ELSEVIER Physica C 275 (1997) 333-336

PHYSICA ®

Superconductivity in the metallic amorphous alloy Zr41.2Ti 13.8 C u 12.5 N i 10 B e 22.5

A. Gerber a, A. Milner a, A. Voronel a, A. Rubstein a, Yu. Rosenberg a,l, M.P. Macht u

" School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Ramat Avio, 69978 Tel Aoio, Israel

b Hahn-Meimer-lnstitute Berlin, Glienicker Strasse 100, 14109 Berlin, Germany

Received 16 August 1996; revised manuscript received 29 December 1996

Abstract

We report an observation of the superconducting transition in the metallic amorphous alloy Zr41.2Ti13.8Cu12.sNi~oBe22.5. The resistive superconducting transition temperature is 1.1 K and the temperature gradient of the upper critical field ( - d H c 2 / d T ) r c is 2 T/K. Annealing of the alloy leads to a reduction of T c by 0.2 K and a decrease of Hc2 to ( - d H c J d T ) r c = 1 T/K.

Keywords: Superconductivity; Metallic glass; Zr41.zTi x 3s Cu J 25 Ni i oBez2.5

Recently, a new class of " b u l k " metallic glass forming alloys has been found [1-3]. These alloys exhibit remarkable resistance to crystallization in their liquid state permitting thermophysical studies of the melts over previously unaccessible tempera- tures in the deeply undercooled region [2]. The en- tropy of the bulk glasses is found to approach the values of the crystalline state, which makes them physically interesting amorphous systems close to "ideal glass" [4]. The remarkable resistance to crys- tallization originates from the high density (high atomic packing) in their amorphous state which slows down an atomic transport and, therefore, prevents

Present address: Wolfson Applied Materials Research Centre, The Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978, Israel.

them from both separation and ordering of any kind. Low temperature properties of these materials are of special interest. In particular, one can expect the development of superconductivity in these dense metallic systems with highly disordered structure. We, herewith, report the low temperature electric transport and magnetic susceptibility study and an observation of the superconducting transition in the Z r - T i - N i - C u - B e alloy.

The palets of Zr41.2Tit3.sCu12.sNi]oBe22.5 were produced in the Structural Research Laboratory of the Hahn-Meitner Institute by cooling from the melt at the rate of about 1 K / sec . X-ray diffraction pattern was measured and analyzed in Wolfson Ma- terial Research Center at Tel Aviv University. Fig. 1 shows the X-ray diffraction picture of our sample before and after annealing. One can see that while the initial sample is fully disordered, its structure

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334 A. Gerber et al./Physica C 275 (1997) 333-336

400

~ " 300

2oo

1 O0

(a)

/ ¢

/ /

/ '

J '

20 Diffraction

4'0 ' - 60 8'0 I 0 0

angle 2 0

(b) 600

4oo

200

0 20 4 0 6 0 g0

Diffraction angle 2(9

Fig. 1. X-ray diffraction patterns of the same Zr4L2Ti~3.sCuz2.5 NiloBez2.5 sample before (a) and after (b) annealing at 550°C.

after annealing exhibits diffraction peaks characteriz- ing the crystallized constituting components: Zr2Cu, TiBe2, CuTi 2 and others not identified.

Electrical resistance of the samples was measured by a four probe technique in a dc mode. Magnetic permeability was measured in a two coils configura- tion with a sample installed between the driving and pick-up coils.

Resistivity of the amorphous (A) and annealed (B) samples was measured from room temperature down to 0.3 K. The result is plotted in Fig. 2. The glass sample contains atoms with unusually high size disparity (size ratio of Be to Zr is 1.12/1.6 = 0.7) and this produces an extremely high atomic disorder in the solid resulting in high electrical resistivity values. The oversimplified estimation based on the Drude model [5] gives for a mean free path of electron a value ( 1 - 3 ) × 10 -7 cm . This roughly corresponds to a size of a possible grain 50-250 atoms which is still small enough to be distinguished by usual means.

The annealing results in a drop of the room temperature resistivity from 195 IXf~ cm in the amor- phous sample A to 75 ixll cm in the annealed sample B. The resistivity temperature dependence changes as well from the semiconductor-like with d p/dT < 0 in sample A to the metallic-like (dp/dT> 0) in the annealed sample B. The ratio of the helium to room temperature resistivity p(4.2 K)/p(300 K) decreases from 1.05 for sample A to 0.65 for sample B. The resistivity temperature coefficient dp/dT is usually correlated to the resistivity value p. Following Mooij [6] the slope dp/dT becomes negative above a critical resistivity Pc = 150 Ixlq cm. Although not universally accepted [7] the criteria is often met, including our data. The amorphous sample with a room temperature resistivity 195 ixf~cm demon- strates a negative slope dp/dT, whereas the an- nealed sample with p (300K)= 75 IXf~ cm shows a positive dp/dT down to the superconducting transi- tion temperature.

2 0 5 x 1 0 "4

2 .00xlO ~

1 9 5 x 1 0 ~

(a)

50 100 150 200 250 300 T (K)

( 7×10 .5

6x10 -s -

5XI0 --~

, I I , _ _ I , _ _ ~ I i _ _

0 50 100 150 200 250 300

T ( K )

Fig. 2. Resistivity as a function of temperature of the amorphous (a) and annealed (b) samples of Zr41.2Til3.sCul2.sNi joBe225.

A. Gerber et al . / Physica C 275 (1997) 333-336 335

I. Superconducting transition

Low temperature resistance and magnetic perme- ability of the amorphous sample are plotted in Fig. 3. Both experiments demonstrate unambiguously the presence of the superconducting transition: resistance drop below the resolution of the measuring equip- ment, followed by a development of a strong dia- magnetic shielding. As expected for the supercon- ducting transition of a finite width the onset of the susceptibility transition corresponds to the offset of the transport transition, when an infinite supercon- ducting path is created.

