Zinc-blende ferromagnetic CrSb film on KCl (100) substrates

Article abstract of DOI:10.1016/j.ssc.2008.11.022

CrSb film was deposited on KCl (100) substrates by magnetron sputtering. Strong ferromagnetism was observed in the CrSb film, which can be attributed to the CrSb phase with ferromagnetic zinc-blended structure. The investigated ZB-CrSb film about 5 nm in

Full text of DOI:10.1016/j.ssc.2008.11.022

Solid State Communications 149 (2009) 196–198
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Solid State Communications
journal homepage: www.elsevier.com/locate/ssc
Zinc-blende ferromagnetic CrSb film on KCl (100) substrates
Shandong Lia,∗, Zongjun Tianb, Jianglin Fangc, Jenq-Gong Duhd, Kai-Xin Liud, Zhigao Huanga,
Yinhui Huangb, Youwei Due
a Department of Physics, Fujian Normal University, Fuzhou 350007, China
b College of Mechanical and Electrical Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
c Centre for Materials Analysis, Nanjing University, Nanjing 210093, China
d Department of Materials Science and Engineering, National Tsing Hua Universtiy, Hsinchu, Taiwan
e National Laboratory of Solid State Microstructure, Nanjing University, Nanjing 210093, China
a r t i c l e i n f o
a b s t r a c t
Article history:
CrSb film was deposited on KCl (100) substrates by magnetron sputtering. Strong ferromagnetism was
observed in the CrSb film, which can be attributed to the CrSb phase with ferromagnetic zinc-blended
structure. The investigated ZB-CrSb film about 5 nm in thickness is sufficiently thicker to be investigated
the half-metallic nature of ZB-CrSb and to be practically applied in spintronics devices.
© 2008 Elsevier Ltd. All rights reserved.
Received 10 June 2008
Received in revised form
25 August 2008
Accepted 19 November 2008 by
S. Miyashita
Available online 25 November 2008
PACS:
85.75.-d
81.15.Cd
81.15.Np
Keywords:
A. Zinc-blende CrSb
A. KCl substrates
B. Magnetron sputtering
C. Half-metals
1. Introduction
spin channel conducting, while the other is insulating (or semicon-
ducting) [12], so that, in the ideal case, half-metals can conduct a
current which is 100% spin polarized.
In the last two decades, spintronics has become one of fast de-
veloping research branches. Spintronic devices, originating from
the discovery of giant magnetoresistance in 1988 and the subse-
quent development of spin valve, tunneling magnetoresistance, as
well as spin injection into metals, can be understood by assum-
ing that any current of spins is carried by two ‘types’ of carriers,
i.e. spin-up and spin-down [1–11]. The rapid advancement of mag-
netoelectronics and spintronics in recent years has given a strong
boost in the search for novel half-metallic ferromagnets. These are
spin polarized materials, which exhibit the property of having a
metallic density of electron states for the one spin direction (usu-
ally majority spin), while there is a band gap around the Fermi
level, EF , for the states of the opposite spin. This half-metallic prop-
erty (the name coined by de Groot and collaborators makes the one
In 2000, Akinaga and collaborators reported growth of a few
monolayers of ferromagentic CrAs in the metastable ZB phase
with magnetic moment 3 µB/f.u. and Cuire temperature higher
than 400 K for the first time [13]. This findings initiated a strong
activity, because several merits were derived: the half-metallic
property, coherent growth on a semiconductor, and TC higher than
room temperature. The activity was extended beyond ZB–CrAs,
encompassing a variety of tetrahedrally bonded transition metal
compounds (TBTMC) with sp atoms of the IV, V and VI groups of
the periodic table. However, ZB–TBTMC phases are substantially
higher in total energy than the corresponding ground state phases.
Thus, it is difficult to fabricate ZB-structured thick films. Although
the ferromagnetic ZB–TBTMC mono- or multilayer films have been
successfully grown on GaAs, AlGaSb, and GaSb substrates by MBE,
the thickness of only few molecular layers was achieved, which
is too thin to be used in practice [14–18]. Thus, it is desirable to
fabricate thicker and stable ZB–TBTMC films for the application and
understanding their half-metallic nature. The effort to fabricate the
∗
Corresponding author. Fax: +86 591 83486160.
