EPR and optical study of Mn2+ doped ammonium oxalate monohydrate

Article abstract of DOI:10.1016/j.ssc.2005.02.042

Studies on fine and hyperfine structures of paramagnetic resonance spectra in single crystals of Mn²⁺: ammonium oxalate monohydrate are reported. As sufficient numbers of lines were not obtained at room temperature, measurements have been done at liquid nitrogen temperature and at the frequency of X-band. The Mn²⁺ spin Hamiltonian parameters have been evaluated employing a large number of resonant line positions observed for various orientations of the external magnetic field and the surrounding crystalline field has been discussed. The values of the zero field parameters that give good fit to the observed EPR spectra have been evaluated. The values obtained for g, A, B, D, E and a are 2.0002±0.0002, (100±2)×10 ^-4, (79.5±2)×10^-4, (257±2)×10^-4, (85±2)×10^-4 and (-18±1)×10^-4 cm^-1, respectively. The percentage of covalency of the metal-ligand bond is also determined. The optical absorption study has been done at room temperature. The observed bands are assigned as transitions from the ⁶A_1g(S) ground state to various excited quartet levels of Mn²⁺ ion in a cubic crystalline field. The electron repulsion parameters (B and C), the crystal field splitting parameter(Dq) and the Trees correction (α) providing good fit to the observed optical spectra have been estimated and the values obtained for the parameters are B=897, C=2144, Dq=910 and α=76 cm^-1.

Full text of DOI:10.1016/j.ssc.2005.02.042

Solid State Communications 134 (2005) 699–704
www.elsevier.com/locate/ssc
2C
EPR and optical study of Mn doped ammonium
oxalate monohydrate
Ram Kripal , Vishal Mishra
*
Department of Physics, EPR Laboratory, University of Allahabad, Allahabad 211002, India
Received 27 December 2004; received in revised form 17 February 2005; accepted 21 February 2005 by C. Lacroix
Available online 17 March 2005
Abstract
2C
Studies on fine and hyperfine structures of paramagnetic resonance spectra in single crystals of Mn : ammonium oxalate
monohydrate are reported. As sufficient numbers of lines were not obtained at room temperature, measurements have been done
2C
at liquid nitrogen temperature and at the frequency of X-band. The Mn spin Hamiltonian parameters have been evaluated
employing a large number of resonant line positions observed for various orientations of the external magnetic field and the
surrounding crystalline field has been discussed. The values of the zero field parameters that give good fit to the observed EPR
K4
spectra have been evaluated. The values obtained for g, A, B, D, E and a are 2.0002G0.0002, (100G2)!10 , (79.5G2)!
K4
K4
, (257G2)!10 , (85G2)!10 and (K18G1)!10 cm , respectively. The percentage of covalency of the metal–
K4
K4
K1
1
ligand bond is also determined. The optical absorption study has been done at room temperature. The observed bands are
0
6 2C
assigned as transitions from the A1g(S) ground state to various excited quartet levels of Mn ion in a cubic crystalline field.
The electron repulsion parameters (B and C), the crystal field splitting parameter(Dq) and the Trees correction (a) providing
good fit to the observed optical spectra have been estimated and the values obtained for the parameters are BZ897, CZ2144,
K1
DqZ910 and aZ76 cm
q 2005 Elsevier Ltd. All rights reserved.
.
PACS: 76.30
Keywords: D. Covalency; D. Electron repulsion parameter; D. Optical spectra; D. Zero field parameter; E. Spin Hamiltonian
1
. Introduction
supplementary tools to investigate the site symmetry and
the dynamic behaviour of the substituents of the lattice.
2
C
5
EPR provides a great deal of information about the
EPR of Mn , high spin d ion, has been studied quite
extensively, particularly in octahedral coordination [2–6].
magnetic properties of transition metal ions and enables
to identify site symmetry around the metal ion [1].
Optical absorption is important in studying the elec-
tronic structure of transition ions in crystals giving
knowledge of the energy levels and crystal field
parameters. Thus EPR and optical absorption are two
2C
6
Mn has five 3d electrons and the ground state is S5/2. As
the resultant angular momentum is zero, only the electron
spin is responsible for the paramagnetism. The zero-field
splittings in these ions are sensitive with respect to small
structural changes.