As shown in Figs. 2 - 4 both amorphous and an- nealed alloys pass the superconducting transition at low temperatures. The normalized resistive super- conducting transition at zero magnetic field of amor- phous (A) and annealed (B) samples is plotted in Fig. 4 as a function of temperature. The critical temperature T c is defined at the point at which the resistivity reaches half of its normal state value. T c = 1.1 K in the amorphous sample and drops to T c = 0.9 K in the annealed sample. The transition is sharper in sample A, the transition offset temperature (temperature at which the resistivity is restored to its normal state value) is the same in both samples. The latter can be an evidence of an incomplete crystal- lization of the material, i.e. a fraction of the samples' volume remained in an amorphous form after the thermal treatment.

The critical temperature values defined as the middle points of the magnetic permeability transi-

Amorphous a l.e-,..~. ~=eem~Ra~ 25

12 / 20

10

15 ~o

~ 10 6

5 4

, - ~ , ~ ' " " , ° o o , , , 0

0.7 0.8 0.9 1.0 11 1.2 ] 3

T (K)

Fig. 3. Resistance and magnetic permeability of the amorphous Zr41.2Til3.sCul2 5NiloBe22 5 sample as a function of temperature.

c.

1.0

0.5

0 a

x b

X O

X

X O

O

X O O

X O

x o ~ mu ~ ~ ~ooooooO

05 10 1.5 T (K)

2.0

Fig. 4. Normalized zero magnetic field superconducting transition of the amorphous (a) and annealed (b) samples.

tions are 0.96 and 0.35 K for the amorphous and annealed samples respectively.

2. Magnetoresistance

Resistivities of the amorphous (A) and annealed (B) samples as a function of an applied magnetic field at temperatures below the critical are shown in Fig. 5a and 5b. The upper critical field Hc2 defined as a midpoint of the transition is plotted in Fig. 6 as a function of temperature. HcE(T ) of both samples varies linearly in the vicinity of T c with the slope dHcE/dT= - 2 . 0 4 T / K and - 1 T / K for the amor- phous and annealed samples respectively. The transi- tion width H is defined as AH = H(90%)-H(10%), where H(90%) and H(10%), are the field values at which 90% and 10% of the normal state resistivity are restored. A H is significantly wider in the an- nealed sample, which as well can be caused by an incomplete crystallization. In both samples the transi- tion broadens at lower temperatures.

We can compare our results with those published for other superconducting amorphous metals.

(a) The transition temperature T~. A heat treatment, and in particular, an intensive

one, leading to the phase separation and crystalliza- tion of the amorphous metal typically results in a decrease of the critical temperature. This trend was found in annealed Zr60Cu4o [8], Zr70Cu30 [9], Zr76Cu24 and Zr76Ni24 [10], Zr3Pd [1 l]. We find the same behavior in Zr41 2Ti 138Cu ~25Ni ~0Be22.5.

336 A. Gerber et al./Physica C 275 (1997) 333-336

( b ) H c 2 ( T ) The temperature gradient of the upper critical

field Hc2 near T~ (-dHca/dT)T ~ of amorphous Zr41.2Tilx8Cu12.sNi10Be22.5 is about 2 T / K and de- creases to 1 T / K in the annealed sample. The .value 2 T / K falls within the range 1.5-3 T / K usually found in Zr, Nb, Ni and Mo - based amorphous superconductors [8-12]. The M-based amorphous superconductors are the exception with much lower values of (-dHc2/dT)rc of the order of 0.2-0.3 T / K [13].

To conclude, the metallic amorphous alloy Zr4~.2Ti ~3.8Cu t2.sNi ~0Be22.5 was found to become su- perconducting. At zero magnetic field the resistive superconducting transition temperature is 1.1 K and the temperature gradient of the upper critical field

(a)

2O

E 10

(b) :o

I Allloipl+otlS

+ +

4

/ /

,P /

' . /

_ . J ~ : __1 , ~ _u+l i 5

y

- o ~4K ;; ' o 0 44 K

,' ~+ 0 52K ' " 0 63K

X ' • 074K d' • 086K

~;; • 0 97K • I IlK

I 0 ] 5 20

H IkO¢)

1 5 -

~" 1 0 - ' ' ' d ' d - -o - 044K ,~ " " ? ,° " ~-052K • ' ,' d; d

j - ,' Y ,' ff d' • 074K 05 " ' X , • 086K

,' ,4 ,d' ,d a -~-- 097K l ig =' 4 , d d - • 1 IlK

0 0

0 5 10 15

It ,kOe)

Annealed

/ °~,

o 034K

20

Fig. 5. Resistance as a function of magnetic field of the amor- phous (a) and annealed (b) samples at different temperatures below T~.

,5 2o7°7s

"6" 10 ~ c~(T) = 2"04x(Tc 'T)

o 0.4 0.6 0.8 1.0

r (K)

F i g . 6 . U p p e r cr i t i ca l f i e l d a s a f u n c t i o n o f t e m p e r a t u r e o f the

a m o r p h o u s a n d a n n e a l e d s a m p l e s o f Zr41 .2Ti 1 3 8 C u 12.sNi ioBe22 .5 .

(-dHc2/dT)rc is 2 T /K . Annealing of the alloy leads to recrystallization and a reduction of T~ by 0.2 K and a decrease of (-dHc2/dT)rc to 1 T/K.

This work was supported by the Israel Ministry of Science and the Arts, grant No. 6277295.

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