MOSSBAUER SPECTROSCOPY OF MAGNETIC PHASES IN FeCl

~ong the easy axis a at 4.2 K induces phase transi­ tionsatHI =39 kOe andH2 =46 kOe [1-3]. In this ~t1er we report the use of Mossbauer spectroscopy in external magnetic fields to study the magnetic struc­ (ure of each of the three phases. Previous Mossbauer work in FeCI2 · 2HZ0 includes apower study by Chandra and Hoy [4] and a single z crystal study by Johnson [5]. They found a magnetic o hyperfine field of 250 kOe at 4.2 K and an electric 1= 11. cr o quadrupole interaction of 2.30 mm/sec with asymme­ l/J 1Il « try parameter 1/ = 0.3. The principle component of the efgis at right angles to the magnetic hyperfine field. Johnson [5] also determined that the spins lay in the ac plane at an angle of 66.2° from a axis, in agreement with results obtained by Narath [1] from susceptibili· ty and proton magnetic resonance measurements. In the present work, a large single crystal was grown by slow evaporation at 85°C. A slice was cut parallel to the bc plan and placed at 32° to the ')'-ray beam and external magnetic fieldHo' so thatHo was parallel to the easy axis a. The direction of the posi­ tive caxis was determined by orienting the sample in asmall magnetic field at room temperature. The H0 = 0,4.2 Kspectrum is shown in fig. 1a. There is a small