Strong magnetic pair breaking in Mn substituted MgB_2 single crystals

Magnetic ions (Mn) were substituted in MgB_2 single crystals resulting in a strong pair-breaking effect. The superconducting transition temperature, T_c, in Mg_{1-x}Mn_xB_2 has been found to be rapidly suppressed at an initial rate of 10 K/%Mn, leading to a complete suppression of superconductivity at about 2% Mn substitution. This reflects the strong coupling between the conduction electrons and the 3d local moments, predominantly of magnetic character, since the nonmagnetic ion substitutions, e.g. with Al or C, suppress T_c much less effectively (e.g. 0.5 K/%Al). The magnitude of the magnetic moment, derived from normal state susceptibility measurements, uniquely identifies the Mn ions to be divalent, and to be in the low-spin state (S = 1/2). This has been found also in X-ray absorption spectroscopy measurements. Isovalent Mn^{2+} substitution for Mg^{2+} mainly affects superconductivity through spin-flip scattering reducing T_c rapidly and lowering the upper critical field anisotropy H_{c2}^{ab}/H_{c2}^c at T = 0 from 6 to 3.3 (x = 0.88% Mn), while leaving the initial slope dH_{c2}/dT near T_c unchanged for both field orientations.Comment: 9 pages, 9 figure

Cantilever-like micromechanical sensors

The field of cantilever-based sensing emerged in the mid-1990s and is today a well-known technology for label-free sensing which holds promise as a technique for cheap, portable, sensitive and highly parallel analysis systems. The research in sensor realization as well as sensor applications has increased significantly over the past 10 years. In this review we will present the basic modes of operation in cantilever-like micromechanical sensors and discuss optical and electrical means for signal transduction. The fundamental processes for realizing miniaturized cantilevers are described with focus on silicon- and polymer-based technologies. Examples of recent sensor applications are given covering such diverse fields as drug discovery, food diagnostics, material characterizations and explosives detection