In the present investigation, the EPR and optical study of
2C
Mn ions doped in ammonium oxalate monohydrate are
2C
reported in order to obtain information whether Mn ion
enters the lattice substitutionally or interstitially and to have
better understanding of the physical interactions present in
the system. The study is further used to find energy of
*
Corresponding author. Tel.: C91 53 226 41312; fax: C91 53 22
090 00.
E-mail addresses: ram_kripal2001@rediffmail.com (R. Kripal),
vishalrohit1@rediffmail.com (V. Mishra).
5
0038-1098/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.ssc.2005.02.042

700
R. Kripal, V. Mishra / Solid State Communications 134 (2005) 699–704
various orbital levels as well as to describe the nature of
bonding in the complex.
2
. Crystal structure
The crystal structure [7] of ammonium oxalate mono-
hydrate (NH ) C O $H O, is orthorhombic with the space
4
2
2
4
2
1 1
group P2 2 , containing two formula units per unit cell. The
˚
unit cell dimensions are aZ8.04, bZ10.27 and cZ3.82 A.
Distances within the oxalate group are: C–CZ1.581G0.01,
˚
O –CZ1.25G0.02, and O –CZ1.23G0.02 A the angle O–
1
2
C–OZ129G28. The angle between the O–C–O plane and
001) is 148 and thus the angle between the two O–C–O
planes of an oxalate group is 288.
(
2C
Fig. 1. EPR spectra of Mn
doped ammonium oxalate mono-
3
. Experimental
hydrate when the applied magnetic field (B) is parallel to the a axis.
Single crystals of ammonium oxalate monohydrate are
grown at room temperature by slow evaporation of an
the surrounding ions. Consequently, fine structure results
from the crystal field and the spin–spin interactions, and the
hyperfine structure arises from the interaction between the
2
C
aqueous solution of ammonia and oxalic acid. For Mn
doped crystals 0.1 wt% manganese sulphate is added as
paramagnetic impurity to the mixture. The colourless
crystals grow in about 15–20 days. The ESR spectra are
recorded using X-band Varian E-112 ESR spectrometer
with 100 kHz field modulation. As sufficient numbers of
lines were not obtained at room temperature, spectra have
been recorded at liquid nitrogen temperature. The single
crystals are mounted at the end of a quartz-rod using quick-
fix and the crystal rotations are performed along the three
mutually perpendicular axes a, b and c using a goniometer.
The magnetic field was measured using a Varian flux meter
5
5
nuclear spin of Mn(IZ5/2) and its electronic spin.
Accordingly, the experimental results for the resonance
fields can be analysed with the usual spin Hamiltonian
H Z H CH CHh
(1)
z
zfs
where Hz is the Zeeman interaction term, Hzfs the fine
structure(zero-field splitting) term and Hh the hyperfine
interaction term, respectively. The Zeeman term is
H Z m B:g:S
(2)
z
B
3
and a proton probe having 0.2 cm of 0.25 molar solution of
GdCl in H O with the help of a Hewlet–Packard frequency
where m
B
is the Bohr magneton, B is the external magnetic
3
2
counter. The optical absorption spectra have been recorded
on a Unicam-5625 spectrophotometer in the wavelength
range 195–1100 nm at room temperature.
field vector, g is the spectroscopic splitting factor, and S is
the effective electron spin vector. The zero-field splitting
term for orthorhombic symmetry is [8,9]
4
. Results and discussion
A typical EPR spectrum of Mn in ammonium oxalate
2C
monohydrate recorded at 77 K when the applied magnetic
field B is parallel to the ‘a’ axis given in Fig. 1 shows five
sets with six lines in each set. The five sets of lines are the
2
C
fine structure of Mn
(SZ5/2), and the six lines within
55
each set are the hyperfine structure of Mn(IZ5/2, 100%
abundance).
Crystal rotations have been performed in the three
orthogonal crystallographic planes ab, bc, and ca. The
rotation pattern of fine structure in ab plane is shown in Fig.
