Microscopic theory of magnetic phase transitions in HoNi2B2C

We present a microscopic theory for the low-temperature metamagnetic phase diagram of HoNi2B2C that agrees well with experiments. For the same model we determined the zero-field ground state as a function of temperature and found the c-axis commensurate-to-incommensurate transition in the expected temperature range. The complex behavior of the system originates from the competition between the crystalline electric field 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].