A huge increase of thermal conductivity is observed at the phase transition in stoichiometric NaV2O5. This anomaly decreases and gradually disappears with deviation from stoichiometry in Na1 xV2O5 (x = 0.01, 0.02, 0.03, and 0.04). This behavior is compared with that of pure and Zn-doped CuGeO3 where only modest kinks in the (T) curves are observed at the spin-Peierls transition. The change of at critical temperature Tc could be partially attributed to the opening of an energy gap in the magnetic excitation spectrum excluding the scattering of thermal phonons on spin uctuations. However, the reason for such a strong anomaly in the (T) may lie not only in the di erent energy scales of CuGeO3 and NaV2O5, but also in the di erent character of the phase transition in NaV2O5 which can have largely a structural origin, e.g. connected with the charge ordering. 75.30.Kz, 66.70.+f

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We performed Raman studies and a dielectric characterization of the pseudo-kagome Cu 3 Bi(SeO 3 ) 2 O 2 X (X = Cl, Br). These compounds share competing nearest-neighbour ferromagnetic exchange and frustrating next-nearest-neighbour antiferromagnetic exchange as well as highly noncollinear magnetic ground state. However, at low temperature they differ with respect to the existence of inversion symmetry. For both compounds there exists a pronounced interplay of polar phonon modes with quantum magnetic fluctuations. A novel Raman mode appears for temperatures below the Neel temperature with a Fano lineshape and an enormous intensity that exceeds most of the phonon lines. We discuss a possible contribution of longitudinal magnons to this signal. In contrast, one magnon scattering based on linear transvers magnons is excluded based on a symmetry analysis of spin wave representations and Raman tensor calculations. There exists evidence that in these pseudo-kagome compounds magnetic quantum fluctuations carry an electric dipole moment. Our data as well as a comparison with previous farinfrared spectra allow us to conclude that Cu 3 Bi(SeO 3 ) 2 O 2 Cl changes its symmetry most likely from Pmmn to P2 1 mn with a second order structural phase transition at T*=120 K and becomes multiferroic. Cu 3 Bi(SeO 3 ) 2 O 2 Br represents an interesting counter part as it does not show this instability and stays inversion symmetric down to lowest temperatures, investigated.PACS:

Ferromagnetic resonance and static magnetic properties of CoFe/Al 2 O 3 /CoFe/Py and CoFe/Al 2 O 3 /CoFeB/Py magnetic tunnel junctions and of 25nm thick single-layer Permalloy (Py) films have been studied as a function of temperature down to 2K. The temperature dependence of the ferromagnetic resonance excited in the Py layers in magnetic tunnel junctions shows "knee-like" enhancement of the resonance frequency accompanied by an anomaly in the magnetization near 60K. We attribute the anomalous static and dynamic magnetic response at low temperatures to interface stress induced magnetic reorientation transition at the Py interface which could be influenced by dipolar soft-hard layer coupling through the Al 2 O 3 barrier. (28nm) for sample C. The entire wafers were covered with a Ta(5nm)/Cu(5nm) layers to prevent oxidation and were annealed at 250ºC in the sputtering chamber during one hour in an in-plane applied magnetic field of 20mT. For more details on sample growth and characterization see references.8,9The low temperature FMR experiments were carried out with a commercial AgilentVector Network Analyzer (VNA) working up to 8.5GHz by employing VNA-FMR technique 10 which uses a coplanar wave guide to create the pumping field h RF . For cryogenic measurements (2K

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