Title: Negative Refraction Observed in a Metallic Ferromagnet in the Gigahertz Frequency Range. Abstract: It is generally believed that nature does not provide materials with negative refraction. Here we demonstrate experimentally that such materials do exist at least at GHz frequencies: ferromagnetic metals reveal a negative refraction index close to the frequency of the ferromagnetic resonance. The experimental realization utilizes a colossal magnetoresistance manganite La2/3Ca1/3MnO3 as an example. In this material the negative refractive index can be achieved even at room temperature using external magnetic fields. Phys. Rev. Lett. 98, 197401 (2007)
It is a surprise to find a naturally occurring negative refractive index material. If the material is not so scarce, it could be cheaper to use than fabricated materials. It is promising that it works at room temperature but I wonder how large the magnetic field has to be? The frequency range limit will restrict the uses. Negative refractive index materials can be used to construct superlenses that have a much higher resolution compared to the wavelength used. I can see this being useful in medical imaging devices and possibly photolithography to make ever smaller computer chips.
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