A reflective-type display device based on phase change materials is attractive because of its ultrafast response time and high resolution compared with a conventional display device. This paper proposes and demonstrates a unique display device in which multicolour changing can be achieved on a single device by the selective crystallization of double layer phase change materials. The optical contrast is optimized by the availability of a variety of film thicknesses of two phase change layers. The device exhibits a low sensitivity to the angle of incidence, which is important for display and colour consistency. The non-binary colour rendering on a single device is demonstrated for the first time using optical excitation. The device shows the potential for ultrafast display applications.

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We have coated phase change materials (PCMs) on rough and flexible substrates to achieve multicolor changeable devices. The principle of the device is based on an earlier discovery that lights have strong interference effect in PCM films, leading to various colors by reflection. In this work, paper substrates are laminated by parylene layers to protect the device from water before coated with functional PCM films. The PCM-based color printing (PCP) on paper is not affected by rough surfaces and shows a similar color appearance as that on smooth surfaces. In particular, the color-printed device can be patterned by UV lithography to display a clear and tunable optical image, and it exhibits a low sensitivity to the angle of view. Such PCP has potential applications for low-cost, disposable, and flexible displays.

Spin Hall magnetoresistance (SMR) has been investigated in Ta/CoFe2O4 nanostructures grown on different substrates. Spin currents in CoFe2O4 films are electrically detected in adjacent Ta layers owing to inverse spin Hall effects. The sign of the magnetic-field-dependent resistivity signal shows different polarities along different axes, showing different spin-dependent electron transports. A cosinelike curve of the angular dependence signal with opposite polarity is observed in two orthogonal magnetization planes, whereas a basic line is observed in another plane, revealing the spin accumulation phenomenon. The roughness of the CoFe2O4 surface tuned by substrate strains is responsible for the extent of spin accumulations and the strength of the SMR signal in the nanostructures.