The Spectral and Magnetic Properties of Er3+ and Yb3+ Ions in Y2Ti2O7 Crystals with a Pyrochlore Structure

EPR spectra and magnetization of XY-type rare-earth ions in pyrochlores Y2Ti2O7: RE3+ (RE=Yb, Er)

“…The crystal field approach was used to interpret the measured magnetic field and temperature dependences of the magnetization and the characteristics of the EPR spectra. The sets of the CF parameters determined earlier from the analysis of the optical spectra [24] allowed us to reproduce successfully the values of resonance fields and relative intensities of EPR signals for different orientations of the applied field and the magnetic anisotropy induced by strong fields in cubic pyrochloresY 2 Ti 2 O 7 :Yb 3+ and Y 2 Ti 2 O 7 :Er 3+ containing small concentrations of 0.5 at.% of RE ions. The shapes of EPR lines including the fine hyperfine structures due to odd 171 Yb, 173 Yb and 167 Er isotopes were successfully modeled and the corresponding line widths and parameters of hyperfine interactions were determined from the fitting procedure.…”

“…The temperature dependences of the static magnetic susceptibility ( )  is the Bohr magneton, k B is the Boltzmann constant, g is the Lande factor of the ground multiplet with the total angular moment J, g || and g  are the g-factors of the ground Kramers doublet determined from the EPR spectra (see below)).As the magnetic field increases, a noticeable dependence of the magnetization on the field direction appears due to mixing of wave functions of the ground and excited CF levels by the Zeeman interaction (see Figure 1). Of particular interest for justification of the CF parameter sets is the difference in the relative shifts of magnetization curves of Er 3+ and Yb 3+ ions in magnetic fields along the tetragonal [001] axis, in this case the observed magnetization in strong magnetic fields has maximum values for the Yb 3+ ions but minimum values for the Er 3+ ions.The gaps of ~600 cm -1 and ~50 cm -1 between the ground  4 doublet and the first excited state ofYb 3+ and Er 3+ ions [24], respectively, differ by more than an order of magnitude, and, in agreement with the nonlinear mechanism of the single-ion magnetic anisotropy in cubic paramagnetic centers, it is remarkably stronger in Y 2 Ti 2 O 7 :Er 3+ than in Y 2 Ti 2 O 7 :Yb 3+ single crystals.…”

“…The measurements of the magnetization M(B,T)parallel to the external magnetic field B with magnetic fields in the range of 0−9 T applied along the crystallographic axes [100], [111] and [110] were performed using a vibrating sample magnetometer option of the PPMS-9 system (Quantum Design) on Y 2 Ti 2 O 7 :Yb 3+ and Y 2 Ti 2 O 7 :Er 3+ single crystals with the content of 0.5 at.% of impurity ions grown by the optical floating-zone method [25]. The details of the single crystal growths were described in [24]. The pyrochlore structure of the samples was confirmed by X-ray diffraction measurements.…”

“…In recent work [24], stimulated by the increasing interest to the unconventional magnetic properties of geometrically frustrated RE pyrochlores, we presented the measured electron paramagnetic resonance (EPR) and site-selective emission and excitation optical spectra of Y 2 Ti 2 O 7 single crystals doped with Er 3+ or Yb 3+ ions (0.5 at.%). The CF parameters were calculated in the framework of the semi-phenomenological exchange charge model and then corrected to fit the experimental data.…”

“…%) single crystals. The shape and the hyperfine structure of EPR signals presented in [24] and magnetization curves are analyzed by making use of the corresponding sets of CF parameters.…”