2. However, it is to be noted here that in all the three planes
only one magnetically distinct site is observed.
2C
Fig. 2. Angular variation of the fine structure of Mn
doped
2C
When the Mn , an S-state ion, is introduced in a
crystal, it experiences an intense crystal field produced by
ammonium oxalate monohydrate in ab plane (showing the
experimental points and the calculated curves).

R. Kripal, V. Mishra / Solid State Communications 134 (2005) 699–704
701
2
z
2
x
2
y
4
x
evaluated [12] using Matumura’s plot [13] and is found as
K4 K1
4. The value of hyperfine splitting constant 78!10 cm
Hzfs Z D½S K1=3SðS C1Þꢀ CEðS KS Þ Ca=6½S
1
predicted from the graph is in a reasonable agreement with
4
4
2
CS CS K1=5SðS C1Þð3S C3S K1Þꢀ
(3)
y
z
K4
the observed value of 86!10 cm , (AC2B)/3.
K1
where D and E are the second order axial and the rhombic
zero-field splitting parameters and a is the cubic splitting
parameter, respectively.
The spin-orbit coupling parameter for the transition ions
in a crystal are different from those of the free ion due to the
covalency [14,15]. In fact, experimental values in a crystal
are less than those of the free ion. The covalent bonding
The hyperfine interaction is
d
modifies the spin-orbit coupling z in a crystal as
H ¼ AS I þ BðS I þ S I Þ
where A and B are hyperfine structure constants.
(4)
h
z z
x x
y y
2
0
d
z Z N z
(6)
d
Bleaney and Trenum [10] gave the allowed transitions
assuming the Zeeman interaction to be dominant occurring
at fields B given by [8]
0
d
where z
average covalency parameter [15].
is the free ion spin-orbit coupling and N is the
The deviations DgZgK2.0023 are observed in crystals
where a fair amount of covalent bonding is present. It has
been suggested [16] that in the presence of covalent bonding
M Z jG5=2i4jG3=2i
(5)
6
2
excited sextets T1g are present, whose single electron states
gm B ¼ gm B K½2Dð3 cos q K1Þ þ 2paꢀ K32d þ 4d
B
B
0
1
2
tend to be full or empty according to whether electrons are
transferred to or from the central ion by the action of
bonding. A second order shift is then possible in the g-value,
whose sign depends upon the direction of electron transfer.
The value K0.0021 of Dg in the present study is consistent
with this explanation.
þ 31
M Z jG3=2i4jG1=2i
2
gm B ¼ gm B K½Dð3 cos q K1Þ K5pa=2ꢀ þ 4d K5d
B
B
0
1
2
þ 32
5
. Optical spectra
In a cubic crystalline field Mn 3d electron configur-
M Z jG1=2i4j K1=2i
2
C
5
6
4
4
4
gm B ¼ gm B þ 16d K8d þ 3
1g 1g g 1g
ation yields various electronic states A , A , E , T ,
B
B
0
1
2
3
4
4
4
4
2g, A2g, A2g(F), T1g(F) and to a number of doublet
T
states as discussed earlier [12]. A of these lies lowest and
0 B
where B Zhn/gm is the field at which a line would have
6
1
g
occurred if all the fine structure terms had been zero. q is the
angle of rotation and the remaining terms have been
explained elsewhere [8].
2
C
all the absorption bands of high spin Mn result from spin
forbidden transitions.
The observed optical absorption spectrum at room
temperature is shown in Figs. 3 and 4. The spectrum
consists of seven main bands located at 13,623, 14,430,
Direction cosines of the distortion axis have been
determined using the method of Rao and Subramanian
[
11] and are given in Table 1 together with the direction
K1
15,220, 21,186, 21,691, 26,455, 29,585 cm . In addition,
K1
to the above, one weak band at 16,271 cm is observed.
cosines of some NH –O bonds. The EPR parameters were
4
obtained by computer fitting of the experimental data and
we selected the parameters which best satisfy simul-
taneously the resonance fields measured on the crystal-
lographic ab, bc and ca planes. The values of g, A, B, D, E
Among the bands observed in the present study, the bands at
K1
1
5,220, 21,186, and 26,455 cm
are found to be sharp.