E-mail address: dylsd007@yahoo.com.cn (S. Li).
0038-1098/$ – see front matter © 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.ssc.2008.11.022

S. Li et al. / Solid State Communications 149 (2009) 196–198
197
thicker ZB–TBTMC films has been carried out. Recently, Deng et al.
enhanced the thickness of ZB-CrSb films from 1 to 9 monolayer
(ML) (∼3 nm) by MBE using (In, Ga)As buffer layers [17].
Moreover, nanodots and ultrathin multilayer ZB–TBTMCs have
been achieved experimentally by molecular beam epitaxy (MBE)
growth on III–V semiconductors [19–23]. In our previous work,
nanocrystalline ferromagnetic ZB-CrSb particles was prepared by
pulse laser deposition and rapidly annealing [24]. In this paper, KCl
(100) substrates were used to deposit the CrSb thick film, and a
room-temperature ferromagnetic CrSb film with ZB structure was
obtained by magnetron sputtering.
2. Experiment
KCl (100) substrates were cleaved from a single crystal KCl bar.
The cleaved substrates were immediately put into the vacuum
chamber. The fresh KCl surface with roughness in the atomic scale
was used as the film growth plane. CrSb films were co-deposited at
◦
250 C for 60 s under powers of 20 W for Cr target and 10 W for Sb.
−5
The base pressure was less than 1.0 × 10 Pa, and the working
pressure was 0.5 Pa at Ar floating rate of 20 sccm. The nominal
thickness of the CrSb films was 5.0 nm, deduced from deposition
rate of 5 nm/min.
The magnetic properties of the films were measured by a
superconducting quantum interference device (SQUID) magne-
tometer from 5 to 350 K and a paramagnetic resonance (PMR)
spectrometer at room temperature. The microstructure and com-
position of the films were characterized by high resolution
transmission electron microscope (HRTEM), atomic force micro-
scope (AFM) and field emission electron probe microanalyzer
(FE–EPMA).
Fig. 1. (a) The hysteresis loops of the CrSb film at 5 and 300 K, respectively; (b) the
M–T cure of the film from 5 to 350 K in the magnetic field of 2 kOe.
3. Results and discussion
The hysteresis loops at various temperatures and the M–T
curve for a 5 mm × 5 mm sample with the film plane along the
magnetic field direction were measured by SQUID. Fig. 1 shows the
magnetic properties of CrSb films. The diamagnetic contribution of
KCl was subtracted from the total hysteresis loops. As illustrated
in Fig. 1(a), the CrSb film exhibits strong ferromagnetic properties
with saturation magnetization (MS ) up to 530 emu/cm3 at 5 K.
Even at 300 K, MS is as high as 410 emu/cm3. Fig. 1(b) reveals
that the strong ferromagentic property of the films maintains over
room temperature. These facts demonstrate that a strong room-
temperature ferromagnetic property is achieved for the CrSb film
deposited on KCl (100) substrates.
The PMR of the CrSb film with dimension of 4 mm × 8 mm was
measured using X-band microwave frequency of 9.7 GHz in the
magnetic field ranges from 0 to 10 kOe. The angles (θ) between
magnetic field direction and film normal direction are varied from
◦
Fig. 2. The differential PMR spectrum of CrSb film at θ = 0 .
◦
0 to 90 . Fig. 2 shows the strongest PMR spectrum including the
Table 1
◦
ferromagnetic resonance (FMR) peaks with θ = 0 . As illustrated,
Compositions of the CrSb film at various test positions.
a broad FMR peak at 2239 Oe with resonance linewidth of 164 Oe
was observed, which can be attributed to the ferromagnetic CrSb
film. The PMR spectrum of CrSb film verifies the room-temperature
ferromagnetic property of CrSb, which agrees with the SQUID
results.
