FIELD-INDUCED MAGNETIC-STRUCTURES IN ERGA2

ErGa2 crystallizes in the hexagonal A1B(2)-type structure and shows a two-step magnetization process along the c-axis below T-N=7 K. The com pound has a magnetic structure with a wavevector of Q(1)=1/2b() at H= 0, and for the intermediate field range it has a structure with Q(1), Q(2)=1/2a(), Q(3)=-1/2a(*) + 1/2b(*) and Q(0)=0. The magnetization pr ocess is studied in terms of a wave-like molecular field H-m(u,v,w)=Si gma(q) lambda(m)(q)<J(q)>cos(2 pi qr(uvm)) acting on Er at point r(urw ). The analysis involves wavevector-dependent molecular field coeffici ents lambda(m)(q) with q=0, Q(1), Q(2) and Q(3) and one crystal field coefficient B-2(0). The dipole field due to the dipole-dipole interact ion is also involved. Calculations give a reasonable fit with the magn etization data with lambda(m)(O) = -1.84 kOe; lambda(m)(Q(1))=lambda(m )(Q(2))=lambda(m)(Q(3)) = 0.68 kOe and B-2(0) = -0.48 K. A possible ex planation for the appearance of the magnetic structure in the intermed iate field range is presented.