  The results of an extensive investigation of structure, surface morphology,
composition and the superconducting-normal phase diagram of a new
unconventional superconductor LaAg1-cMnc with nominal composition c = 0.0,
0.025, 0.05, 0.1, 0.2 and 0.3, reveal the following. The alloys with c = 0,
0.025 and 0.05 are essentially single phase alloys with the actual Mn
concentration, x, same as the nominal one, i.e., c = x, whereas in the alloys
with c = 0.1, 0.2 and 0.3, the actual Mn concentration of the majority phase
(crystalline grains) is x = 0.050(1), 0.080(1) and 0.100(1), respectively. The
ternary Mn addition does not alter the CsCl structure of the parent compound
LaAg. Neither a structural phase transition occurs nor a long-range
antiferromagnetic order exists at any temperature within the range 1.8K < = T <
= 50K in any of the Mn containing alloys. Mn has exclusive La (Ag) site
preference in the alloy (alloys) with x = c = 0.025 (x < = 0.05 or c < = 0.1)
whereas in the alloy with x = c = 0.05, Mn has essentially no site preference
in that all the Mn atoms either occupy the La sites or the Ag sites. In the
alloys (alloy) with x < = 0.05 (x = c = 0.025), substitution of Ag (La) by Mn
at the Ag (La) sub-lattice sites in LaAg host gives rise to unconventional
superconductivity (destroys the conventional phonon-mediated superconductivity
prevalent in the parent LaAg compound).
