Magnetic, thermal and transport behavior in single crystalline RCu₂Ge₂ (R=La, Ce, Pr and Sm) compounds

Magnetic behavior of single crystalline RCu₂Ge₂ (R=La, Ce, Pr and Sm) compounds is reported. Single crystals were grown using Cu–Ge flux. The compounds crystallize in a tetragonal structure with space group I4/mmm. LaCu₂Ge₂ shows a diamagnetic behavior. CeCu₂Ge₂, PrCu₂Ge₂ and SmCu₂Ge₂ orders antiferromagnetically at ≈4.2, 15 and 14.5 K respectively with [001] as the easy axis of magnetization. CeCu₂Ge₂ shows a Kondo behavior. The Kondo temperature T_K, calculated using two different models is of order of 5 K. In PrCu₂Ge₂, an additional magnetic transition is observed below 4 K. The origin of the magnetic behavior is attributed to magnetoelastic effects. A possibility of change in easy axis of magnetization after field cycling (below 4 K) is discussed and such effect is rarely observed. The magnetic and specific heat behavior of CeCu₂Ge₂ and PrCu₂Ge₂ are analyzed on the basis of crystalline electric field (CEF) model. The CEF splited ground state of rare earth ions is calculated. The magnetic isotherm of SmCu₂Ge₂ exhibits de Haas-van Alphen oscillations. It is inferred from the frequency spectrum analysis that, the Fermi surface cross-section along [001] is large compared to [100]. - Highlights: • RCu₂Ge₂ single crystals are grown by self-flux • Anomalous magnetic behavior was observed in PrCu₂Ge₂, which was explained on the basis of possible change in the easy axis of magnetization after field cycling. • Crystal electric field calculations were done to explain the observed magnetic properties. • de Haas–van Alphen oscillations were observed in SmCu₂Ge₂