Electronic structure of MnSb and MnP

Article abstract of DOI:10.1016/S0368-2048(98)00331-4

We have investigated the valence-band and conduction-band electronic structure of MnSb and MnP by means of ultraviolet photoemission and inverse-photoemission spectroscopies. The photoemission and inverse-photoemission spectra are qualitatively consistent

Full text of DOI:10.1016/S0368-2048(98)00331-4

Journal of Electron Spectroscopy and Related Phenomena 101–103 (1999) 657–660
Electronic structure of MnSb and MnP
a
a ,
a
b
b
a,b
*
H. Okuda , S. Senba , H. Sato , K. Shimada , H. Namatame , M. Taniguchi
a
Faculty of Science, Hiroshima University, Kagamiyama 1-3-1, Higashi-Hiroshima 739-8526, Japan
b
Hiroshima Synchrotron Radiation Center, Hiroshima University, Kagamiyama 2-313, Higashi-Hiroshima 739-8526, Japan
Abstract
We have investigated the valence-band and conduction-band electronic structure of MnSb and MnP by means of
ultraviolet photoemission and inverse-photoemission spectroscopies. The photoemission and inverse-photoemission spectra
are qualitatively consistent with the results of band-structure calculations. The spectral shapes are substantially different
between MnSb and MnP, which indicates that the Mn 3d electrons in MnP are more itinerant than those in MnSb.
Elsevier Science B .V . All rights reserved.
 1999
Keywords: MnSb; MnP; Electronic structure; Photoemission; Exchange splitting
1
. Introduction
anion p states is indispensable. Coehoorn et al. [4],
Motizuki [5], and Shirai and Tokioka [6] have done
first-principle band-structure calculations on MnSb
and discussed its physical properties from the itiner-
ant electron point of view. These calculations have
revealed a large magnetic moment on Mn atoms and
strong p–d hybridization. Rader et al. [7]performed
spin- and angle-resolved photoemission studies for
MnSb, and discussed the Sb 5p and Mn 3d contribu-
tions to the valence-bands and larger exchange
energies than those given by the band-structure
calculations. Yanase and Hasegawa [8] reported the
density of state (DOS) of MnP and revealed that the
Mn 3d minority-spin states mainly contribute to the
DOS near the Fermi level. Kakizaki et al. [9] carried
out photoemission measurements for MnP and
pointed out the strong itinerant nature of Mn 3d
electrons.
Manganese pnictides MnX (X5P, As, Sb, Bi) have
attracted considerable interest because of their vari-
ous physical properties associated with their ferro-
magnetism, such as strong magneto-optical effects,
uniaxial magnetic anisotropy and structural phase
transition. MnSb with a NiAs-type crystal structure
is ferromagnetic below T 5587 K [1]. On the other
c
hand, MnP has a crystal structure, so called MnP-
type, which slightly distorts from the NiAs-type. The
compound is antiferromagnetic with a helical spin
structure below T 547 K, ferromagnetic between Ta
a
and T 5291.5 K and paramagnetic above T [2,3].
c
c
In order to understand the physical properties of
these compounds, knowledge of the electronic struc-
ture, in particular, hybridization between Mn 3d and
To our knowledge, however, there has been no
direct information on the conduction bands. In this
paper, we report the valence-band and conduction-
band electronic structures of MnSb and MnP by
*
0
Corresponding author. Tel.: 181-824-24-7400; fax: 181-824-24-
719.
E-mail address: senba@hisor.material.sci.hiroshima-u.ac.jp (S.
Senba)
0
368-2048/99/$ – see front matter
 1999 Elsevier Science B .V . All rights reserved.
PII: S0368-2048(98)00331-4

