ORIGINAL PAPER Structural and Magnetic Properties of CdCoFe 2 O 4 Nanoparticles Nehru Boda 1 & K. Chandra Babu Naidu 2 & D. Baba Basha 3 & D. Ravinder 1 Received: 24 June 2019 /Accepted: 2 August 2019 # Springer Science+Business Media, LLC, part of Springer Nature 2019 Abstract We studied the structure, morphology, and magnetic (at room and low temperature) behavior of Cd x Co 1-x Fe 2 O 4 (x = 0.0–0.6) (CCFO) nanoparticles prepared via citrate gel auto combustion technique. The diffraction pattern indicated the formation of single phase cubic spinel structure. The average crystallite size (D) was altered from 37 to 42 nm with ‘x’. The lattice constants were noticed to be increasing from 0.8419 to 0.8496 nm with ‘x’. The unique morphology was observed for all samples. The saturation magnetization (M s ) was decreased from 28.4 to 3.8 emu/g for x = 0.0 to 0.6 Cd-content. The X-ray (d x ) and exper- imental (d E ) densities were observed to be increased from 5.222 ± 0.013 to 5.777 ± 0.020 g/c.c, and 5.351 ± 0.020 to 5.619 ± 0.019 g/c.c respectively. Furthermore, we observed that the coercivity was changed from 922 to 2600 Oe as a function of composition. The zero field cooled (ZFC) and field cooled (FC) curves of x = 0.5 content revealed the blocking temperature T B ~ 359 K suggesting the superparamagnetic nature above T B . Keywords Nanoparticles . Crystal structure . Surface morphology . Magnetic materials 1 Introduction Magnetic spinels are the important class of materials with a common chemical formula AB 2 O 4 , where A refers to divalent cation and B refers to trivalent metal ion [1]. Due to the con- siderable magnetic property of magnetic spinels, they got more importance for magnetic device applications. It was ob- served that the CoFe 2 O 4 behaves like a hard magnetic material [2]. In addition, the cobalt ferrite and its based materials showed several applications in removal of lead, electronic goods, magnetic devices, superparamagnetism, acetone sen- sors, biomedical, hyperthermia, and photocatalytic activity [3–19]. Specifically, in the literature [1], the CoSmFe 2 O 4 nanoparticles revealed the soft magnet nature at room temperature. In addition, the CoZnFe 2 O 4 nanoparticles showed the superparamagnetism and antimicrobial activity nature [2]. The Sr 0.5 Ba 0.5 Fe 12-2x Co x Cu x O 19 (x = 0.0–0.8) nanoparticles exhibited wide band-gap from 2.80 to 3.54 eV. Thus, these compositions showed the optoelectronic, photo catalytic, and sensor applications [3]. The pure CoFe 2 O 4 en- sured the pure phase structure at 343 K using co-precipitation method [6]. Besides, it showed the blocking temperature T B at 250 K revealing the superparamagnetic nature at room tem- perature. Therefore, the nanoparticles can be used for magnet- ic hyperthermia applications. In the same way, Zhang et al. [7] reported the formation of cobalt ferrite nanoparticles of 10-nm size which were useful for acetone sensor applications. The citric acid–coated cobalt ferrite nanoparticles provided the ef- ficient magnetic hyperthermia applications as reported by Munjal et al. [9]. The Nb-doped CoFe 2 O 4 showed the high magnetization of 50 emu/g by possessing the hard magnet nature (due to high coercivity) [10]. The Ni-doped CoFe 2 O 4 offered high saturation magnetization [12]. Moreover, the same material compositions revealed the single-domain mag- netic nature. From the literature survey, it was observed that the research work related to structural, room and low temperature magnetic properties of Cd-doped CoFe 2 O 4 nanoparticles is not reported. * D. Ravinder ravindergupta28@reddifmail.com 1 Department of Physics, Osmania University, Hyderabad, Telangana 500007, India 2 Department of Physics, GITAM Deemed to be University, Bangalore, Karnataka 562163, India 3 College of Computer and Information Sciences, Majmaah University, Al’Majmaah 11952, Kingdom of Saudi Arabia Journal of Superconductivity and Novel Magnetism https://doi.org/10.1007/s10948-019-05242-1