Abstract
The magnetic fieldβtemperature (BβT) phase diagram of the Mn~0.9~Co~0.1~P single crystal is studied in the vicinity of the Lifshitz point by means of isothermal magnetocaloric coefficient (M~T~) and alternating current (AC) susceptibility measurements. Results confirm previously reported shape of the BβT phase diagram and locations of characteristic temperatures and fields. At the Curie temperature (T~C~) the critical exponent Ο, which describes a singularity of M~T~ as a function of magnetic field ($M_{T} ,{\propto} ,B^{{-} \omega } $), is estimated for B parallel to the easy axis to be equal to Οβββ0.35. Below T~C~ an evidence of a new enigmatic phase, reported previously for pure manganese phosphide (MnP), is found in susceptibility data also for Mn~0.9~Co~0.1~P. However, the range of existence of this phase is significantly larger here, than in MnP. At the LP we observe a sharp peak in the imaginary part of the magnetic susceptibility. A phenomenological theory is introduced to describe the field dependence of the critical lines from the disordered phase (paramagnetic) to ordered phases (ferromagnetic and modulated). The temperature and field dependences of the magnetocaloric coefficient and susceptibility are also calculated within the same framework.