MICROSCOPIC THEORY OF MAGNETIC PHASE-TRANSITIONS IN HONI2B2C

We present a microscopic theory for the low-temperature metamagnetic p hase diagram of HoNi2B2C that agrees well with experiments. For the sa me model we determined the zero-field ground state as a function of te mperature and found the c-axis commensurate-to-incommensurate transiti on in the expected temperature range. The complex behavior of the syst em originates from the competition between the crystalline electric fi eld and the Ruderman-Kittel-Kasuya-Yosida interaction, whose effective form is obtained. No essential influence of superconductivity has to be invoked to understand the magnetic phase diagram of this material. [S0163-1829(98)10217-5].