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.     

Low temperature magnetic structure of erbium iron garnet

The magnetic and crystallographic structure of erbium iron garnet {Er₃}[Fe₂](Fe₃)O₁₂ has been refined simultaneously from powder and single crystal neutron diffraction data. At 5 K the ferrimagnetic structure has a spin direction parallel to [100]. Magnetic moments of iron and erbium and canting angles for the erbium sublattices were derived in space groupI4₁/acd for 5 K<T<65 K. The magnetic moments of the two erbium sites are 6.9 _B and 4.3 _B at 5 K. An indication of further symmetry reduction of the magnetic structure from tetragonal to orthorhombic below 5 K is discussed.     

Phase Transitions of Fel2 in high magnetic field parallel to the spin direction,static field up to 150 kOe,pulsed field up to 250 kOe

Study of parallel and perpendicular susceptibilities shows that ferrous iodide presents at low temperature an antiferromagnetic order, with spins oriented along the anisotropy axis (c axis).Phase transitions of Fel₂ in a magnetic field parallel to c axis are studied by help of magnetization measurements. At low temperature (2.2 K) saturation is reached only for a magnetic field of 140 kOe. Results obtained in high static fields (Bitter and supraconductive coils allowing respectively 140 and 150 kOe) and in pulsed field are presented.At low temperature, two successive first order phase transitions are observed at 46 and 120 kOe. In the intermediate phase, the magnetization presents two minor discontinuities. An original phase diagram is given.The complexity of the Fel₂ behavior, in parallel magnetic field shows that the magnetic structure is not the same as the two sublattices one characteristic of FeCl₂ and FeBr₂. An estimate of the principal exchange coupling parameters and a study by neutron diffraction measurements (to be published) confirm an original magnetic structure.     

Spin reorientation in erbium iron garnet

⁵⁷Fe Mössbauer measurements in the temperature range from 1.5 to 297 K on erbium iron garnet confirm the occurence of a spin reorientation from the [ 100 ] to the [ 111 ] direction. They show that the reorientation takes place gradually between 74 and 95 K. The values and the signs of the quadrupole coupling constants at the octahedral and tetrahedral sites are determined.     

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.     

Optical and magnetic properties of iron garnet films with high defect density

We have used spectroscopic and magneto-optic methods to study the effect of defects on the transmission spectrum, thickness, refractive index, and period of the striated domain structure in thin iron garnet films exposed to fast neutron fluences of 4.5·10¹⁷ and 10¹⁹ cm^–2. We observed both a decrease in transmission and a smearing of the interference maxima. The decrease in the quality of the interference fringes was observed in the visible spectrum for these samples. It was due to increased diffuse scattering of light by nonuniformities whose dimensions were comparable to the wavelength of the scattered light. It was determined that radiation defect clusters had no influence on the film thickness, but they did significantly alter the wavelength dependence of the refractive index and increased the period of domain structure striations.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 45–48, August, 1988.We wish to thank A. G. Shishkov for discussions of the experimental results.     

Low temperature magnetization of graphite in magnetic fields up to 150 kG

The c-axis magnetisation of pyrolytic graphite at 4.2 K has been measured in fields up to 150 kG. Contrary to the predictions of a recent calculation, graphite remains diamagnetic in the ultra-quantum region.     

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.     

Heat capacity and resistivity of Sm0.55Sr0.45MnO3 in magnetic fields of up to 26 kOe

Heat capacity and resistivity of Sm_0.55Sr_0.45MnO₃ ceramics were measured over the temperature range 80–300 K in magnetic fields of up to 26 kOe. These quantities show anomalies caused by the magnetic and structural phase transitions. The critical temperature T _c and the heat capacity jump ΔC _p (T _c ) at T _c increase with increasing applied magnetic field H, while the resistivity decreases. The temperature dependences of the measured quantities show hysteresis, which is strongly suppressed in a field of 26 kOe but is sensitive nor to the temperature range neither to the rate of temperature change. The hysteresis of the heat capacity and resistivity of Sm_0.55Sr_0.45MnO₃ is caused by a change in T _c with changing lattice parameters upon second-order structural phase transition. The results are discussed in terms of the electron phase separation model.     

