Optically reconfigurable magnetic materials

Abstract

Structuring of materials is the most general approach for controlling waves in solids. As spin waves-eigen-excitations of the electrons' spin system-are free from Joule heating, they are of interest for a range of applications, such as processing 1-5 , filtering 6-8 and short-time data storage 9 . Whereas all these applications rely on predefined constant structures, a dynamic variation of the structures would provide additional, novel applications. Here, we present an approach for producing fully tunable, two-dimensionally structured magnetic materials. Using a laser, we create thermal landscapes in a magnetic medium that result in modulations of the saturation magnetization and in the control of spin-wave characteristics. This method is demonstrated by the realization of fully reconfigurable oneand two-dimensional magnonic crystals-artificial periodic magnetic lattices.There are two general approaches in designing the properties of a material: changing its chemical composition and structuring. Structuring has been used to control mechanical 10 , optical 11 , and even magnetic properties 12,13 . Periodic variation of the magnetic material's parameters allows the realization of magnonic crystals with novel properties not found in the unstructured material. For example, the dispersion relation of spin waves can be controlled to achieve new schemes for spin-wave-based computing [1][2][3][4][5][14][15][16][17] . The spin-wave dispersion relation depends on many parameters, such as the geometry of the spin-wave waveguide (film thickness and waveguide width), external magnetic field H ext , and saturation magnetization M S . In fact, all of these parameters have already been used to fabricate magnonic crystals [6][7][8]12,13,[18][19][20] : arrays of metallic stripes, etched grooves or antidots, biasing magnetic field or periodic variation of the saturation magnetization using ion implantation.However, all available methods for the fabrication of such spintronic devices result in spatially constant magnetic materials. J. Topp et al. have shown that the parameters of magnetic materials can be changed locally after the rather time-consuming fabrication of the spintronic device 21 -but the functionality of the device stays the same. Here, we present an alternative method for structuring and use it for the manipulation of spin waves-namely fully tunable light patterns (computer-generated holograms), in which optically induced thermal patterns/landscapes modify the spinwave dispersion relation and, hence, the propagation. Thus, the proposed optically reconfigurable magnetic material allows the functionality of a magnetic element to be tuned on demand; the same element can be used as a conduit, a logic gate or a data buffering element.The set-up used for the realization of the light patterns consists of a continuous wave laser as light source, an acousto-optical modulator for temporal intensity control, and a spatial light modulator for spatial intensity control (see Fig. 1a). To study the influence of the thermal gradient ...

Role of internal demagnetizing field for the dynamics of a surface-modulated magnonic crystal

“…15,16 In addition, MCs, in particular one-dimensional systems, possess the possibility of reprogramming the magnonic properties by a switching between different states in the magnetic hysteresis. [17][18][19][20][21][22] In previous studies, it was already shown that MCs can be used as grating couplers, 23 for magnonic logic, [24][25][26][27] filter 28 and sensor 29 applications, and moreover, as a tool to access important material properties, such as the exchange constant, at high precision.…”

Spin-wave propagation in the presence of inhomogeneous Dzyaloshinskii-Moriya interactions

“…As spin waves, the collective precessional motion of localized electron spins, do not involve the motion of electrons, magnonic devices avoid Joule heating and thus allow low-power computing [36,38,46,47]. Moreover, their wave properties provide distinct functionalities [49][50][51][52][53] such as multi-input/output (nonlinear) operations [54,55]. Despite their attractive features, however, magnonic devices suffer from a small on/off ratio of spin-wave signal.…”

Reconfigurable wave band structure of an artificial square ice

“…A paradigm that is the focus of recent investigation consists of actively modifying the band structure of magnonic crystals [15]. This has been achieved to date by use of Meander-type structures [16] and, more recently, via heating [17] in one-dimensional ferromagnets.…”