Chromium , ferromagnets

Mag netic Tapes. Chromium dioxide, Cr02, is used as a ferromagnetic material in high fidelity magnetic tapes (qv). Chromium dioxide has several technical advantages over the magnetic iron oxides generally used (58,246). 

Chromium, tetraaquadichloro-chloride dihydrate hydrate isomerism, 1, 183 Chromium, tetrabromo-solvated, 3, 758 synthesis, 3, 763 Chromium, tetrachloro-antiferromagnetic, 3, 761 ferromagnetic magnetic properties, 3,7559 optical properties, 3,759 structure, 3,759 solvated, 3. 758 synthesis. 3, 759 Chromium, tetrachlorooxy-tetraphenylarsenate stereochemistry, 1,44 Chromium, tetrahalo-, 3,889 Chromium, tetrakis(dioxygen)-stereochemistry, 1,94 Chromium, triamminediperoxy-structure. 1, 78 Chromium, tricyanodiperoxy-structure, 1, 78 Chromium, trifluoro-electronic spectra, 3, 757 magnetic properties, 3, 757 structures, 3, 757 synthesis, 3, 756 Chromium, trihalo-clcctronic spectra, 3, 764 magnetic properties, 3, 764 structure, 3, 764 synthesis, 3, 764 Chromium, tris(acetylacetone)-structure. 1, 65 Chromium, tris(bipyridyl)-... 

Chromium metal is important in metallurgy, because it is used to make stainless steel and for chromium plating (Section 12.13). Chromium(IV) oxide, Cr02, is a ferromagnetic material that is used for coating chrome" recording tapes. 

Cadmium chromium(III) selenide is a ferromagnetic semiconductor with a Curie temperature of 130 K. Crystals grown by this method are p type. Cadmium chromium(III) selenide has the spinel structure with a cubic cell edge of 10.75 A. 

Chromium dioxide, Cr02, of surface 28.5 m2 g I and Tc = 394 0.5 K has been reported by Arias and Selwood (27) to have negligible activity as normally prepared. But pretreatment with pure flowing helium at 623 K produces a surface with conveniently measurable activity at room temperature. All activity was quickly lost in hydrogen near Tc. It is necessary, therefore, to restrict measurements to the ferromagnetic phase. At 298 K and atmospheric pressure k0 = 1.2 /urnol m-2 s-1. At 17.5 kOe the change in conversion rate was less than 0.5%. It cannot be said that there is any measurable field effect. 

Fig. 80. Simplified density of states curve for metallic chromium. Energy scale is referred to bottom of s-p band. The Fermi level relative to the d bands is also shown for b.c.c. Ti, V, and Mn given the same relative positions of d and s-p bands. Ferromagnetic, simple-cubic sublattices are coupled antiferro-magnetically in b.c.c. Cr-Mn alloys.

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