[en] Magnetic resonance techniques at frequencies of 9.4, 34, 110, and 219 GHz were used to investigate the magnetism of the recently discovered ferromagnetic superconducting system RuSr₂RECu₂O₈ (RE=Eu, Gd). One absorption is observed in both compounds below the magnetic ordering temperature, T_M∼135 K, and can be ascribed to the ferromagnetic resonance of the ordered Ru ions. The resonance field of this absorption is frequency dependent and is well described assuming an in-plane ferromagnetic component with strong out-of-plane (H_z) and weak in-plane (H_x) anisotropy fields. We have derived almost the same anisotropy fields for both compounds at 70 K (< H_z>∼250 kOe and < H_x>∼165 Oe). Another absorption is observed only in the Gd compound and arises from the paramagnetic resonance of the Gd³⁺ ions. Below T_M the Gd³⁺ signal shifts from g=2 evidencing the appearance of a homogeneous internal field, H_i,Gd, that is frequency (and hence field) dependent. This variation is probably due to the nonsaturated nature of the Ru lattice. Below 10 K there is an additional shift of the Gd³⁺ line arising from the Gd dipole-dipole interaction. [copyright] 2001 American Institute of Physics

[en] The magnetization was measured in a single crystal sample of the orthorhombic ferroelectric paramagnetic β'-Tb₂(MoO₄)₃ along the [0 0 1], [0 1 0] and [1 0 0] axes in the magnetic field up to 19 T at 4.2 K< T<300 K. An expression for the field and temperature dependence of the magnetization M(H,T) along the main directions was derived using the theory of the magnetism of singlets. Three lowest singlets of the spectrum of Tb³⁺ ion in β'-Tb₂(MoO₄)₃ were taken into account. The existence of two types of sites for Tb³⁺ ions in β'-Tb₂(MoO₄)₃ was taken into account. Magnetization curves were calculated by fitting this expression to the experimental curves. The results of the calculations agree with the experiment satisfactorily at low temperatures. As the results of fitting the saturation magnetic moments of Tb³⁺ ions at nonequivalent sites were found for three main directions. Their relative values reflect the symmetry of the nearest surrounding of Tb³⁺ ions

[en] We report on the application of ¹⁴N electron nuclear double resonance (ENDOR) at 8.5 T and 239 GHz (λ=1.2 mm) in a γ-irradiated betaine arsenate single crystal. A laser was used as a far-infrared radiation source in a transmission-type electron paramagnetic resonance (EPR) setup without a cavity. The four expected nitrogen ENDOR lines were observed, but due to insufficient saturation of the EPR transitions the signal/noise ratio was not larger than 10 and the signals vanished at temperatures above 20 K. copyright 1995 American Institute of Physics

No abstract available

[en] A nitrogen-related pair defect is studied as a function of doping density in 4H and 6H SiC. Electron paramagnetic resonance measurements verify that one nucleus in the pair is nitrogen, but the second part of the pair remains uncertain. The pair concentration varies monotonically with nitrogen concentration in samples with doping density 10¹⁸-10¹⁶ cm^-3 and the boron concentration is an order of magnitude less than that of nitrogen. The pair center is not observed in the dark or under ultraviolet illumination when the nitrogen and boron concentrations are similar. We conclude that the pair is generated in all nitrogen-doped samples, but like the isolated nitrogen impurity, may be compensated by boron

[en] We report a magnetization and electron spin resonance (ESR) study of the clinoatacamite Cu₂(OH)₃Cl, which is known to have a S = 1/2 distorted pyrochlore lattice. The static magnetic susceptibility shows a strong increase at temperatures below T_N2 = 6.4 K without any appreciable anomalies at T_N1 = 18.1 K. The magnetization vs. field curve exhibits the presence of a weak ferromagnetic moment of 0.1 μ_B/Cu at T = 2 K, possibly due to an antisymmetric Dzyaloshinsky-Moriya (DM) interaction and/or weak ferromagnetic interplane interactions. From the ESR linewidth, we estimate the magnitude of the DM interaction as 10% of the leading isotropic exchange interaction, J ∼ 170 K. The temperature dependence of the linewidth is characterized by three distinct temperature regions: (i) a high-temperature exchange narrowing region at temperatures above 170 K, (ii) a two-dimensional short-range ordered region at temperatures between 170 K and 36 K, and (iii) a low-temperature region at temperatures below 36 K where an antiferromagnetic-like resonance mode develops. The evolution of the ESR linewidth is comparable to that of the S = 1/2 kagome lattice in Cu₃Zn(OH)₆Cl₂ [Zorko et al., Phys. Rev. Lett. 101, 02640 (2008)]. This suggests that the magnetic properties of Cu₂(OH)₃Cl may be described in terms of a stack of kagome lattices.

