Magnetic properties of Y1-xTbxMn6 Sn6 alloys

We have made low- and high-field magnetization measurements and neutron diffraction experiments on Y 1-x Tb x Mn 6 Sn 6 alloys with the hp13-type structure. YMn 6 Sn 6 (x = 0) shows an inhomogeneous helical antiferromagnetism with the Neel temperature of 333 K. The magnetization shows a steep increase in a field of 20 kOe and approaches saturation around 110 kOe. The alloys with x ≥ 0.2 have the spontaneous magnetization. The magnetization curves show saturation around 40 kOe. The Curie temperature is 347 K for x = 0.2 and increases with increasing x. It is likely that the magnetic moments of Mn ( = 2.0 μ B /Mn atom) and Tb ( = 9.0μ B /Tb atom) are antiferromagnetically coupled to each other. At low temperatures around 12 K, the spin direction for the alloy with x = 0.2 deviates slightly from the c-axis, and the small components on the c-plane have a helical structure with a propagation vector parallel to the c-axis. This structure transforms to a different type of helical structure above 160 K.