Using the Tanabe–Sugano diagram [17] and our earlier
study [12] the assignments of different bands has been done.
The wavelengths and the wave numbers of the bands are
given in Table 3, together with the assignments.
2C
and a obtained for Mn in ammonium oxalate monohy-
drate are summarized in Table 2.
The percentage of covalency of the Mn–O bond is also
The energy values for different electronic states have
been calculated [12] using computer for different values of
crystal field splitting parameter Dq with Racah parameters
Table 1
Direction cosines of NH
the distortion axis of Mn
4
2
4 2
with surrounding oxygen; NH –O and
C
derived from EPR
K1
K1
BZ897 cm , CZ2144 cm
and Trees correction aZ
6 cm [18]. A good fit of the observed band positions is
K1
7
Direction
C–NH
–O
l
m
n
K1
obtained for DqZ910 cm as can be seen from the graph
in Fig. 5. It is interesting to note that the observed and
calculated values are in good agreement, justifying the
assignments.
4
G0.6890
G0.2981
G0.4316
G0.7564
G0.7655
G0.6043
G0.9235
G0.8455
G0.3113
G0.1061
G0.3998
G0.2412
G0.3189
G0.5752
G0.6346
O
1
2
NH
NH
4
–O
–O
1
4
2
The Racah parameters B and C are reduced considerably in
crystals from those offree ion value due to the covalency [14].
Distortion axis

702
R. Kripal, V. Mishra / Solid State Communications 134 (2005) 699–704
Table 2
using Table 1 of Zhao et al. [23] and eighth-order
perturbation contribution from the formula
2
C
Spin Hamiltonian parameters for Mn
monohydrate
in ammonium oxalate
Â
ð8Þ
K26
4
d
4
K28
g
A
B
D
E
a
a
Z 1=3 ð2:023050!10 Þz Dq N
2
.0002
100
79.5
257
K4
85
K18
K26
5
3
K28
Cð1:269239!10 Þz Dq N
d
K1
A, B, D, E and a all in units of !10 cm . Estimated error for g
K4
is G0.0002. Estimated error for A, B, D are G2!10 cm
K1
K27
6
2
K28
.
Cð1:511472!10 Þz Dq N
d
K4
Estimated error for a is G1!10 cm
K1
.
Ã
K28
7
d
K28
Cð5:453156!10 Þz DqN
(8)
These parameters in terms of N are given by the following
relations [15]
where N is obtained to be 0.939 using B Z960 and C Z
0
0
0
d
K1 2C
325 cm for free Mn ion [19] and z
2 0
d
3
3
1
d
ZN z
with z
Z
4
4
B Z N B ; C Z N C
(7)
K1
0
0
36.6 cm [23]. The value of a estimated comes out to be
K1
which is in good agreement with the
K4
3.4!10 cm
where 0!N!1(NZ1 for the pure ionic bond) and B
0
and C
0
3
C
experimental value given in Table 2.
are free ion values of Racah parameters. In Fe :YAG, the
2K
3C
The free ion values of the Racah parameters B and C
0
0
value of N is in the range of 0.8–0.9 for the Fe –O bond
15]. Experimental evidence for a reduction of the parameters
K1
are 960 and 3325 cm [19]. In the present investigation,
[
K1
we obtained the values of BZ897 and CZ2144 cm . The
B and C in octahedral crystals is given in the literature [19].
Powell, Gabriel and Johnston [20] showed that the
spin-doublet contribution to the ground state via the spin-
considerable decrease in the values of the Racah parameters
B and C from the free ion values indicates that there exists a
fair amount of covalent bonding between the central metal
ion and the ligand.
orbit interaction, is of major importance, using a value
K1
of z Z400 cm , they found that for a range C1200 to
d
C
K1
K1200 cm of Dq, the cubic splitting parameter a varied
Arrangements of atoms surrounding NH4 ions and
water molecules [7] are shown in Fig. 6. Water molecules
C
are tetrahedrally surrounded by two NH4 ions and two
widely. They also found possible to fit observed value of a
2
for Mn
C
in MgO using rather smaller value of z !
