Ruderman-Kittel-Kasuya-Yosida exchange interaction in many-valley IV-VI semimagnetic semiconductors

Abstract

The Ruderrnan-Kittel-Kasuya-Yosida (RKKY) indirect-exchange interaction via free carriers is analyzed in the case of IV-VI semimagnetic semiconductors (diluted magnetic semiconductors). Carriers responsible for the RKKY interaction in these materials originate from the anisotropic band of heavy holes located at the X point of the Brillouin zone (i.e. , there are 12 equivalent valleys of this band). Both intervalley and intravalley electron processes contribute to the exchange coupling. Calculations of the RKKY exchange integral and the paramagnetic Curie temperature (8) are presented. The exchange integral is anisotropic, and its dependence on the interspin distance is significantly modified in such a way that the role of antiferromagnetic couplings is increased. As a consequence, the value of 8 is reduced.

Correlations between Electronic and Magnetic Properties in Semimagnetic Semiconductors

“…The decisive role of the free carriers in the formation of ferromagnetic phase was explicitly demonstrated for crystals of Pb 1 _ x _ y Sny Mnx Te for which the annealing allows one to control the concentration of carriers in the range p = 5 x 1019 _ 2 x 1021 cm-3 , giving a possibility to study the evolution of magnetic properties as a function of the carrier concentration [18][19][20][21]. The ferromagnetic properties of the high carrier concentration IV-VI semimagnetic semiconductors are related to the Ruderman-Kittel-KasuyaYoshida (RKKY) indirect exchange interaction via free carriers [2,[18][19][22][23]. The argument in favour of this mechanism is its explicit dependence on carrier concentration and its long-range character allowing for the creation of the ferromagnetic order even in quite diluted magnetic systems with only 1 at.% of magnetic ions.…”

Free Carrier Concentration Dependence of Gd-Gd Exchange Constant in SnTe:Gd

“…The Σ band consists of twelve valleys placed at K0(1, 1, 0), K0(-1,1, 0) and so on. The value of K0 is known only approximately [4], in the following K0 = 3π/4α0 , where α 0 = 6.33 Α is the lattice constant. The dispersion relation in the vicinity of the extremum at K0(1, 1, 0), for example, reads where m = 0.2m0 and the factor A = 0.1 [4] takes care on the band's anisotropy.…”

Magnetic anisotropy induced by crystal distortion in Ge1−xMnxTe/PbTe//KCl (001) ferromagnetic semiconductor layers

“…In all known ferromagnetic IV-VI DMS materials with Mn the interspin interactions are driven by the Ruderman-Kittel-Kasuya-Yosida (RKKY) indirect exchange mechanism. The well localized magnetic moments of Mn 2+ ions (electron configuration 3d 5 , spin only state with S=5/2) are exchange-coupled via conducting holes from Σ-and L-valence bands [6]. The 2+ spin and charge state of Mn ions in IV-VI DMS is observed in both magnetically diluted [7] and concentrated systems [8] as verified by electron paramagnetic resonance (EPR) measurements.…”

“…3. During the measurements the samples were rotated by 360° (with the step of 10°) from [001] direction (H=0°, normal to the layer) either to [1][2][3][4][5][6][7][8][9][10] Maxima and minima of the FMR resonant field clearly identify the hard and easy axes of magnetization. In contrast to the expectations based on shape anisotropy mechanism, the easy magnetization axis in Ge0.86Mn0.14Te/PbTe//KCl is not located in the layer plane, but it is close to the layer normal with a broad magnetic anisotropy energy minimum around H=0°.…”