Magnetic phase transitions and ferromagnetic short-range correlations in single-crystalTb5Si2.2Ge1.8

Abstract

Magnetic phase transitions in a ${\text{Tb}}_{5}{\text{Si}}_{2.2}{\text{Ge}}_{1.8}$ single crystal have been studied as a function of temperature and magnetic field. Magnetic-field dependencies of the critical temperatures are highly anisotropic for both the main magnetic ordering process occurring around 120 K and a spin reorientation transition at $\ensuremath{\sim}70\text{ }\text{K}$. Magnetic-field-induced phase transitions occur with the magnetic field applied isothermally along the $a$ and $b$ axes (but not along the $c$ axis) between 1.8 and 70 K in fields below 70 kOe. Strong anisotropic thermal irreversibility is observed in the Griffiths phase regime between 120 and 200 K with applied fields ranging from 10 to 1000 Oe. Our data (1) show that the magnetic and structural phase transitions around 120 K are narrowly decoupled; (2) uncover the anisotropy of ferromagnetic short-range order in the Griffiths phase; and (3) reveal some unusual magnetic domain effects in the long-range ordered state of the ${\text{Tb}}_{5}{\text{Si}}_{2.2}{\text{Ge}}_{1.8}$ compound. The temperature-magnetic field phase diagrams with field applied along the three major crystallographic directions have been constructed.