Cloaking the magnons

Abstract

We propose two approaches to cloak the spin waves (magnons) by investigating magnetization dynamics. One approach is based on a spatially inhomogeneous anisotropic magnetic moment tensor. The other mechanism is using a spatially inhomogeneous anisotropic gyromagnetic factor tensor and an inhomogeneous external magnetic field. For both approaches, the damping tensor is also inhomogeneous and anisotropic. The magnetic characteristic functions of the magnetic materials have been theoretically derived for both mechanisms. A non-magnetic core, which prevents magnons from entering and consequently distorts the spin wave propagation, can be cloaked by a structured magnetic shell to redirect the spin wave around the core using the above design mechanisms. We discuss the feasibility of the proposed mechanisms in an ensemble of quantum dot molecules and magnetic semiconductors. The proposed approaches shed light on transformation magnonics, and can be utilized for future spin-wave lenses, concentrators, low back-scattering waveguides, and ultimately quantum computing.Comment: Accepted for publication in Phys. Rev.

Room-temperature broadband quasistatic magnetic cloak

“…17,18 The efficiency of the bilayer approach proposed by the first group was quickly verified and applied to other Laplace equations governing the evolutions of different physical phenomena. [25][26][27][28][29][30][31] In practice, a magnetic cloak that is able to perform under alternating currents will be more meaningful, as one usually relies on EM induction to uncover hidden metallic or magnetic objects. The same group extended their original two-dimensional bilayer design to A.C. fields and indicated a technical possibility within a frequency range of several hundred Hertz.…”

Graded Magnonic Index and Spin Wave Fano Resonances in Magnetic Structures: Excite, Direct, Capture

“…has two main purposes: to deliver the signals from the input to the output and, as magnonic devices can have multiple inputs and outputs, to steer the signals between them. A graded magnonic index between the inputs and outputs can be used to channel [77][78][79][80] or focus 81 / defocus 82 spin waves, or to "cloak" an object from them, 32 in analogy to a similar research topic in electromagnetics. 25 Spin wave steering is the key prerequisite for creation of efficient magnonic interferometers, [83][84][85] Boolean and analogue computing primitives, 21,[86][87][88][89] splitters (demultiplexers and inverse multiplexers) 26,[90][91][92] and combiners (multiplexers).…”

“…Yet, it would be extremely difficult (if at all possible) to do this, given the plethora of factors that influence the (already complex) spin wave dispersion, with their sheer diversity necessarily limiting any definition to special cases and approximations. [28][29][30][31][32][33][34][35] So, we treat the term "magnonic index" here as merely a tag encompassing the entirety of spin wave dispersion and its modifications dictated by the variation of the magnetic medium's properties.…”

Analysis of the linear relationship between asymmetry and magnetic moment at the M edge of 3d transition metals

“…Since the first experimental observation of ultrafast demagnetization in Ni [1], ultrafast magnetodynamics has attracted significant interest, due to the perspective of controlling the magnetization on sub-picosecond timescales [2][3][4][5][6][7][8][9][10][11][12][13][14][15]. These studies have led to the discovery of novel effects such as all-optical-switching [16,17] and ultrafast spin currents [18][19][20][21][22].…”