MAGNETIC AND STRUCTURAL INSTABILITIES IN U1-XTHXNISN

We have measured magnetic susceptibility, ultrasound velocity, powder X-ray diffraction and Sn-119 Mossbauer spectra of U1-xThxNiSn. We clar ify that Th-doping separates a sample into two phases with different T h-concentration. With increasing x, the first order antiferromagnetic (AF) transition temperature T-N decreases and hyperfine fields at Sn-s ites have a distribution. For x less than or equal to 0.1, a structura l transition is found to occur concomitantly with the magnetic transit ion.