Specific heat of field-dependent magnetic orderings in HoNi2B2C

We have investigated the, low-temperature specific heat of HoNi2B2C down to T = 1 K in various magnetic fields from 0 T to 5 T. At zero field, the spe cific heat exhibits a large peak at T-N = 5.1 K, which is due to commensura te antiferromagnetic ordering, and other Smaller peak at T-1 = 5.5 K, which is related to incommensurate ordering. As the field is increased up to 0.5 T, the first peak broadens and moves to a lower temperature, while the oth er peak at T-1 moves to a higher temperature, which indicates that the phas e between T-N and T-1 is more favored in magnetic fields. Among possible ca ndidates for the phase, the a-axis modulation phase, which is an extension of a low temperature metamagnetic state, is the most probable. In the high- field region above 1 T, the two-peak feature is replaced by a broad-hill on e that fades away with increasing fields, which is the typical smearing fea ture of the magnetic order at high fields.