ORIGINAL PAPER Comparative study of microscopic, spectroscopic and magneto-optic response of ferrofluids subjected to c-radiation M Devi 1 *, D Mohanta 1 and A Saha 2 1 Nanoscience and Soft Matter Laboratory, Department of Physics, Tezpur University, Napaam, Tezpur 784028, Assam, India 2 Department of Atomic Energy Consortium for Scientific Research, Kolkata Centre, University Grants Commission, III/LB-8 Bidhannagar, Kolkata 700 098, India Received: 10 February 2014 / Accepted: 26 May 2014 / Published online: 17 July 2014 Abstract: Present work reports a comparative study of spectroscopic and magneto-optic properties of Fe 3 O 4 based ferrofluids prepared with two different carrier fluid namely milli-Q-water and kerosene. The ferrofluids are labelled as FFW and FFK respectively. Both ferrofluids are subjected to c-irradiation of dose: 2,635 Gy. Transmission electron microscopy and dynamic light scattering studies reveal that c-photon interaction could lead to substantial growth of the dispersed nanoparticles of ferrofluids. In case of FFW, particle sizes are *9 nm (pristine) and *48 nm (irradiated) whereas, in FFK unirradiated particles of size *9 nm show growth to *18 nm after the irradiation. The role of different physical parameters (viz. viscosity, density) of carrier fluid on the growth process is considered in this regard. Viscosity of the carrier fluid is found noteworthy in the measurement of Faraday rotation response of the ferrofluids. In addition to low viscosity of water, irradiation induced particle growth as well as improved size distribution with larger particles leads to a comparatively larger enhancement of Faraday rotation of FFW than that of FFK. Consequently, as a result of c-irradiation, Verdet constant is modified by *70 % in the former case and by *60 % in the latter case. Keywords: Ferrofluid; Carrier; c-Irradiation; Faraday rotation PACS Nos.: 47.65.Cb; 76.80.?y; 78.20.Ls 1. Introduction Gamma (c)-radiation is regarded as the most energetic electromagnetic radiation. It is abundant in outer space environment through which the space shuttles travel [1]. Compared to a and b-rays, c-rays possess highest pene- trating power without any divergence. Typically, c-rays have energy more than 100 keV and wavelength \10 pm with frequency above 10 19 Hz. c-photon interacts with atoms and charged species while traversing through matter. It has mixed impact on different materials [2]. In material science, c-radiation has been widely used for the creation of point defects [3–5]. It has been reported that a high dose c-radiation could lead to production of second order point defects [6]. This high energetic photon is also capable of creating/annihilating defects in chemically stable system for example, (Gd 2 O 3 )[7]. It is also reported that rheolog- ical property of rare earth based nanoscale system is modified as a result of c-irradiation on the system [8]. A ferrofluid (FF) is basically a colloidal system com- prising of surfactant coated magnetic nanoparticles (MNPs) suspended in an appropriate carrier fluid [9]. Originally, it is developed by NASA to unravel some of the hurdles (pumping, sealing, shielding etc.) of space craft and space shuttle [10]. Now-a-days, FF based sealing and shielding are widely used in aerospace devices [11]. Experimental condition and/or the constituents adequately govern the physical, chemical, magnetic properties of a FF. FF pre- pared with ion irradiated MNPs exhibits enhanced mag- neto-optic responses than its counterpart prepared with pristine nanopartilces [12]. Morphology and structure of MNPs play a crucial role in determining the overall prop- erties of a FF [13, 14]. Stability of FF is largely controlled by surfactants [15]. Additionally, carrier fluid influences flow property of the dispersed particles of a FF [16]. Till date, the role of carriers in determining magnetic properties *Corresponding author, E-mail: manasidevi25@gmail.com Indian J Phys (February 2015) 89(2):115–121 DOI 10.1007/s12648-014-0522-6 Ó 2014 IACS