Photon Factory Activity Report 2022 #40 (2023)
BL-16A/2021G501

Study of Electronic and Magnetic Characteristics of CoMn2O4 Nanoparticles using XRay Magnetic Circular Dichroism
A. KUMARI1, M. ZZAMAN1, R. PAL2, V. K. VERMA3, K. KUMAR4, K.
AMEMIYA5, and V. R. SINGH1*
1

Department of Physics, Central University of South Bihar, Gaya 824236
Department of Chemistry, Madanapalle Institute of Technology & Science, Angallu,
Madanapalle 517325, India

2

3

Department of Physics, VIT-AP University, Amaravati 522237 A.P. India
4
Department of Physics, Ranchi University, Ranchi 834008, India
5
Photon Factory, IMSS, High Energy Accelerator Research Organization, Tsukuba,
Ibaraki 305-0801, Japan

Introduction: Spinel structure metal oxides
have been the subject of current investigation
due to their unique optical, electronic,
mechanical and thermal characteristics.
According to Bragg and Nishikawa, theAB2O4 spinel, is made up of a cubic, densely
packed arrangement of cations that havemore than one oxidation state and areoccupied by oxygen atoms in the tetrahedral(A) and octahedral (B) sites. Spinel's cationic
distribution is expressed by the formula (A1xBx)[AxB2-x]O4, where x represents thedegree of inversion [1-2]. Normal spinels are
created when x=0, while inverted spinels are
created when x=1. A mixed spinel isproduced when x selects a number halfway
between 0 and 1. Spinel oxides
characteristics can be significantly changedby the cation distribution. Cation site choice
is influenced by ion size, ion electronic
configuration, and the strength and symmetryof the crystals present at the site [3]. The typeof magnetic ordering formed in the material
is determined by the dominant exchange
contact between and within the octahedral(B) and tetrahedral (A) sub-lattices. A-B
interactions are more powerful than A-A or
B-B interactions, according to Neel's two
sub-lattice paradigm. Ferrimagnetic ordering
is caused by the disparity between theamount of ions present in the tetrahedral andoctahedral sites and by the robust exchangeinteraction between the sub-lattices [4].
When compared to Fe-rich spinel oxides(such as Fe3O4, MnFe2O4, and NiFe2O4),
magnetic properties of Mn-rich spinel oxides(ZnMn2O4, CoMn2O4, and FeMn2O4) areinvestigated relatively less. This might bebecause Mn-rich spinels have complicatedmagnetic behaviour and low-temperaturemagnetic
measurement
systemsarenecessary. Instead of adhering to Neel's
antiparallel spin, Mn3O4 is a ferrimagnetic
spinel that exhibits a triangle spinarrangement as proposed by Yafet and Kittel[5]. Magnetic dilution effect can be seen,
leading to weak exchange contacts, when
non-magnetic ions like Mg or Zn are
substituted at tetrahedral sites. However,when magnetic ions like Co, Ni, or Fe areused in place of Mn ions, complex magnetic
behaviour is seen. This could be because thelattice sites are varying for exchange with
one another. Understanding this complicatedbehaviour seen in the magnetic ion
substituted Mn-rich spinels is therefore
urgently needed. Therefore a study carriedout using advanced synchrotron-based X-ray
Absorption Spectroscopy (XAS) and X-ray
Magnetic Circular Dichroism (XMCD)
technique for the CMO samples to unveil
their magnetization behaviour.

Photon Factory Activity Report 2022 #40 (2023)

The polycrystalline CMO
nanopowders were synthesized using coprecipitation method. The ultra-pureprecursors CoCl2. 6H2O and MnCl2. 6H2O
were used to prepare the high-purity
polycrystalline samples of CMO. A clearsolution was produced after combining theinitial ingredients in a stoichiometric ratiowith DI water. The required amount ofconcentrated ammonia solution wasintroduced to keep the pH of the solution at
7. A greenish-blue colloidal gel was createdby heating it to 80° C, then dried attemperatures above 100° C until it wascompletely transformed into CMO powder.
The CMO product was permitted to cool toroom temperature before the powder wasobtained and was calcined for 3h at 300° C.
The finished result was a greyish-pinkcolour. After that, the material was annealedfor 3h at 700° C. The furnace-cooled samples
Experiment:

