M. Robbins

Magnetic properties and site distributions in the system FeCr2O4-Fe3O4(Fe2+Cr2−xFex3+O4

Magnetic and Mossbauer effect measurements have been used to characterize the system Fe2+Cr2−xFex3+O4,. We obtain information on the transition with increasing x between the normal spinel FeCr2O4 with conical spiral spin structure and the inverse spinel Fe3O4 with a Neel antiferromagnetic structure. Fe3+ substituted for Cr3+ in FeCr2O4 goes into the B site up to x = 0·68 and has a spin canted relative to the A site moment. In the region 0·68 < x < 1·38 the Fe3+ goes into the A site displacing corresponding amounts of Fe2+ to the B site and leading to the beginning of charge hopping. In this region Curie points and saturation moments rise rapidly as the iron canting angle decreases because of Zener double exchange and A−B exchange between Fe3+. From x = 1·38 to magnetite the B site tends to have equal amounts of Fe2+ and Fe3+ presumably because of pairwise charge hopping. The Verwey transition and the attendant lattice distortion are suppressed by the presence of Cr3+ in the B site.

Solid solution formation in the systems CuMIIIX2-AgMIIIX2 where MIII=Al, Ga, In and X2=S, Se

Abstract A study of solid solution formation in the systems CuAlX2-AgAlX2, CuGaX2-AgGaX2 and CuInX2-AgInX2, where X=S, Se, has shown that when MIII=Al and Ga, CuMIIIX2 and AgMIIIX2 were not completely miscible. The CuInX2-AgInX2 system, however, showed complete solid solubility. The limits of solid solubility are explained in terms of the c/a ratio, and the internal atomic coordinate u. The lattice constant a is a linear function of composition, while c bows upwards. This behavior is also discussed in terms of trends in 2-c/a.

New ferrimagnetic spinel compositions in the system MCr2S4−xSex where M=Fe, Co, Mn

Phase relationship between ferrimagnetic semiconducting spinels of the type MCr2S4 and defect NiAs compositions of the type MCr2Se4 (where M=Mn, Fe, Co) are established. It was found that the amount of Se which can be substituted, with retention of the spinel structure, decreases from MnCr2S4−xSex (x=0 to x=2) to FeCr2S4−xSex (x=0 to x=1·25) to CoCr2S4−xSex (x=0 to x=1). This phenomena is accounted for on the basis of sulfide spinel stability and unit cell size. The Curie temperatures of the spinel compositions decrease slowly with increasing Se content. This is presumably caused by weakening of the spinel A-B superexchange interaction.

Preparation and properties of polycrystalline cerium orthoferrite (CeFeO3)

Abstract Cerium orthoferrite (CeFeO3) was prepared by the reaction 3CeO2 + Fe2O3 + Fe → 3CeFeO3. CeFeO3 forms with an orthorhombic unit cell where a = 5.541 A, b = 5.577 A, and c = 7.809 A. Magnetic measurements and Mossbauer spectra both show that the cation valencies in CeFeO3 are Ce3+ and Fe3+. CeFeO3 undergoes spin reorientation at 230°K and has a Curie temperature of 719°K.

Magnetic and crystallographic evidence for localization to delocalization of V d-electron levels in CuCr2−xVxS4 spinels

Abstract Spinels in the system CuV 2 S 4 -CuCr 2 S 4 (CuV x Cr 2− x S 4 ) were prepared and studied. CuV 2 S 4 is a superconductor and CuCr 2 S 4 is metallic conducting and ferromagnetic ( T c = 398°K). Magnetic measurements indicate that initially from x = 0 to x = 0.375 the substituted vanadium ions exhibit essentially localized d -levels and magnetic moments which are magnetically polarized antiparallel to the carriers in the Cu d -band and parallel to the localized Cr 3+ moments. With further addition of vanadium ( x = 0.5 to x = 2) it appears that the V d -levels broaden into a band which merges with the Cu σ * A -band, the total moment of which is polarized antiparallel to the localized Cr 3+ moments. This behavior is manifested in the unit cell parameters, which increase between x = 0 and x = 0.375 since r v 3+> r Cr 3+, followed by a linear decrease, with increasing vanadium content ( x = 0.5 to x = 2), to CuV 2 S 4 . The change from local to band behavior for vanadium occurs over a rather small compositional range (Δ x = 0.125). An attempt is made to explain most of the observed properties using Goodenoughs [4] band structure models for CuCr 2 S 4 and CuV 2 S 4 .

