Megnetization measurements on diethylenetriammonium chlorocuprate(II): Anisotropy and exchange fields in a two-dimensional Heisenberg ferromagnet

Isothermal magnetization measurements have been carried out on [(N${\mathrm{H}}_3$ C${\mathrm{H}}_2$ C${\mathrm{H}}_2$) ${}_2{}^{}{}_{}{}^{}\mathrm{N}$ ${\mathrm{H}}_2$] [Cu${\mathrm{Cl}}_4$]Cl along the three orthorhombic crystal axes below the Néel temperature of 11.87 °K. When the measurements were made along the preferred axis ($c$ crystal axis), the antiferromagnetic to spin-flop transition followed by the spin-flop to paramagnetic transition were observed. Along the other two axes the biaxial anisotropy of this material can be seen in the different antiferromagnetic to paramagnetic phase transitions. These critical fields have been sketched as a function of reduced temperature and when extrapolated to zero temperature provide a means for calculating the exchange and anisotropy fields in the molecular-field approximation. When this calculation is performed the following fields result: $H_f\approx 5.1\times {10}^5$ G (intralayer ferromagnetic exchange), $H_{\mathrm{af}}\approx 2900$ G (interlayer antiferromagnetic exchange), $H_A^{\mathrm{in}}\approx 300$ G (in-plane anisotropy), and $H_A^{\mathrm{out}}\approx 2800$ G (out-of-plane anisotropy). The dipolar contribution to these anisotropy fields has been accounted for and finally a comparison is made between [(N${\mathrm{H}}_3$ C${\mathrm{H}}_2$ C${\mathrm{H}}_2$) ${}_2{}^{}{}_{}{}^{}\mathrm{N}$ ${\mathrm{H}}_2$] [Cu${\mathrm{Cl}}_4$] Cl and structurally similar [${\mathrm{C}}_2$ ${\mathrm{H}}_5$ N${\mathrm{H}}_3$] [Cu${\mathrm{Cl}}_4$].