Magnetic properties of erbium iron garnet in high magnetic fields up to 150kOe

The magnetic properties of single crystals of erbium iron garnet (ErIG) were studied in applied fields up to 150kOe between 1.4 and 300K. At low temperature, the macroscopic easy direction of the bulk magnetization is [100]; below the compensation temperature (80±2K), the magnetization presents non-linear field evolution. On the assumption of an isolated ground doublet, the anisotropy constantsK _i (i=1,2) of ErIG are given byK _i (Er)+K _i (YIG); theK _i are calculated as a function of theG andg tensor components. It is worthwhile noting that theK _i (Er) are strongly temperature dependent; so at low temperature the anisotropy of the garnet is determined by the rare earth ions, while in the 50 K regionK ₁(Er) becomes comparable toK ₁(YIG) with the opposite sign which results in a very weak anisotropy of the garnet. Above 50 K,K ₁(YIG) is predominant and the Fe³⁺ ions determine the garnet anisotropy.     

Room temperature magnetization measurements of some substituted rare earth iron garnets

The saturation magnetization (M _s) and the initial magnetic susceptibility (χ _in) of substituted yttrium iron garnet (YIG) Ho_3−x Y _x Fe₅O₁₂ where (x=0,0.3,1.5), pure terbium iron garnet Tb₃Fe₅O₁₂, and substituted aluminum iron garnet (AlIG) Ho₃Fe_5−x Al _x O₁₂ where (x=0.05,0.7) at room temperature are reported. It has been observed that M _s and χ _in decrease in a linear manner as Ho³⁺ replaces Y³⁺ in yttrium iron garnet. For substituted (AlIG), a drastic decrease in both M _s and χ _in as Al³⁺ ions replace Fe³⁺ ions. The rate of decrease of M _s and χ _in with the increase of Al³⁺ for substituted (AlIG) is greater than that for substituted (YIG). That is attributed to the decrease in the superexchange interaction (self and mutual iron interactions) with Al substitution.     

Study on dielectric and magnetic properties of Ho3Fe5O12 ceramics

Ho₃Fe₅O₁₂ ceramics with garnet structure were prepared by the solid-state reaction method. The results revealed the existence of Fe²⁺ ions have intensive influence on dielectric and magnetic properties of Ho₃Fe₅O₁₂ ceramics, which could be further confirmed by oxygen treatment. With a magnetic field lower than 10 kOe, the ME coefficient reaches 33 ps m⁻¹ at room temperature. And the ME coupling was further verified by dielectric anomaly near Néel temperature.     

Linear magnetic birefringence in the quadratic-layer antiferromagnet K2MnF4

The linear optical birefringence of the quasi-Heisenberg antiferromagnet K₂MnF₄ has been determined between 5 and 300 K. A large magnetic contribution (LMB) is found at temperatures below 200 K. According to the earlier results with the iron-group difluorides the LMB can be related to the magnetic internal energy. Below 30 K the LMB of K₂MnF₄ obeys a T³-law. The temperature derivative of the LMB follows a course expected for the magnetic heat capacity of pronounced two-dimensional systems: a broad, rounded maximum above the three -dimensional transition point. At T_N a kink occurs in the LMB.     

Indirect measurements of the Jahn-Teller quenched spin-orbit splitting in the 5T2g-state of KMgF3:Fe2+

The energy separation of the first excited spin-orbit States Γ_3g, Γ_4g from the Γ_5g ground state, in the orbital ⁵T_2g triplet state of Fe²⁺ in KMgF₃, has been estimated from temperature dependence measurements on the 7860 cm^-1 zero-phonon-line (ZPL) transition from Γ_5g to the orbital ⁵E_g doublet state. Using a simplified crystal field energy level model, we find the Γ_5g Γ_3g, Γ_4g separation to be ～30 cm^-1, indicating that the vibronic Jahn-Teller coupling is considerably stronger in KMgF₃:Fe²⁺ than in MgO:Fe²⁺. Far infrared absorption data on KMgF₃:Fe²⁺ in magnetic fields up to 6T, are found to be consistent with this interpretation.     

