Influence Of Crystallite Size And Temperature On The Antiferromagnetic Helices Of Terbium And Holmium Metal

We report on the results of grain-size and temperature-dependent magnetization, specific-heat, and neutron-scattering experiments on the heavy rare-earth metals terbium and holmium, with particular emphasis on the temperature regions where the helical antiferromagnetic phases exist. In contrast to Ho, we find that the helical structure in Tb is relative strongly affected by microstructural disorder, specifically, it can no longer be detected for the smallest studied grain size of D = 18 nm. Moreover, in coarse-grained Tb a helical structure persists even in the ferromagnetic regime, down to about T = 215 K, in agreement with angle-resolved photoelectron spectroscopy (ARPES) data, which reveal a nesting feature of the bulk Fermi surface at the L point of the Brillouin zone at T = 210 K. As samples for the ARPES measurements, we used 10-nm-thick single-crystalline Tb films that show a bulk electronic valance-band structure. Thus our ARPES measurements are used to discuss temperature-induced effects observed in the coarse-grained samples.