Competing magnetic correlations and uniaxial anisotropy in (Fe${}_{1-x}$Mn${}_x$)${}_2$AlB${}_2$ single crystals

Abstract

We have succeeded for the first time in synthesizing single crystals of nanolaminated borides (Fe${}_{1-x}$Mn${}_x$)${}_2$AlB${}_2$ in the entire Fe-Mn composition range using the Al self-flux method, and have established $T$-$x$, $H$-$T$ and three-dimensional $H$-$T$-$x$ magnetic phase diagrams from the results of magnetization measurements. The ferromagnetic correlation of Fe${}_2$AlB${}_2$ is weakened with the Mn substitution, whereas the antiferromagnetic correlation of Mn${}_2$AlB${}_2$ is enhanced with the Fe up to $x=0.65$. The spin direction in the magnetic ordered states changes from the $a$ to the $b$ axis with increasing Mn concentration and temperature. At $x$ = 0.31-0.46, there are three magnetic phases; ferromagnetic, antiferromganetic, and intermediate phases in between. At $x$ = 0.65 and 0.74, a spin-flop-like metamagnetic transition was observed at a finite field parallel to the spin direction. These observations indicate that in (Fe${}_{1-x}$Mn${}_x$)${}_2$AlB${}_2$ the ferromagnetic and antiferromagnetic correlations coexist and the uniaxial magnetic anisotropy competes between the $a$ and $b$ axes.

12pages, 15 figures