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Currently, complex ferromagnetic semiconductor systems are of significant interest due to their potential applicability in spintronics. A key feature in order to use semiconductor materials in spintronics is the presence of room temperature ferromagnetism. This feature was recently observed and is intensively studied in several Mn-alloyed II-IV-V2 group diluted magnetic semiconductor systems. The paper reviews the origin of room temperature ferromagnetism in II-IV-V2 compounds. In view of our recent reports the room temperature ferromagnetism in Mn-alloyed chalcopyrite semiconductors with more than 5 molar % of Mn is due to the presence of MnAs clusters. The solubility of magnetic impurities in bulk II-IV-V2 materials is of the order of a few percent, depending on the alloy composition. High values of the conducting hole - Mn ion exchange constant Jpd have significant value equal to 0.75 eV for Zn0.997Mn0.003GeAs2. The sample quality has significant effect on the magnetotransport of the alloy. The magnetoresistance of the alloy change main physical mechanism from spin-disorder scattering and weak localization for homogeneous samples to cluster-related geometrical effect observed for nanocomposite samples. The magnetoresistance of the II-IV-V2 alloys can be then tuned up to a few hundreds of percent via changes of the chemical composition of the alloy as well as a degree of disorder present in a material. [Projekat Ministarstva nauke Republike Srbije, br. III45003]

A study was conducted to analyze the structure of amorphous and crystalline YbaCuO films determined in on-axis and off-axis deposition geometries. The crystalline films were predominantly (001) oriented. Experimental results indicated the existence of amorphous continuum of spatially disordered atoms and crystalline clusters supporting quasi-two dimensional or long range orders. Findings also showed that the off-axis films supported a periodic repetition of the elements of atomic order or disorder along the direction of the plasma plume.

(YBa2Cu3O7-/Nd0.67Sr0.33MnO3-y)n superlattices were developed using the high-pressure direct current sputtering technique. X-ray analyses reveal that the LaAlO3 (100) substrates exhibit c-axis epitaxial growth. Lattice parameter discrepancies between the substrate and YBa2Cu3O7 sublayers strained the Nd0.67SrO.33MnO3-y films which exhibited ferromagnetic order less than 200 K.

Positron annihilation spectroscopy is used to study point defects in Zn1-xMnxGeAs2 crystals with low Mn content 0 ≤ χ ≤ 0:042 with disordered zincblende and chalcopyrite structure. The role of negatively charged vacancies and non-open-volume defects is discussed with respect to the high p-type conductivity with carrier concentration 1019 ≤ p ≤ 1021 cm-3 in our samples. Neutral As vacancies, together with negatively charged Zn vacancies and non-open-volume defects with concentrations around 1016 - 1018 cm-3, are observed to increase with increasing Mn content in the alloy. The observed concentrations of defects are not sufficient to be responsible for the strong p-type conductivity of our crystals. Therefore, we suggest that other types of defects, such as extended defects, have a strong influence on the conductivity of Zn1-xMnxGeAs2 crystals. [ABSTRACT FROM AUTHOR]

We present the studies of structural, electrical, and magnetic properties of bulk Cd1-xMnxGeAs2 crystals with low Mn content, x, varying from 0 to 0.037. The studied samples have excellent crystallographic quality indicated by the presence of diffraction patterns never before observed experimentally for this compound. The electrical transport in our samples is dominated by thermal activation of conducting holes from the impurity states to the valence band with activation energy of about 200 meV. The defect states acting as ionic scattering centers with concentration in the range from 6 to 15 × 1017 cm-3 are observed. The effective Mn content in our samples, xθ, determined from fit of the susceptibility data to the Curie-Weiss law, is very close to the average chemical content, x. It indicates that the Mn ions are distributed randomly, substituting the Cd sites in the host CdGeAs2 lattice. We observe a negative Curie-Weiss temperature, ∣θ∣ ⩽ 3:1K, increasing as a function of x. This indicates the significance of the short-range interactions between the Mn ions. © 2014 AIP Publishing LLC. [ABSTRACT FROM AUTHOR]

We present systematic studies of magnetic and transport properties of Zn1-xMnxGeAs2 semimagnetic semiconductor with the chemical composition varying between 0.053≤x≤0.182. The transport characterization showed that all investigated samples had p-type conductivity strongly depending on the chemical composition of the alloy. The Hall effect measurements revealed carrier concentrations p≥1019 cm-3 and relatively low mobilities, μ≤15 cm2/(V s), also chemical composition dependent. The magnetic investigations showed the presence of paramagnet-ferromagnet phase transitions with transition temperatures greater than 300 K for the samples with x≥0.078. We prove by means of x-ray diffraction, nuclear magnetic resonance, and scanning electron microscopy techniques that the observed room temperature ferromagnetism is due to the presence of MnAs inclusions. The high field magnetoresistance showed the presence of giant magnetoresistance effect with maximum amplitudes around 50% due to the presence of nanosize ferromagnetic grains. [ABSTRACT FROM AUTHOR]

Magnetic and transport properties of [Zn.sub.1-x][Mn.sub.x]Ge[As.sub.2] semimagnetic semiconductor with the varying the chemical composition are studied. The high field magnetoresistance has displayed the presence of giant magnetoresistance effect with maximum amplitudes around 50% because of the presence of nanosize ferromagnetic grains. .

It is shown that progressive crystallization of non-magnetostrictive Co-based metallic glass (VITROVAC 6030) leads to an increase of coercivity by more than three orders of magnitude. The mechanisms responsible for this phenomenon are interpreted showing that the main source for the giant increase of the coercivity is the pinning effect on the domain walls originating from the created crystallites of the size much smaller than the domain width (correlation length for ferromagnetic exchange interactions). It is also shown that gradually devitrified non-magnetostrictive metallic glass is an excellent model material for verification of Neel's theory describing the Rayleigh rule. Index Terms-Coercivity, nanocrystalline magnets, non-magnetostrictive metallic glass, Rayleigh rule.

Series of Al2O3(0001)/Pt/(Fe/Pt)n/Pt multilayers with variable number of bilayers n and thicknesses of individual layers were grown using molecular beam epitaxy to investigate influence of buffer layer structure, number of bilayers, and individual layer thickness on their structural and magnetic properties. Both columnar and monocrystalline 10 nm Pt (111) buffer layers were used in the experiment. Structure of Pt buffer layer determined the roughness of Fe/Pt interfaces and consequently magnetic properties of the multilayers. When multilayers were deposited on columnar Pt buffer layer, we observed increase of Fe/Pt interfaces roughness with increasing number of bilayers to values exceeding the nominal Fe/Pt bilayer thickness in the upper part of the sample volume, which resulted in the increment of coercivity in the sample with n = 15 determined from hysteresis loops measured for perpendicular orientation of magnetic field. When Fe/Pt multilayers were deposited on monocrystalline Pt buffer layer, Fe/Pt interfaces were smooth regardless the number of bilayers. All samples, despite of the quality of buffer layer, number of bilayers, and individual layer thickness revealed easy magnetisation axis oriented in the sample plane. [ABSTRACT FROM AUTHOR]