Transition between antiferromagnetic and ferromagnetic states in itinerant-electron La(Fe_xAl_1-x)₁₃ compounds

The transition between the antiferromagnetic (AF) and the ferromagnetic (F) states has been investigated with regard to the magnetovolume effect and the spin-fluctuation characteristics in La(Fe_xAl_1-x) ₁₃ compounds. The volume V and amplitude of the local magnetic moment M_loc are different between the AF and F states. In the AF state, the field-induced first-order AF-F transition appears and the transition proceeds with two steps in higher Fe concentration regions. The complex temperature dependence of the AF-F transition field is explained by the contribution from both the magnetic and elastic energies caused by the significant temperature variation of amplitude of M^loc. For the two-step transitions, the spin-floplike transition and the increase in amplitude of M_loc occur at the first- and second-step transitions, respectively. In other words, both the localized moment and the itinerant-electron characteristics are concurrently observed.