Transition metal-doped oxide semiconductor exhibiting room-temperature ferromagnetism

Abstract

An oxide semiconductor doped with a transition metal and exhibiting room-temperature ferromagnetism is disclosed. The transition metal-doped oxide semiconductor is preferably manufactured in powder form, and the transition metal is preferably evenly distributed throughout the oxide semiconductor. The preferred embodiments are iron-doped tin dioxide and cobalt-doped tin dioxide. Gases may be detected by passing them across a material and measuring the change in magnetic properties of the material; the preferred material is iron-doped tin dioxide.

1 . An oxide semiconductor material comprising Fe-doped tin oxide nanoparticles, wherein the Fe-doped tin oxide nanoparticles exhibit room-temperature ferromagnetism. 
   
   
       2 . The material of  claim 1  wherein the Fe-doped tin oxide nanoparticles are Fe-doped SnO 2  nanoparticles wherein the Fe is evenly distributed through the SnO 2  lattice and the material of comprises no iron oxide phases. 
   
   
       3 . The material of  claim 1  wherein the Fe-doped tin oxide nanoparticles are Fe-doped SnO 2  nanoparticles wherein the Fe is evenly distributed through the SnO 2  lattice and the material of comprises no iron oxide phases of magnetite, hematite, maghemite, or goethite. 
   
   
       4 . The material of  claim 1  wherein no traces of iron, iron oxides, or tin metal are observable by X-ray diffraction studies utilizing the Debye-Scherrer technique. 
   
   
       5 . The material of  claim 1  having a Curie temperature of at least 850 K. 
   
   
       6 . The material of  claim 1  having a coercivity of at least 60 Oe. 
   
   
       7 . The material of  claim 1  wherein the Fe-doped tin oxide nanoparticles are Sn 0.95 Fe 0.05 O 2 . 
   
   
       8 . Oxide semiconductor powder comprising Fe-doped SnO 2  nanoparticles made by the process comprising:
 adding SnCl 2 , FeCl 2 , and NH 4 OH to water to produce at least one solution;   reacting the at least one solution together to produce a precipitate; and   annealing the precipitate.   
   
   
       9 . The powder of  claim 8  wherein the ratio of SnCl 2  to FeCl 2  is between 200 to 1 and 20 to 1. 
   
   
       10 . The powder of  claim 8  wherein the precipitate is annealed at a temperature between 350° C. and 600° C. 
   
   
       11 . The powder of  claim 10  wherein the ratio of SnCl 2  to FeCl 2  is between 200 to 1 and 20 to 1. 
   
   
       12 . An oxide semiconductor material comprising Fe-doped tin oxide exhibiting room-temperature ferromagnetism, wherein the Fe atoms take the place of Sn atoms in the SnO 2  lattice so that the Fe atoms are substitutionally incorporated into the SnO 2  lattice at the Sn sites, and wherein the oxide semiconductor material comprises no iron oxide phases. 
   
   
       13 . The oxide semiconductor material of  claim 12 , wherein said material is a film comprising said Fe-doped tin oxide exhibiting room-temperature ferromagnetism. 
   
   
       14 . The oxide semiconductor material of  claim 13 , wherein said film is a thin film of Sn 0.95 Fe 0.05 O 2 . 
   
   
       15 . An oxide semiconductor material comprising Fe-doped SnO 2  particles, wherein the Fe-doped SnO 2  particles exhibit room-temperature ferromagnetism and 95% of which particles are less than 100 nm in length. 
   
   
       16 . A method of detecting a gas comprising:
 causing the gas to flow across a material that comprises transition-metal-doped tin oxide that exhibits room-temperature ferromagnetism; and   measuring a change in a magnetic property of the material.   
   
   
       17 . The method of  claim 16  wherein the transition-metal-doped tin oxide is Fe-doped SnO 2  nanoparticles, wherein Fe takes the place of Sn atoms in the SnO 2  lattice so that the Fe atoms are substitutionally incorporated into the SnO 2  lattice at the Sn sites. 
   
   
       18 . The method of  claim 17  wherein the nanoparticles comprise no iron oxide phases of magnetite, hematite, maghemite, or goethite. 
   
   
       19 . The method of  claim 17  wherein no traces of iron, iron oxides, or tin metal are observable in said nanoparticles by X-ray diffraction studies utilizing the Debye-Scherrer technique. 
   
   
       20 . The method of  claim 16 , wherein said material is a film. 
   
   
       21 . The method of  claim 20 , wherein said film is a thin film of Sn 0.95 Fe 0.05 O 2 . 
   
   
       22 . An apparatus for detecting a gas comprising a gas inlet, a flow controller, a device which is configured to measure magnetic properties, and a ferromagnetic material, wherein the ferromagnetic material comprises Fe-doped SnO 2  nanoparticles that exhibit room-temperature ferromagnetism. 
   
   
       23 . The apparatus of  claim 22  wherein the ferromagnetic material is Sn 0.95 Fe 0.05 O 2 .