Remote two-dimensional imaging of giant magnetoresistance with spatial resolution

Abstract

High-field magnetoresistance, giant magnetoresistance, and superparamagnetism in Co/Cu multilayers J. Appl. Phys. 91, 8590 (2002); 10.1063/1.1451890 Dominant role of the size effect for saturation resistivity and giant magnetoresistance in Co/Cu multilayers

Two-Dimensional Imaging of Giant Magnetoresistance with Improved Sensitivity

“…IR imaging techniques thus allow 2-D images of GMR to be constructed. This has been demonstrated for GMR and spin-valve multilayers down to a resolution of 30 m [5], [6]. However, in our previous studies we were constrained to use an IR camera sensitive in the 3-5 m regime, which is not ideal.…”

“…The Stefan-Boltzmann law must be modified to (4) where is the radiated intensity, is a modified Stefan-Boltzmann constant, is the actual sample temperature (typically around 320 K), is the temperature of the environment, and the power to which is raised; when integrating over the entire spectrum, . The result for the correlation between GMR and the apparent temperature change given in (3) is now modified to (5) New values of and which correspond to the wavelength window of the camera are found by simulation. The value of is found to be 9.4 for a camera window of 3-5 m [5], and 5.0 in the 8-12 m range.…”

“…The GMR can, therefore, be written as (3) where and are the apparent temperatures measured in zero and applied field, respectively [3]. Measuring the change in with an IR camera enables a 2-D image of GMR to be constructed [5].…”

Modelling the sensitivity of infrared emissivity of magnetic thin films to giant magnetoresistance

“…Furthermore, the emissivity technique lends itself readily to spatial resolution using an IR camera to remotely sense changes in the IR temperature image of a magnetic multilayered material, and this can be developed into an image of GMR. Imaging GMR in this manner has been demonstrated in Co/Cu [7], synthetic spin-valve [8] and CoFe/Cu [9] multilayers, most recently with a spatial resolution of 30 mm.…”

“…Also, no consideration has yet been made of the thin-film nature of the magnetic materials being investigated, and this is addressed here by adapting a thin-film model of emissivity by Pigeat et al [10]. It is used to directly model the link between emissivity and GMR as a function of film thickness at far IR wavelengths, and is compared to the bulk-material results used in previous studies [6][7][8][9]. The spectral dependence of the emissivity effect at mid-to-far IR wavelengths is also examined using a Drude-type model of refractive index combined with the thin-film emissivity model, and an analytic interpretation at far IR wavelengths is presented.…”