Superconducting aluminum electrodes have typically been used to measure the spin polarization of tunneling current using superconducting tunneling spectroscopy but at temperatures well below 1K. Using NbN superconducting electrodes we show that measurements at elevated temperatures (1.2K) are possible, thereby eliminating the need for the He3 dilution refrigerators. Tunneling spin polarization values can be extracted from the experimental data by fits using a strong coupling theory of the quasiparticle density of states of NbN. Nb and Ta electrodes were also explored but NbN, with its much lower spin-orbit scattering rate, yet higher superconducting transition temperature, is the most attractive.

1.
J. S.
Moodera
,
L. R.
Kinder
,
T. M.
Wong
, and
R.
Meservey
,
Phys. Rev. Lett.
74
,
3273
(
1995
).
2.
T.
Miyazaki
and
N.
Tezuka
,
J. Magn. Magn. Mater.
139
,
L231
(
1995
).
3.
S. S. P.
Parkin
,
X.
Jiang
,
C.
Kaiser
,
A.
Panchula
,
K.
Roche
, and
M.
Samant
,
Proc. IEEE
91
,
661
(
2003
).
4.
S. S. P.
Parkin
,
C.
Kaiser
,
A.
Panchula
,
P.
Rice
,
B.
Hughes
,
M.
Samant
, and
S.-H.
Yang
,
Nat. Mater.
3
,
862
(
2004
).
5.
M.
Julliere
,
Phys. Lett.
54A
,
225
(
1975
).
6.
R.
Feder
,
Polarized Electrons in Surface Physics
(
World Scientific
,
Singapore
,
1985
).
7.
Y. S.
Dedkov
,
U.
Rüdiger
, and
G.
Güntherodt
,
Phys. Rev. B
65
,
064417
(
2002
).
8.
R. J.
Soulen
,
J. M.
Byers
,
M. S.
Osofsky
,
B.
Nadgorny
,
T.
Ambrose
,
S. F.
Cheng
,
P. R.
Broussard
,
C. T.
Tanaka
,
J.
Nowak
,
J. S.
Moodera
,
A.
Barry
, and
J. M. D.
Coey
,
Science
282
,
85
(
1998
).
9.
R.
Meservey
and
P. M.
Tedrow
,
Phys. Rep.
238
,
173
(
1994
).
10.
C.
Kaiser
,
S.
van Dijken
,
S.-H.
Yang
,
H.
Yang
, and
S. S. P.
Parkin
,
Phys. Rev. Lett.
94
,
247203
(
2005
).
11.
C.
Kaiser
,
A. F.
Panchula
, and
S. S. P.
Parkin
,
Phys. Rev. Lett.
95
,
047202
(
2005
).
12.
S. S. P.
Parkin
,
K. P.
Roche
,
M. G.
Samant
,
P. M.
Rice
,
R. B.
Beyers
,
R. E.
Scheuerlein
,
E. J.
O’Sullivan
,
S. L.
Brown
,
J.
Bucchigano
,
D. W.
Abraham
,
Y.
Lu
,
M.
Rooks
,
P. L.
Trouilloud
,
R. A.
Wanner
, and
W. J.
Gallagher
,
J. Appl. Phys.
85
,
5828
(
1999
).
13.
C.
Kaiser
and
S. S. P.
Parkin
,
Appl. Phys. Lett.
84
,
3582
(
2004
).
14.
T.
Ishiguro
,
K.
Matsushima
, and
K.
Hamasaki
,
J. Appl. Phys.
73
,
1151
(
1993
).
15.
A.
Kawakami
,
Y.
Uzawa
, and
Z.
Wang
,
Appl. Phys. Lett.
83
,
3954
(
2003
).
16.
K.
Maki
,
Prog. Theor. Phys.
31
,
731
(
1964
).
17.
E. L.
Wolf
,
Principles of Electron Tunneling Spectroscopy
(
Oxford University Press
,
New York
,
1989
).
18.

We note that the resistivity of our NbN films varies little with temperature even for thick NbN films. For example, the resistance of a NbN film 100nm thick is 1.2 times higher at 15K than at 300K.

19.
B. Y.
Jin
and
J. B.
Ketterson
,
Adv. Phys.
38
,
189
(
1989
).
20.
G. A.
Gibson
,
P. M.
Tedrow
, and
R.
Meservey
,
Phys. Rev. B
40
,
137
(
1989
).
21.
G. A.
Gibson
and
R.
Meservey
,
Phys. Rev. B
40
,
8705
(
1989
).
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