We have investigated the optical absorption spectra of metamagnetic DyA103 (TN= 3.4 ~ above and below the N6el temperature. We find that the magnetic interactions are predominantly between the ions along the crystallographic c-axis; the interaction energy between two ions is We=--(2.9-t-0.6) cm -1. Additional line-shifts below 3.4 ~ yield the N6el temperature.Zeeman effect studies give the magnetic moment of the groundstate as /~= (9.2_ 0.9)g B . The direction of the magnetic moments is in the a--b plane, with angles of _ 33.5 ~ and + 146.5 ~ from the b-axis. The Zeeman effect studies reveal two metamagnetic transitions (for next[la) at 7.0 and 7.3 kOe respectively.Additional susceptibility and M6ssbauer measurements confirm the N6el temperature and the magnetic moment.
The absorption spectrum of single crystals of ErFeO 3 has been investigated in the red and near infrared spectral region in the temperature range between 1.2 ~ and 4.2 ~ and at 20 ~ and 77 ~ Between 77 ~ and 4.2 ~ a constant splitting of the absorption lines is observed. Below the N6el-temperature of the erbium sublattice at 4.5 ~ the splitting of the absorption lines increases; the saturation value extrapolated to 0 ~ of the splitting of the lowest crystal field level of the 4115/2 groundterm is (6.08 __ 0.30) cm -1. By measuring the Zeeman effect the groundstate magnetic moment is determined as/~ = (6.6 _+ 0.2)/1B. The measured temperature dependence of the splitting of the lowest crystalfield level of the 4Ils/2 groundterm is compared with that calculated by a Monte Carlo method.
Optical absorption spectra of DyFeO 3 have been investigated at 1.2_< T_<4.2 ~ and T---77 ~ From the temperature dependent lineshift a N6el temperature of T N = (3.8 __ 0.5) ~ is deduced for the dysprosium sublattices. The groundstate splitting due to the iron-dysprosium interactions is about 1.5 cm -1 and due to the dysprosiumdysprosium interactions (5.0_+ 1.4)cm -1. Zeeman studies give the magnetic moment of the dysprosium ions as/t= (9.2_+ 1.0)PB.
The absorption spectra of HoFeO 3 were investigated in the near infrared spectral region at temperatures of 1.2, 4.2, 20 and 77 ~ respectively. At every temperature T_-< 20 ~ all the absorption lines show the same splitting which is attributed to the groundstate; this splitting is (7.2 _ 0.5) cm -1 at 20 ~ and decreases to (4.9 _+ 0.8) cm -a extrapolated to 0 ~ From these splittings the holmium-iron and the holmiumholmium interactions can be deduced. Measurements with an external magnetic field yield a magnetic moment of /~= (7.6+ 0.7)PB per holmium ion. The moments are directed at angles of --28 ~ and --152 ~ with respect to the b-axis.
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 Néel 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 Néel 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.
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