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Highlights • We examine magnetic transitions in graphene + α-Fe 2 O 3 nanocomposite materials. • We show the presence of magnetic impurities in pure graphene samples. • We show that the studied samples show superparamagnetic blocking. • We show the presence of a large exchange bias in our samples. Abstract We present studies of structural and magnetic properties of graphene + Fe 2 O 3 composite samples with the magnetic oxide content changing from 0 to 50%. Our studies revealed that irrespective of the cleaning procedure the magnetic behavior of pure graphene samples changed from diamagnetic to paramagnetic for samples made with either acetone or ethanol, respectively. The paramagnetic samples contained a significant concentration of magnetic moments. For all our samples with Fe 2 O 3 at T < 110 K we observed the superparamagnetic blocking. Moreover, due to the presence of Fe 2 O 3 nanoparticles with diameter >10 nm we observed a transition at T ≈ 495 K and another at T > 600 K. The synthesis solvent changes modified the magnetic behavior of our samples resulting in higher effective magnetic moment for the ethanol related samples. The shape and the parameters characterizing the magnetic hysteresis loop change strongly with the change of preparation method and the amount of Fe 2 O 3. Large exchange bias was observed for all our samples indicating the significance of antiferromagnetic surface spin-alignment of Fe 2 O 3 nanoparticles. It is therefore possible to control the magnetic properties of graphene + Fe 2 O 3 composites over a wide range of parameters. [ABSTRACT FROM AUTHOR]

We have studied optical, electrical and structural properties of the semimagnetic semiconducting ZnGeAs 2 crystals, undoped and doped with 1.5, 3 and 3.5 wt% Mn, which is perspective material for spintronics. We used Raman spectroscopy as a sensitive method for precise determination of crystal structure. In addition to the vibrational frequencies of a ZnGeAs 2 lattice, MnAs clusters and Mn complexes, which we have already experimentally registered at similar materials, the existence of As clusters in this material is revealed for the first time. Based on the obtained results we concluded that arsenic clusters of various sizes exist, including form of molecules – As 4 . We assume that they are located in the vicinity of the grain boundaries and that the distribution of free carriers in the samples was inhomogeneous. [ABSTRACT FROM AUTHOR]

Abstract: The magnetic properties of a Cd1−x Mn x GeAs2: MnAs hybrid micro-composite have the signature of ferromagnetic order at room temperature. Magnetotransport reveals the presence of a large linear positive magnetoresistance, with maximum values of about 550% ( T) for . This is interpreted in terms of an effective medium approximation with the value and the shape of the magnetoresistance depending on the structural and electronic properties of the semiconductor rather than on its magnetic properties. The absence of an anomalous Hall effect leads to the conclusion that ferromagnetic ordering is not the only factor necessary for the occurrence of asymmetric scattering in granular ferromagnetic materials. [Copyright &y& Elsevier]

Abstract: Glassy system with the composition xLa2O3–30PbO–(70− x)B2O3 with (0≤ x ≤10mol%) has been prepared using the well known melt quenching technique. The transmittance and the reflectance spectra of the glasses have been measured and the optical constants such as: the refractive index, the optical band gap for indirect transition, the optical basicity and the average electronic polarizability have been calculated for the investigated glassy system. A correlation between the optical constants and the elastic moduli was performed. The AC magnetic susceptibility of the investigated glasses was studied above 4.3K. The temperature dependent magnetic susceptibility deviates from the Curie law indicating that weak antiferromagnetic interactions between La ions were present in the studied system. The magnetic entropy change of the glasses was determined. [Copyright &y& Elsevier]

Abstract: Optical properties of p-type Zn1− x Mn x GeAs2 for 0⩽ x ⩽0.078 were investigated by Raman spectroscopy at room temperature. Phonons of ZnGeAs2 are experimentally determined and they are in excellent agreement with those theoretically predicted. Existence of MnAs clusters was confirmed in the sample with the highest concentration of Mn. MnAs was found in α and β phases and their vibrational frequencies are obtained experimentally. Plasmon – two different phonons interaction in Zn1− x Mn x GeAs2 is registered and analyzed. [Copyright &y& Elsevier]