanccd

(0.8

amorphous

I and 2, we show 1Y-,(E=)

WI

5.11 0.367 174 2.17

80 5.45 0.336 180 2.31

75 f 0.04 -+0.002 +2 kO.04 6.23 0.306 185 2.64

70

Fe,oZrw Fe,Zr,s FeMZr,

1.31 1.48 1.85

2.17 2.3 1 2.64

3.07 + 0.01 1.82 + 0.01 - 0.50 0.65 0.56 0.43

(eV-’ at-‘)

(eV_’ at-‘)

2)

0.27 f 0.02 193 *5 1

=

N&-F)

f 0.05 f 0.00 1 +1 2 0.05

65

&(EF)

&J

Table 2. Parameters related to superconductivity in Fe2,,Zrso, Fe2sZr2, arrd Fe,Zrm

Cfi).

rt 0.05 + 0.001 *1 + 0.05

’ Values affected by magnetic contribution

iV7 (EF) (eV_’ at-‘)

e,(o)

-y(mJ mol-’ Kb2) fl (mJ mol-’ Kg)

X

Table 1. Parameters of Cp for the amorphous alloys Fe,,_,Zr,

0.50 0.38 0.23

(eV at)

&J&@-F)

0.25 + 0.02 198 +5 a

1.27 x lo6 1.01 x106 0.64 x IO”

(gm K2 eV at)

x,MO~(0)/N(J(/:‘jv)

0.13 + 0.03 248 +7 B

10 a

60 a

:: > F:

: rl

S

iIl

% 0

$ c1 ;: Y

k -2 ‘i’ p

-z 2

?

<

2 =!

2

3 ?t

E

SUPERCONDUCTIVITY

Vol. 47, No. 6

IN Fe-Zr,

Fig. 1. Cp/Tas a function of T3 for amorphous

AMORPHOUS METAL ALLOYS

481

Fe2sZr7s.

. FeZr

‘\ t’

AND Cu-Zr

\

\

2-

5

Ni-Zr

\

I\ ,

oN12r

\

-

\ i

i\ I

,

I I

(b)

i

240-

/; ;

-c)6

0

2200

s _0200*

aa

+

. FeZr

* I80

-

0 NiZr

+ 8

t zr 1 Fig. 2. (a) Superconducting transition temperature as a function of [Zr]. (b) Debye temperature OD(0) as a function of [Zr]. (c) Enhanced and bare electronic densities of states N,(EF) and IyO(E~) as a function of [Zr] for the Fe-Zr and Ni-Zr amorphous alloys. and N,,(EF) compared with values of Ni-Zr amorphous alloys [I J. While N(EF) decreases rapidly with [Zr] for the Fe-Zr alloys it increases equally rapidly with [Zr] in the same composition range for Ni-Zr alloys. Here we discuss only two important conclusions from our results. 3d-Zr alloy bard structures. Recent photoemission studies of Zr based amorphous alloys [8 ] show the following characteristics of the band structure: (1) two separate peaks related to the d-bands of the components. (2) d-band peak splitting increasing with the increasing number of groups between the two components in the periodic table and (3) that the high binding energy peak is mainly related to the d-states of the 3d or late transition metal while the peak near EF is related to the

, -04

-02

I EF

I

02

I

I

04

06

Fig. 3. (a) Sketch of the probable electronic density of states for the Ni-Zr alloys with the solid line representing the higher Ni concentration. (b) Sketch of the probable electronic density of states for the Fe-Zr alloys with the solid line representing the higher Fe conccntration. Both sketches are referred to a common E, for comparative purposes. Zr d-states. These features appear to be shared by crystalline alloys of the same composition [9]. Theoretical models show the same general pattern in the band structure and additionally confirm some hybridization features. Fujiwara has calculated the electronic band structure of amorphous Cu-Zr alloys as a function of [Zrj [IO] while Fairlie et al. have studied the structure of MmZr,,, (M = Pd, Fe, Co, Ni and Cu) 1111. Combining these experimental and theoretical results we can sketch the probable No(E) for Ni-Zr and Fe-Zr alloys relative to a common Fermi level as shown in Fig. 3. The position of the 3d element peak in No(E) relative to EF dictates the trend of!&(EF) with [Zr]. For Ni-Zr EF is in the Zr d-band peak and consequently rises with [Zr] while for Fe-Zr EF is within the Fe 3d-band peak and hence decreases with increasing [Zr]. These trends in No(EF) are seen to be consistent with the trends from our specific heat studies shown in Fig. 2(c). Factvrs affecting

T, fix the 3d-Zr amorphous coupling constant X, is

alloys. The electron-phonon

defined by: x

=

P

M~-FN~2) Mu2)

’

SUPERCONDUCTIVITY

482

Fe-Zr,

IN

Ni-Zr

AND Cu-Zr

Vol. 47, No. 6

AMORPHOUS METAL ALLOYS

ofNo

and (1’)

and Ni-Zr

alloys

ment

those

with

composition

exactly

compensate

in the Fe-Zr

to give values of q in excellent from

the Cu-Zr

variations

alloys

of NO(EF)

agree-

for which

and (1’)

the

are much

weaker. From alloys

Fig. 4(d)

studied

we conclude

to date,

This value of 9 combined of 0,(O)

from

amorphous of

with

Fig. 2(b)

Zr permits

A,=

[equation

that

ten times

us to make an excellent and:

= 5.1 f 0.1 K. This value is about

T, for crystalline

however,

A,

(c) ApM0,(0)2/No(~~)

into

account

apparently

universal

with

higher

series with

higher

where

(i2)

is the electron-ion

ion mass and (w2)

quency

factor

experiments (w*)

defined

by McMillan

are needed

that (w2)

duce a small error trend

in phonon

sition (f2)

“C&(O)

related

dependence for Fe-Zr.

which

our C,, results

shows

T, trends in Fe-Zr

the compo-

A,. X,,/N,,(EF) with

the dominance

and

4(b)

and 4(c) show

of A,, over NO(EF)

itself

parameters

are in clear disagreement

Varma

with

and Dynes

line transition

composition.

