  The Hall effect in LuNi_2B_2C and YNi_2B_2C borocarbides has been
investigated in normal and superconducting mixed states. The Hall resistivity
rho_{xy} for both compounds is negative in the normal as well as in the mixed
state and has no sign reversal below T_c typical for high-T_c superconductors.
In the mixed state the behavior of both systems is quite similar. The scaling
relation rho_{xy}\sim\rho_{xx}^\beta (\rho_{xx} is the longitudinal
resistivity) was found with \beta=2.0 and 2.1 for annealed Lu- and Y-based
compounds, respectively. The scaling exponent \beta decreases with increasing
degree of disorder and can be varied by annealing. This is attributed to a
variation of the strength of flux pinning. In the normal state weakly
temperature dependent Hall coefficients were observed for both compounds. A
distinct nonlinearity in the \rho_{xy} dependence on field H was found for
LuNi_2B_2C in the normal state below 40K, accompanied by a large
magnetoresistance (MR) reaching +90% for H=160kOe at T=20K. At the same time
for YNi_2B_2C only linear \rho_{xy}(H) dependences were observed in the normal
state with an approximately three times lower MR value. This difference in the
normal state behavior of the very similar Lu- and Y-based borocarbides seems to
be connected with the difference in the topology of the Fermi surface of these
compounds.