d
K1
00 cm [21]. A value for z
K1
oxygen atoms. Interatomic distances for one set are near
˚
2.80 A and for the other near 3.20 A. The planes of the
3
obtained from the optical spectrum of Mn
d
of 320G10 cm has been
˚
2
C
in RbMnF
K1
3
K
4
K1
O–C–O parts of the C O group are at an angle of 288 to
2
[22]. In the range C1000 cm %Dq%C1500 cm the
parameter a was found to be a sensitive function of z and
one another.
d
The principal models of charge compensation when
divalent impurity cations are substituted for the monovalent
cations in a crystal lattice have been discussed earlier [24–
Dq.
Zhao et al. [23] have given the contribution of the sixth-
order and the eighth-order perturbation to cubic splitting
parameter a and showed that the eighth-order perturbation
cannot be neglected for large Dq. In the present study the
sixth-order perturbation magnitude to a has been obtained
2
6]. In these models the magnetic tensors have their unique
axes pointing towards the divalent impurity-positive ion
vacancy directions. Watkins [24] as well as Yokozawa and
Kazumata [27] have obtained a spectrum IV showing
orthorhombic symmetry which they assigned to an associ-
2
C
2K
2K
2K
ated pair Mn : X where X is an impurity like O ,
etc. occupying a nearest neighbour anion site. The spin
2K
S
Hamiltonian parameters in the present case are given in
Table 3
The experimental data and the analysis of the absorption spectrum
2C
of Mn ions in ammonium oxalate monohydrate
˚
Observed (A)
Transition
6
from A1g(S)
Observed
K1
Calculated
K1
(cm
)
(cm
)
4
T
T
E
1g(G)
7340
6930
6570
6146
13,623
14,430
15,220
16,271
21,186
21,691
26,455
29,585
13,646
4
4
4
2g(G)
g
(G)
22,293
21,210
A
1g(G)
4
720
4
4
4
T
2g(D)
(D)
4610
3780
3380
20,822
26,342
29,846
E
g
2
C
Fig. 3. Absorption spectrum of Mn
in ammonium oxalate
T1g(P)
monohydrate in the wavelength range 325–1100 nm (the incident
K1
K1
K1
K1
(
BZ897 cm , CZ2144 cm , DqZ910 cm , aZ76 cm ).
beam is perpendicular to the ab face of the crystal).

R. Kripal, V. Mishra / Solid State Communications 134 (2005) 699–704
703
the metal ion. The direction cosine of the distortion axis
calculated from EPR spectra nearly coincides with the
2
C
direction of NH –O bond. Therefore, Mn is expected to
4
2
C
be substituted for NH
4
C
in (NH
in NaCl, corresponding to an
4
)
2
C
2
O
4
$H
2
O,similar to
2
spectrum IV of Mn
2C
2K
associated pair Mn : O where O occupies a nearest
2K
2
K
2C
neighbour site. As the ion O is next to Mn ion, a large
Coulombic binding energy is expected. The close proximity
of the negative charge also explains the observed crystal
field splittings. The asymmetry, as measured by E, could
arise as a result of partial electron transfer away from the
2
O
K
leaving a partial hole whose orbital degeneracy could
be lifted by the Jahn–Teller distortion [8]. As only one set of
allowed hyperfine lines is observed in all the three planes of
rotation, it appears that only one type of site is preferentially
2C
2C
occupied by Mn . Thus in our case though the Mn ion
2
C
enters the lattice of (NH ) C O $H O substitutionally, the
4
4
2
2
2
Fig. 4. Absorption spectrum of Mn
in ammonium oxalate
2C
charge compensation model is different to that of Cu
doped (NH ) C O $H O [29]. According to theory [30] the
monohydrate in the wavelength range 195–325 nm (incident beam
is perpendicular to the ab face of the crystal).