[I?] originally

metal

superconductors

extended

to some amorphous

transition

metal

(12)/M(w2)

alloy

is constant

Varma-Dynes

and in 4d-4d

conclusion,

q = N&,)(f2)

the 3d-Zr including

alloys Cu-Zr

metal

alloys.

Fig. 4(d)

for which

For a given

amorphous

alloys

independent Fe-Zr,

Ni-Zr

that the for all of available,

composition

amorphous with

previous

show the following:

of superconductivity

in the number

of groups

in

the two components.

in N,,(E,)

are consistent

studies

and with

both

with

theoretical

temperature

depends

only

of the

Sd-Zr amor-

on Zr concentration

and is

of the 3d element. 77 = N0(E~)<12)

and Cu-Zr

is constant

superconducting

for

amorphous

trends

the results

(3) and (4) above

we can

T, of pure amorphous Zr would be 5.1 f 0.2 K compared with 0.55 K for crystalline Zr.

estimate

that

REFERENCES

I. 3 _.

alloys

to the

constant

data is presently

[ 2 I. The opposite

phous

asserts that

shows

alloy

models.

of

for crystal-

[ 131. In contrast

is remarkably

of these

the model

but recently

series this model

this has been demonstrated

of (12)/M(W2)

developed

To find

alloys.

amor-

The trends with

series if one

dependence.

for Fe-Zr

alloys

between

photoemission

(5) Combining

the trends

and of (f2)

alloy

combined

for the onset

table

(4) The factor

alloys.

Figures

recent

Figs. 2(a)

and Ni-Zr

when

an increase

(3) The Debye

4(a) compared

and (c) clearly

factor

to intro-

[Zr]

(2) The trends

the usual

is known

of the parameters

T,

7) values.

and Cu -Zr

with

the periodic

values of

2 we show

of

the highest

of 17 and the

O,,(O) vs [Zr]

alloys,

The

decreases

parameters.

and Table

Figure

(I)

fre-

values but gives the correct

in determining phous

accurate

also represents

in the 3d-Zr

0.55 K)

M is an

phonon

of such data we make

in absolute

In Figs. 4(a)-(c)

element,

17 ]. Tunneling

to provide

but in the absence

assumption

matrix is an average

Zr (-

Our estimate

T, one must seek amorphous

In summary, superconducting data for Ni-Zr

average

0.062.

the constancy

alloys

and

is only

Zr probably

T, that can be achieved takes

(b) X,/A’,,(EF); (d) (I IN,(EF).

estimate

using the McMillan

(2)

T,(u-Zr)

for amorphous

as func(a) A,;

zirconium

(4)]

the value of

for which,

to superconductivity amorphous alloys:

extrapolation

t, WMO)12~

We find

Fig. 4. Parameters related tion of [Zr] for the 3d-Zr

x 106(gmK2).

reasonable

to a value of 150 K for pure

T, for pure amorphous

equation

that for the 3d-Zr

~1 = (1.7 f 0.1)

3. 4. 5.

D.G. Onn, L.Q. Wang & K. Obi, Solid Sfafe Commun. 46,37 (1983). G. von Minnigerode & K. Samwer, Physica Scripta 108B. 1217 (1981);K. Samwer & H. v. LGhneysen (to be published). D.G. Onn. L.Q. Wang & K. Fukamichi (to be published). D.P. Goshorn. D.G. Onn & J.P. Remeika, Phys. Rev. B15.3527 (1977). Y. Obi, L.Q. Wang, R. Motsay & D.G. Onn,J. A&. Phys. 53,2304 (1982).

Vol. 47, No. 6 6.

7. 8. 9. 10.

SUPERCONDUCTIVITY

IN Fe-Zr,

R.O. Pohl, Amorphous Solids: Low Temperature boperfies, (Edited by W.A. Phillips), SpringerVeriag, Berlin (1981). W.L. McMillan, Phys. Rev. 167.33 1 (1968). P. Oelhafen, E. Hauser & H.J. Giintherodt, Solid Sfate Commun. 35.1017 (1980). A. Amamou, R. Kuentzler, Y. Dossman, P. Forey, J.L. Glimois & J.L. Feron,J. Phys. F: Met. Phys. 12,2509 (1982). T. Fujiwara,J. Phys. F: Met. Phys. 12,251 (1982).

Ni-Zr 1 1. 12.

13.

AND Cu-Zr

AMORPHOUS METAL ALLOYS

483

R.H. Fairlie, W.M. Temmerman & B.L. Gyorffy, J. Phys. F: Met. Phys. 12. 1641 (1982). C.M. Varma & R.C. Dynes, Superconductiviry in d- andf_Band Metals, (Edited by D.H. Douglass), p. 507. Plenum Press, New York (1976). W.L. Johnson & M. Tenhover, The Magnetic Chemical and Structural Properties of Glassy Metallic Alloys. (Edited by R. Hasegawa), Chemical Rubber Co. Press, Boca, Florida (1982).