Response of Itinerant-Electron Weak Ferromagnet LaFe4As12 to Pressure and Magnetic Field

To investigate the quantum criticality and spin fluctuations in LaFe4As12, we have investigated the pressure and magnetic field dependences of electrical resistivity (rho). The Curie temperature T-C (similar to 5.2K at ambient pressure) is gradually suppressed by pressure (P) and disappears at approximately 2 GPa (similar to P-c). The coefficient A of the T-2 dependence of rho increases near P-c, and the exponent n of rho(T) similar to rho(0) + beta T-n changes into 5/3, which is expected for 3d ferromagnetic spin fluctuations. The low-field longitudinal magnetoresistance Delta rho/rho(T) is negative at low temperatures, as was commonly observed in typical itinerant-electron weak ferromagnets, reflecting a field-suppressed spin-fluctuation scattering. Above T-C, it becomes positive and shows a peak against magnetic field, which is hardly ascribable only to the ordinary positive magnetoresistance due to the Lorentz force on conduction electrons. Possible origins of the unexpected positive magnetoresistance are discussed by considering Kohler's plot for both the longitudinal and transverse magnetoresistances.