Dariusz Sztenkiel

Structural and paramagnetic properties of dilute Ga 1 − x Mn x N

Systematic investigations of the structural and magnetic properties of single crystal (Ga,Mn)N films grown by metal organic vapor phase epitaxy are presented. High resolution transmission electron microscopy, synchrotron x-ray diffraction, and extended x-ray absorption fine structure studies do not reveal any crystallographic phase separation and indicate that Mn occupies Ga-substitutional sites in the Mn concentration range up to 1%. The magnetic properties as a function of temperature, magnetic field and its orientation with respect to the c-axis of the wurtzite structure can be quantitatively described by the paramagnetic theory of an ensemble of non-interacting Mn

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

^{3+}

Homogeneous and heterogeneous magnetism in (Zn,Co)O : From a random antiferromagnet to a dipolar superferromagnet by changing the growth temperature

ions in the relevant crystal field, a conclusion consistent with the x-ray absorption near edge structure analysis. A negligible contribution of Mn in the 2+ charge state points to a low concentration of residual donors in the studied films. Studies on modulation doped p-type (Ga,Mn)N/(Ga,Al)N:Mg heterostructures do not reproduce the high temperature robust ferromagnetism reported recently for this system.

Manipulating Mn–Mgk cation complexes to control the charge- and spin-state of Mn in GaN

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+.

Thickness dependent magnetic properties of (Ga,Mn) As ultrathin films

For more than a decade ZnO doped with Mn and Co has remained as one of the most prospected diluted magnetic semiconductor for spintronic applications with conflicting outcome concerning the genuineness of its room temperature ferromagnetism. In order to clarify this issue we investigate (Zn,Co)O layers grown by atomic layer deposition at low temperatures. We employ and relay on wide range of extensive material characterization, which in combination with superconducting quantum interference device magnetometry allow us decisively exemplify the growth temperature as the key factor discriminating between paramagnetic (obtained at 160 °C) and various forms of ferromagnetic responses, seen when the grows is carried out at 200 °C and above.

Stretching magnetism with an electric field in a nitride semiconductor.

Owing to the variety of possible charge and spin states and to the different ways of coupling to the environment, paramagnetic centres in wide band-gap semiconductors and insulators exhibit a strikingly rich spectrum of properties and functionalities, exploited in commercial light emitters and proposed for applications in quantum information. Here we demonstrate, by combining synchrotron techniques with magnetic, optical and ab initio studies, that the codoping of GaN:Mn with Mg allows to control the Mnn+ charge and spin state in the range 3≤n≤5 and 2≥S≥1. According to our results, this outstanding degree of tunability arises from the formation of hitherto concealed cation complexes Mn-Mgk, where the number of ligands k is pre-defined by fabrication conditions. The properties of these complexes allow to extend towards the infrared the already remarkable optical capabilities of nitrides, open to solotronics functionalities, and generally represent a fresh perspective for magnetic semiconductors.

Homogenous and heterogeneous magnetism in (Zn,Co)O

X iv :1 20 5. 48 24 v1 [ co nd -m at .m tr lsc i] 2 2 M ay 2 01 2 Thickness dependence of magnetic properties of (Ga,Mn)As O. Proselkov, a) D. Sztenkiel, W. Stefanowicz, M. Aleszkiewicz, J. Sadowski, 2 T. Dietl, 3 and M. Sawicki b) Institute of Physics, Polish Academy of Sciences, Warszawa, Poland MAX-lab, Lund University, Lund, Sweden Institute of Theoretical Physics, Faculty of Physics, University of Warsaw, Warszawa, PolandWe report on a monotonic reduction of Curie temperature in dilute ferromagnetic semiconductor (Ga,Mn)As upon a well controlled chemical-etching/oxidizing thinning from 15 nm down to complete removal of the ferromagnetic response. The effect already starts at the very beginning of the thinning process and is accompanied by the spin reorientation transition of the in-plane uniaxial anisotropy. We postulate that a negative gradient along the growth direction of self-compensating defects (Mn interstitial) and the presence of surface donor traps gives quantitative account on these effects within the p–d mean field Zener model with adequate modifications to take a nonuniform distribution of holes and Mn cations into account.

Quantum effects in linear and nonlinear transport of T -shaped ballistic junction patterned from GaAs / Al x Ga 1 − x As heterostructures

The significant inversion symmetry breaking specific to wurtzite semiconductors, and the associated spontaneous electrical polarization, lead to outstanding features such as high density of carriers at the GaN/(Al,Ga)N interface—exploited in high-power/high-frequency electronics—and piezoelectric capabilities serving for nanodrives, sensors and energy harvesting devices. Here we show that the multifunctionality of nitride semiconductors encompasses also a magnetoelectric effect allowing to control the magnetization by an electric field. We first demonstrate that doping of GaN by Mn results in a semi-insulating material apt to sustain electric fields as high as 5 MV cm−1. Having such a material we find experimentally that the inverse piezoelectric effect controls the magnitude of the single-ion magnetic anisotropy specific to Mn3+ ions in GaN. The corresponding changes in the magnetization can be quantitatively described by a theory developed here.

Reconciling results of tunnelling experiments on (Ga,Mn)As

For more than a decade ZnO doped with Mn and Co has remained as one of the most prospected diluted magnetic semiconductor for spintronic applications with conflicting outcome concerning the genuineness of its room temperature ferromagnetism. In order to clarify this issue we investigate (Zn,Co)O layers grown by atomic layer deposition at low temperatures. We employ and relay on wide range of extensive material characterization, which in combination with superconducting quantum interference device magnetometry allow us decisively exemplify the growth temperature as the key factor discriminating between paramagnetic (obtained at 160 °C) and various forms of ferromagnetic responses, seen when the grows is carried out at 200 °C and above.

Impact of substrate temperature on magnetic properties of plasma-assisted molecular beam epitaxy grown (Ga,Mn)N

J. Wróbel, P. Zagrajek, M. Czapkiewicz, M. Bek, D. Sztenkiel, K. Fronc, R. Hey, K. H. Ploog, and B. R. Bu lka Institute of Physics, Polish Academy of Sciences, al Lotników 32/46, 02-668 Warszawa, Poland Institute of Molecular Physics, Polish Academy of Sciences, ul. M. Smoluchowskiego 17, 60-179 Poznań, Poland Paul Drude Institute of Solid State Electronics, Hausvogteiplatz 5-7, D-10117 Berlin, Germany (Dated: December 10, 2009)