Hole Transport in Impurity Band and Valence Bands Studied in Moderately Doped GaAs:Mn Single Crystals

We report on simple experiment on temperature-dependent Hall effect measurements in GaMnAs single crystalline samples with Mn composition estimated at 0.05-0.3 at.% which is slightly below the onset of ferromagnetism. Impurity band transport is visible for Mn compositions of ~0.3 at.% as a clear metallic behaviour. The results show interesting situation that the Metal-Insulator transition in GaAs:Mn occurs within the impurity band which is separated from the valence bands for Mn concentrations studied here. We also discuss on the equilibrium high temperature solubility limit of Mn in GaAs, unknown precisely in the literature.Comment: 9 pages, 2 figures, Proc. of 35th International School on the Physics of Semiconducting Compounds, Jaszowiec 2007, Poland, to appear in Acta Physica Polonica A (2007

Properties and Curie Temperature (130 K) of Heavily Mn-doped Quaternary Alloy Ferromagnetic Semiconductor (InGaMn)As Grown on InP

We have studied magnetic properties of heavily Mn-doped [(In0.44Ga0.56)0.79Mn0.21]As thin films grown by low-temperature molecular-beam epitaxy (LT-MBE) on InP substrates. The (InGaMn)As with high Mn content (21%) was obtained by decreasing the growth temperature to 190 degC. When the thickness of the [(In0.44Ga0.56)0.79Mn0.21]As layer is equal or thinner than 10 nm, the reflection high-energy electron diffraction (RHEED) pattern and transmission electron microscopy (TEM) show no MnAs clustering, indicating that a homogeneous single crystal with good quality was grown. In the magnetic circular dicroism (MCD) measurement, large MCD intensity and high Curie temperature of 130 K were observed.Comment: 3 pages, 5 figure

Anaysis of the skilled performance of mentally deficient adults

It was observed that mental defectives, who were unable to draw a diamond, revealed an associated decrease in their performance time end increase in hand pressure. Closer study of the failure to execute a diamond suggested the hypothesis that the chief difficulty consisted in the patient's inability to draw the obtuse angles, i.e. to make that particular change in the direction of the moving hand. Subsequent experiments confirmed the close relationship between the ability or inability to draw a diamond and the drawing of an obtuse angle. Various degrees of difficulty involved in drawing of different angles were also demonstrated. These experiments also indicated that patients with an IQ below 38 could not draw an obtuse angle or a diamond, while subjects with an IQ above 57 could. The main experiment consisting of a battery of tests was carried out on two groups of defectives and third group composed of nursing staff. The IQ’s of both groups of defectives varied between 38 and 57. The subjects in the first group could not while those in the second group could draw an obtuse angle. The results of the main experiment showed a significant difference between the means of the three groups for Simple Reaction Time, Pressure and Performance Time tests. There was also a significant difference between the means of verbal and practical tests of both groups of defectives. In all three groups positive correlation was established between the Pressure and Performance Time tests. On the whole, drawings, as other skilled performances, were shown to depend on the ability of the individual to maintain and vary direction and pressure, and the correct timing of these activities. These three factors could appear to be the essential components of skill studied