Physical properties of Β-TmAlB₄; An AlB₂ -type analogous "tiling" compound

Β -TmAlB₄ was synthesized, and the magnetic properties and specific heat investigated in comparison with those of the α -type structure. Recent developments in rare earth aluminoboride compounds with two-dimensional boron layers have attracted interest due to the heavy fermion superconductivity in Β -YbAlB4, multiple anomalies manifesting below the Ńel temperatures in α -TmAlB₄ attributed to intrinsic building defects, and field stable state in Tm₂ AlB₆. Strikingly, despite similarities in the metal-metal nearest neighbor distances and structural motifs, the strength of the magnetic interactions (temperature scale) in Β -TmAlB₄ was discovered to be approximately 60% stronger that of the alpha phase (i.e., TN=9.2 versus 5.8 K). An anomaly in the specific heat with extreme field stability was also found with a temperature scale significantly higher compared to that of the α -type structure. This anomaly is conjectured to be a precursor to the antiferromagnetic transition and may be a particular feature of these "tiling" compounds with analogy to _AlB2 -type structure.