Faraday rotation in single crystal erbium iron garnet

Measurements of the Faraday rotation of ErIG, Er₃Fe₅O₁₂, have been performed in the 4.2–300 K temperature range in magnetic field up to 20 kOe applied along the [111] direction and at 1.15 μm wavelength. The results are analysed under the assumption that the contribution of the Fe³⁺ ions to the total Faraday rotation is the same as that of YIG, Y₃Fe₅O₁₂. The temperature and field dependences of the contribution of the Er³⁺ ions are deduced. Both magnetic and electric dipole contributions of the Er³⁺ ions are calculated; the electric dipole coefficient C_e is found to present a linear temperature dependence between 30–300 K. The temperature dependence of the Faraday rotation susceptibility differs strongly from that of the magnetic susceptibility.     

EPR and magnetic susceptibility studies of iron ions in ZnO-Fe2O3-SiO2-CaO-P2O5-Na2O glasses

Room temperature electron paramagnetic resonance (EPR) spectra and temperature dependent magnetic susceptibility data have been obtained on bulk x(ZnO,Fe₂O₃)(65−x)SiO₂20(CaO, P₂O₅)15Na₂O (6≤x≤21 mole%) glasses prepared by melt quenching method. EPR spectra of the glasses revealed absorptions centered at g≈2.1 and 4.3. The variations of the intensity and line width of these absorption lines with composition have been interpreted in terms of the variation in the concentration of the Fe²⁺ and Fe³⁺ ions in the glass and the interaction between the iron ions. EPR and magnetic susceptibility data of the glasses reveal that both Fe²⁺ and Fe³⁺ ions are present in the glasses, with their relative concentration being dependent on the glass composition. The studies reveal superexchange type interactions in these glasses, which are strongly dependent on their iron content.     

Magnetic properties of erbium iron garnet in high magnetic fields up to 150kOe

The magnetic properties of single crystals of erbium iron garnet (ErIG) were studied in applied fields up to 150kOe between 1.4 and 300K. At low temperature, the macroscopic easy direction of the bulk magnetization is [100]; below the compensation temperature (80±2K), the magnetization presents non-linear field evolution. On the assumption of an isolated ground doublet, the anisotropy constantsK _i (i=1,2) of ErIG are given byK _i (Er)+K _i (YIG); theK _i are calculated as a function of theG andg tensor components. It is worthwhile noting that theK _i (Er) are strongly temperature dependent; so at low temperature the anisotropy of the garnet is determined by the rare earth ions, while in the 50 K regionK ₁(Er) becomes comparable toK ₁(YIG) with the opposite sign which results in a very weak anisotropy of the garnet. Above 50 K,K ₁(YIG) is predominant and the Fe³⁺ ions determine the garnet anisotropy.     

Magnetic linear birefringence in Yb<Subscript>3</Subscript>Ga<Subscript>5</Subscript>O<Subscript>12</Subscript> gallate garnet

The magnetic linear birefringence and the magnetic susceptibility of Yb₃Ga₅O₁₂ gallate garnet was investigated experimentally in the temperature range 78–295 K. It was shown that, in this temperature range, the magnetic linear birefringence of the garnet studied depends linearly on inverse temperature 1/T. The magnitude of this effect is determined only by the part of the crystal magnetization that is due to the difference in the thermal population of the ground state of the Yb³⁺ ion rather than the total magnetization. The results obtained are interpreted within the microscopic theory. According to this theory, the magnetic linear birefringence is determined by the quadrupole moment of the magnetoactive ion, which is induced by an external magnetic field.     