4 2
2
4
2
4
degeneracy of the E
g
(G) level is expected to be lifted in
Table 2. The orthorhombic symmetry is evident due to the
K4 K1
presence of the E term. The values of D(814.9!10 cm
tetragonal or rhombic but not in trigonal distortion. The
4
6
splitting of the sharp band A1g(S)/ E
g
(G) in the present
)
2C
2
C
K4
K1
2C
study suggests that Mn
octahedral site.
The comparison of the present EPR investigation with
is in a rhombically distorted
and E(163.8!10 cm ) for Mn in BiVO
4
with Mn
[28] having approximately orthor-
hombic local field symmetry, are larger as compared to this
3C
substituting for Bi
2
C
K4
K1
K4
K1
the previous EPR study [12] of Mn
K4
doped KHSO4
K1 K4
study(DZ257!10 cm , EZ85!10 cm ). This
may be due to different local ionic arrangement around
K4
K1
(
AZ66!10 cm , BZ26!10 cm , DZ59!10
K1
K4
K1
K4
K1
cm , EZ32!10 cm , aZK8!10 cm , BZ
K1
K1
K1
6
that the parameters A, B, D, E, a, B, C and Dq are larger
27 cm , CZ2580 cm
and DqZ790 cm ) shows
in the present case. This can be explained on the basis of
2
C
bonding. The hyperfine splitting for Mn substituted in a
number of crystals depends on the host lattice, it is
appreciably larger for ionic crystals as compared to covalent
ones [31]. The mechanism of covalent reduced hyperfine
splitting involved covalency hindered 3s/4s excitation
with a partially occupied 4s orbital. It was suggested [32]
that the reduction of hyperfine splitting was due to the
2C
Fig. 5. The energy level diagram of Mn in ammonium oxalate
monohydrate showing the variation of the levels with Dq for a case
K1
Fig. 6. The configuration of the oxalate group and the atomic
surroundings of the water molecule and the ammonium ion in
K1
K1
and aZ76 cm (the circles
with BZ897 cm , CZ2144 cm
show the experimental energies).
4 2 2 4$ 2
(NH ) C O H O.

704
R. Kripal, V. Mishra / Solid State Communications 134 (2005) 699–704
2
C
2C
the previous study of Mn
discussion has been presented.
decrease of the 3d electron spin density at the Mn site due
to covalency. The relative amount of 4s-bonding increases
on going to more covalent crystals. The reduction of
doped KHSO4 and a brief
2
C
4
hyperfine splitting of Mn doped KHSO is consistent
with the larger covalency (20%) in it as compared to the
Acknowledgements
2C
present system (14%). The larger D and E values of Mn
doped ammonium oxalate monohydrate than that of Mn
˚
doped KHSO are because of NH –O bond length (2.85 A)
2
C
One of the authors (Vishal Mishra) is grateful to Council
of Science and Technology, U.P. (India) for financial
support.
4
4
˚
being shorter than the K–O bond length (2.98 A). However,
2
C
the local ionic arrangement around Mn is different in the
two cases giving different crystal field strength and
consequently different zero field splitting parameters [15].
References
2C
4
The rise in a in Mn doped KHSO would be expected to
be associated with the decrease of ionicity of the Mn ion
2
C
[
1] J.A. Weil, et al., Electron Paramagnetic Resonance, Wiley,
New York, 1994.
2C
[
8]. The smaller B, C and Dq values of Mn doped KHSO4
as compared to the present case may also be expected to be
[
[
2] C. Rudowicz, et al., J. Phys. Chem. Solids 53 (1992) 1227.
3] B. Aktas, et al., J. Magn. Magn. Mater. 258 (2003) 409.
2
C
associated with the larger covalency of Mn in KHSO
9].
The ionic radii of Mn , K and NH
4
[8,
1
[4] P.S. Rao, et al., Mol. Phys. 54 (1985) 415.
2
C
C
C
4
are 0.80, 1.33
[5] S.K. Misra, et al., Magn. Reson. Rev. 16 (1991) 57.
[6] R.S. de Biasi, et al., J. Phys. Chem. Solids 64 (2003) 1965.
