Magnetic tricritical behavior of ethylammonium tetrachlorocuprate

In order to investigate the prediction by Tuthill that a tricritical point may exist in the phase diagram of spin_flop antiferromagnets with intermediate anisotropy, an experimental reexamination of the phase diagram of the quasi_two_dimensional system (C2H5NH3)2CuCl4 was performed. Measurements were made of the differential magnetic susceptibility,d M/d H, vs dc field and temperature in the (10 K, 100 Oe) region of the proposed tricritical point. A low amplitude, low frequency, ac biphase SQUID susceptometer was used. The sample was a single crystal with field along the antiferromagnetic easy (orthorhombic a_axis) direction. The data show some evidence of the existence of at least one tricritical point, but the results are not definitive.