Wavelength and temperature characteristics of BiYbIG film/YIG crystal composite structure for magneto-optical applications

We report the wavelength and temperature characteristics of novel Bi-substituted rare-earth iron garnet films grown on a YIG substrate by a modified liquid phase epitaxy (LPE) technique. The Faraday-rotation spectrum was measured by the magneto-optically modulated dual-frequency technique with the wavelength varied from 800 nm to 1700 nm. The resultant Bi_0.37Yb_2.63Fe₅O₁₂ (BiYbIG) LPE film/YIG crystal structure showed an increased Faraday-rotation coefficient due to Bi³⁺-ion doping on the dodecahedral sites of the iron garnet without increasing absorption loss; therefore, a good magneto-optical figure of merit, defined by the ratio of Faraday rotation and optical absorption loss, has been achieved (21.5 deg/dB and 30.2 deg/dB at 1300-nm and 1550-nm wavelengths, respectively, at room temperature). In addition, since the Yb³⁺ and Y³⁺ ions provide opposite contributions to the wavelength and temperature characteristics of the Faraday rotation, the resultant BiYbIG LPE film/YIG crystal structure showed a flat Faraday-rotation curve versus wavelength and temperature. The Faraday-rotation wavelength coefficient was reduced to 0.06 %/nm at 1550-nm wavelength. The Faraday-rotation temperature derivative was reduced to 0.006 deg/°C at 1300-nm wavelength and 0.007 deg/°C at 1550-nm wavelength, respectively. PACS 78.20.Ls; 81.15.Lm; 75.50.Gg     

Submillimetre EPR spectrometer

A wide-band submillimetre EPR spectrometer is described. A set of tunable backward wave oscillators and quasioptic lens system enables one to operate in the frequency region 79–535 GHz. The sample is placed in a magnetic field of up to 1 T at 4.2 K. The spectrometer is intended for the investigation of EPR spectra of rare-earth ions in solids with zero field splittings of the ground states near the frequency of operation and/or electron systems with ag-factor exceeding 5. The spectrometer’s capabilities are demonstrated with an investigation of the EPR spectra of Dy²⁺ and Dy³⁺ ions in CaF₂. As a result the exact value of the zero field splitting between the ground Γ₈ quartet and the first exited Γ₇ doublet of Dy³⁺ in CaF₂, Δ=257±0.5 GHz, has been measured directly.     

Discussion of the linear magnetic birefringence of NiF2 in terms of the Ewald-Born theory

By means of the Ewald-Born theory it is investigated whether magnetostriction can be regarded as the sole reason for the linear magnetic birefringence (LMB). Using the temperature dependent structural data of NiF₂ it is found that the variations of the unit-cell alone cannot explain the LMB. A change of the fluorine parameter u by 0.0004, however, is sufficient to account for the whole LMB effect.     

Mössbauer effect in YbBe13: Mixed valence and magnetic ordering

Mössbauer effect investigations on the cubic intermetallic compound YbBe₁₃ in the temperature range between 0.065 K and 81 K are reported. Above the magnetic ordering temperatureT _Neel=1.27 K the results cannot be explained by a Γ₇ groundstate of Yb³⁺. There is evidence for the Yb ion being in a mixed valent state and the degree of hybridisasation being dependent on the magnetic ordering. Below the magnetic ordering temperature a Γ₇ groundstate of a 3⁺ Yb ion is found.     

Magnetic properties on holmium iron garnet in high magnetic field. Optical absorption spectra in the infra-red region

On single crystals of holmium iron garnet (HoIG), magnetic properties have been studied in magnetic field up to 150kOe applied parallel to the main crystallographic directions in the 4.2–300K temperature range. Above 130 K, the magnetization is isotropic and linear magnetic field dependent as previously found in polycrystals and predicted by Néel's ferrimagnetic theory. Nevertheless the paramagnetic Curie temperature is much higher than the polycrystal value. Below 130K, due to the onset of the umbrella structure, the ferrite magnetization presents a non linear field variation with [111] as easy direction. The field evolutions of the anisotropy constants (K ₁ andK ₂) were calculated. Optical absorption measurements of both 5₈5I ₆ and 5I ₈5I ₇ transitions are reported and compared to the results of the literature in terms of inequivalent magnetic sites.     

Valence states of iron ions in nanostructured yttrium iron garnet Y3Fe5O12 studied by means of soft X-ray absorption spectroscopy

Nanostructured samples of yttrium iron garnet Y₃Fe₅O₁₂ obtained by plastic deformation method (high-pressure torsion) were studied with help of soft X-ray absorption spectroscopy using Fe 2p and O 1s spectra. Experimental spectra were compared with crystal field multiplet calculations for Fe ions. Some amount of Fe²⁺ ions in nanostructured Y₃Fe₅O₁₂ was found. The concentration of Fe²⁺ ions was found to be increased with the increase of the degree of plastic deformation.     

