Ab initiostudy of the magnetic ordering in Si/Mn digital alloys

Abstract

We present a first-principles study of the electronic structure and exchange interactions in Si/Mn digital magnetic alloy (DMA) consisting of Mn monolayers embedded in a Si matrix stacking along [001] direction. The main focus of our study is on the dependence of magnetic properties on the morphology of the Mn monolayer. Three different structural models for the Mn monolayer are considered: manganese in substitutional (i), interstitial (ii), and both interstitial and substitutional (iii) positions. The atomic positions in Si/Mn DMA are determined by means of the VASP code and then serve as input for multiple-scattering calculations of the electronic and magnetic structure. The magnetic force theorem is used to evaluate the exchange coupling parameters. A Heisenberg model based on those parameters is used to estimate magnon frequencies and magnetic phase-transition temperatures for different anisotropies. The magnetic properties of Si/Mn DMA are found to be strongly dependent on the underlying crystalline structure.

Spin-polarized half-metallic state of a ferromagneticδlayer in a semiconductor host

“…Ab initio calculations for a regular array of δ layers obtain an estimate for the ground-state spin stiffness, which is subsequently used to obtain an estimate for the critical temperature within Monte Carlo simulations of the resulting effective (anisotropic) Heisenberg model. 15,16 In Ref. 15, the critical temperature for the Ge/Mn system is estimated as T c ≈ 200-300 K, which compares well with our result in the Ising (easy-axis) case.…”

Search for stable ferromagnets amongAIV/Fe digital alloys (AIV=Si, Ge) using first-principles calculations

“…In this case, the system will feature no magnetic order at any temperature except 0 K, 28 since, according to the MerminWagner theorem, the ordering will be destroyed by long-range spin fluctuations. 32,33 In the limit of strong enough easy-plane anisotropy such systems were shown to undergo relatively sharp phase change, so-called Berezinskii-Kosterlitz-Thouless (BKT) transition.…”

“…In the spirit of our previous works, 27,28 we investigated magnetism depending on the structure of the DA considering two cases: the substitutional Fe ML and the interstitial Fe ML. Since epitaxial growth is a nonequilibrium process, both structural situations are in principle possible and should be considered.…”

“…[17][18][19][20] For instance, ab initio calculations predict A IV /Mn DAs (A IV = Si,Ge), in which Mn MLs formed substitutionally, to be half metallic ferromagnets. [21][22][23][24][25][26][27][28][29] Recently, the critical temperatures of the intralayer magnetic ordering in A IV /Mn DAs were estimated for the case of easy-axis anisotropy by means of Monte Carlo (MC) simulations. 27,28 The most realistic estimates, based on the disordered local moment (DLM) picture, 30,31 yielded temperature values well below room temperature (≈200 K) for FM DAs, contrary to expectations.…”

“…[21][22][23][24][25][26][27][28][29] Recently, the critical temperatures of the intralayer magnetic ordering in A IV /Mn DAs were estimated for the case of easy-axis anisotropy by means of Monte Carlo (MC) simulations. 27,28 The most realistic estimates, based on the disordered local moment (DLM) picture, 30,31 yielded temperature values well below room temperature (≈200 K) for FM DAs, contrary to expectations. 23 Nevertheless, the results are encouraging, since some ferrimagnetic alloys were predicted to be ordered up to room temperature, 27 revealing the potential of the digital doping for fabrication of magnetic semiconductors with high enough transition temperatures.…”