Pulsed Field-Induced Magnetization Switching in Antiferromagnetic Ferrihydrite Nanoparticles

Abstract

The dynamic magnetization switching of ferrihydrite nanoparticles has been investigated by a pulsed magnetometer technique in maximum fields H max of up to 130 kOe with pulse lengths of 4, 8, and 16 ms. Ferrihydrite exhibits antiferromagnetic ordering and defects cause the uncompensated magnetic moment in nanoparticles; therefore, the behavior typical of magnetic nanoparticles is observed. The dynamic hysteresis loops measured under the above-mentioned conditions show that the use of pulsed fields significantly broadens the temperature region of existence of the magnetic hysteresis and the coercivity can be governed by varying the maximum field and pulse length. This behavior is resulted from the relaxation effects typical of conventional ferro-and ferrimagnetic nanoparticles and the features typical of antiferromagnetic nanoparticles.

Longitudinal remagnetization of uniaxial antiferromagnetic nanoparticles: the role of spontaneous magnetic moment

“…As expected, the value of q c grows with an increase of the field amplitude and the rate of its change. This behaviour of the coercivity is indeed observed in experiments on remagnetization of ferrihydrite and nickel oxide nanoparticles [24,25]. Moreover, in full agreement with the measurements, the dependence of q c on the field change rate is not universal: the actual curve is determined by the frequency ωτ 0 .…”

“…This effect distinguishes antiferromagnetic particles with a spontaneous magnetic moment from ferromagnetic ones, since for the latter the dependence of H c on (dH/dt) max is practically independent of the field frequency [26]. It is noteworthy that the sequences of the curves in figure 8a,b are opposite: at a fixed field amplitude, the frequency growth leads to an increase of the coercivity, while at a fixed field change rate, to a decrease, exactly as in experiments [24][25][26]. Finally, note that the initial parts of the plots in figure 8a are straight lines.…”

Features of the quasi-static and dynamic magnetization switching in NiO nanoparticles: Manifestation of the interaction between magnetic subsystems in antiferromagnetic nanoparticles

“…Here, the pulsed technique for studying the dynamic magnetization switching is advantageous as well, since it covers an essentially broader range of the H 0 amplitude than the conventional loop-scope methods. The results of the preliminary investigations of NiO [55] and ferrihydrite [56] nanoparticles showed a significant difference between the effects of parameters of the pulsed field (H 0 and pulse length) on the coercivity in these antiferromagnetically ordered nanoparticles and FM ones. This behavior is apparently the manifestation of the interaction between the magnetic subsystems in AFM nanoparticles.…”

“…This behavior is apparently the manifestation of the interaction between the magnetic subsystems in AFM nanoparticles. This study is devoted to the detailed examination of the quasi-static magnetic properties and effect of the pulsed field-induced magnetization switching on the coercivity of NiO AFM nanoparticles in a wide temperature range (in above-cited studies [55,56], the measurement range was restricted to 78 K). It is demonstrated by the example of NiO nanoparticles that the interaction between the magnetic subsystems in an AFM nanoparticle leads to the nontrivial behavior of the magnetic properties of such objects.…”