KV6O11:: A magnetic metal synthesized at high pressure

An AV(6)O(11)-type magnetic metal KV6O11 was discovered by a high-pressure synthesis. It crystallizes in hexagonal P6(3)/mmc at 295 K, whereas in hexagonal P6(3)mc at 154 K. KV6O11 shows three magnetic transitions at 190, 66.8, and 35.1 K. KV6O11 is paramagnetic above 66.8 K. Its inverse magnetic susceptibility is slightly concave upward with respect to temperature above 190 K, but the relationship is significantly concave upward below 190 K. KV6O11 shows uniaxial magnetic anisotropy with an easy axis of magnetization parallel to the [001] direction below 66.8 K. The magnetization shows an anomaly at 35.1 K. The resistivity normal to [001] is of the order of 10(-4) Omega cm(-1). The resistivity versus temperature shows a positive slope above 190 K, a broad maximum at around 90 K, a linear relationship with a positive slope between 35.1 and 66.8 K, and Fermi-liquid-type behavior below 35.1 K. The paramagnetic state below 190 K is discussed on the basis of two types of spin-gap models. Problems of the models are also pointed out. The saturated magnetization versus temperature shows a hyperbolic relationship. The magnetization cannot be explained by the well-known mean field theory or the spin fluctuation mechanism. [S0163-1829(99)01630-6].