6
58
H. Okuda et al. / Journal of Electron Spectroscopy and Related Phenomena 101–103 (1999) 657–660
means of ultraviolet photoemission and inverse-
photoemission spectroscopies (UPS and IPES). We
discuss the electronic structures of MnSb and MnP
comparing the UPS and IPES spectra with the DOSs
given by the band-structure calculations.
2
. Experimental
Polycrystals of MnSb and MnP were grown by the
Bridgman method. Equal amounts of pure Mn and
Sb in quartz ampoule was heated to a maximum
temperature of 9508C, kept at this temperature for a
few days, and slowly cooled down to a lower
temperature. In the case of MnP, the same procedure
was employed, except that a maximum temperature
of 11508C was used. We confirmed homogeneous
crystal phases of NiAs- and MnP-type structures by
X-ray powder diffraction analysis. The compositions
of the crystals were evaluated by electron-probe
micro-analysis.
The apparatus used for the present experiments is
composed of three ultrahigh vacuum chambers for
sample preparation, UPS and IPES measurements.
The UPS spectrometer is equipped with a He dis-
charge lamp (hn521.2 and 40.8 eV) and a double-
stage cylindrical-mirror analyzer. The energy res-
olution was set to be 0.2 eV. The IPES spectrometer
consists of a low-energy electron gun of the Erdman-
Zipf type and a bandpass photon detector centered at
Fig. 1. UPS spectra measured at hn521.2 and 40.8 eV, and IPES
spectrum of MnSb. Energy refers to the Fermi level. Vertical bars
indicate the position of structures.
spectrum taken at hn540.8 eV, the main peak
becomes dominant, and a broad structure due to Sb
5s states appears at around 210.1 eV. The difference
between the UPS spectra taken at hn521.2 and 40.8
eV is due to the energy-dependent photoionization
cross-sections of Mn 3d and Sb 5p states. The
cross-section of Mn 3d states is nearly equal to that
of the Sb 5p states at hn521.2 eV, while it is much
larger at hn540.8 eV [12]. The basic features in the
valence bands agree well with the results of
synchrotron radiation photoemission experiments for
MnSb (0001) film grown ex situ by molecular beam
epitaxy [7]. The IPES spectrum shows a main peak
at 1.2 eV and a broad structure at around 4.3 eV.
Fig. 2(a) shows the total DOSs and Mn 3d partial
DOSs for the majority (↑)- and minority (↓)-spin
states given by the band-structure calculation with a
9
.43 eV. The overall energy resolution was 0.56 eV
[10,11]. Clean surfaces of samples were prepared by
scraping them with a diamond file in the preparation
chamber, and transferring them in situ into the UPS
and IPES chamber. The base pressures for sample
2
11
preparation, UPS and IPES chambers are 5310
,
2
10
211
4
310
and 7310
Torr, respectively. All ex-
periments were performed at room temperature.
3
. Results and discussion
full-potential
linearized
augmented-plane-wave
Fig. 1 shows valence-band UPS spectra measured
method [6]. The valence bands and the conduction
bands are composed mainly of strongly hybridized
Mn 3d and Sb 5p orbitals. The Mn 3d↑ and Mn 3d↓
bands are essentially occupied and unoccupied,
respectively. Here, we convolute the theoretical
DOSs with the Gaussian and Lorentzian function,
at photon energies of hn521.2 and 40.8 eV and the
conduction-band IPES spectrum of MnSb. Energy
refers to the Fermi level. The UPS spectrum taken at
hn521.2 eV exhibits a main peak at 23.0 eV and a
small structure at around 25.7 eV. In the UPS

