CRYSTAL-FIELD EFFECTS IN THE ELECTRON-SPIN-RESONANCE OF GD3+ AND ER3+ IN PR2CUO4

The low-temperature (T < 300 K) electron-spin-resonance (ESR) spectra of Gd3+ and Er3+ in Pr2CuO4 show symmetry properties appropriate to the crystal tetragonal symmetry. The completely resolved Gd3+ spectra allowed us to measure, at T = 2 K, the principal g values g parallel-to = 1.985(8), g perpendicular-to =2.040(8), and the crystal-field parameters [b2(0) = -399(2) X 10(-4) cm-1, b4(0) = -33.1(7) X 10(-4) cm-1, and b4(4) = 205(3) X 10(-4) cm-1]. The large broadening of the ESR lines, observed above T approximately 40 K, is due to a relaxation via the thermally populated crystal-field excited Pr levels. For Er3+ in Pr2CuO4 we observe a single ESR line corresponding to a ground-state doublet with g parallel-to = 17.94(5) and g perpendicular-to less-than-or-equal-to 0.2. The absence of any splittings of the ESR lines below the Neel temperature implies that the magnetostatic dipole field at the rare-earth-ion site due to the antiferromagnetically ordered Cu moments is < 45 Oe.44282682

Magnetic properties of Gd2CuO4 crystals.

Magnetic-susceptibility and magnetization measurements on single crystals of the CuO2-planar compound Gd2CuO4 indicate copper moment ordering near 260 K, producing an internal field at the gadolinium site that induces substantial anisotropy in the magnetic response. Dilute substitutions for gadolinium and copper leave the essential physics unaffected. We suggest that copper ordering also occurs in Eu2CuO4 on the basis of substitutional studies but is not detected in other rare-earth-based compounds in this series. Rare-earth size appears to play an important role. © 1989 The American Physical Society

Crystal-field and exchange interactions of dilute Gd3+ ions in Eu2CuO4.

We have measured the electron-spin-resonance spectrum of Gd3+ ions substituting for Eu ions in Eu2CuO4. The fine structure of the spectrum was partially resolved at room temperature and the individual transitions were completely separated below 100 K. The spectrum is described with a crystal-field effective Hamiltonian of tetragonal symmetry. The values obtained at low temperatures for the corresponding parameters are b20=-486(7)×10-4 cm-1, b40=-32(2)×10-4 cm-1, and |b44|=790(50)×10-4 cm-1. These parameters are only weakly temperature dependent. The measured effective g value is shifted from the free-ion value g=1.992, indicating the existence of antiferromagnetic exchange interactions with the ions of the host. © 1988 The American Physical Society

Observation of an unusual ESR signal in antiferromagnetic Eu 2CuO4

We report the observation of an unusual electron spin resonance (ESR) signal in single crystals of Eu2CuO4. The signal appears to be associated with a resonance mode of the CuO2 planes, similar to the midfield and low-field absorptions we have reported previously [Phys. Rev. B 41, 1934 (1990)]. However, it is only observed when the projection of the applied dc magnetic field in the CuO2 plane is within a few degrees of the 〈110〉 crystallographic direction. Additionally the sample must be field cooled in the CuO2 plane, but with a component of the cooling field perpendicular to the 〈110〉 ESR observation direction. Both the field for resonance and the linewidth exhibit a 1/cos θ dependence, where θ is the angle of the applied dc field between the c axis and the 〈110〉 observation direction. Additional constraints for observation of the resonance are that the microwave rf magnetic field must have a component in the CuO2 plane, but perpendicular to the dc field. The signal disappears above ∼215 K, which we assume is associated with the antiferromagnetic ordering temperature

Magnetic properties of Gd2CuO4 crystals.

Magnetic-susceptibility and magnetization measurements on single crystals of the CuO2-planar compound Gd2CuO4 indicate copper moment ordering near 260 K, producing an internal field at the gadolinium site that induces substantial anisotropy in the magnetic response. Dilute substitutions for gadolinium and copper leave the essential physics unaffected. We suggest that copper ordering also occurs in Eu2CuO4 on the basis of substitutional studies but is not detected in other rare-earth-based compounds in this series. Rare-earth size appears to play an important role. © 1989 The American Physical Society