Ferrimagnetic Compositions in the System Fe1+xCr2−xS4

Materials in the system Fe2+Fex3+Cr2−xS4 have been prepared between x=0 and x=0.5. All of the compositions form with the spinel structure. Curie temperatures increase with increasing Fe3+ from 180°K for FeCr2S4 to 302°K for Fe12+Fe0.53+Cr1.5S4. Magnetic data suggest an ionic distribution of Fe1−x2+Fex3+[Fex2+Cr2−x]S4. From low‐temperature resistivity measurements, it appears that all of the materials are semiconductors.

Magnetic properties of fluoride substituted orthoferrites

Abstract Substituted rare earth orthoferrites (LnFeO 3 ) with the general formula LnM x 2+ Fe 1− x O 3− x F x where Ln=Y, La−Yb, and M 2+ =Ni 2+ , Mn 2+ , Cu 2+ , have been prepared and studied. When M 2+ =Ni 2+ and x =0·2 the substituted materials exhibited magnetic moments which were of the order of four times those of the unsubstituted orthoferrites. Curie temperatures were observed to decrease ≈ 20°. Cu 2+ and F − ( x =0·2) substitution did not bring about appreciable changes in either the magnetic moments or T c . Mn 2+ −F ( x =0·2) subsitution resulted in appreciable decreases in T c (30–60°) but did not produce a uniform trend in magnetic moments. In Ni 2+ −F − substituted HoFeO 3 and SmFeO 3 magnetic moments were found to increase with increasing substitution.

Magnetic Properties of 3d Transition Metal Ion Substituted CdCr2S4 Spinels

Substituted CdCr2S4 spinels containing Ni, Co, V, and Ti were prepared for magnetic study. Substitution of In3+ for Cd2+ was used for charge compensation when divalent transition‐metal ions were substituted for Cr3+. In the spinels Cd0.8In0.2[Cr1.8Ni0.2]S4, Cd0.8In0.2[Cr1.8Co0.2]S4 and Cd0.8In0.2[Co0.2Cr1.8]Se4 the Ni2+ and Co2+ were both found (by magnetic measurements) to interact negatively (antiferromagnetically) with the Cr3+ ion. The V3+ and Ti3+ ions in CdV0.2Cr1.8S4 and CdTi0.2Cr1.8S4 appear to have no magnetic moment. The measured magnetic moments of these spinels are in excellent agreement with theoretical values based only on the moment of Cr3+. In the compound Cd0.8In0.2[Cr1.8V0.2]S4 the measurements indicated that the V2+ ion is not stable with respect to the Cr2+ ion. The resulting ionic distribution would be Cd0.8In0.2[V0.23+Cr0.22+Cr 1.63+]S4 instead of Cd0.8In0.2[V0.22+Cr1.83+] S4. Two additional compositions containing 0.1 and 0.3 mole of vanadium exhibited magnetic moments which are con...

A non‐alloyed ohmic contact formation on n‐type GaAs

The ohmic contact characteristics of nickel antimonide in n‐type GaAs semiconductor circuits are evaluated. Deposition techniques, structural, and electrical properties were studied. The structural analysis revealed a well‐defined, sharp interface of a polycrystalline nickel antimonide phase with various solid‐phase interactions at higher annealing temperatures. The sheet resistance of 1000‐A‐thick films decreased to 7–10 Ω/⧠ after annealing at 400 °C. The ohmic contact formation was demonstrated using transmission line measurements. Subtractive etching of the contacts was accomplished by a wet etchant system which was found not to attack the GaAs substrate.

Properties of Polymer‐Coated, Submicron Magnetic Alloy Particles

Submicron particles of Fe–Co and Fe–Co–Ni alloys were prepared and stabilized with respect to air oxidation by surface polymerization. The addition of Co to Fe served to increase the saturation magnetic moment of polymer‐coated Fe particles up to 50%. The coercivity also increased. Addition of small amounts of Ni to Fe–Co alloys decreased the coercivity. Aging tests were made to test the protection afforded by the surface polymer. The submicron alloy particles were found to be stable when heated at 97°C in air.