Hartman effect for spin waves in exchange regime

TL;DR

This paper theoretically demonstrates the Hartman effect for spin waves tunneling through a barrier in a nanoscale magnetic film, showing group delay saturation with barrier width, and proposes an experimental setup using CoFeB with perpendicular magnetic anisotropy.

Contribution

It derives the group delay formula for spin waves in an exchange regime and predicts the Hartman effect in this magnetic system, considering general boundary exchange conditions.

Findings

Group delay saturates with increasing barrier width.

Hartman effect observed in exchange-dominated spin wave tunneling.

Proposed experimental system using CoFeB with MgO overlayer.

Abstract

Hartman effect for spin waves tunnelling through a barrier in a thin magnetic film is considered theoretically. The barrier is assumed to be created by a locally increased magnetic anisotropy field. The considerations are focused on a nanoscale system operating in the exchange-dominated regime. We derive the formula for group delay $\tau_{gr}$ of spin wave package and show that $\tau_{gr}$ saturates with increasing barrier width, which is a signature of the Hartman effect predicted earlier for photonic and electronic systems. In our calculations we consider the general boundary exchange conditions which take into account different strength of exchange coupling between the barrier and its surrounding. As a system suitable for experimental observation of the Hartman effect we propose a CoFeB layer with perpendicular magnetic anisotropy induced by a MgO overlayer.