Three types of optical magnetic-field induced second harmonic (MFISH) generation are observed in ${\mathrm{C}\mathrm{u}\mathrm{B}}_2{\mathrm{O}}_4$. Unusually sharp and intense electronic transitions in MFISH and linear absorption spectra provide selective access to the two nonequivalent ${\mathrm{C}\mathrm{u}}^{2+}$ sublattices. The magnetic phase diagram for both sublattices is determined by MFISH. Magnetic structure is dominated by antiferromagnetic order at the $4b$ site. Sublattice interactions transfer it to the $8d$ site where it coexists with a discoupled paramagnetic component.

• Received 26 January 2004

DOI:https://doi.org/10.1103/PhysRevLett.93.037204