Magnetic ordering in the nano-laminar ternary Mn₂AlB₂ using neutron and X-ray diffraction

The nano-laminar ceramic Mn₂AlB₂ belongs to the orthorhombic M₂AlB₂ system (M = Cr, Fe, Mn), in which Fe₂AlB₂ was shown to be ferromagnetic near room temperature. Herein, the magnetic state of Mn₂Al¹¹B₂ is investigated using magnetization measurements, in the 5–360 K temperature range, X-ray diffraction in the 300–800 K range and neutron diffraction in the 1.6–300 K range. From the totality of our results we conclude that below ∼390 K Mn₂AlB₂ becomes a canted antiferromagnet. The crystallographic unit cell is doubled along the c axis (i.e. a propagation vector of 0,0,1/2) and the ordered Mn magnetic moments are oriented either along the a or the b axes, with a magnetic moment reaching 0.71(2) µ_B per Mn atom at 1.6 K. This magnetic structure is in excellent agreement with, and contributes to the validity of the recently reported theoretical calculations for the (Fe_1−xMn_x)₂AlB₂ system.