Gd3+ spin-lattice relaxation via multi-band conduction electrons in Y(1-x)Gd(x)In3: an electron spin resonance study.

Interest in the electronic structure of the intermetallic compound YIn3 has been renewed with the recent discovery of superconductivity at T ∼ 1 K, which may be filamentary in nature. In this work we perform electron spin resonance (ESR) experiments on Gd(3+) doped YIn3 (Y1-xGdxIn3; 0.001 ⪅ x ⩽̸ 0.08), showing that the spin-lattice relaxation of the Gd(3+) ions, due to the exchange interaction between the Gd(3+) localized magnetic moment and the conduction electrons (ce), is processed via the presence of s-, p- and d-type ce at the YIn3 Fermi level. These findings are revealed by the Gd(3+) concentration dependence of the Korringa-like relaxation rate d(ΔH)/dT and g-shift (Δg = g - 1.993), that display bottleneck relaxation behavior for the s-electrons and unbottleneck behavior for the p- and d-electrons. The Korringa-like relaxation rates vary from 22(2) Oe/K for x ⪅ 0.001 to 8(2) Oe/K for x = 0.08 and the g-shift values change, respectively, from a positive Δg = +0.047(10) to a negative Δg = -0.008(4). Analysis in terms of a three-band ce model allows the extraction of the corresponding exchange interaction parameters Jfs, Jfp and Jfd.

Origin of magnetism in undoped TiO2 nanotubes.

Magnetic properties of undoped anatase, rutile, and amorphous titanium dioxide (TiO2) nanotubes grown by electrochemical anodization were studied by superconducting quantum interference device (SQUID) and electron spin resonance (ESR) methods in the temperature range 1.8-300 K. All anatase, rutile, and amorphous TiO2 nanotubes were found to exhibit paramagnetic behaviors in the entire temperature range when tested with magnetic center concentrations of 6×10(17), 3×10(16), and 3 × 10(15) cm(-3), respectively. The diameter of the TiO2 nanotubes varied from 40-160 nm and has no significant effect on the magnetic properties observed. SQUID data showed strong nonlinear M-H relationships for anatase at low temperatures, and Arrot plot analysis suggested ferromagnetism in the sample with a Curie temperature T(C) ~ 6 K. However, ESR studies showed no evidence for long-distance magnetic ordering. ESR studies revealed two magnetic centers with g1 = 1.928 and g2 = 2.028 that were common to all samples. The resonance peak at g1 = 1.922 was ascribed to Ti(3+) cations centers resulting from oxygen vacancies, while the peak at g2 = 2.028 was ascribed to surface absorbents. The amorphous sample ESR spectrum contained additional resonance peaks with corresponding g values at 2.228, 1.873, and 1.715 that possibly resulted from the disordered nature of these samples.

Quantum critical Kondo quasiparticles probed by ESR in ß-YbAlB4.

Electron spin resonance (ESR) can probe conduction electrons (CE) and local moment (LM) spin systems in different materials. A CE spin resonance (CESR) is observed in metallic systems based on light elements or with enhanced Pauli susceptibility. LM ESR can be seen in compounds with paramagnetic ions and localized d or f electrons. Here we report a remarkable and unprecedented ESR signal in the heavy-fermion superconductor ß-YbAlB4 [S. Nakatsuji et al., Nature Phys. 4, 603 (2008)] which behaves as a CESR at high temperatures and acquires characteristics of the Yb³âº LM ESR at low temperature. This dual behavior strikes as an in situ unique observation of the Kondo quasiparticles in a quantum critical regime. The proximity to a quantum critical point may favor the appearance of this dual character of the ESR signal in ß-YbAlB4.

Absence of exchange interaction between localized magnetic moments and conduction-electrons in magnetic ions diluted in Ag-nanoparticles.

The Electron Spin Resonance (ESR) of diluted magnetic ions (MI) of Er3+, Yb3+ and Mn2+ in Ag nanoparticles (NPs) is reported. Monodisperse samples of Ag NPs doped with these MI were synthesized by reducing silver nitrate and MI-oxides. This simple method can be extended to all rare-earths. The measurements of the g-values and hyperfine splittings indicates that the MI are located at cubic sites in the Ag:MI NPs. The ESR spectra show that there is no g-shift and Korringa-relaxation due to the exchange interaction between the MI and the conduction electrons, suggesting that the exchange interaction is absent in the Ag:MI NPs. Thus, the nature of this interaction needs to be reexamined at the nanoscale range.

Improved route for the synthesis of colloidal NaYF4 nanocrystals and electron spin resonance of Gd3+ local probe.

This paper presents the synthesis and characterization of colloidal NaYF4 and NaYF4:20% Gd lanthanide nanocrystals. The nanoparticles were prepared by chemical route using co-thermolysis of Na(CF3COO), Y(CF3COO)3 and Gd(CF3COO)3 precursor in oleylamine surfactant/phenylether at Ts = 250 degrees C. By tuning the precursor/surfactant molar ratio during the process, it was possible to control the crystalline phase, chemical order and size of the nanocrystals. The nanocrystals were characterized by Transmission Electron Microscopy, Small Angle X-ray Scattering, powder X-ray Diffraction, dc-magnetization and Electron Spin Resonance (ESR) techniques. The ESR experiments show the so called U-spectrum for the Gd3+ ions in bulk counterpart materials, where characteristic powder spectra of cubic and lower crystal field symmetries were observed.