Position number
Composition (at.%)
Cr
Sb
1
2
49.84
49.79
50.32
50.07
49.99
49.68
51.06
50.22
50.03
49.65
50.16
50.21
49.68
49.93
50.01
50.32
48.94
49.78
49.97
50.35
3
To investigate the origin of ferromagnetism in CrSb films, line
scanning by FE–EPMA was carried out for each sample to detect
the composition distribution in the film. Each sample was scanned
with at least two trace lines. FE–EPMA results, listed in Table 1,
reveal that the atomic ratio of Cr and Sb is very close to 1:1,
suggesting the composition of the films is CrSb. The surface of
KCl substrates and deposited films were scanned by AFM. A very
smooth surface with average roughness less than 0.6 nm was
present in the substrates and films, and no aggregated particle was
observed.
4
5
6
7
8
9
10
Fig. 3 shows HRTEM image and electron diffraction spectra
(EDS) of the CrSb film. It can be seen that the CrSb film is composed

198
S. Li et al. / Solid State Communications 149 (2009) 196–198
in an atomic scale, which is especially suitable for the epitaxial
growth of materials with a face-centered cubic structure. A small
lattice mismatch of 0.05 between KCl substrate (a = 6.260 Å) and
ZB-CrSb (a = 5.92 Å) is estimated in ZB-CrSb/KCl (100) systems.
This favorable lattice matching gives rise to a relatively thicker film
thickness of ZB-CrSb on the KCl (100) substrates.
4. Conculsions
Room temperature ferromagnetism in CrSb film is attributed to
the ferromagnetic ZB-CrSb. Relatively thicker ZB-CrSb films with
a critical thickness of about 5 nm were achieved by deposition on
the KCl (100) substrates.
Acknowledgements
Fig. 3. The HRTEM image and EDS (insert) of the CrSb film.
This work was financially supported by National Science
Foundation of China (NSFC) (Grant No. 10504010) and Science
Foundation of Sci. & Tech. Department of Fujian Province (Grant
No.: 2005J023, 2006H0018 and 2006J0152).
of nanocrystallites with a crystal size about 10 nm. From the EDS
circles, the d-spacings of 2.09 and 1.48 Å are calculated, which may
be assigned to the zinc-blende CrSb (220) and (400), respectively.
Although there are no ZB-CrSb X-ray diffraction (XRD) JCPDS cards
at this moment, XRD pattern can be calculated based on the ZB
structure. According to the report by Galanakis et al. [15], the lattice
constant of ZB-CrSb is 5.92 Å, thus, the d-spacings of ZB-CrSb (220)
and (400) should be at 2.093 and 1.480 Å, respectively, which
are well consistent with the EDS result. On the other hand, no d-
spacings of KCl and other Cr–Sb compounds, such as, hexagonal
NiAs-type CrSb (NA-CrSb), CrSb2, Cr0.1Sb0.9, etc., are near these two
values. Based on the analysis above, two circles can be assigned
as (220) and (400) of ZB-CrSb, respectively. The HRTEM and EDS
results reveal that a pure ZB-CrSb phase was formed in the CrSb
film deposited on KCl substrates.
ZB-CrSb is a robust ferromagnetic half-metal in theory [25,26].
The microstructure analysis above demonstrates that the strong
ferromagnetic properties of CrSb film are attributed to the ZB-CrSb.
The real MS of ZB-CrSb is not reported up to now. However, the
strong ferromagnetic coupling in ZB-CrSb with 3 µB per formula
unit was predicted by theoretical calculation [25,26]. With the
lattice constant of a = 5.92 Å for ZB-CrSb, the theoretical Ms of
ZB-CrSb is estimated as 536 emu/cm3, analogy to the calculation
method reported by Akinaga et al. [13]. If taking the MS at 5 K
as the saturation magnetization of ferromagnetic CrSb, the MS of
530 emu/cm3 is very close to theoretical MS of ZB-CrSb. The film
thickness of ZB-CrSb phase of about 5 nm is relatively thicker
compared with the ones reported up to now.
References
[1] M.N. Baibich, J.M. Broto, A. Fert, F. Nguyen Van Dau, F. Petroff, P. Eitenne,
G. Creuzet, A. Friederich, J. Chazelas, Phys. Rev. Lett. 61 (1988) 2472.
[2] G. Binasch, P. Grünberg, F. Saurenbach, W. Zinn, Phys. Rev. B 39 (1989) 4828.
[3] B. Dieny, Phys. Rev. B 43 (1991) 1297.
[4] N.F. Mott, Proc. R. Soc. Lond. A 153 (1936) 699.
