Spectroscopic study of metallic magnetism in single-crystallineNb1−yFe2+y

Abstract

We have investigated single crystals and polycrystals from the series Nb1−yFe2+y, −0.004 ≤ y ≤ 0.018 by electron spin resonance, muon spin relaxation and Mössbauer spectroscopy. Our data establish that at lowest temperatures all samples exhibit bulk magnetic order. Slight Feexcess induces low-moment ferromagnetism, consistent with bulk magnetometry, while Nb-rich and stoichiometric NbFe2 display spin density wave order with small magnetic moment amplitudes of the order ∼ 0.001 − 0.01µB /Fe. This provides microscopic evidence for a modulated magnetic state on the border of ferromagnetism in NbFe2.

Metallic quantum ferromagnets

“…This has recently been confirmed by a microscopic study with electron spin resonance, muon spin relaxation and Mössbauer spectroscopy on single crystals (Rauch et al, 2015). However, this state is characterized by an unusually high magnetic susceptibility, χ ≈ 0.02 in SI units, which corresponds to a large Stoner enhancement factor of the order of 180 (Brando et al, 2008).…”

μSR study of stoichiometric NbFe2

“…Although an extensive amount of bulk magnetic, thermodynamic, transport and theoretical work has been performed, no definitive ground state has been unambiguously identified. Direct evidence of a modulated SDW has recently been reported using muon spin relaxation (µSR) [12]. Clear evidence of long range order in the doped samples was observed, the muon signal relaxed with an oscillatory behaviour which is a strong indication of static and ordered bulk magnetism.…”

“…The high temperature paramagnetic metal becomes a weakly ordered ferromagnet at relatively low temperatures in Nb-rich (y<−0.02) and Fe-rich (y>0.01) compounds and the magnetic transition can be tuned to zero temperature at a doping of y = −0.015 [5]. Long-range antiferromagnetism Email address: marginedad@cardiff.ac.uk (D. Margineda) (AF) or a spin density wave (SDW) have both been suggested to describe the magnetic ground state around criticality (−0.02 <y<0.01) [5][6][7][8][9][10][11][12]. However ferrimagnetism in Fe-rich samples found by magnetic Compton scattering [13] and the current failure to detect the magnetic order by neutron scattering [5,8] suggests further experiments are required to clarify the nature of the ground state.…”

“…The AF or SDW ground state is characterised by a high magnetic susceptibility, non-Fermi liquid behaviour and the absence of magnetic remanence. Recently, significant efforts have been made in order to further understand the nature of the apparently ambiguous magnetic ground state in NbFe 2 [5,[7][8][9][10][11][12]. Furthermore the possibility of competing and frustrated interactions can be postulated from the crystal structure since NbFe 2 crystallizes in the C14 hexagonal Laves phase with the magnetic Fe atoms (6h sites) forming two planar triangular kagome lattices, separated by linking Fe (2a sites) atoms in a hexagonal lattice and Nb atoms occupying interstitial sites, leading to numerous possible exchange pathways.…”

Quantum Phase Transitions and Multicriticality in Ta(Fe1−xVx)2

“…Some examples are Nb 1−y Fe 2+y , 12,13 Ta(Fe 1−x Al x ) 2 14 or Ta(Fe 1−x V x ) 2 . 15 The system Nb 1−y Fe 2+y is of particular interest and it has been investigated in detail during the last years: [16][17][18] It exhibits three magnetically ordered low-T states within a narrow composition range (−0.02 ≤ y ≤ 0.02) at ambient pressure. At slightly off-stoichiometric compositions, both towards the Fe-rich and the Nb-rich side, it has been reported to be FM and at y ≈ 0 it assumes SDW order below 10 K. The QCP is located at y ≈ −0.01 at which non-FL (NFL) temperature dependencies of the heat capacity (C/T ∝ − log T ) and of the electrical resistivity ρ ∝ T 3/2 were * E-mail address: brando@cpfs.mpg.de found, but no superconductivity.…”