S. Hüfner

Optical investigation of metamagnetic DyAlO3

We have investigated the optical absorption spectra of metamagnetic DyAlO3 (TN=3.4 °K) above and below the Néel temperature. We find that the magnetic interactions are predominantly between the ions along the crystallographicc-axis; the interaction energy between two ions isWC=− (2.9±0.6) cm−1. Additional line-shifts below 3.4 °K yield the Néel temperature.Zeeman effect studies give the magnetic moment of the groundstate as μ=(9.2 ± 0.9)μB. The direction of the magnetic moments is in thea-b plane, with angles of ± 33.5° and ± 146.5° from theb-axis. The Zeeman effect studies reveal two metamagnetic transitions (forHext∥μ) at 7.0 and 7.3 kOe respectively.Additional susceptibility and Mössbauer measurements confirm the Néel temperature and the magnetic moment.

Crystal Field in Samarium and Dysprosium Garnets

The crystal‐field energy levels of the 6H and 6F multiplets of Sm3+ and Dy3+ in yttrium aluminium (YAG) and yttrium gallium garnet (YGG) have been fitted to the Hamiltonian appropriate for the D2 site symmetry of the rare earth ion. A good fit has been obtained for both garnets. For the dysprosium garnets also the groundstate g factors were found to agree well with the calculated ones.

Crystal field interaction in erbium garnets

A crystal field analysis has been performed for erbium aluminum garnet (ErAG) and erbium gallium garnet (ErGG). Good agreement between the measured and calculated energy levels was obtained.

Optical absorption spectra of erbium iron garnet (ErIG)

Absorption spectra of the transition4I15/2→4I9/2 have been measured in erbium iron garnet (ErIG). From these spectra the exchange tensors for four Kramers dubletts can be obtained. A tentative analysis of these data in terms of a phenomenological exchange Hamiltonian will be presented.

Optical Measurements in Erbium Iron and Erbium Gallium Garnet

Optical absorption spectra of erbium iron garnet (ErIG) have been measured at 4.2°, 20°, and 62°K with external magnetic fields up to 25 kOe. From these measurements, the magnetic moment of the groundstate for the two magnetically inequivalent sites can be deduced as μ1=7.0 μB and μ2=4.6 μB yielding an average moment of μ=5.4 μB in the [100]‐direction. In addition, we have measured the G‐tensor of one excited state (4I9/2) as Gx=(10.0±0.5) cm−1, Gy=(15.0±0.5) cm−1, and Gz=(10.0±0.5) cm−1. The comparison with the g‐tensor of this state in the gallium garnet (gx=3.1, gy=3.1, gz=3.9) shows a large anisotropic exchange. Crystal‐field energy levels and g‐factors of erbium gallium garnet and erbium aluminium garnet have been measured and a good fit to a set of nine crystal‐field parameters Akq〈rk〉 has been obtained.

Optical spectroscopy of Dysprosium Aluminum Garnet (DAG)

The absorption spectrum of antiferromagnetic dysprosium aluminium garnet (DAG) (TN=2.50 °K) has been investigated at low temperatures.The groundstate splitting due to all interactions in the antiferromagnetic state is (5.27±0.10) cm−1 extrapolated to 0 °K. The temperature dependence of the lineshift of the absorption lines is measured. Zeeman effect studies give theg-tensor of the groundstate asgz=18.4±0.5,gx=gy=0.5±0.2. The studies also allow the determination of the critical fields asHc[100]=(5.0±0.1) koe,Hc[111]=(3.9±0.2) koe andHc[110]=(4.9±0.6) koe. In addition an investigation of a number of satellite lines is performed. Some of them can be interpreted as spin wave sidebands (Stokes and anti-Stokes); others obviously come from dysprosium ions which have impurity ions on regular lattice sites as neighbours.

Optical investigation of ErFeO3

The absorption spectrum of single crystals of ErFeO3 has been investigated in the red and near infrared spectral region in the temperature range between 1.2 °K and 4.2 °K and at 20 °K and 77 °K. Between 77 °K and 4.2 °K a constant splitting of the absorption lines is observed. Below the Néel-temperature of the erbium sublattice at 4.5 °K the splitting of the absorption lines increases; the saturation value extrapolated to 0 °K of the splitting of the lowest crystal field level of the4I15/2 groundterm is (6.08±0.30) cm−1. By measuring the Zeeman effect the groundstate magnetic moment is determined asμ=(6.6±0.2)μB. The measured temperature dependence of the splitting of the lowest crystalfield level of the4I15/2 groundterm is compared with that calculated by a Monte Carlo method.

Hyperfine Fields in Nickel Alloys Measured by the 61Ni Mössbauer Effect

The hyperfine (hf) fields at the nickel sites were measured in the alloy series NixFe1−x (0≤x≤1) using the Mossbauer effect of 61Ni. The field at the 61Ni nucleus follows the relation Hhf = aμNi+bμ with a≃ −20 kOe/μB and b≃−100 kOe/μB, μ being the average magnetic moment of the alloy. This indicates that the conduction electron polarization produces the main contribution. In GdNi2 and ErNi2 intermetallic compounds the fields are less than 25 kOe as dededuced from linewidth.

Optical Spectroscopy of Rare Earth Perovskites

High‐resolution optical absorption spectra have been obtained on antiferromagnetic DyAlO3 and weakly ferromagnetic HoFeO3 and DyFeO3 at low temperatures. In DyAlO3 the absorption lines show a triplet structure which vanishes in Y(Dy)AlO3. From this it is concluded that the magnetic interactions take place for each Dy ion with only two neighbors. At 3.5°K the splitting of the absorption lines starts to increase with decreasing temperature yielding a Neel temperature of (3.5±0.1)°K. The magnetic moment of the ground state is determined to be μ = (8.6±1.0)μB. In DyFeO3 a Neel temperature of (4.5±0.3)°K is deduced from the temperature dependent lineshift, the magnetic moment of the ground state is found to be μ = (8.9±1.0)μB.

The concentration dependence of the Ni hyperfine field in NiPd alloys

Abstract The hyperfine field at the Ni site in NiPd alloys is measured by the Mossbauer effect in 61 Ni. The concentration dependence of the hyperfine field can be fitted for this alloy as well as for FePd and CoPd alloys under the assumption that a positive field contribution is proportional to the polarization of the Pd matrix.