Pulse magnetization measurements in ferrofluids

Influence of Magnetic Field on the Two-Photon Absorption and Hyper-Rayleigh Scattering of Manganese–Zinc Ferrite Nanoparticles

“…The Néel relaxation contributes when magnetic nanoparticles are fixed to a solid phase, which is not the case in this work, or unstable aggregated magnetic fluids contain sediments, that if existent in our samples, do not contribute to the optical signal since only suspended nanoparticles are being illuminated by the laser beam. Therefore, in the present case, the main mechanism of orientation is the Brownian process, which occurs on a short time scale, around hundreds of microseconds. , When the optical experiments take place, there is alignment of the axis of easy magnetization to the magnetic field lines, and because nanoparticles are monocrystalline, the alignment of crystallographic planes of the material. In this case, the characteristic time to complete the alignment is hundreds of microseconds. , Therefore, the differences verified on the nonlinear optical parameters shown on Figures to are due to the alignment of crystallographic planes and, consequently, the anisotropy of the system.…”

“…Therefore, in the present case, the main mechanism of orientation is the Brownian process, which occurs on a short time scale, around hundreds of microseconds. 27,72 When the optical experiments take place, there is alignment of the axis of easy magnetization to the magnetic field lines, and because nanoparticles are monocrystalline, the alignment of crystallographic planes of the material. In this case, the characteristic time to complete the alignment is hundreds of microseconds.…”

“…The presence of uniform magnetic field leads to the orientation of the magnetic momentum of individual nanoparticles to the field direction. It is well-known that, in general, for liquid samples, both Brownian and Néel mechanisms contribute to the alignment and relaxation of magnetic nanoparticles, ,, and the effective relaxation time τ eff = τ B τ N /(τ B + τ N ), where τ B is the Brownian relaxation time and τ N the Néel relaxation time. Nevertheless, the time dependencies of Brownian and Néel relaxations are clearly different, and for a stable ferrofluid dispersed in a liquid of low viscosity, the Brownian mechanism is dominant.…”

Bifurcating Instability of the Free Surface of a Ferrofluid

“…Over the past 15 years this and related phenomena have been under investigation. Formal mathematical techniques have produced results in agreement with experimental data.…”

“…Since the effect studied is a surface deformation and the ferrofluids are liquid, the fluid is assumed to be incompressible and of large but finite depth, D. After any short-term effects have died out [15] (say, two seconds) and prior to any long-term separation of carrier fluid and suspended particles [16] (say, two hours), it is reasonable to assume that the ferrofluid is magnetically linear, isotropic and free of internal currents when a magnetic field of limited strength is applied [17]. Since the effect studied is a surface deformation and the ferrofluids are liquid, the fluid is assumed to be incompressible and of large but finite depth, D. After any short-term effects have died out [15] (say, two seconds) and prior to any long-term separation of carrier fluid and suspended particles [16] (say, two hours), it is reasonable to assume that the ferrofluid is magnetically linear, isotropic and free of internal currents when a magnetic field of limited strength is applied [17].…”