Ti8(TixMn1−x)6Mn39 (‘TiMn∼4’): a metallic spin fluctuation system

The crystal structure of Ti8(TixMn1−x)6Mn39, x = 0.187, was obtained from x-ray single-crystal diffraction data, confirming it to have rhombohedral symmetry (space group ; ahex = 1.100 70(2) nm, chex = 1.944 11(4) nm; RF = 0.0293) and isotypism with the prototype Mo0.38Cr0.16Co0.46 (the so-called R-phase). On the basis of electron probe micro-analyser results and structure determination, the homogeneity region of the phase TiMn∼4 was determined for temperatures in the range 800 °C < T < 1200 °C and is in between 16.0 at.% Ti and 20 at.% Ti. Various physical properties, determined in the temperature range from ∼2 K to room temperature, characterize the compound with composition TiMn4.26 as a metallic spin fluctuation system, evidenced from a T3lnT dependence of the heat capacity in combination with large values of the electronic Sommerfeld constant of the order of 140 mJ mol−1 K−2. The occurrence of a small anomaly in the heat capacity and magnetization data around 10 K is attributed to a scenario involving spin freezing phenomena, since a fraction of the order of 10% of all Mn–Mn distances within the unit cell are above a critical distance, where Mn atoms carry a spontaneous magnetic moment.