We present the investigation of a monoclinic compound SeCuO 3 using x-ray powder diffraction, magnetization, torque, and electron-spin-resonance. Structurally based analysis suggests that SeCuO 3 can be considered as a three-dimensional network of tetramers. The values of intratetramer exchange interactions are extracted from the temperature dependence of the susceptibility and amount to ∼ 200 K. The intertetramer coupling leads to the development of long-range antiferromagnetic order at T N = 8 K. An unusual temperature dependence of the effective g tensors is observed, accompanied with a rotation of macroscopic magnetic axes. We explain this unique observation as due to site-selective quantum correlations.

We report a novel synthesis route of homogeneously manganese-doped TiO2 nanotubes in a broad concentration range. The scroll-type trititanate (H2Ti3O7) nanotubes prepared by hydrothermal synthesis were used as precursors. Mn 2+ ions were introduced by an ion exchange method resulting MnxH2−xTi3O7. In a subsequent heat-treatment they were transformed into MnyTi1−yO2 where y = x/(3 + x). The state and the local environment of the Mn 2+ ions in the precursor and final products were studied by Electron Spin Resonance (ESR) technique. It was found that the Mn 2+ ions occupy two positions: the first having an almost perfect cubic symmetry while the other is in a strongly distorted octahedral site. The ratio of the two Mn 2+ sites is independent of the doping level and amounts to 15:85 in MnxH2−xTi3O7 and to 5:95 in MnyTi1−yO2. SQUID magnetometry does not show long-range magnetic order in the homogeneously Mn 2+ -doped nanotubes.

The magneto-electric (ME) coupling on spin-wave resonances in single-crystal Cu2OSeO3 was studied by a novel technique using electron spin resonance combined with electric field modulation. An external electric field E induces a magnetic field component µ0H i = γE along the applied magnetic field H with γ = 0.7(1) µT/(V/mm) at 10 K. The ME coupling strength γ is found to be temperature dependent and highly anisotropic. γ(T ) nearly follows that of the spin susceptibility J M (T ) and rapidly decreases above the Curie temperature Tc. The ratio γ/J M monotonically decreases with increasing temperature without an anomaly at Tc. PACS numbers: 75.85.+t, 76.50.+g, Magneto-electric (ME) materials exhibiting coupled and microscopically coexisting magnetic (M) and electric (P) polarizations have attracted considerable interest in recent years [1][2][3][4]. This coupling allows one to influence the magnetic state of a ME material via an external electric field, thus opening a broad range of possible technical applications of such materials [3,5]. Moreover, it is very interesting to investigate the microscopic mechanism of ME coupling, since P and M tend to exclude each other [4]. In order to detect the ME effect, sensitive and reliable experimental techniques are required, since this coupling is generally quite small. Usually, for the determination of the ME coupling either the dielectric properties of ME materials are measured as a function of magnetic field or the magnetization is studied as a function of an applied electric field [3].Cu 2 OSeO 3 is a paraelectric ferrimagnetic material with a Curie temperature of T c 57 K [6][7][8]. The ME effect in Cu 2 OSeO 3 was first observed by magnetocapacitance experiments [6]. Later on, a small abrupt change of the dielectric constant below T c was reported by infrared reflection and transmission studies [9,10]. Recent µSR investigations showed a rather small change of the internal magnetic field by applying an electric field [8]. X-ray diffraction [6] and nuclear magnetic resonance [11] studies revealed no evidence of any lattice anomaly below T c , suggesting that lattice degrees of freedom are not directly involved in the ME effect. Moreover, a metastable magnetic transition with enhanced magnetocapacitance was observed [6] and later on was also investigated under hydrostatic pressure [12]. Very recently, ME skyrmions were observed in Cu 2 OSeO 3 by means of Lorentz transmission electron microscopy [13] and small angle neutron scattering [14].Here we report a study of the ME coupling in single crystal of Cu 2 OSeO 3 . For this investigation a novel microscopic method for the direct determination of the ME effect based on the standard FMR/EPR technique combined with electric field modulation was developed. As a result, to our knowledge for the first time spin-wave resonance (SWR) excitations [15] were detected via ME coupling. The linear ME coupling strength γ was determined quantitatively in Cu 2 OSeO 3 . In particular, the temperature and angular dependence of γ and the SWR...

We employed electron spin resonance (ESR) technique in the investigation of a series of graphene flakes with different size distributions. Graphene oxide (GO) samples with three distinct size distributions were prepared by the Brodie method. Large flakes of $2500 mm On this batch a thermal method of reduction was applied such that in polar solvent the suspension of GO was heat treated at temperatures below 200 8C. ESR susceptibility shows that this reduction can recover some of the Pauli-like contribution of the pristine graphene. However, our study shows that the full optimization of oxidation/reduction parameters is yet to be achieved. Having a gapless and a linear band dispersion in the vicinity of the Fermi level, graphene shows many outstanding properties such as exceptionally high carrier mobility, unconventional quantum Hall effect, resilience to very high electrical current densities [1], etc. These properties open a wide range of potential applications. Nevertheless, for some of them, like new generation of integrated circuits and quantum computational devices, the full implementation and realization is still missing. One of the reasons is the absence of a production route which might give high quality graphene flakes with a good control of size and the type of the edge termination (zigzag or armchair).Concerning large scale production of graphene one of the most promising methods is the so called graphene oxide (GO) route. There are several variants of making of GO [2,3] with a common expectation to recover the pristine properties of graphene simply by reducing formerly oxidized graphite

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