Macroscopic quantum tunneling of ferromagnetic domain walls

Abstract

Quantum tunneling of domain walls out of an impurity potential in a mesoscopic ferromagnetic sample is investigated. Using improved expressions for the domain-wall mass and for the pinning potential, we find that the crossover temperature between thermal activation and quantum tunneling is of a different functional form than found previously. In materials such as Ni or yttrium iron garnet, the crossover temperatures are around 5 mK. We also find that the WKB exponent is typically two orders of magnitude larger than current estimates. The sources for these discrepancies are discussed, and precise estimates for the transition from threedimensional-to-one-dimensional magnetic behavior of a wire are given. The crossover temperatures from thermal-to-quantum transitions and tunneling rates are calculated for various materials and sample sizes.

Quantum Nucleation in a Single-Chain Magnet

“…The most important arguments concerned the introduction of magnetic anisotropy and finite-size effects. Indeed, their influence on the static and dynamic properties of the SCMs was confirmed experimentally [7,8,9,10].Quantum tunneling of domain walls in a 1D mesoscopic ferromagnetic sample was theoretically investigated [11,12,13,14,15,16] and crossover temperatures between the classical and quantum regime were predicted. Domain wall nucleation and depinning were studied in single Ni wires and showed indeed a flattening of the temperature dependence of the mean switching field (H sw ) below about 5 K [17] and 1 K [18].…”

“…The authors proposed that a domain wall escapes from its pinning site by thermal activation at high temperatures and by quantum tunneling below T c ∼ 5 K [17] and 1 K [18]. However, such crossover temperatures are about three orders of magnitude higher than the T c predicted by current theories [15]. The propagation of a domain wall across an energy barrier in a domain wall junction was also studied and preliminary investigations seems to indicate the possibility of quantum tunneling below 0.7 K [19].…”

“…Then, due to the applied field, the magnetization of the entire chain reverse via a domain wall propagation process. The domain wall nucleation can be thermally activated at high temperatures or driven by quantum tunneling at low temperatures [11,12,13,14,15,16].…”

Macroscopic Quantum Coherence of an Antiferromagnetic Spin Chain with Biaxial Anisotropy in an External Magnetic Field

“…Although quantum tunneling in the context of field theory, for instance the tunneling of domain walls [8][9][10][11][12][13][14][15][16][17][18], has been investigated, the explicit, multidimensional (time-space) instanton configurations have not been studied extensively. In almost all the literature, a collective coordinate of the domain wall is introduced to describe the behavior of quantum tunneling, or the situation is simplified to the case of a uniform spin configuration, namely, single domain magnetic grain.…”

Hysteresis from antiferromagnet domain-wall processes in exchange biased systems

“…Following the treatment of Braun et al for ferromagnetic walls [6], we can obtain a simple physical picture of pinning in the antiferromagnet by considering an impurity of the form K u ðxÞ ¼ K u0 f1 À rd½ðx À x d Þ=lg; which represents a small local pointlike reduction r in the uniaxial anisotropy energy K u at a distance x d from the interface. In addition to the interlayer coupling, the energy arising from deformations to the antiferromagnetic spin structure is given by…”