Spin dynamics and spin disorder in frustrated TbCo xNi 1− xC 2

Abstract

The orthogonal dicarbides RTC 2 ( R= rare earth , T= transition metal ) show ferromagnetic (fm) order of the R ions below T C ≈30 K for T=Co with a being the easy axis and antiferromagnetic (afm) order (with about the same transition temperature) for T=Ni with c as easy axis. The spin turning is caused by changes in the crystalline electric field (CEF) interaction. In the mixed TbCo x Ni 1− x C 2 alloys, fm and afm exchange on the one side and different CEF interactions on the other compete as a function of x. These competing interactions are a source of magnetic frustration. They also cause the materials to undergo several magnetic transitions into fm, afm or spin modulated structures which are well documented by neutron diffraction. Zero, longitudinal and transverse field μSR was carried out on TbCo x Ni 1− x C 2 with x=0.3, 0.5 0.7 and 0.85 using the same samples as in the neutron studies. Marked local spin disorder and persistent spin dynamics were seen in all magnetically ordered states as a consequence of frustration, but distinct differences exist for different values of x. Not all reported phase transition show clearly in the μSR data. In TbCo 0.85Ni 0.15C 2, a short-range dynamically correlated spin state having a strong fm polarizability exists above T C =30 K extending for about 50 K .