Observation of an unusual ESR signal in antiferromagnetic Eu 2CuO4

We report the observation of an unusual electron spin resonance (ESR) signal in single crystals of Eu2CuO4. The signal appears to be associated with a resonance mode of the CuO2 planes, similar to the midfield and low-field absorptions we have reported previously [Phys. Rev. B 41, 1934 (1990)]. However, it is only observed when the projection of the applied dc magnetic field in the CuO2 plane is within a few degrees of the 〈110〉 crystallographic direction. Additionally the sample must be field cooled in the CuO2 plane, but with a component of the cooling field perpendicular to the 〈110〉 ESR observation direction. Both the field for resonance and the linewidth exhibit a 1/cos θ dependence, where θ is the angle of the applied dc field between the c axis and the 〈110〉 observation direction. Additional constraints for observation of the resonance are that the microwave rf magnetic field must have a component in the CuO2 plane, but perpendicular to the dc field. The signal disappears above ∼215 K, which we assume is associated with the antiferromagnetic ordering temperature

Observation of complex magnetic behavior in the perovskite rare earth copper oxide systems, R2CuO4

EPR, microwave absorption, and dc magnetization measurements were made on single crystals of the form R2CuO4, which are the host compounds for the newly discovered series of electron cuprate superconductors. These measurements reveal two characteristic transition temperatures associated with a novel complex magnetic behavior, including weak ferromagnetism, two sharp peaks in the low field DC magnetization, an unusual anisotropy in the EPR resonance field for R = Gd, and two additional anisotropic microwave absorption modes. The higher characteristic transition temperature, at ≈270K, is attributed to AF ordering of the Cu moments, and the lower, at ≤20K, to a spontaneous canted spin reorientation. An understanding of this magnetic behavior is important in order to ascertain its relationship to possible mechanisms of high temperature superconductivity. © 1989

Crystal-field effects in the electron-spin resonance of Gd3+ and Er3+ in Pr2CuO4.

The low-temperature (T&lt;300 K) electron-spin-resonance (ESR) spectra of Gd3+ and Er3+ in Pr2CuO4 show symmetry properties appropriate to the crystal tetragonal symmetry. The completely resolved Gd3+ spectra allowed us to measure, at T=2 K, the principal g values g?=1.985(8), g=2.040(8), and the crystal-field parameters [b20=-399(2)×10-4 cm-1, b40=-33.1(7)×10-4 cm-1, and b44=205(3)×10-4 cm-1]. The large broadening of the ESR lines, observed above T40 K, is due to a relaxation via the thermally populated crystal-field excited Pr levels. For Er3+ in Pr2CuO4 we observe a single ESR line corresponding to a ground-state doublet with g?=17.94(5) and g0.2. The absence of any splittings of the ESR lines below the Néel temperature implies that the magnetostatic dipole field at the rare-earth-ion site due to the antiferromagnetically ordered Cu moments is &lt;45 Oe. © 1991 The American Physical Society

Eu2CuO4: An anisotropic Van Vleck paramagnet.

Magnetic susceptibility measurements have shown anisotropic Van Vleck paramagnetism in Eu2CuO4 single crystals. This behavior is associated with the singlet ground state (7F0) of Eu3+ ions, and the measured anisotropy is related to a crystal-field splitting of the excited multiplets (7FJ). From the experimental data at low temperatures (T50 K) a crystal-field parameter A20r2=-93(5) cm-1 and a spin-orbit coupling constant =303(15) cm-1 have been estimated. The temperature dependence of the magnetic susceptibility is predicted in terms of the Boltzmann population of the excited multiplets, and a comparison with experimental data up to 350 K is made. The possibility of a magnetic contribution arising from the Cu ions is discussed in connection with some discrepancies observed between the experimental and calculated magnetic susceptibilities. © 1989 The American Physical Society

Eu2CuO4: An anisotropic Van Vleck paramagnet.

Magnetic susceptibility measurements have shown anisotropic Van Vleck paramagnetism in Eu2CuO4 single crystals. This behavior is associated with the singlet ground state (7F0) of Eu3+ ions, and the measured anisotropy is related to a crystal-field splitting of the excited multiplets (7FJ). From the experimental data at low temperatures (T50 K) a crystal-field parameter A20r2=-93(5) cm-1 and a spin-orbit coupling constant =303(15) cm-1 have been estimated. The temperature dependence of the magnetic susceptibility is predicted in terms of the Boltzmann population of the excited multiplets, and a comparison with experimental data up to 350 K is made. The possibility of a magnetic contribution arising from the Cu ions is discussed in connection with some discrepancies observed between the experimental and calculated magnetic susceptibilities. © 1989 The American Physical Society