Comparative study of the relaxation process of cobalt ferrite via time-resolved differential reflectivity

Ping-Yi Wang^1*, Chih-Chao Chang¹, Tahta Amrillah^2,3,4, Hao-Che Chan¹, Jenh-Yih Juang¹, Yu-Miin Sheu^1,5

¹Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu, Taiwan
²Nanotechnology Engineering, Faculty of Advanced Technology and Multidiscipline, Universitas Airlangga, Surabaya, Indonesia
³Airlangga Functional Nanomaterials Research Group, Faculty of Advanced Technology and Multidiscipline, Universitas Airlangga, Surabaya, Indonesia
⁴Research Centre for New and Renewable Energy Engineering, Universitas Airlangga, Surabaya, Indonesia
⁵Center for Emergent Functional Matter Science, National Yang Ming Chiao Tung University, Hsinchu, Taiwan

* Presenter:Ping-Yi Wang, email:iamkingoffool@gmail.com

Cobalt ferrite, CoFe₂ O₄ (CFO), continues to attract significant research interest owing to its potential in artificial multiferroic heterostructures, catalysis, and spintronics. To gain further insight into energy transfer in the heterostructures and the magnetism or spintronic devices, we perform the time-resolved differential reflectivity, measuring the energy relaxation following photon absorption in CFO. In this study, we aim to pump the d-d transition to directly probe the d-orbital electrons and compare it with excitation above the optical bandgap for comparison. The time-resolved differential reflectivity measurement requires four time constants to accurately capture all decay features. In the fluence-dependent experiment, the fastest decay observed in the above-bandgap excitation accelerates with the increase in fluence, whereas the corresponding decay in the d-d transition is not affected. In addition, the phonon-related time constant monotonically decreases with increasing sample temperature for both pump energies.

Keywords: ultrafast, cobalt ferrite, d-d transition