Theory of quantum tunneling of the magnetization in magnetic particles

Abstract

Theory of quantum tunneling of the magnetization in magnetic particles de Raedt, Hans; Miyashita, S.; Saito, K.; García-Pablos, D.; García, N. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. We study the response of the magnetization to a time-dependent applied magnetic field H(t) in a model for a uniaxial magnet. It is shown that a staircase structure in the magnetization curve results from Landau-Zener tunneling between different pairs of nearly-degenerate energy levels. This mechanism might be relevant to the analysis of the hysteresis of nanoscale magnets at low temperatures, allowing one to extract the energy splittings from the hysteresis curve. We investigate the dependence of the staircase structure on the sweep rate dH(t)/dt, and point out some universal features of the staircase in uniaxial magnets. We also study the effect of a step-wise ͑instead of continuous͒ increase in the field, and show that the size of the steps depends sensitively on the procedure used to change the applied field. ͓S0163-1829͑97͒06042-6͔

Detailed single-crystal EPR line shape measurements for the single-molecule magnetsFe8BrandMnHill1, Maccagnano2, Park3 et al. 2002Phys. Rev. B1188771View full textAdd to dashboardCite

“…Indeed, each of these effects have been discussed in MQT literature, e.g. dipolar fields [39], distributed crystal field parameters caused by dislocations [40], thermally assisted tunneling [14,41,42], the Landau-Zener effect [43,44,45], and hyperfine interactions [46,47]. Based on our recent theoretical work [37], we find that a distribution in the uniaxial crystal field parameter, so called D−strain, contributes significantly to the EPR linewidths for the Fe 8 Br and Mn 12 −ac systems.…”

Nontrivial Response of Nanoscale Uniaxial Magnets to an Alternating Field

“…Steplike magnetization curves have been found, and the importance of level crossing has been pointed out [16 -18]. We also showed that successive NAT's lead to a steplike magnetization curve which is very sensitive to the speed with which the the field changes [19]. To fully describe the experimental situation, the temperature [20,21] and also the effect of random modulations due to the environment [22] need to be taken into account.…”

Effects of the environment on nonadiabatic magnetization process in uniaxial molecular magnets at very low temperatures

“…This quantum-mechanical transition has been studied from the point of view of the nonadiabatic transition. [7][8][9][10] There are two characteristic features of each nonadiabatic transition. 9 One is the localization of the transition because it occurs only around avoided level crossing points.…”

“…[7][8][9][10] There are two characteristic features of each nonadiabatic transition. 9 One is the localization of the transition because it occurs only around avoided level crossing points. The other is the dependence of the transition probability on sweeping rate of the magnetic field, the energy gap, and the gradients of the levels.…”