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The samples of (Mn$_{1-x}$Co$_x$)Si with $x=0.15$ and $x=0.17$ were grown and their physical properties: magnetization and magnetic susceptibility, resistivity and heat capacity were studied. The data analysis included also the previous results at $x=0.057, 0.063, 0.09$. The indicated doping MnSi with Co completely destroys the helical phase transition whereas basically saves the helical fluctuation area normally situated slightly above the phase transition temperature. This area spreading from $\sim$5 to 0 K is not changed much with doping and forms some sort of helical fluctuation cloud revealing the quantum critical properties: $C_p/T\rightarrow\infty$ at $T\rightarrow0$., Comment: 5 pages, 13 figures

We report results of studying the magnetization, specific heat and thermal expansion of a single crystal with nominal composition Mn 0.85 Fe 0.15 Si . We found no thermodynamic evidences in favor a second order phase transition in the 15 % Fe substituted MnSi. The trajectory corresponding to the present composition of (MnFe)Si is a critical one, i.e. approaching quantum critical point at lowering temperature, but some properties may feel the cloud of helical fluctuations bordering the phase transition line., Comment: 6 pages, 11 figures

We present a study of the magnetoresistivity of thin film MnSi in high magnetic fields. We establish that the magnetoresistivity can be understood in terms of spin fluctuation theory, allowing us to compare our data to studies of bulk material. Despite of a close qualitative resemblance of bulk and thin film data, there are clear quantitative differences. We propose that these reflect a difference of the spin fluctuation spectra in thin film and bulk material MnSi., Comment: submitted to Jounal of the Physical Society of Japan (JPSJ)

The enhanced thermopower of the correlated semiconductor FeSi is found to be robust against the sign of the relevant charge carriers. At $T$\,$\approx$\,70 K, the position of both the high-temperature shoulder of the thermopower peak and the nonmagnetic-enhanced paramagnetic crossover, the Nernst coefficient $\nu$ assumes a large maximum and the Hall mobility $\mu _H$ diminishes to below 1 cm$^2$/Vs. These cause the dimension-less ratio $\nu$/$\mu_H$ $-$ a measure of the energy dispersion of the charge scattering time $\tau(\epsilon)$ $-$ to exceed that of classical metals and semiconductors by two orders of magnitude. Concomitantly, the resistivity exhibits a hump and the magnetoresistance changes its sign. Our observations hint at a resonant scattering of the charge carriers at the magnetic crossover, imposing strong constraints on the microscopic interpretation of the robust thermopower enhancement in FeSi., Comment: 5 pages, 3 figures

MnGe has been grown as a thin film on Si(111) substrates by molecular beam epitaxy. A 10 \AA\ layer of MnSi was used as seedlayer in order to establish the B20 crystal structure. Films of a thickness between 45 and 135 \AA\ have been prepared and structually characterized by RHEED, AFM and XRD. These techniques give evidence that MnGe forms in the cubic B20 crystal structure as islands exhibiting a very smooth surface. The islands become larger with increasing film thickness. A magnetic characterization reveals that the ordering temperature of MnGe thin films is enhanced compared to bulk material. The properties of the helical magnetic structure obtained from magnetization and magnetoresistivity measurements are compared with films of the related compound MnSi. The much larger Dzyaloshinskii-Moriya interaction in MnGe results in a higher rigidness of the spin helix., Comment: 5 pages, 6 figures

Strong spin-orbit interaction in the two dimensional compound Sr2IrO4 leads to the formation of Jeff=1/2 isospins with unprecedented dynamics. In Raman scattering a continuum attributed to double spin scattering is observed. With higher excitation energy of the incident Laser this signal crosses over to an incoherent background. The characteristic energy scale of this cross over is identical to that of intensity resonance effects in phonon scattering. It is related to exciton-like orbital excitations that are also evident in resonant X-Ray scattering. The crossover and evolution of incoherent excitations are proposed to be due to their coupling to spin excitations. This signals a spin-orbit induced entanglement of spin, lattice and charge degrees of freedoms in Sr2IrO4., Comment: 20 pages, 7 figures