H. Okuda et al. / Journal of Electron Spectroscopy and Related Phenomena 101–103 (1999) 657–660
659
O symmetry, the Mn 3d states are classified into t
h
2
and e symmetries. The Mn 3d–e states strongly
hybridize with Sb 5p states and their bonding and
antibonding states spread over the valence bands and
conduction bands. On the other hand, the Mn 3d–t2
states have an almost nonbonding nature, giving
small band dispersions and narrow peak structures in
the DOS. Therefore, the main peak at 23.0 eV and
the small structure at around 25.7 eV in the UPS
spectrum are assumed to reflect the Mn 3d↑ state
with t symmetry and p–d hybridized states, respec-
2
tively. A main peak at 1.2 eV and a broad structure at
around 4.3 eV in the IPES spectrum stem from Mn
3
d↓ with t2 symmetry and sp states, respectively.
From the energy separation of the two main peaks,
the Mn 3d exchange splitting energy (U ) is esti-
eff
mated to be 4.260.2 eV, which is larger than that
given by the band-structure calculation (|3 eV) [6].
Fig. 3 shows valence-band UPS spectra measured
Fig. 2. (a) Theoretical total (solid lines) and Mn 3d partial (shaded
area) DOSs for the majority and minority spin of MnSb [6]. (b)
The calculated broadened DOS (solid lines) compared with the
experimental spectra (dotted lines) of MnSb.
which represent experimental resolution and life
time. We also take into account the photoionization
cross-section at hn540.8 and 9.43 eV. The results are
shown in Fig. 2(b) as thin solid curves together with
experimental spectra. The overall calculated spectra
are consistent with the experimental spectra, al-
though the two calculated peaks are closer than the
two UPS and IPES peaks.
We consider the electronic structure of MnSb
referring to the schematic energy diagram proposed
by Wei and Zunger [13]. MnSb has a NiAs-type
structure in which Mn atoms are coordinated by six
Fig. 3. UPS spectra measured at hn521.2 and 40.8 eV, and the
IPES spectrum of MnP (dotted lines), and the broadened DOS
derived by band-structure calculation (solid lines) [8]. Energy
refers to the Fermi level. Vertical bars indicate the position of
structures.
Sb atoms occupying nearly octahedral (O ) sites. In
h

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60
H. Okuda et al. / Journal of Electron Spectroscopy and Related Phenomena 101–103 (1999) 657–660
at hn521.2 and 40.8 eV, and conduction-band IPES
spectra of MnP with the DOS calculated by Yanase
and Hasegawa [8]. The DOS is broadened as de-
scribed above. Energy refers to the Fermi level. The
UPS spectrum exhibits a small peak at 20.4 eV, just
below the Fermi level, and broad structures at 22.6,
effect of Mn 3d states in MnP is weaker and that the
Mn 3d electrons in MnP have more itinerant charac-
ter compared with those in MnSb.
Acknowledgements
2
6.4 and |210 eV, whereas we only recognize a
broad structure at around 2 eV in the IPES spectrum.
The features of UPS and IPES spectra are in good
agreement with the results of the band-structure
calculation, which reveal that the Fermi level is
located within Mn 3d↓ bands, and all Mn 3d↑ bands
are occupied. Therefore, the structures at 22.6 and
The authors are grateful to Prof. M. Shirai for
providing us with the calculated DOSs of MnSb, to
A. Minami for the electron-probe micro-analysis and
also to M. Nakatake, K. Takada, Y. Umetani and K.
Murakami for their technical assistance. This work is
partly supported by the Grant-in Aid for Scientific
Research from the Ministry of Education, the Kurata
Foundation, the Japan Securities Scholarship
Foundation and Izumi Science and Technology
Foundation.
2
0.4 eV in the UPS spectra are attributed to the
occupied Mn 3d↑ and Mn 3d↓ states [9], respective-
ly. The U -value of MnP is thus estimated to be
eff
2
.260.2 eV, which is smaller than that of MnSb. The
result is consistent with the smaller Curie tempera-
ture and magnetic moment of MnP rather than those
of MnSb.
References
The UPS and IPES spectra of MnP are substantial-
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Mn 3d states shift towards the Fermi level, which
reduces exchange splittings. Therefore, the difference
of the electronic structure, in particular, the Mn 3d
states between MnSb and MnP would be attributed
to the differences in their crystal structures.
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