Patent Application: US-59634205-A

Abstract:
a semi - conducting material being a non - oxide material or an already doped oxide material , wherein said material is doped with manganese , mn , and is ferromagnetic at least at one temperature in the range between room temperature and 500 k . preferably , the manganese doped material has a manganese concentration at or below 5 at %.

Description:
this invention is based on the concept to create ferromagnetism in doped dilute magnetic semiconductors by doping with manganese ( mn ) into the materials ( that are non - oxides or into materials that are oxides and already doped by another dopant ). examples of the materials that are doped with manganes are cadmium sulfid , cadmium selenide , zinc sulfide , zink selenide , gallium phosphide , copper doped gallium nitride , copper doped gallium phosphide , copper doped zinc oxide , copper doped gallium arsenide . our experiments show successful tailoring of ferromagnetism above room temperature in bulk mn doped materials . the mn doping level should then be less than 6 at % ( atomic percent ) for bulk materials . theoretically we find that the upper limit for ferromagnetism is about 5 at % mn . experimentally we have found that due to materials problems , above 4 at % mn there is a clear tendency for the mn atoms to form clusters which are then antiferromagnetic and that suppresses the ferromagnetic order . sem observations show , on samples above 2 at %, local clustering and the samples becomes inhomogeneous , which affects the material so that the around room temperatures ferromagnetic effect is nearly suppressed at 4 - 5 at %. ferromagnetic resonance ( fmr ) data confirm the existence of ferromagnetic order at temperatures as high as 425k in both pellets and thin films . in the paramagnetic state the epr spectra show that mn is in the 2 30 state ( mn2 + ). furthermore , ferromagnetism above room temperature is also observed in the calcined ( below 500 ° c .) powder . our ab initio calculations confirm the above findings . if sintering of the mn doped materials is carried out at higher temperatures the doped material shows an additional large paramagnetic contribution at room temperatures and the ferromagnetic component becomes negligible . on sintering the bulk at temperatures above 700 ° c ., ferromagnetism around room temperatures is completely suppressed giving rise to the often reported pronounced ‘ ferromagnetic - like ’ ordered state below 40k . experiments with sintering temperatures of 700 ° c ., 800 ° c . and 900 ° c . have confirmed this fact . room temperature ferromagnetic ordering has also been obtained in 2 - 3 μm thick films deposited on fused quartz substrates at temperatures below 600 ° c ., by pulsed laser deposition or sputtering using the same bulk materials as targets . the doping concentration in these film materials should be less than 6 at % in order to obtain controlled homogeneity . experiments have shown that samples below 2 at % can be tailored to be homogeneous in composition with slight variations but containing no clusters . in laser ablation the substrate temperature effects the mn concentration in the film . films deposited at higher temperatures are found to have a high concentration of mn in comparison to films deposited at low temperatures . this means that the temperature could be used to control the mn concentration . the effect of sintering temperature on the magnetic properties of nominal 2 % mn doped materials was studied . we found ferromagnetic ordering above room temperature ( tc & gt ; 420k ). the room temperature ferromagnetic phase as a function of sintering temperatures , as indicated by m ( h ) measurements . elemental mapping for the pellet sintered at 500 ° c . showed a uniform distribution of mn in the sample . however local mn concentration was found to be much lower (˜ 0 . 3 at %) than the nominal composition . taking this fact into consideration , we evaluate the saturation magnetization of the ferromagnetic phase and determine the moment per mn atom to be 0 . 16 μb . sometimes on sintering the pellets in the temperature range 600 ° c .- 700 ° c . in addition to the ferromagnetic component we observe a linear paramagnetic contribution in the magnetic hysteretic loops at high fields . however , sintering the pellets above 700 ° c . completely suppresses ferromagnetism around room temperature . the doped dilute semiconductor can also be processed , by particle size selection , into transparent and ferromagnetic nanoparticles . manganese doped materials can be manufactured with a sputtering system where either two metallic ( material and manganese ) targets are used simultaneously or one sintered ceramic target as described previously . when using two metallic targets the sputtering energy on the material and manganese targets are adjusted in such a way that the resulting manganese content is in the 1 - 6 % range . an exact recipe has to be adjusted to the sputtering equipment that is used and depends on energy , geometry and gases . the substrate temperature on the deposition substrate is in the same range as when using laser deposition . x - ray diffraction as well as sem high resolution elemental mapping analyses on both the bulk as well as thin film mn doped materials obtained by us are found to be homogeneous with no sign of cluster formation or distribution in them . incidentally in both the bulk and the transparent films we obtained their ferromagnetic resonance spectra which provide convincing evidence for the existence of ferromagnetism . the demonstrated new capability renders possible the realization of complex elements for spintronic devices . these type of films materials are transparent and could be used for magneto - optical components . these types of materials have a large electromechanical coupling coefficient and is therefore also good for piezoelectric applications and combinations for optical , magneto and mechanical sensor or component solutions . the table below shows the results of magnetic measurements on cds : mn samples . cds samples doped with mn , labelled as sample - 1 ( 5 %) and sample - 2 ( 4 %) were investigated for their magnetic properties . the following measurements were made on each sample : 1 . temperature dependence of magnetization , m ( t ), at a measuring field of 1000 oe . 2 . field dependence of magnetization , m ( h ), at 300k and 5k . the saturation magnetisation ms , obtained after subtracting the linear part showing up at higher fields in m ( h ) curves , and the corresponding coercivity values , hc are listed in the table given below . ms at 300k ms at 5k hc at 300k sample ( emu / g ) ( emu / g ) ( oe ) hc at 5k oe ) 1 ˜ 1 . 61 × 10 − 3 ˜ 1 . 59 × 10 − 2 ˜ 105 ˜ 250 2 ˜ 3 . 07 × 10 − 3 ˜ 3 . 84 × 10 − 2 ˜ 100 ˜ 98 fig1 shows the calculated density of states for manganese doped cadmium sulphide . fig2 m ( h ) at 300 k showing the ferromagnetic phase , at manganes doped zinc sulphide , obtained after subtracting the linear term from the as obtained data . the coercivity is ˜ 130 oe and saturation magnetisation is ˜ 7 . 45 e - 4 emu / g . the inset shows the as obtained data having a paramagnetic term at high fields . fig3 is showing cadmium sulphide doped with 5 % manganese . fig3 ( a ) m ( t ) at 1000 oe and fig3 ( b ) 1 / χ at 1000 oe . science 281 , 951 - 956 ( 1998 ); 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