Search

Magnetic doping of semiconductors has been actively pursued because of their potential applications in the spintronic devices. Central to these efforts is a drive to control the mutual interactions between their magnetic properties (supported by d electrons of the magnetic ions) and their semiconductor properties (supported by s and/or p electrons) at room temperature (RT). Despite the long, intensive efforts, the experimental evidence of thermally robust s, p-d coupling in a semiconductor remains scarce and controversial. Here, we report the enhancement of RT ferromagnetic s, p-d exchange interaction by means of carrier doping in single crystalline Co0.4Zn0.6O epitaxial films with a high Co concentration. Magneto-transport measurements reveal that spin-polarized conducting carriers are produced at RT and are increased with the carrier density through Ga3þ doping, owing to the s, p-d coupling between Ga (4s), O (2p), and Co (3d) orbitals. With the ability to individually control carrier density and magnetic doping, single crystalline Ga(Co, Zn)O films can lay a solid foundation for the development of practical semiconductor spintronic devices operable at RT

While semiconductor spintronics promises lower switching energy and faster speed, a major limitation on its development as a viable technology is the lack of room temperature ferromagnetic semiconductor materials. The material challenge is great, because not only magnetic and electronic doping but also thermally robust coupling between them are required for a room temperature ferromagnetic semiconductor. Here, we report the growth-controlled engineering of magnetic exchange interactions in single crystalline GaCoZnO1-v epitaxial films with high Co concentrations (0.3 ≤ x ≤ 0.45) by controlling oxygen vacancy and carrier density through Ga3+ doping. Strong ferromagnetism, spin-split impurity states, and spin-polarized electrical transport are realized and well controlled at room temperature by tailoring the s,p-d exchange coupling. This room temperature ferromagnetic semiconductor, which offers the ability to individually control carrier density and magnetic doping, will lay a solid foundation for the development of practical spintronic devices operating at room temperature.

Strong pinning depends on the pinning force strength and number density of effective defects. Using the hydrostatic pressure method, we demonstrate here that hydrostatic pressure of 1.2 GPa can significantly enhance flux pinning or the critical current density (Jc) of optimally doped Ba0.6K0.4Fe2As2 crystals by a factor of up to 5 in both low and high fields, which is generally rare with other Jc enhancement techniques. At 4.1 K, high pressure can significantly enhance Jc from 5 x 105 A/cm2 to nearly 106 A/cm2 at 2 T, and from 2 x 105 A/cm2 to nearly 5.5 x 105 A/cm2 at 12 T. Our systematic analysis of the flux pinning mechanism indicates that both the pinning centre number density and the pinning force are greatly increased by the pressure and enhance the pinning. This study also shows that superconducting performance in terms of flux pinning or Jc for optimally doped superconducting materials can be further improved by using pressure.