2
C
˚
and 1.43 A, respectively. Thus for the substitutional Mn
in KHSO4 and (NH ) C O $H O, the amount of local
distortion may be expected to be slightly larger in the former
lattice than that in the latter. According to Owen [33] and
Stevens [34] the d3 electrons of manganese having
[
[
7] S.B. Hendricks, et al., J. Chem. Phys. 4 (1936) 102.
8] A. Abragam, et al., EPR of Transition Ions, Clarendon Press,
Oxford, 1970.
4 2
2
4
2
[
9] C.P. Poole Jr., et al., Theory of Magnetic Resonance, Wiley,
New York, 1972.
3
2
(
d3) (dg) configuration will move into the orbits of the
[
[
[
10] B. Bleaney, et al., Proc. R. Soc. A 223 (1954) 1.
11] P.S. Rao, et al., Mol. Phys. 54 (1985) 429.
adjacent oxygen ions (2pp orbits) and form p bonding and
the dg electrons will interact with 2ps and 2s electrons of
the oxygen ions and form s bonding. The effect of p and s
bonding increases the crystal field strength and conse-
quently the crystal field splitting. The smaller the strength of
p bond the smaller will be the amount of local distortion
12] Ram Kripal, et al., Solid State Commun. 133 (2005) 23.
[13] O. Matumura, J. Phys. Soc. Jpn. 1959; 14108.
[14] M.G. Zhao, et al., in: Xie Xide (Ed.), Statistical Physics and
Condensed Matter, World Scientific, Singapore, 1986.
[
15] T.H. Yeom, et al., Phys. Rev. B 53 (1996) 3415.
2
C
[16] H. Watanabe, J. Phys. Chem. Solids 25 (1964) 1471.
[
35]. Thus stronger covalent bonding in Mn
KHSO gives larger amount of distortion in the lattice.
doped
[
[
[
[
[
[
17] Y. Tanabe, et al., J. Phys. Soc. Jpn. 9 (1954) 753.
18] A. Mehra, J. Chem. Phys. 48 (1968) 4384.
4
19] J. Owen, et al., Rep. Prog. Phys. 29 (1966) 675.
20] M.J.D. Powell, et al., Phys. Rev. Lett. 5 (1960) 145.
21] J.R. Gabriel, et al., Proc. R. Soc. A 264 (1961) 503.
22] A. Mehra, et al., Phys. Rev. Lett. 19 (1967) 145.
6
. Conclusion
The EPR study of Mn
2C
doped Ammonium Oxalate
[23] M.L. Du, et al., J. Phys. C: Solid State Phys. 18 (1985) 3241.
[24] G.D. Watkins, Phys. Rev. 113 (1953) 79.
Monohydrate has been done at 77 K. The spin Hamiltonian
parameters g, A, B, D, E and a have been determined. From
the results a rhombically distorted octahedral substitutional
[25] M.M. Zaripov, et al., Sov. Phys. Solid State 6 (1964) 1290.
[
26] T.E. Freeman, et al., J. Phys. C 7 (1974) 2365.
2
C
[27] Y. Yokozawa, et al., J. Phys. Soc. Jpn. 16 (1961) 694.
site is predicted for the Mn
species. The optical
[
[
[
[
[
[
28] T.H. Yeom, et al., J. Phys.: Condens. Matter 4 (1992) 587.
29] M. Korkmaz, et al., Phys. Status Solidi B 112 (1982) 423.
30] L.L. Lohr Jr., J. Chem. Phys. 45 (1966) 3611.
absorption study has been done at room temperature and
the bands observed have been assigned to transitions from
6
the A1g(S) ground state to various excited levels of Mn
2C
31] J.S. Van Wieringen, Discuss. Faraday Soc. 19 (1955) 118.
32] E. Simanek, et al., J. Phys. Chem. Solids 31 (1970) 1027.
33] J. Owen, Proc. R. Soc. A 227 (1955) 183.
ion in cubic crystalline field. The observed band positions
have been fitted with four parameters B, C, Dq and a and
covalency of the metal–ligand bond has been discussed. The
results of this investigation have been compared with that of
[34] K.W.H. Stevens, Proc. R. Soc. A 219 (1953) 542.
[35] M. Sharnoff, et al., J. Chem. Phys. 43 (1965) 2993.