We investigate the nano-physics of atom bridges made from magnetic atoms formed between a Scanning Tunneling Microscope-tip (STM-tip) and a solid surface within the density functional theory. We consider a twisted ladder structure to represent the atom bridge. In the case of an Fe atom bridge, we find that the magnetic and transport properties depend on the distance between the nearest neighbor atoms along the bridge axis. We consider the alloy atom bridges whose components are found on both the right and left hand side of the Pauling-Slater curves, and show their corresponding magnetic and transport properties. On the basis of our numerical results, we discuss the origin of these interesting properties and the possibility for designing the properties of the atom bridge by STM-tip manipulation and/or alloying.