A Study of Magnetoresistance of Yb$_{14-x}$La$_{x}$MnSb$_{11}$: an Ordered Dilute Magnetic Semiconductor*

Yb$_{14-x}$La$_{x}$MnSb$_{11 }$is an ordered dilute magnetic semiconductor, showing evidence for partial screening of the Mn magnetic moments and mass renormalization from 2 m$_{e}$ near room temperature to 20 m$_{e}$ at 5 K. We have measured both the transverse (I$\bot $H) and longitudinal (I//H) magnetoresistance (MR) of Yb$_{14-x}$La$_{x}$MnSb$_{11 }$(x=0, 0.7) single crystals above and below the ferromagnetic (FM) transition temperature T$_{c}$ = 53 K (x=0) and 39 K (x=0.7). While it is negative in a wide temperature range, the MR becomes positive below T$_{c}$/2 and increases with decreasing temperature. Strikingly, the positive MR increases linearly with applied field, showing no sign of saturation up to 32 tesla. Quantitative analysis and implications of the data will be reported.