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A detailed EPR study of Mn2+ is carried out from melting temperature to 77K. In Co(ClO4)2.6H2O, two new structural phase transitions are detected at T1 approximately 354K and T2 approximately 243K in addition to the previously known transition at T3 approximately 155K. In Ni(ClO4)2.6H2O the recently reported new phase transitions at T1 approximately 361K and T2 approximately 311K are confirmed and a new phase transition at T3 approximately 245K is observed. The phase transition occurring at T3 in both the crystals seems to be purely a structural one, while all the other phase transitions in both crystals involve changes in both structure and configurational disorder of the perchlorate ions. The space group symmetry C2v7 (Pmn21) of the crystal remains unchanged from melting temperature to T3 in Co(ClO4)2.6H2O and from melting temperature to 100K in Ni(ClO4)2.6H2O. The transitions at T1 and T2 in both crystals involve changes in the water-perchlorate sublattice symmetry. The two crystals are isostructural in the phases between the melting temperature and T1, and between T1 and T2.

EPR of Mn2+ doped in ammonium iodide single crystal has been studied at X-band in the temperature range 573–577 K. The observed temperature dependence of line widths and spin Hamiltonian parameter b20 below room temperature is related to the structural transformations in the crystal. The coexistence of high temperature phase (NaCl) and low temperature phase (CsCl) is attributed to the large thermal hysteresis in line widths and b20. The dissociation of ion vacancy pairs occurs near 500 K and is reflected in the reversible change of an anisotropic EPR spectrum in an isotropic sextet near this temperature. The ion vacancy pair models for NaCl and CsCl phases are discussed along with the effects of thermal processing of the samples. Heating the crystals above 500 K leads to expulsion of Mn2+ impurity from the crystal.

The results of the EPR study of VO2+ doped in NH4I and NH4Br single crystals in the temperature range 430–77 K are reported. The observed spectra suggest a liquid‐like behavior of these crystals for VO2+. A single eight line isotropic spectrum was observed in the temperature ranges ∼373 to ∼245 K in NH4I and ∼430 to ∼233 K in NH4Br. No spectrum was observed in the temperature ranges ∼245 to ∼173 K and ∼ 233 to ∼223 K in NH4I and NH4Br crystals, respectively. A spectrum with two sets of eight isotropic lines was observed from ∼173 K for NH4I and ∼223 K for NH4Br to 77 K. The observed mI dependence and temperature variation of linewidths are discussed. The anomalies in temperature dependence of linewidth confirmed the structural phase transitions in the host lattices.

The optical absorption and EPR spectra of Cr3+ in binary sodium borate glasses have been studied as functions of chromium concentration and Na2O/B2O3 ratio in the glass; the ligand field and EPR parameters have been calculated and were found to be independent of Cr3+ concentration in any particular glass. In low-alkali borate glasses (Na2O = ∼ 11 or ∼ 14 mol %) a single symmetrical EPR line was observed with g ¦=g⊥ =1.984±0.001 corresponding to perfect octahedral symmetry of the Cr3+ ion in these glasses. With increasing Na2O content of the glass, the EPR line becomes more asymmetric (characteristic two-peaked pattern); this has been explained as being due to axial elongation of the six co-ordinated Cr3+-complex in these glasses.

Electron paramagnetic resonance (EPR) of Mn2+ doped in CoSO4⋅7H2O single crystals has been studied from 300 to 77 K and at ∼9.3 GHz. Two different types of crystals of CoSO4⋅7H2O have been obtained, which grow in two different temperature ranges about 298 K. The two forms exhibit different types of spectra: one form [to be referred to as CoSH(I)] shows two 30 line Mn2+ spectra with D=459×10−4 cm−1, ‖E‖=134×10−4 cm−1 and the other form [to be referred to as CoSH(II)] shows only a single 30 line spectrum with D=234×10−4 cm−1, ‖E‖=19 ×10−4 cm−1. The observation of resolved Mn2+ spectra at 300 K and its broadening on lowering the temperature in CoSO4⋅7H2O:Mn2+ crystals has been discussed in terms of ’’host spin–lattice relaxation narrowing.’’ The observed shift in the Mn2+ gz value from that in diamagnetic hosts is probably due to the Co2+ ions, which produce a local static magnetic field at the site of Mn2+ ions. From the observed linewidth in the EPR spectrum of Mn2+ in single crystals of CoSO4⋅7H2O the T1 ...