[en] We report a temperature and frequency dependent electron spin resonance (ESR) study of the kagome spin-1/2 compound ZnCu₃(OH)₆Cl₂. Our results demonstrate that two spin species are simultaneously detected; copper spins on the intra-plane Cu²⁺ kagome sites and those on the inter-plane Zn²⁺ sites, the latter resulting from the Cu²⁺/Zn²⁺ antisite disorder. We examine all the possible magnetic anisotropy terms, which could lead to the observed extremely broad ESR lines in this system. We argue that the line broadening is due to Dzyaloshinsky-Moriya interaction.

[en] We report electron spin resonance (ESR), Raman scattering, and interband absorption measurements of the multiferroic FeTe₂O₅Br with two successive magnetic transitions at T_N1 = 11.0 K and T_N2 = 10.5 K. ESR measurements show all characteristics of a low-dimensional frustrated magnet: (i) the appearance of an antiferromagnetic resonance (AFMR) mode at 40 K, a much higher temperature than T_N1, and (ii) a weaker temperature dependence of the AFMR linewidth than in classical magnets, ΔH_pp(T) ∝ Tⁿ with n = 2.2–2.3. Raman spectra at ambient pressure show a large variation of phonon intensities with temperature while there are no appreciable changes in phonon numbers and frequencies. This demonstrates the significant role of the polarizable Te⁴⁺ lone pairs in inducing multiferroicity. Under pressure at P = 2.12–3.04 GPa Raman spectra undergo drastic changes and absorption spectra exhibit an abrupt drop of a band gap. This evidences a pressure-induced structural transition related to changes of the electronic states at high pressures. (paper)

[en] We report pulse-field magnetization, ac susceptibility, and 100 GHz electron spin resonance (ESR) measurements on the S = 5/2 two-dimensional triangular compound Ba₃NbFe₃Si₂O₁₄ with the Néel temperature T_N = 26 K . The magnetization curve shows an almost linear increase up to 60 T with no indication of a one-third magnetization plateau. An unusually large frequency dependence of the ac susceptibility in the temperature range of T = 20-100 K reveals a spin-glass behavior or superparamagnetism, signaling the presence of frustration-related slow magnetic fluctuations. The temperature dependence of the ESR linewidth exhibits two distinct critical regimes; (i) ΔH_pp(T) ∝ (T-T_N)^-p with the exponent p = 0.2(1)-0.2(3) for temperatures above 27 K, and (ii) ΔH_pp(T) ∝ (T-T*)^-p with T* = 12 K and p = 0.8(1)-0.8(4) for temperatures between 12 and 27 K. This is interpreted as indicating a dimensional crossover of magnetic interactions and the persistence of short-range correlations with a helically ordered state. (paper)

[en] Temperature variations (300-4K) of the electron magnetic resonance (EMR) spectra of ferrihydrite (FeOOH.nH₂O) nanoparticles of size ∼5nm are reported at the frequencies of ν=190.62 and 285.93GHz. The EMR line at 300K, occurring near g∼2, broadens and shifts to lower fields with decreasing T for T>Ts=30K. For TTs, the trend reverses in that the line narrows and shifts to higher fields. In magnetic studies, the coercivity H_c is maximum at Ts (approaching zero at the blocking temperature TB∼65K) with the appearance of exchange bias H_E for TTs. The magnetic viscosity is also maximum near Ts, approaching zero above TB. These observations lead to the suggestion that Ts represents a phase transition to a new magnetically ordered state, with spin-glass-like ordering of the uncompensated Fe³⁺ spins