Complex magnetic order in Pr2Pd3Ge5: a single crystal study

We have investigated the magnetic and electronic transport properties of single crystal Pr2Pd3Ge5 grown by the Czochralski method. Complex magnetic behaviour (multiple magnetic transitions) is clearly seen in this compound from the magnetic susceptibility chi(T), isothermal magnetization M(H)and electrical resistivity rho(T) data. For the magnetic field applied along the crystallographic c-axis (H parallel to [001]) the chi(T) data exhibit two sharp transitions at 6.9 and 6.3 K and a broad hump near 8 K. Four anomalies at 8.0, 7.3, 6.2 and 4.9 K are observed for the magnetic field along both a- and b-directions (H parallel to [100] and H parallel to [010]). Further, the ordered state chi(T) presents a large anisotropy with an easy axis along the c-axis. The presence of magnetocrystalline anisotropy is also inferred from the isothermal M(H) data. The M(H) data measured at 1.9 K for H parallel to [001] exhibit a step-like increase due to field-induced metamagnetic transitions at H-c1(c) = 2.0 T and H-c2(c) = 4.0 T. For H parallel to [100] and H parallel to [010] sharp step-like field-induced metamagnetic transitions occur at H-c1(a) = H-c1(b) = 1.6 T and H-c2(a) = H-c2(b) = 1.8 T which are accompanied by a weak S-shaped spin-flop metamagnetic transition at H-c3(a) = H-c3(b) similar to 4 T. We have extracted the H-T phase diagram from the M(H) data collected at different temperatures in the magnetically ordered state which shows the existence of three magnetic phases below T-N for H parallel to [100] and H parallel to [010], and two magnetic phases for H parallel to [001]. A sharp transition due to the onset of long range antiferromagnetic order is also seen in the rho(T) data which also exhibit anisotropic behaviour. The observation of an upturn near T-N in the rho(T) data suggests the formation of a super-zone gap and hence the existence of incommensurate magnetic structure. Further, in the ordered state, the rho(T) data present a gap in the excitation spectrum of magnons with a characteristic energy gap Delta similar to 0.23 meV.