The Ge-site-doped MnNiGe alloys with nominal compositions ${\mathrm{MnNiGe}}_{0.9}{\mathrm{Al}}_{0.1}$ and ${\mathrm{MnNiGe}}_{0.928}{\mathrm{Ga}}_{0.072}$ are investigated through neutron powder diffraction studies in the presence of external magnetic fields ($H$). The application of external $H$ is found to result in a number of interesting features, which include (i) a decrease in the intensity of the incommensurate antiferromagnetic (AFM) satellite peaks, (ii) an increase in some of the nuclear reflections, and (iii) unchanged intensities of the commensurate AFM satellite peaks. We also noticed a small increase in the incommensurate propagation vector ${\mathbf{k}}_{\text{AFM}}^{\text{o}}=(k_a,0,0)$ with increasing $H$. The enhanced nuclear reflections point to the introduction of a ferromagnetic (FM) component into the otherwise AFM alloy, represented by the FM propagation vector ${\mathbf{k}}_{\text{FM}}^{\text{o}}=(0,0,0)$. This FM component modifies the helical modulation of the incommensurate AFM structure, driving it toward a conical configuration, but even an applied $H$ of 80 kOe is insufficient to fully establish a FM alignment of the Mn moments in the presently studied alloys.

Close

PrevNext

View figure in article

• First order phase transitions
• Magnetism
• Transition metal alloys
• Arc discharge
• Neutron diffraction