Coexistence of tetragonal and cubic phase induced complex magnetic behaviour in CoMn2O4nanoparticles

Sanjna Rajput; Manish Yadav; Taranga Dehury; Akhilesh Kumar Yadav; Pratap Kumar Sahoo; Chandana Rath

doi:10.1088/1361-6528/ace3cb

Coexistence of tetragonal and cubic phase induced complex magnetic behaviour in CoMn₂O₄nanoparticles

Nanotechnology. 2023 Jul 31;34(42). doi: 10.1088/1361-6528/ace3cb.

Authors

Sanjna Rajput¹, Manish Yadav¹, Taranga Dehury¹, Akhilesh Kumar Yadav¹, Pratap Kumar Sahoo², Chandana Rath¹

Affiliations

¹ School of Materials Science and Technology, Indian Institute of Technology (BHU), Varanasi, Uttar Pradesh, 221005, India.
² School of Physical Sciences, National Institute of Science Education and Research (NISER) Bhubaneswar, Jatni-752050, Odisha, India.

PMID: 37402363
DOI: 10.1088/1361-6528/ace3cb

Abstract

CoMn₂O₄, known for its extensive range of applications, has been subject to limited investigations regarding its structure dependent magnetic properties. Here, we have examined the structure dependent magnetic properties of CoMn₂O₄nanoparticles synthesized through a facile coprecipitation technique and are characterized using x-ray diffractometer, x-ray photoelectron spectroscopy (XPS), RAMAN spectroscopy, transmission electron microscopy and magnetic measurements. Rietveld refinement of the x-ray diffraction pattern reveals the coexistence of 91.84% of tetragonal and 8.16% of cubic phase. The cation distribution for tetragonal and cubic phases are (Co_0.94Mn_0.06)[Co_0.06Mn_1.94]O₄and (Co_0.04Mn_0.96)[Co_0.96Mn_1.04]O₄, respectively. While Raman spectra and selected area electron diffraction pattern confirm the spinel structure, both +2 and +3 oxidation states for Co and Mn confirmed by XPS further corroborate the cation distribution. Magnetic measurement shows two magnetic transitions, Tc₁at 165 K and Tc₂at 93 K corresponding to paramagnetic to a lower magnetically ordered ferrimagnetic state followed by a higher magnetically ordered ferrimagnetic state, respectively. While Tc₁is attributed to the cubic phase having inverse spinel structure, Tc₂corresponds to the tetragonal phase with normal spinel. In contrast to general temperature dependentH_Cobserved in ferrimagnetic material, an unusual temperature dependentH_Cwith high spontaneous exchange bias of 2.971 kOe and conventional exchange bias of 3.316 kOe at 50 K are observed. Interestingly, a high vertical magnetization shift (VMS) of 2.5 emu g^-1is observed at 5 K, attributed to the Yafet-Kittel spin structure of Mn³⁺in the octahedral site. Such unusual results are discussed on the basis of competition between the non-collinear triangular spin canting configuration of Mn³⁺cations of octahedral sites and collinear spins of tetrahedral site. The observed VMS has the potential to revolutionize the future of ultrahigh density magnetic recording technology.

Keywords: Jahn–Teller effect; Yafet–Kittel spins; exchange bias; spinel; vertical magnetization shift (VMS).