The x-T magnetic phase diagram of the LaMn 2 − xFe xGe 2 (0≤ x≤1) system by neutron diffraction study

Abstract

The ThCr 2Si 2-type structure LaMn 2 − x Fe x Ge 2 ( x = 0.125, 0.25, 0.375, 1.0) compounds were studied by neutron diffraction. LaMn 1.875Fe 0.125Ge 2 is antiferromagnetic below T N = 435 K with antiferromagnetic (001) Mn planes. Below T C = 280 K, the moments are canted and hence display a ferromagnetic component on the (001) Mn planes. Simultaneously, the interplane coupling of the in-plane antiferromagnetic components becomes incommensurate ( T ic = 280 K). LaMn 1.75Fe 0.25Ge 2 displays identical magnetic phenomena ( T N = 420 K, T C = T ic = 225 K). At 2 K, the antiferromagnetic component ( μ MnAF = 2.65(9) μ B) lies in the (001) plane whilst the ferromagnetic component ( μ MnF = 1.34(39) μ B) is aligned along the c axis. The LaMn 1.625Fe 0.375Ge 2 compound is antiferromagnetic at room temperature and contains antiferromagnetic (001) Mn planes with the moments aligned along the c axis. Below T C = 200 K, the Mn moments become canted and, as before, display a ferromagnetic component in the (001) plane. Below T SF = 175 K, a rotation of the moment takes place. At 2 K, the antiferromagnetic component ( μ MnAF = 2.61(7) μ B) makes an angle of 55(11)° with the c axis while the ferromagnetic component ( μ MnF = 1.77(24) μ B) makes an angle of 35(11)° with the c axis. The antiferromagnetic component gives rise to a commensurate interplane arrangement down to 2 K. The LaMnFeGe 2 compound is antiferromagnetic below T N = 230 K and is also made up of antiferromagnetic (001) Mn planes. This magnetic behaviour remains unchanged down to 2 K. The moment ( μ Mn = 276 μ B) is aligned along the c axis. The x - T magnetic phase diagram is depicted and compared with those of the LaMn 2 − xCu x Ge 2 and NdMn 2 − x Fe x Ge 2 systems.