Interlayer Exchange Field in (CnH2n+1NH3)2CuCl4 with n=1-6 and (C6H5CmH2mNH3)2CuCl4 with m=1, 2 Determined by Parallel Pumping Experiment

To determine the interlayer exchange field H ' E in quasi-two-dimensional magnets (C n H 2 n +1 NH 3 ) 2 CuCl 4 with n =1-6 and (C 6 H 5 C m H 2 m NH 3 ) 2 CuCl 4 with m =1, 2, the lowest Brillouin-zone-boundary magnons are parametrically excited by parallel pumping technique in the temperature range from 1.2 to 4.2 K and at a pumping frequency of 8.9 GHz. The values of H ' E extrapolated to T =0 K are as follows: 45±5 Oe( n =1), -850±20 Oe( n =2), -17±3 Oe( n =3), -17±3 Oe( n =4), -16±3 Oe( n =5), -11±3 Oe( n =6), 9±3 Oe( m =1) and 6±3 Oe( m =2), where positive and negative values correspond to the ferromagnetic and antiferromagnetic fields, respectively. The ratio of the interlayer exchange field to the intralayer exchange field for the m =2 compond is 1.1×10 -5 , which is the smallest value among these componds. The orthorhombic anisotropy fields for these compounds are determined by means of ferromagnetic resonance. The relation between the transition temperature and H ' E is discussed.