were pulverised into a fine powder. The
single phase of the substance was confirmed
by characterizing the produced samples
using a Rigaku Smart Lab powder X-ray
diffractometer. The variable polarisation soft
x-ray beam-line BL-16A of the Photon
Factory was used to perform X-ray
spectroscopy, scattering, and imaging studies(KEK, Japan). The experimental geometry
for the investigations of x-ray magnetic
circular dichroism (XMCD) and soft x-ray
absorption (XAS) is shown in Figures 1 and2. A 5 T superconducting magnet was used
to place the sample in the 10-9 Torr vacuum
chamber. Right and left circularly polarised(RCP and LCP) x-rays were used to measure
the XAS and XMCD signals at varying
magnetic fields of 0T, 1T and 2T using thesurface-sensitive total electron yield (TEY)technique near the Co L2,3 and Mn L2,3
absorption edges (only the XAS data of 1Thas been shown here).

Figure 1(a) XAS spectra, 1(b) XMCD intensity ratio for Mn L-edge w.r.t applied field of 0, 1and 2T.

Photon Factory Activity Report 2022 #40 (2023)

Figure 2(a) XAS spectra, 2(b) XMCD intensity ratio for Co L-edge w.r.t applied field of 0, 1,
and 2T respectively.
surface. Henceforth, based on obtained result
Results and Discussions: The XAS spectra
it can be concluded that unlike Mn, Co 2p tocollected at the applied magnetic fieldCo 3d transition is not-localized and infuses
strength of +1.0 and -1.0T are represented bymore oxidation of the material. XMCD++μ and μ . The symbols μ and μ denotes left
signal collected for Co L2,3 and Mn L2,3 edges
and right circularly polarized light as shown
are not shown here. The XMCD signal at thein Figure 1(a) and 2(a). The XMCD spectrum
Mn L2 edge and Co L2 edge is notably
was collected by taking a difference of two
suppressed, indicating magnetic ordering due
XAS spectra with opposite helicities i.e.,
to fully occupied t2g level. The XMCD
negative and positive of the circularly
intensity ratio w.r.t. the variable magnetic
polarized light. It is known from the literaturefield with 0T, 1T and 2T are shown in Figure
that; CMO shows a paramagnetic behaviour
1(b) for Co and Mn-edges. This result is quite
at room temperatures. In the CMO, the Mn
relatable with the XMCD graphs. Figure 1(b)and Co absorption spectra both shows aand 2(b) exhibits that the intensity ratio ofmultiplet structure at the L3 edges. FromXMCD data increases with increasing
XAS spectra Co L edge, it is clear that Comagnetic-field strength.
shows multiple absorption peak at L3 edge
along with a satellite peak positioned at E=
779.01 eV; here the L2 peak shows singlet
feature at 794.53 eV. Well-resolved peaks at
the absorption maxima of Mn L3-edge at E =Acknowledgements: The experiments at the640.55 eV and 642.5 eV exhibits a doublet
Photon Factory was approved by thestructure at the L3 edge, whereas, maxima at
E = 651.85 eV at L2 edge is clearly
Program Advisory Committee (Proposalobservable. This verifies that the fineNos. 2021G501). Authors acknowledges
structures of the Mn 2p → 3d transition
support from UGC-BSR Start-up Researchshould result from the localization of Mn 3dGrant F. 30-395/2017(BSR).
electrons rather than the oxidation of thePhoton Factory Activity Report 2022 #40 (2023)

References:
1. W.H. Bragg, The structure of the spinelgroup the crystals. Philos. Mag. 6, 305(1915).
2. S. Nishikawa, Structure of some crystalsof spinel group. J. Mat. Phy. Soc. Japan 8,
199 (1915).
3. A.H. Morrish, The Physical Principles ofMagnetism (Wiley-IEEE Press, New York,
2001).
4. L.M. Neel, Properietes magnetiques desferrites;
ferrimagnetism
etantiferromagnetism. Ann. Phys. 12, 137(1948).
5. K. Dwight, N. Menyuk, Magnetic
properties of Mn3O4 and the canted spin
problem. Phys. Rev. 119, 1470 (1960).

*corresponding Email: vijayraj@cusb.ac.in