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The presence of dusty debris around main sequence stars denotes the existenceof planetary systems. Such debris disks are often identified by the presence ofexcess continuum emission at infrared and (sub-)millimetre wavelengths, withmeasurements at longer wavelengths tracing larger and cooler dust grains. Theexponent of the slope of the disk emission at sub-millimetre wavelengths, `q',defines the size distribution of dust grains in the disk. This sizedistribution is a function of the rigid strength of the dust producing parentplanetesimals. As part of the survey `PLAnetesimals around TYpical Pre-mainseqUence Stars' (PLATYPUS) we observed six debris disks at 9-mm using theAustralian Telescope Compact Array. We obtain marginal (~3-\sigma) detectionsof three targets: HD 105, HD 61005, and HD 131835. Upper limits for the threeremaining disks, HD20807, HD109573, and HD109085, provide further constraint ofthe (sub-)millimetre slope of their spectral energy distributions. The valuesof q (or their limits) derived from our observations are all smaller than theoft-assumed steady state collisional cascade model (q = 3.5), but lie wellwithin the theoretically expected range for debris disks q ~ 3 to 4. Themeasured q values for our targets are all < 3.3, consistent with bothcollisional modelling results and theoretical predictions for parentplanetesimal bodies being `rubble piles' held together loosely by theirself-gravity.

New constraints on the millimetre emission of six debris disks