O. N. Pashkova

Cluster ferromagnetism in Mn-doped InSb

We have studied cluster ferromagnetism in InSb〈Mn〉 and have refined kinematic exchange theory with application to such diluted magnetic semiconductors.

Synthesis and properties of In1−xMnxSb solid solutions

InSb-Mn (1 at % Mn) and InSb-MnSb (1.33 at % Mn) solid solutions have been synthesized under nonequilibrium conditions in the form of large-grained polycrystals. As shown by electron probe x-ray microanalysis, some of the manganese impurity in the samples has precipitated at grain boundaries as isolated micron-sized maganese-containing inclusions. Electrical measurements have shown that the synthesized In1−xMnxSb materials are p-type, with a hole concentration of 2 × 1019 cm−3, which is an order of magnitude higher than that in the terminal solid solutions obtained under near-equilibrium conditions.

Dislocations in manganese-doped InSb

Electron probe X-ray microanalysis data for quenched InSb〈Mn〉 samples demonstrate that most of the manganese goes to doping of dislocations in the semiconductor lattice. The manganese-doped dislocations in InSb determine the magnetic and electrical properties of the material at room temperature and above. According to magnetic measurements, this is accompanied by the formation of several magnetic phases. Codoping of InSb with manganese and zinc with the aim of neutralizing one of the magnetic phases allowed us to obtain a ferromagnetic semiconductor with a Curie temperature of 320 K.

Manganese solubility in quenched InSb

We have studied the magnetic properties of supersaturated In1 − xMnxSb substitutional solid solutions prepared by quenching from the liquid state. All of the materials in the range 0.07–2 at % Mn were found to be ferromagnets. Judging from their Curie temperatures, they contained microinclusions of variable composition, similar to solid solutions based on the ferrimagnetic compound Mn2Sb at Mn contents below 0.5 at % and to solid solutions based on the ferromagnetic compound MnSb at higher Mn contents.

Cluster ferromagnetism in InSb codoped with Mn and Zn

Using direct melting and quenching of InSb + 0.058-0.23 wt % Mn + 1.1 wt % Zn, we have prepared polycrystalline InSb〈Mn, Zn〉 solid solutions containing much less impurity phases in comparison with earlier studied InSb〈Mn〉 substitutional solid solutions containing manganese on the indium site. As shown by electron probe x-ray microanalysis and electrical and magnetic measurements, the synthesized solid solutions consist of InSb〈Mn〉 substitutional solutions and InSb〈Zn〉 interstitial solutions. The room-temperature hole concentration and magnetization of InSb〈Mn, Zn〉 p exceed those of InSb〈Mn〉. The electrical and magnetic properties of the magnetic material InSb〈Mn, Zn〉 fit well with indirect kinematic ferromagnetic exchange theory.

A microstructural study of a quenched InSb ingot

Samples cut from a quenched ingot of the compound semiconductor InSb have been characterized by precision X-ray diffraction. The results show that the central and top parts of the ingot have [110] texture, whereas its bottom part is polycrystalline, which is interpreted in terms of the heat removal geometry during quenching. The texture plane coincides with the easy cleavage plane (110), typical of the III–V compound semiconductors and due to dislocation pile-ups. The microstructure of the quenched InSb ingot includes characteristic microcracks, dotted with dislocation outcrops on the polished surface. The observed increase in the unit-cell parameters of quenched InSb is tentatively attributed to the high dislocation density in the quenched ingot.

InSb codoped with Mn and Zn: A new ferromagnetic semiconductor

We have studied the magnetic properties of In1 − xMnxSb substitutional solid solutions. The results indicate that, at Mn contents below 0.5 at %, the materials contain microinclusions close in composition to the ferrimagnetic compound Mn2Sb, which has a layered structure with magnetically active manganese in two structurally inequivalent sites, Mn1 and Mn2. Zinc doping of Mn2Sb breaks up one of its magnetic sub-lattices and converts the ferrimagnet to a ferromagnet. This property is basic to the proposed ferromagnetic semiconductor based on InSb codoped with Mn and Zn, which has a Curie temperature near 320 K.

Cluster magnetism in doped InSb

Magnetic properties of indium antimonide doped by Mn and by, simultaneously, Mn and Zn, and Mn and Cd have been analyzed. It has been established that the basic contribution to the formation of the magnetic properties of these materials comes from clusters, whose composition and Curie temperature change depending on the content of manganese, zinc, and cadmium.

Microstructure of quenched doped InSb

Magnetic characterization results indicate that, after liquid quenching, InSb samples doped with manganese, manganese + zinc, and manganese + cadmium are magnetic semiconductors. According to microstructural analysis data, polished sections of these materials demonstrate surface order: the grains have the form of wedges directed from the periphery of the section to its center, occupy essentially the entire surface of the section, and have low-angle boundaries with dislocation outcrops on the sample surface. According to X-ray diffraction data, quenched doped InSb samples are free of impurity phases and have preferential crystallographic orientations. Analysis of the present experimental data leads us to conclude that the surfaces of metallographic specimens of doped InSb are sections through textures whose orientation—under given quenching conditions—depends on the dopant composition.

Magnetically soft semiconductor InSb〈Mn,Zn〉 with the curie temperature of 320 K

The magnetic properties of a ferromagnetic semiconductor based on indium antimonide doped with manganese and zinc having the Curie temperature Tc = 320 K are studied. Field dependences of magnetization of InSb〈Mn,Zn〉 recorded at 4 and 260 K indicate that this material is magnetically soft with the coercive force no higher than 18 Oe at T = 300 K.