Experimental probing of exchange interactions between localized spins in the dilute magnetic insulator (Ga,Mn)N

Abstract

The sign, magnitude, and range of the exchange couplings between pairs of Mn ions is determined for (Ga,Mn)N and (Ga,Mn)N:Si with x 3%. The samples have been grown by metalorganic vapor phase epitaxy and characterized by secondary-ion mass spectroscopy; high-resolution transmission electron microscopy with capabilities allowing for chemical analysis, including the annular dark-field mode and electron energy loss spectroscopy; high-resolution and synchrotron x-ray diffraction; synchrotron extended x-ray absorption fine-structure; synchrotron x-ray absorption near-edge structure; infra-red optics and electron spin resonance. The results of high resolution magnetic measurements and their quantitative interpretation have allowed to verify a series of ab initio predictions on the possibility of ferromagnetism in dilute magnetic insulators and to demonstrate that the interaction changes from ferromagnetic to antiferromagnetic when the charge state of the Mn ions is reduced from 3+ to 2+.

Two-Probe Measurements of Electron Transport in GaN:Si/(Ga,Mn)N/GaN:Si Spin Filter Structures

“…These higher resistances are only partially due to the reduced size of the mesa. Actually, in an ideal case, the insulating (Ga,Mn)N middle layer [4] is expected to block the current through the whole stack, and only a tunneling current weakly dependent on the mesa size should be observed. In contrast, from all tested structures only the smaller size mesas exhibit a noticeable increased resistance and nonlinear I-V characteristics.…”

“…The importance of GaN-based compounds and heterostructures stems from the growing significance of wide band-gap materials in conventional electronics, particularly in opto-and high power electronics. The established a strong mid-gap Fermi-level pinning and a lack of a depletion layer, in combination with its insulating character due to a strong electron trapping by mid-gap Mn 2+ /Mn 3+ level [4,5] and a sizable dielectric strength of 5 MV/cm [6], point at (Ga,Mn)N as insulating buffer material for applications in (high power) nitride devices and make it an ideal building block for spin harnessing structures like spin filters [7] and resonant tunneling devices [8]. Besides these technologically relevant concepts, the spin imbalance in these systems may allow probing spin-orbit coupling, quantum Hall effects, and pairing in unconventional superconductors [9].…”

Theory of ferromagnetism driven by superexchange in dilute magnetic semi-conductors

“…Dilute magnetic insulators constitute an emerging class of magnetic semiconductors in which rather than the p-d Zener mechanism [1], ferromagnetic superexchange accounts for the coupling between diluted transition metal (TM) spins [2]. Due to its compatibility with IIInitrides that have reached the status of the most important semiconductors next to Si, particularly attractive is Ga 1−x Mn x N, in which there are no itinerant holes but nevertheless ferromagnetic spin-spin interactions are observed [2].…”

“…Due to its compatibility with IIInitrides that have reached the status of the most important semiconductors next to Si, particularly attractive is Ga 1−x Mn x N, in which there are no itinerant holes but nevertheless ferromagnetic spin-spin interactions are observed [2].…”

“…A high degree of crystallinity, a random distribution of the Mn ions, and a weak degree of compensation by residual donors were checked in these samples by a range of electron microscopy, synchrotron radiation, ion beam, optical, and magnetic resonance techniques [2,3,5].…”