[5] R.E. Camley, J. Barnaś, Phys. Rev. Lett. 63 (1989) 664.
[6] J. Barnaś, A. Fuss, R.E. Camley, P. Grünberg, W. Zinn, Phys. Rev. B 42 (1990)
8110.
[7] A. Barthélémy, A. Fert, Phys. Rev. B 43 (1991) 13124.
[8] T. Valet, A. Fert, Phys. Rev. B 48 (1993) 7099.
[9] W.H. Butler, X.G. Zhang, T.C. Schulthess, D.M.C. Nicholson, J.M. MacLaren,
V.S. Speriosu, B.A. Gurney, Phys. Rev. B 56 (1997) 14574.
[10] J.S. Moodera, L.R. Kinder, T.M. Wong, R. Meservey, Phys. Rev. Lett. 74 (1995)
3273.
[11] M. Johnson, R.H. Silsbee, Phys. Rev. B 37 (1988) 5326.
[12] R.A. de Groot, F.M. Mueller, P.G. van Engen, K.H.J. Buschow, Phy. Rev. Lett. 50
(1983) 2024.
[13] H. Akinaga, T. Manago, M. Shirai, Jpn. J. Appl. Phys. 39 (2000) L1118.
[14] F. Matsukura, H. Ohno, A. Shen, Y. Sugawara, Phys. Rev. B 57 (1998) R2037.
[15] I. Galanakis, P. Mavropoulos, Phys. Rev. B 67 (2003) 104417.
[16] J.H. Zhao, F. Matsukura, K. Takamura, E. Abe, D. Chiba, H. Ohno, Appl. Phys. Lett.
79 (2001) 2776.
[17] J.J. Deng, J.H. Zhao, J.F. Bi, Z.C. Niu, F.H. Yang, X.G. Wu, H.Z. Zheng, J. Appl. Phys.
99 (2006) 093902.
[18] H. Akinaga, M. Mizuguchi, J. Phys.: Condens. Matter. 16 (2004) S5549.
[19] K. Ono, J. Okabayashi, M. Mizuguchi, M. Oshima, A. Fujimori, H. Akinaga, J. Appl.
Phys. 91 (2002) 8088.
[20] C.Y. Fong, M.C. Qian, J.E. Pask, L.H. Yang, S. Dag, Appl. Phys. Lett. 84 (2004) 239.
[21] M. Mizuguchi, H. Akinaga, T. Manago, K. Ono, M. Oshima, M. Shirai, M. Yuri,
H.J. Lin, H.H. Hsieh, C.T. Chen, J. Appl. Phys. 91 (2002) 7917.
[22] J.H. Zhao, F. Matsukura, K. Takamura, D. Chiba, Y. Ohno, K. Ohtani, H. Ohno,
Mater. Sci. Semicond. Proc. 6 (2003) 507.
[23] J. Okabayashi, M. Mizuguchi, K. Ono, M. Oshima, A. Fujimori, H. Kuramochi, H.
Akinaga, Phys. Rev. B 70 (2004) 233305.
As for the formation of relatively thicker ZB-CrSb films, it can
be attributed to the good lattice matching between KCl and ZB-
CrSb. If using a good lattice matching buffer layer, e.g. (In, Ga) as
a buffer layer, the critical thickness of ZB-CrSb can be increased
from 1 to 3 nm [16,17]. For the films grown on a GaAs substrate, the
critical thickness of ZB–CrAs thicker than that of ZB-CrSb can also
be attributed to that the lattice mismatch between ZB–CrAs and
GaAs is smaller than that between ZB-CrSb and GaAs [13,17,27].
The KCl substrate has (h00) a cleavage face with surface plainness
[24] S.D. Li, L.Y. Lü, Z.G. Huang, J. Magn. Magn. Mater. 312 (2007) 305.
[25] B.G. Liu, Phys. Rev. B 67 (2003) 172411.
[26] M. Shirai, J. Appl. Phys. 93 (2003) 6844.
[27] J.F. Bi, J.H. Zhao, J.J. Deng, Y.H. Zheng, S.S. Li, X.G. Wu, Q.J. Jia, Appl. Phys. Lett.
88 (2006) 142509.