Spin–phonon coupling in ferrimagnet spinel CoMn2O4

Abstract

Coupling of material properties provides new fundamental insights and possibilities toward multifunctional devices. The spinel structures display strong coupling between different order parameters, as a consequence, exhibiting many fascinating properties like multiferroicity, superconductivity etc. Here, we have investigated structural, magnetic, and vibrational properties of mixed-spinel CoMn2O4, stabilized in distorted tetragonal structure as evidenced from X-ray diffraction measurements. Magnetization measurements reveal two ferrimagnetic phase transitions at 185 K and 90 K. Raman scattering measurements reveal the renormalization of phonon parameters for a few phonon modes at low temperatures, arising from spin-phonon coupling. The obtained value for λS2 is ~ 2 cm-1. The strength of the spin-phonon coupling (λ) is estimated according to the spins involved in corresponding lattice vibrations and discussed.

Coexistence of tetragonal and cubic phase induced complex magnetic behaviour in CoMn2O4 nanoparticles

“…Further structural characteristics have been confirmed via Raman spectroscopic technique at room temperatures as shown in figure 4. According to the group theory, the tetragonal CoMn 2 O 4 with a space group of I41/amd should have ten first-order Raman-modes namely 2A 1g , 3B 1g , B 2g and 4E g [38]. Here, we observe six Raman modes present within 100-1300 cm −1 .…”

“…The remaining modes are either too weak in intensity or have energies below the experimental cut-off wave number. The observed broad peaks at 174, 307, 363, 480, 594 and 641 cm −1 correspond to B 1g , A 1g , B 2g , E g , B 1g and A 1g modes, respectively [38,47]. In the low-fRequency region, the first Raman mode B 1g is assigned to the cobaltoxygen stretching in the tetrahedral site [16].…”

“…In the low-fRequency region, the first Raman mode B 1g is assigned to the cobaltoxygen stretching in the tetrahedral site [16]. A 1g and B 2g modes are related to the oxygen vibrations in both MnO 6 octahedral / MnO 4 tetrahedral site [16,38]. While E g mode is ascribed to the Co-O/Mn-O movement in tetrahedral site [38,48], high frequency B 1g and A 1g are assigned to the oxygen vibrations in octahedral site [16].…”

“…A 1g and B 2g modes are related to the oxygen vibrations in both MnO 6 octahedral / MnO 4 tetrahedral site [16,38]. While E g mode is ascribed to the Co-O/Mn-O movement in tetrahedral site [38,48], high frequency B 1g and A 1g are assigned to the oxygen vibrations in octahedral site [16]. It is further observed that above Tp 1 the ZFC and FC curves coincide, showing that the system is in equilibrium due to the fast fluctuations of the magnetic moments of the nanoparticles [24].…”

“…For instance, Mehata et al synthesized bulk CoMn 2 O 4 by thermal decomposition of metal-organic framework compound [CoMn 2 (C 6 H 3 (COO) 3 ) 2 ], and have reported transitions at 190 and 90 K [22] while Boucher et al report a single transition at 100 K for bulk [34]. Polycrystalline CoMn 2 O 4 in bulk prepared by solid state reaction method owns these transitions at 185 and 90 K [38], whereas nanoparticles synthesized by thermal decomposition show transitions at 167.5 and 86.3 K; 177.7 and 82.3 K [24]. Here, one may conclude that these transition temperatures can vary from 165 to 190 K and 78 to 90 K. While the former high transition temperature has been attributed to impurity phase related to Co 3−x Mn x O 4 , the later low transition temperature is due to the presence of Y-K spin structure [34].…”