Tuneable Magnetic Phase Transitions in Layered CeMn(2)Ge(2-x)Si(x) Compounds

The structural and magnetic properties of seven CeMn(2)Ge(2-x)Si(x) compounds with x = 0.0–2.0 have been investigated in detail. Substitution of Ge with Si leads to a monotonic decrease of both a and c along with concomitant contraction of the unit cell volume and significant modifications of the magnetic states - a crossover from ferromagnetism at room temperature for Ge-rich compounds to antiferromagnetism for Si-rich compounds. The magnetic phase diagram has been constructed over the full range of CeMn(2)Ge(2-x)Si(x) compositions and co-existence of ferromagnetism and antiferromagnetism has been observed in CeMn(2)Ge(1.2)Si(0.8), CeMn(2)Ge(1.0)Si(1.0) and CeMn(2)Ge(0.8)Si(1.2) with novel insight provided by high resolution neutron and X-ray synchrotron radiation studies. CeMn(2)Ge(2-x)Si(x) compounds (x = 0, 0.4 and 0.8) exhibit moderate isothermal magnetic entropy accompanied with a second-order phase transition around room temperature. Analysis of critical behaviour in the vicinity of T(C)(inter) for CeMn(2)Ge(2) compound indicates behaviour consistent with three-dimensional Heisenberg model predictions.