Tuning in magnetic modes in Tb(Co_{x}Ni_{1-x})_{2}B_{2}C: from longitudinal spin-density waves to simple ferromagnetism

TL;DR

This study investigates how magnetic structures in Tb(Co_xNi_{1-x})_2B_2C evolve from modulated spin-density waves to simple ferromagnetism as the cobalt concentration increases, revealing a sequence of magnetic modes.

Contribution

First experimental observation of the k=(0,0,1/3) magnetic mode in borocarbides, confirming a theoretical model of magnetic mode evolution in this series.

Findings

Identified a sequence of magnetic modes with increasing x

First observation of the k=(0,0,1/3) mode in borocarbides

Correlated magnetic mode changes with structural distortions

Abstract

Neutron diffraction and thermodynamics techniques were used to probe the evolution of the magnetic properties of Tb(Co_{x}Ni_{1-x})_{2}B_{2}C. A succession of magnetic modes was observed as x is varied: the longitudinal modulated k=(0.55,0,0) state at x=0 is transformed into a collinear k=([nicefrac]<LaTeX>\nicefrac{1}{2}</LaTeX>,0,[nicefrac]<LaTeX>\nicefrac{1}{2}</LaTeX>) antiferromagnetic state at x= 0.2, 0.4; then into a transverse c-axis modulated k=(0,0,[nicefrac]<LaTeX>\nicefrac{1}{3}</LaTeX>) mode at x= 0.6, and finally into a simple ferromagnetic structure at x= 0.8 and 1. Concomitantly, the low-temperature orthorhombic distortion of the tetragonal unit cell at x=0 is reduced smoothly such that for x >= 0.4 only a tetragonal unit cell is manifested. Though predicted theoretically earlier, this is the first observation of the k=(0,0,[nicefrac]<LaTeX>\nicefrac{1}{3}</LaTeX>) mode in borocarbides; our findings of a succession of magnetic modes upon increasing x also find support from a recently proposed theoretical model. The implication of these findings and their interpretation on the magnetic structure of the RM_{2}B_{2}C series are also discussed.