The Nanoelectronics Research Institute (NeRI) of the National Institute of Advanced Industrial Science and Technology (AIST) has developed a (Zn,Cr)Te ferromagnetic semiconductor that functions at the highest temperatures seen to date. Thus far, scientists have only been able to produce ferromagnetic properties at temperatures below -100^oC, but this research has significantly increased this temperature to +27^oC (300 K). The research team also observed semiconductor-like electrical conductivity that is vital for use in technology applications. The material is the first-ever ferromagnetic material that is classified as a II-VI semiconductor compound suited for use in optical device applications.

A global race is currently underway to develop ferromagnetic semiconductor materials. A number of reports published between 2000 and 2001 claimed to have developed semiconductor substances that exhibited ferromagnetic properties at room temperature. However, all of these claims were subsequently proved false or questionable, and to date no substance has been proved to be a room-temperature ferromagnetic semiconductor. The AIST has identified interactions between the ferromagnetic and semiconductor functionality - the main feature of ferromagnetic semiconductors - using an independently developed magnetic circular dichroism (MCD) spectroscopy method and confirmed that the (Zn,Cr)Te is a true ferromagnetic semiconductor.

The discovery of a new semiconductor material that exhibits ferromagnetic properties at room temperature will enable the combination of magnetic devices and semiconductor devices, which have been developed separately thus far. The research paves the way for the development of new semiconductor elements (functional elements in spintronics) with electronic and optical signal processing functionality and magnetic memory functionality. The material is expected to have various applications, including use in memory devices similar to the current nonvolatile magnetic memory (MRAM), as well as ultra-high capacity nonvolatile memory that does not require a separate element selection function, nonvolatile logic elements required in high-performance mobile devices, and optical isolators for high-speed optical information processing.

• AIST develops a new (Zn,Cr)Te semiconductor material that is ferromagnetic at the highest temperatures seen to date (ferromagnetic Curie temperature of +27^oC)
  The AIST team has synthesized a (Zn,Cr)Te thin film with a ferromagnetic Curie temperature of +27^oC, by using a ZnTe II-VI semiconductor compound and replacing around 20% of the Zn ions with Cr ions. To date, only the III-V semiconductor compounds (In,Mn)As and (Ga,Mn)As had been shown to be ferromagnetic semiconductors. The highest ferromagnetic Curie temperature (T_c) of these substances is, however, 180K (-93^oC).
• First-ever ferromagnetic semiconductors that exhibit semiconductor electrical conductivity
  Semiconductor applications have proved problematic with the conventional (In,Mn)As and (Ga,Mn)As ferromagnetic semiconductors, because significant amounts of carrier doping is needed to produce the ferromagnetic properties, and the electrical properties of these substances are closer to metals than to semiconductors. (Zn,Cr)Te electrical conduction is similar to that seen in a semiconductor, so this material is expected to allow the carrier doping necessary for semiconductor devices.
• Material suited for optical applications using a matrix of wide-gap ZnTe semiconductors that can be penetrated by visible light
  The ZnTe matrix is a wide-gap semiconductor that is transparent to yellow, red, and other visible light frequencies above 550nm. The (Zn,Cr)Te material is expected to be suited to optical applications.
• AIST also detected interactions between the ferromagnetic and semiconductor functionality, proving that (Zn,Cr)Te is a true ferromagnetic semiconductor
  Previously discovered materials were not recognized as room-temperature ferromagnetic semiconductors because researchers were unable to confirm the existence of the interactions (sp-d exchange interaction) that occur between ferromagnetic substances and semiconductor substances and are the key feature of ferromagnetic semiconductors. In its research, the AIST was able to detect sp-d exchange interaction in the (Zn,Cr)Te material, using an independently developed magnetic circular dichroism (MCD) method.

Figure1: Photograph of (Zn,Cr)Te. The substance is transparent, so the letters behind the substance can be seen.

Figure2: Magnetic circular dichroism (MCD) spectrum proving that (Zn,Cr)Te is a true ferromagnetic semiconductor. The key characteristic of (Zn,Cr)Te is that significant magneto-optical effects can be seen in the photon energy (G and L) of the ZnTe semiconductor matrix. The MCD spectrum of NiAs-type CrTe, which could act as a magnetic impurity, has a completely different shape to that of (Zn,Cr)Te, so the research completely discounted the possibility of magnetic impurities. Such information has not been obtained for previous ferromagnetic semiconductors.