Magnetic ordering in the fine particles of some bulk Pauli paramagnets

Abstract

Fine particles of some of the extensively studied "enhanced" Pauli paramagnets, LuCo 2 , ScCo 2 , ZrCo 2 , and CeRu 2 Si 2 , have been prepared by high-energy ball milling and investigated for their magnetic behaviors. In the case of Co systems, these particles show ferromagnetic features even at room temperature. Even in the case of CeRu 2 Si 2 -a well-known Kondo lattice which is nonmagnetic in the bulk form, features attributable to the onset of magnetic order below about 8 K could be seen in fine particles. The magnitudes of the magnetic moment of these small particles at high fields are sufficiently large to conclude that the observed magnetic ordering is not just a surface effect. This transformation to magnetic ordering in small particles could be widespread among enhanced Pauli paramagnets.

Magnetism of fine particles of Kondo lattices, obtained by high-energy ball-milling

“…During the course of our investigations, similar studies were reported on YbAl 3 [4]. In recent years, we have carried out substantial investigations on ball-milled specimens of rare-earth intermetallics, e.g., RCo 2 [5,6], RMn 2 Ge 2 [7], RCr 2 Si 2 C [8]. One of the important outcomes was that the exchange-enhanced Pauli paramagnets (in bulk form), like YCo 2 , LuCo 2 , and ZrCo 2 , which have been known to undergo itinerant electron metamagnetism at very high fields (>500 kOe), are found to become ferromagnetic in nanoform at room temperature [5,6].…”

“…There are corresponding anomalies in the ac χ(T) data as well (H ac = 1 Oe) for both real and imaginary parts (not shown here, see Ref. 6). Though these results establish the existence of a magnetic transition near 8 K, we could not confirm from these data whether the ordering is of a ferromagnetic type or a spin-glass type.…”

“…In recent years, we have carried out substantial investigations on ball-milled specimens of rare-earth intermetallics, e.g., RCo 2 [5,6], RMn 2 Ge 2 [7], RCr 2 Si 2 C [8]. One of the important outcomes was that the exchange-enhanced Pauli paramagnets (in bulk form), like YCo 2 , LuCo 2 , and ZrCo 2 , which have been known to undergo itinerant electron metamagnetism at very high fields (>500 kOe), are found to become ferromagnetic in nanoform at room temperature [5,6]. With this clue, we wanted to probe how a heavy fermion with a non-magnetic ground state (in bulk) behaves in the nanoform far away from the quantum critical point (QCP) as well as at the QCP.…”

Magnetic behavior of bulk and fine particles of RCr2Si2C (R = La, Ce) compounds: possible magnetic ordering from Cr

“…Keeping above controversy in mind, we have reinvestigated the compounds, LaCr 2 Si 2 C and CeCr 2 Si 2 C. These two compounds have been chosen for this purpose as there is no magnetic ordering from the rare-earth ions (including Ce as it is mixed-valent [8,9]). In addition, we have investigated the magnetic behavior of these compounds in the fine particle form (less than 1 micron) as a part of our recent initiative [10] to probe electron correlation effects in Ce systems in nano form. The main conclusions are: (i) One can not rule out itinerant magnetism from Cr for the bulk form, supporting Janatova et al [8], (ii) possible magnetism from Cr appears to get gradually suppressed with a reduction in particle size, and (iii) Ce is distinctly mixed-valent in the bulk form and the fine particles of Ce are characterized by higher values of χ in the paramagnetic state which could imply that the magnetic moment on Ce is influenced with varying particle size.…”

Ferromagnetic feature from Mn near room temperature in the fine particles of GdMn 2 Ge 2 and TbMn 2 Ge 2

“…The present investigation is primarily aimed at addressing how a reduction in particle size influences magnetism in this family, focusing on the RMn 2 Ge 2 series. Recently, we reported [20] that, in the case of a well-known non-magnetic heavy-fermion compound, CeRu 2 Si 2 , the nanoparticles obtained by high-energy ball-milling are in fact magnetic below about 8 K, corresponding to the lattice expansion effect on magnetism caused by partial La (for Ce) or Ge (for Si) substitution. With this clue, we wanted to explore whether the antiferromagnetism seen in the room temperature range in the heavy R members in RMn 2 Ge 2 can be driven towards the ferromagnetism observed for light R members.…”