Quasi-One-Dimensional Itinerant Electron System (La–Y)Mn₄Al₈with Soft Spin Gap

Abstract

La 1Àx Y x )Mn 4 Al 8 (0 x 1) is a very unique itinerant electron system, in which the spin pseudogap can be controlled continuously and nearly uniformly in a wide range of the gap width from Á ' 250 to 500 K by the anisotropic volume shrinkage induced by the chemical pressure. The hydrostatic pressure on LaMn 4 Al 8 also increases Á but tends to fill the gap. The strong and anisotropic volume dependence of Á strongly supports the idea that the origin of the gap formation is associated with the one-dimensional geometry of the Mn spin arrangement.The effect of geometry is now known to be important in describing magnetism even in itinerant electron magnets, provided that electron correlations are sufficiently strong. For example, geometric frustration plays a nonnegligible role in determining the physical properties of strongly correlated itinerant electron magnets such as the Laves phase compounds RMn 2 (R ¼ rare earth) 1) and one of allotropes of manganese -Mn. 2) On the other hand, spin-gap formation in correlated electron systems is one of the extensively investigated topics in a wide variety of fields in the magnetism. Among itinerant electron magnets, a unique correlated-electron gap system, FeSi, attracts much attention, and the origin of the spin compensation at the ground state is still a matter of debate. 3) Recently, we have confirmed a susceptibility maximum at T max ' 500 and 200 K for the itinerant electron compounds YMn 4 Al 8 and LaMn 4 Al 8 , respectively, and interpreted this as due to the presence of a narrow pseudogap in the spin excitation spectrum, 4,5) but the origin of the gap remains open for question. The crystal structure of YMn 4 Al 8 and LaMn 4 Al 8 is of the tetragonal CeMn 4 Al 8 type (space group I4=mmm) derived from the ThMn 12 type, in which Mn atoms at the 8 f site form linear chains along the c axis. The large difference in intrachain and interchain Mn-Mn interatomic distances (d intra ' 2:6 and d inter ' 4:4 # A 6,7) ) suggests a quasi-onedimensional (1D) nature of magnetic interaction. YMn 4 Al 8 and LaMn 4 Al 8 show relatively large electronic specific heat coefficients, . 8) Therefore, RMn 4 Al 8 has appeared as another candidate for strongly correlated itinerant electron systems in which the effect of geometry plays a leading role in determining the magnetism. Thus far, no indication of phase transitions has been reported, at least, for YMn 4 Al 8 . For example, the C=T vs T 2 relation (C: specific heat) shows a good linearity down to 1.5 K for both compounds. 8) Although Yamasaki et al. 9) did not find any appreciable evidence of a phase transition in an 27 Al NMR experiment of LaMn 4 Al 8 down to 4.2 K, our recent experiments suggested that magnetic correlation develops below $ 50 K. 5) A recent zero-field SR experiment detected the appearance of static internal fields in LaMn 4 Al 8 at low temperatures, and suggested an antiferromagnetic order below 4.5 K. 10) In this paper, we report the concentration dependences of lattice volume, susceptibility and resistivity for poly...

Magnetovolume effects of quasi-one-dimensional itinerant electron magnets

“…The temperature dependence of susceptibility exhibits a broad maximum at $200 and $500 K for LaMn 4 Al 8 and YMn 4 Al 8 , respectively. We have ascribed this feature to the pseudogap in the spin excitation spectrum [2,3], and the difference in the characteristic energy to the volume effect (chemical pressure effect) on the band structure [4]; the lattice volume of LaMn 4 Al 8 is slightly larger than that of YMn 4 Al 8 . The origin of pseudogap formation is of interest.…”

Electronic structure and magnetic properties of RT4Al8 (R = Sc, Y, La, Lu; T = Fe, Mn, Cr) compounds. Hydrostatic pressure effects

“…The large spread in published data on the magnetic properties of RFe 4 Al 8 compounds is noteworthy and may be a consequence of the different techniques used to prepare the samples and of the high sensitivity of their characteristics to deviations from stoichiometry. More unique information on the magnetic properties has been obtained for RMe 4 Al 8 compounds with nonmagnetic elements R. 14,15 Magnetic ordering has not been observed in this system and the maxima in the v(T) curves observed at high temperatures (200-400 K) are apparently caused by the character of the band structure. 1063-777X/2016/42(6)/8/$32.00…”

Thermoelectric properties of YMn4+xAl8−x for −2≤x≤2.5

“…Recent studies on YMn 4 Al 8 have indicated similar properties to that of the FeSi system with presence of a strong electron correlation [20][21][22]. Moreover, the crystal structure of YMn 4 Al 8 is the tetragonal CeMn 4 Al 8 type, derived from the ThMn 12 type, in which Mn atoms form linear chains along the c axis [23,24], suggesting a quasi-one dimensional (1D) nature of the magnetic interaction [25].…”