Observation of paramagnetic relaxation in the NpCu4Al8 intermetallic compound

²³⁷Np Mössbauer spectroscopy between 77 and 4.2 K was carried out in connection with neutron diffraction studies between 300 and 2 K on the tetragonal intermetallic NpCu₄Al₈. The Mössbauer spectra give an isomer shift of + 14.3 mm/s vs. NpAl₂ indicating the non-Kramers Np³⁺(⁵I₄)-ion to be present. Below 45 K the onset of magnetic hyperfine splitting is observed. It develops into a fully resolved Zeeman pattern at 4.2 K with B_eff≈330 T. Neutron diffraction finds no evidence for magnetic order over the whole temperature range scanned. All these results can consistently be explained by paramagnetic relaxation phenomena involving a low lying Γ^t₅ doublet closely followed by a Γ^t₄ singlet as the tetragonal crystalline field states of the Np³⁺ ion.     

Special features of linear magnetic birefringence in an α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>:Ga single crystal

Experimental investigations of the field dependence of the linear magnetic birefringence (LMB) in an α-Fe₂O₃:Ga single crystal are presented. It is established that during crystal magnetization in the basal plane near directions perpendicular to the С₂ axes in the region of magnetic field saturation, the LMB changes nonmonotonically. The observed special feature of the field LMB dependence is due to the reorganization of the magnetic α-Fe₂O₃:Ga structure during magnetization.     

Mössbauer effect study of monoclinic Fe2TiO5

The spectra of ⁵⁷Fe in monoclinic Fe₂TiO₅ were interpreted as hyperfine patterns belonging to two nonidentical iron sites. They confirm that Fe³⁺ ions are distributed over 4a and 8f sites. The spectra of mosaic-like crystals indicate that all iron spins lie in the (100) plane. The temperature dependences of hf parameters gave a magnetic ordering temperature 350 K, average saturation effective field 505 kG and Debye temperature 430 K. Above 1500 K, monoclinic Fe₂TiO₅ transformed into the stable pseudobrookite form.     

Role of Er<Superscript>3+</Superscript> ion in the formation of the ErFeO<Subscript>3</Subscript> magnetic properties in the region of spin-reorientation phase transition

The 90° reorientation of Er³⁺ spins in ErFeO₃ have been directly observed using optical spectroscopy. The peculiarities of the absorption spectrum of ErFeO₃ in the region of the ⁴ I _15/2 → ⁴ F _9/2 transition of the Er³⁺ ion in the temperature range of ac-spin reorientation have been studied. It is shown that the spin reorientation phase transition (SRPT) is accompanied by splitting of the ground and excited states into Kramers doublets in the iron exchange field. This fact is a direct evidence of purely magnetic origin of SRPT. The experimental results were used to analyze the magnetic properties of ErFeO₃. This analysis showed that the order of magnitude of the magnetic moment, its variation in the SRPT region, and the existence of T _comp can be interpreted in terms of the single-ion model, taking into account the influence of the crystal field and the molecular field produced by the iron subsystem ions.     

Specific features of local structural,valence, and magnetic states of iron ions in the perovskite Bi0.5Ca0.5FeO3

The perovskite Bi_0.5Ca_0.5FeO₃ has been investigated using the Mössbauer effect at temperatures of 295 and 675 K. The measured temperature of the magnetic phase transition (Néel temperature) is T _N = 640 ± 10 K. Above the Néel temperature, there are two nonequivalent structural states of iron ions. In the perovskite Bi_0.5Ca_0.5FeO₃ at room temperature, there are seven most probable nonequivalent magnetic states of iron ions with significantly different values of the hyperfine interaction parameters. Four iron states correspond to Fe³⁺ ions in the octahedral oxygen environment, and three iron states correspond to Fe³⁺ ions in the tetrahedral oxygen environment.