Effect of the location of Mn sites in ferromagneticGa1−xMnxAson its Curie te

Abstract

We report a strong correlation between the location of Mn sites in ferrromagnetic Ga 1-x Mn x As measured by channeling Rutherford backscattering and by particle induced x-ray emission experiments and its Curie temperature. The concentrations of free holes determined by electrochemical capacitance-voltage profiling and of uncompensated Mn ++ spins determined from SQUID magnetization measurements are found to depend on the concentration of unstable defects involving highly mobile Mn interstitials. This leads to large variations in T C of Ga 1-x Mn x As when it is annealed at different temperatures in a narrow temperature range. The fact that annealing under various conditions has failed to produce Curie temperatures above ~110K is attributed to the existence of an upper limit on the free hole concentration in low-temperature-grown Ga 1-x Mn x As.

All-Wurtzite (In,Ga)As-(Ga,Mn)As Core–Shell Nanowires Grown by Molecular Beam Epitaxy

“…pattern for [11][12][13][14][15][16][17][18][19][20] zone axis fits well to the experimental image (see Fig. 3d).…”

The essential role of carefully optimized synthesis for elucidating intrinsic material properties of (Ga,Mn)As

“…The common trends in annealing (at temperatures close to the growth temperature) suggest the presence of competing mechanisms. One mechanism yields the increase of T C and is ascribed in a number of reports to the removal of charge and moment compensating interstitial Mn impurities 57,58 . The removal is slowed down by the growth of an oxide surface layer during annealing 54 and an additional mechanism can eventually yield reduction of T C after sufficiently long annealing times, depending on the annealing temperature.…”

Prospects for high temperature ferromagnetism in (Ga,Mn)As semiconductors

“…14,42 In this picture, the sign of the indirect kinetic-exchange Mn Ga u Mn Ga coupling fluctuates as cos͑2k F d͒, where d is the distance between Mn Ga moments, and its amplitude decays as d 3 . We can estimate the average Mn Ga u Mn Ga separation in a ͑Ga,Mn͒As random alloy as d =2͑3/4 N Mn ͒ 1/3 .…”

“…After some frustration in the community caused by the difficulties encountered in overcoming the apparent Curie temperature limit in ͑Ga,Mn͒As of T c = 110 K, [1][2][3][4] the record transition temperature has been steadily increasing over the last two years. [5][6][7][8][9] The maximum T c = 173 K reported 9 to date is likely another short-lived record in bulk ͑Ga,Mn͒As ferromagnets.…”

“…It is now established that the success has been made possible by the technological progress in controlling crystallographic quality of the materials, namely, in reducing the number of unintentional charge and moment compensating defects through optimized growth and post-growth annealing procedures. [3][4][5][6][7][8][9][10] Experiments also suggest that the general picture of ferromagnetism that applies to these metallic ͑Ga,Mn͒As systems is the one in which magnetic coupling between local Mn moments is mediated by delocalized holes in the ͑Ga,Mn͒As valence band. The fact that the mechanism does not imply a fundamental T c limit below room temperature motivates a detailed analysis of our understanding of the T c trends in currently available high quality metallic materials with Mn doping ranging from approximately 2% to 9%.…”