Room-temperature (≈ 300 K) EPR studies of Cu 2+ -doped in NH 4 I single crystals are reported. The Cu 2+ ion is found to substitute for NH 4 + and get associated with a second or fourth neighbour cation vacancy. The spectra for the two distinct types of centres have been analysed and the parameters presented.

The EPR of Mn 2+ in NH 4 Br single crystals has been studied at X-band in the temperature range from 573 K to 77 K. At room temperature, an isotropic spectrum (spectrum-I) comprising a sextet superimposed on a broad line is observed. On heating the crystal up to 400 K the sextet disappears due to explulsion of Mn 2+ impurity from the crystal. On lowering the temperature, the isotropic spectrum-I disappears about at 230 K and a new spectrum (spectrum-II) appears below this temperature. The spectrum-II is highly anistropic and unusual and is believed to be due to very large zero field splitting of Mn 2+ . Spectrum-I is attributed to Mn 2+ ions substituting for NH 4 + with charge compensating NH 4 + vacancies far away from Mn 2+ . The transformation of spectrum-I into spectrum-II is attributed to the structural transformation of NH 4 Br.

The electron paramagnetic resonance of Mn2+ ion doped in single crystals of sodium nitrite (NaNO2) has been studied at 9.5 kmc from room temperature (∼27°C) to 180°C. Only one magnetic complex of Mn2+ has been found. The complex gives different spectra in the ferro- and para-electric phases of the host crystal. The resonance lines of the allowed transitions at room temperature have been fitted to a spin-Hamiltonian of orthorhombic symmetry. The resonance lines show a strong angular dependence in their widths. The differences in line width and the presence of forbidden transitions along the principal axes are attributed to the spread in the crystal field due to the torsional oscillations of the NO-2 groups.

Electron paramagnetic resonance of Mn2+ has been studied in single crystals of magnesium sulfate heptahydrate (MgSO4 · 7 H2O) at 300°K. Mn2+ was found to substitute for Mg2+ and exhibit four inequivalent magnetic complexes corresponding to the tetramolecular unit cell of MgSO4 · 7 H2O. The results are compared with those for Mn2+ in isostructural NiSO4 · 7 H2O. The observed differences in the EPR of Mn2+ in crystals of the two salts are attributed to the magnetic interaction of Ni2+ and Mn2+.

Electron paramagnetic resonance of Mn2+ has been studied in nickel acetate tetrahydrate [Ni(CH3COO)2·4H2O] and nickel sulfate heptahydrate (NiSO4·7H2O) at 300°K. The Mn2+ was found to substitute for Ni2+ in both the systems and exhibit inequivalent magnetic complexes, two for the bimolecular Ni(CH3COO)2·4H2O and four for the tetramolecular NiSO4·7H2O. Besides, the Mn2+ resonance lines exhibited a direct dependence of linewidth on the intensity of Zeeman field and a shift in g value towards the lower side from the free‐spin g value. These features have been explained in terms of the interaction of the Mn2+ ion with Ni2+ host ions.

X‐band EPR of Mn2+,Cu2+, and Co2+ ions doped in ammonium iodide single crystals have been studied at low temperatures. The Mn2+ and Cu2+ spectra show the presence of only one type of complex for each with features similar to those observed at room temperature with no unusual changes. The results on Co2+ ion, reported here for the first time, reveal the presence of three equivalent Co2+ complexes having tetragonal symmetry with their tetragonal axes orthogonal to each other. The charge‐compensation mechanism and possible vacancy complexes are discussed, and the spin‐Hamiltonian parameters reported.

The results of the EPR study of VO2+ doped in NH4I and NH4Br single crystals in the temperature range 430–77 K are reported. The observed spectra suggest a liquid‐like behavior of these crystals for VO2+. A single eight line isotropic spectrum was observed in the temperature ranges ∼373 to ∼245 K in NH4I and ∼430 to ∼233 K in NH4Br. No spectrum was observed in the temperature ranges ∼245 to ∼173 K and ∼ 233 to ∼223 K in NH4I and NH4Br crystals, respectively. A spectrum with two sets of eight isotropic lines was observed from ∼173 K for NH4I and ∼223 K for NH4Br to 77 K. The observed mI dependence and temperature variation of linewidths are discussed. The anomalies in temperature dependence of linewidth confirmed the structural phase transitions in the host lattices.