A. Twardowski

Magneto-optic effect of the ferromagnetic diluted magnetic semiconductor Ga1−xMnxAs

Magnetic circular dichroism (MCD) of a ferromagnetic diluted magnetic semiconductor Ga1−xMnxAs films was measured to clarify their electronic structure. Strong enhancement of MCD by Mn substitution indicated a strong sp–d hybridization. The p–d exchange interaction was concluded to be antiferromagnetic, which was in contrast with the reported ferromagnetic p–d exchange in very diluted paramagnetic GaAs:Mn bulk crystals. The change of the character of the p–d exchange interaction is due to the unique feature of Ga1−xMnxAs that the relative abundance of the neutral and ionized Mn acceptors controls the p–d exchange.

Paramagnetism and antiferromagnetic d–d coupling in GaMnN magnetic semiconductor

The magnetization of Ga1−xMnxN (x<0.1) crystals was measured as a function of the magnetic field and temperature. Paramagnetic behavior typical of spin S=5/2 expected for Mn2+ (d5) magnetic centers was observed in the temperature range of 2 K<T<300 K. On the other hand, antiferromagnetic coupling between Mn ions was clearly visible. The nearest neighbor (NN) coupling constant JNN/kB=−1.9 K was estimated from the temperature dependence of the magnetization.

Possible origin of ferromagnetism in (Ga,Mn)N

Ferromagnetic behavior of GaN doped with Mn (Ga1−zMnzN) grown by the ammonothermal and chemical transport methods is discussed in terms of a second phase (ferromagnetic one) produced during the growth process. The reference manganese nitride samples grown by the same method as (Ga,Mn)N reveal room-temperature ferromagnetic behavior, depending on the growth details. Different MnxNy phases are suggested to be responsible for ferromagnetic behavior of (Ga,Mn)N.

Magnetic properties of Fe‐based diluted magnetic semiconductors (invited)

In recent years considerable interest was focused on diluted magnetic semiconductors (DMS), mainly Mn‐based DMS. Mn++ ions in these materials possess only spin momentum (S=5/2), which is the source of the permanent magnetic moment localized on Mn ions. On the other hand, a new class of Fe‐type DMS can serve as a much more general example, since Fe++ ions possess both spin and orbital momenta (S=2, L=2). Consequently the ground state of an Fe++ ion is a magnetically inactive singlet, and one is dealing only with field induced magnetic moments associated with Fe ions. This situation yields a substantially different magnetic behavior of Fe‐based DMS with respect to Mn‐type materials. In that respect, we review the magnetic properties of Fe‐type DMS‐like ZnFeSe, CdFeSe, HgCdFeSe, and HgFeSe. The influence of nonvanishing orbital momentum on specific heat, susceptibility, and magnetization is pointed out. We also show evidence of antiferromagnetic exchange interaction between Fe ions in these crystals. A possi...

Antiferromagnetic interlayer coupling in ferromagnetic semiconductor EuS/PbS(001) superlattices

Antiferromagnetic coupling between ferromagnetic layers has been observed for the first time in an all-semiconductor superlattice structure EuS/PbS(001), by neutron scattering and magnetization measurements. Spin-dependent superlattice band structure effects are invoked to explain the possible origin and the strength of the observed coupling.

Structure and magnetism of MnAs nanocrystals embedded in GaAs as a function of post-growth annealing temperature

Self-organized Ga(Mn)As nanoclusters, embedded in GaAs, were formed during post-growth thermal annealing of Ga1−xMnxAs layers. Structural and magnetic properties of such composites were systematically studied as a function of the annealing temperature. Small (∼3 nm) Mn-rich zinc-blende Mn(Ga)As clusters, coherent with the GaAs matrix, were formed at the annealing temperature of 500 °C. An increase of the annealing temperature of up to 600 °C led to the creation of 10–20 nm large NiAs-type hexagonal MnAs nanocrystals. Magnetization measurements showed that the MnAs nanoprecipitates were superparamagnetic, with a distribution of blocking temperatures that depended on the MnAs cluster size. Some intermediate paramagnetic clusters (structurally disordered clusters) were also observed.

Properties of arsenic antisite defects in Ga1−xMnxAs

We report the results of optical absorption measurements on Ga1−xMnxAs layers grown by low-temperature molecular beam epitaxy. In the paramagnetic layers grown at very low temperatures (below 250 °C) the experiments reveal an absorption band at 1.2 eV arising from the presence of neutral arsenic antisites, AsGa. From the magnitude of the absorption we determine the concentration of AsGa to be between 4×1019 and 8×1019 cm−3 in these paramagnetic samples. These values are typical for GaAs specimens grown below 250 °C. Extrapolating the AsGa concentration from low-temperature-grown GaAs to Ga1−xMnxAs, we determine the concentration of this defect in ferromagnetic Ga1−xMnxAs layers grown at temperatures above 250 °C as 1×1019 down to 1×1018 cm−3. We conclude that the compensating role of arsenic antisites in Ga1−xMnxAs becomes gradually less important with increasing growth temperature.

Thermodynamic properties of iron-based II-VI semimagnetic semiconductors

The specific heat, magnetization and low field susceptibility is calculated for iron-based Semimagnetic Semiconductors. Calculations are performed in Extended Nearest Neighbour Pair Approximation taking into account both Heisenberg-type d-d exchange interaction and spin-orbit interaction. Comparison with available experimental data for ZnFeSe and CdFeSe is presented.

Magnetic properties of Cd1-xMnxTe and Zn1-xMnxTe epilayers with high concentration of Mn

Field-cooled, zero-field-cooled and remanent magnetization of Cd 1 x Mn x Te, Zn 1-x Mn x Te (0.5 < x ≤ 1.0) epilayers, including the end-point MnTe, were measured as functions of temperature and magnetic field. For all diluted systems (x < 1.0) a spin-glass-like behavior was observed. Irreversible effects, typical for the spin-glass, tend to decrease in magnitude with an increasing Mn concentration and vanish in MnTe. This spin-glass-antiferromagnet transition is gradual. Magnetic phase diagrams of Cd 1-x Mn x Te and Zn 1-x Mn x Te are discussed.

Magnetospectroscopy of free exciton in CdFeSe semimagnetic semiconductor

The magnetospectroscopy data of free exciton in hexagonal Cd1−xFexSe are presented for different magnetic field orientation. Combining exciton splitting data with magnetic susceptibility data we estimate p-d exchange integral for CdFeSe valence band.