Predicting a major role of surface spins in the magnetic properties of ferrite nanoparticles

Abstract

Room-temperature magnetization hysterisis measurements were conducted on Mn 0.5 Zn 0.5 Gd x Fe (2-x) O 4 ferrite nanoparticles, with x = 0, 0.5, 1.0, 1.5. The structure of this ferrite is normal spinel where the added of Gd 3+ions occupied the octahedral sites and replaces Fe 3+ ions. The saturation magnetization was found to increase with the initial addition of the Gd 3+ ions followed by a sharp decrease with further addition of Gd 3+ ions. The Curie temperature was found to increase up to Gd 3+ concentration of x = 1.0, and then decreases at x = 1.5. These results were attributed to the surface spins. Because the size of Gd 3+ ions is larger than that of Fe 3+ions, the substitution of Fe 3+ ions with the Gd 3+ ions results in surface disorder which results in surface spins. A core-shell magnetization model was introduced where several factors were combined to explain our results.

Magnetization dynamics in rare earth Gd3+ doped Mn0.5Zn0.5Fe2O4 magnetic fluid: Electron spin resonance study

“…One way to do this is to substitute rare earth ion in the system. It is known that when rear earth ions are substituted in ferrite in a very small concentration (as in the present case), it modifies the interaction at octahedral B-site, because of strong coupling of RE 3+ -Fe 3+ ions (3d-4f coupling) compare to Fe 3+ -Fe 3+ ions [22]. The magnetic moment of the core increases by 53% compared to that of MZ5 system, by 5% doping of Gd 3+ [23].…”

The remanence ratio in CoFe2O4 nanoparticles with approximate single-domain sizes

“…Surface spin is another factor to affect the magnetic properties for the nano-sized magnetic materials. The total magnetization of a nanoparticle composes of the surface and core spins [10, 11], which is known as the core-shell magnetization model. Surface spins reduce the magnetization of a magnetic nanoparticle due to the disorder of spins at the nanoparticle surface, and the disordered surface spins lower the critical magnetic ordering temperature of magnetic nanoparticles compared with that of the bulk material [12].…”

Simultaneous effects of surface spins: rarely large coercivity, high remanence magnetization and jumps in the hysteresis loops observed in CoFe2O4nanoparticles

“…7,[8][9][10][11][12][13][14] One member of the magnetic material family, cobalt ferrite (CoFe 2 O 4 ), is very attractive because of its high saturation magnetization (M s ) and magnetic anisotropy, which give rise to desirable magnetic behavior at room temperature. 17 Because of finite size effects, the total magnetization of a nanoparticle originates from the surface and core spins, 18,19 which is known as the core-shell magnetization model. 17 Because of finite size effects, the total magnetization of a nanoparticle originates from the surface and core spins, 18,19 which is known as the core-shell magnetization model.…”