Magnetic fluctuations in the itinerant ferromagnet LaCrGe3 studied by La139 NMR

Abstract

LaCrGe3 is an itinerant ferromagnet with a Curie temperature of Tc = 85 K and exhibits an avoided ferromagnetic quantum critical point under pressure through a modulated antiferromagnetic phase as well as tri-critical wing structure in its temperature-pressure-magnetic field (T -p-H) phase diagram. In order to understand the static and dynamical magnetic properties of LaCrGe3, we carried out 139 La nuclear magnetic resonance (NMR) measurements. Based on the analysis of NMR data, using the self-consistent-renomalization (SCR) theory, the spin fluctuations in the paramagnetic state are revealed to be isotropic ferromagnetic and three dimensional (3D) in nature. Moreover, the system is found to follow the generalized Rhodes-Wohfarth relation which is expected in 3D itinerant ferromagnetic systems. As compared to other similar itinerant ferromagnets, the Cr 3d electrons and their spin fluctuations are characterized to have a relatively high degree of localization in real space.PACS numbers:

Magnetic properties of the itinerant ferromagnet LaCrGe3 under pressure studied by La139 NMR

“…In fact the observed spectra are well reproduced by the calculated spectra [red curves in Fig. 2(a)] from the Hamiltonian with those parameters [29]. As in the case of the ambient pressure, 139 La-NMR spectra in LaCrGe 3 under pressure show the typical I = 7/2 quadrupole split lines with a nearly pressure independent value of ν Q = 0.66 MHz and η ∼ 0 in the paramagnetic state well above the magnetic ordering temperature under pressure up to the highest measured p of 2.64 GPa.…”

“…Here H eff is the effective magnetic field at the La site, h is Planck's constant, ν Q is nuclear quadrupole frequency defined by ν Q = 3e 2 QV ZZ /2I (2I − 1)h where Q is the electric quadrupole moment of the La nucleus, V ZZ is the electric field gradient (EFG) at the La site, and η is the asymmetry parameter of EFG at the La site. From the angle dependence of 139 La NMR spectra in the paramagnetic state at ambient pressure, the principal axis of the EFG was determined to be parallel to the c axis and ν Q is estimated to be 0.66 MHz with η ∼ 0 [29]. In fact the observed spectra are well reproduced by the calculated spectra [red curves in Fig.…”

“…Our previous 139 La-NMR study at ambient p evidenced the presence of three-dimensional (3D) isotropic ferromagnetic fluctuations in this system [29]. Furthermore, LaCrGe 3 was found to follow the generalized Rhodes-Wohlfarth (GRW) relation for 3D itinerant ferromagnets, and its location in the GRW plot suggested a high degree of localization in Cr 3d electrons compared to other itinerant ferromagnets that exhibit the tricritical wings structure [26,29]. Our present NMR data show that the 3D FM fluctuations persist to dominate in the paramagnetic state well above T C in LaCrGe 3 throughout the measured p region and suggest a possible ferromagnetic order developing below ∼50 K under higher pressures in a magnetic field of ∼7.2 T.…”

“…With the motivation to investigate the evolution of magnetic properties of LaCrGe 3 under p towards the putative QCP as well as to obtain more insights into the new phase under high pressures, here we carried out nuclear magnetic resonance (NMR) measurements under p up to 2.64 GPa. Our previous 139 La-NMR study at ambient p evidenced the presence of three-dimensional (3D) isotropic ferromagnetic fluctuations in this system [29]. Furthermore, LaCrGe 3 was found to follow the generalized Rhodes-Wohlfarth (GRW) relation for 3D itinerant ferromagnets, and its location in the GRW plot suggested a high degree of localization in Cr 3d electrons compared to other itinerant ferromagnets that exhibit the tricritical wings structure [26,29].…”

“…A. 139 La NMR spectrum 139 La-NMR spectra in LaCrGe 3 at ambient pressure have been reported to show typical quadrupolar-split lines [29], which are well explained by the combination of a large Zeeman interaction due to magnetic field and a small quadrupole interaction whose nuclear spin Hamiltonian is given by…”