Abstract
The results of magnetic susceptibility, magnetization, electrical resistivity and specific heat measurementsperformed on Ho3Co single crystals show that this compound exhibits two different antiferromagnetic structures:AFII at8 K<T<22 K andAFI belowTt≈8 K. Below the Néeltemperature TN = 22 K the application of a magnetic field along the main crystallographic directions inducesmagnetic phase transitions which are accompanied by giant magnetoresistance. AtT<Tt the field-induced phase transitions along the c- and b-axes are found to beirreversible, and a small ferromagnetic component is observed along the a-axis.These peculiarities are associated with the non-Kramers character of the Ho ionand with the presence of a complex incommensurate magnetic structure ofHo3Co belowTN. The temperature coefficient of the electrical resistivity forHo3Co aboveTN over a wide temperature range is found to differ from that observed for otherR3Co compounds. Such a behaviour is attributed to the presence of an additional contribution tothe conduction electron scattering by spin fluctuations induced by f–d exchangein the itinerant d-electron subsystem. The value of this extra contribution andits temperature range is suggested to depend on the spin value of the R ion.The excess of the effective magnetic moment per R ion, which is observed inHo3Co and inother R3M type compounds, is also attributed to spin fluctuations induced by f–d exchange.
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