Ferrite nanocrystals are interesting material due to their rich physical properties. Here we add nonmagnetic dopants Zn and Cu to nickel ferrite nanocrystals, Ni 1-x M x Fe 2 O 4 (0≤x≤1, M{Cu, Zn}), and characterize how relevant properties of the samples are modified accordingly. Basically, these dopings cause a rearrangement of Fe +3 ions into the two preexisting octahedral and tetrahedral sites. In fact, this, we show, induces pertinent magnetic properties of the doped samples. In the case of the Cudoping, the Jahn-Teller effect also emerges, which we identify through the FTIR Spectroscopy of the samples. Moreover, we show an increase in the lattice parameters of the doped samples, as well a superparamagnetic behavior for the doped samples is shown, while the Jahn-Teller effect precludes a similar behavior in the CuFe 2 O 4 nanocrystals. The influences of Zn and Cu substitutions are investigated on the optical properties of nickel ferrite nanocrystals by photoluminescence measurement at room temperature.Keywords: ferrites 75.50.Gg, sol-gel processing 81.20.Fw, nanocrystalline magnetic materials 75.50.Tt, superparamagnetic 75.20.-g, magnetic anisotropy 75.30.Gw, Jahn-Teller effect 71.70.Ej diffraction (refined with the Rietveld method with the MAUD software), Field-Emission Scanning Electron Microscope (FE-SEM), Fourier Transform Infra-Red (FTIR) spectroscopy, Vibrating Sample Magnetometer (VSM), and Photoluminescence (PL), and UV-Vis spectrometer at room temperature. We thus compare the effect of dopings not only regarding structural and magnetic properties, but also in the sense of optical properties. In addition, here the Jahn-Teller effect has is studied through the investigation of the structural and magnetic properties.
Experimental details
Preparation methodThe sol-gel method is widely used in synthesis of ferrite nanocrystals because of its high reaction rate, low preparation temperature, and production of small particles. Hence, in our experiment, magnetic nanocrystalline Ni 1-x Zn x Fe 2 O 4 with x=0, 0.3, 0.5, 0.7, 1 and Ni 1-x Cu x Fe 2 O 4 with x=0, 0.5, 1 were synthesized by this method. Citric acid C 6 H 8 O 7 , ferric nitrate Fe(NO 3 ) 3 .9H 2 O (98%), nickel nitrate Ni(NO 3 ) 2 .6H 2 O (99%), zinc nitrate Zn(NO 3 ) 2 .6H 2 O (99%) and copper nitrate Cu(NO 3 ) 2 .3H 2 O (99%) were produced by Merck ®company and were used as raw materials. The stoichiometric amount of nitrates and acid citric were dissolved separately in deionized water to make 0.5M solutions. The mole ratio of metal nitrates to citric acid was taken as 1:1. To obtain smaller nanocrystals, we added ethylenediamine to the solution until its pH became 1. Next, the sol was heated continuously at 70°C under stirring to form a brown dried gel. This gel was fired at 135°C in oven for 24h, and was then ground into powder. To obtain various Cu +2 and Zn +2 substitutions, we calcined the powder at 300-600°C for 4h.