Magnetic properties of NiO nano particles: Contributions of the antiferromagnetic and ferromagnetic subsystems in different magnetic field ranges up to 250 kOe

The magnetic properties of antiferromagnetic NiO nanoparticles prepared by thermal decomposition of nickel hydroxocarbonate are investigated. According to the data of magnetization measurements in fields of up to 250 kOe, the magnetic moment linearly grows in strong fields, which is caused by the contribution of the antiferromagnetically ordered nanoparticle core, and the antiferromagnetic susceptibility corresponds to that of bulk polycrystalline NiO. This allowed the antiferromagnetic and ferromagnetic contributions to the total magnetic response of a sample to be quantitatively determined. The latter occurs due to the incomplete spin compensation in an antiferromagnetic nanoparticle caused by defects on its surface. It is demonstrated that to correctly determine the superparamagnetic blocking temperature, it is necessary to take into account the antiferromagnetic susceptibility of the particle core.     

Anisotropic behaviour of the faraday rotation in erbium iron garnet

Faraday rotation (FR) measurements performed on single crystals Erbium Iron Garnet (ErIG) at 1.15 μm wavelength are presented in a magnetic field up to 20 kOe applied along the three main crystallographic directions. Spontaneous FR and FR susceptibilities are found to be anisotropic. The results are discussed in terms of electric and magnetic dipole transitions and compared to the magnetic anisotropy. A strong anisotropy of the first order electric dipole coefficient of the Er³⁺ ion is evidenced at low temperature (below 30 K).     

Magnetic and magnetodielectric properties of Bi-substituted yttrium iron garnet ceramics

Effects of Bi substitution upon magnetic and magnetodielectric properties of Y₃Fe₅O₁₂ ceramics were investigated. It was found that the saturation magnetization decreases and the magnetic ordering temperature increases as the amount of Bi increases. The contribution of intrinsic and extrinsic effects to magnetodielectric effects decreases with increase of Bi, which results in the decrease of magnetodielectric coefficient of Y_3−xBi_xFe₅O₁₂ ceramics.     

Local magnetic fields on19F in iron studied up to Tc

The temperature dependence of two local fields for fluorine in iron was studied from 600 K up to T_c by the time differential perturbed angular distribution method (TDPAD). A third local field was found at 1000 K.     

Optical absorption spectra of erbium iron garnet (ErIG)

Absorption spectra of the transition⁴ I _15/2→⁴ I _9/2 have been measured in erbium iron garnet (ErIG). From these spectra the exchange tensors for four Kramers dubletts can be obtained. A tentative analysis of these data in terms of a phenomenological exchange Hamiltonian will be presented.     

Magnetic anisotropy of europium in iron garnet

Magnetization measurements have been made of single crystals of europium iron garnet (EuIG), Ga-doped EuIG and Al-doped EuIG. Cubic anisotropy constants K₁ and K₂ have been evaluated from the magnetization curves. Temperature dependence and concentration dependence of the anisotropy are compared with the theory by Foglio and van Vleck.     

On the movement of iron microcrystals in high magnetic fields

The temperature dependence of the Mößbauer line intensities for iron particles coated with iron oxide is found to be the same for both the iron and the iron oxide subspectra. For the first time, this result gives direct experimental evidence that the dramatic decrease of the line intensities with raising temperaures /1,2/ is not due to changes in the phonon spectrum, but to motions of the particles instead. These motions are not influenced by external magnetic fields up to 10 T. The result is discussed in terms of different possibilities for the movement of the particles. Further more it is shown, that the geometric arrangement is different for the particles contributing to the Mößbauer effect at high, from those contributing at low temperatures.     

Effect of reversible adsorption on the magnetic properties of iron garnet films

The reversible change in the domain structure and the magnetic domain width in bismuth-containing iron garnet films with an easy magnetization axis oriented normal to their surface during adsorption caused by hydrogen bonds is studied by a magnetooptical method. The dependence of the domain width on the vapor pressure of methyl alcohol or water in a cell with a sample is determined, and the time dependence of the domain width induced by the adsorption-desorption processes occurring between methyl alcohol molecules or water molecules on the film surface is studied. A model is proposed to explain the detected effects.     

Structure dependence of magnetic properties in yttrium iron garnet by metal-organic decomposition method

The yttrium iron garnet(YIG) samples are prepared at different temperatures from 900?C to 1300?C by the metalorganic decomposition(MOD) method. The chemical composition and crystal structure of the samples are studied by scanning electron microscope(SEM), XRD, and M ¨ossbauer spectrometer. It is shown that the ratio of ferric ions on two types of sites, the octahedral and the tetrahedral, is increased with the sintering temperature. At 1300?C, the pure garnet phase has been obtained, in which the ferric ions ratio is 2:3 leading to the minimum magnetic coercivity and maximum saturation magnetization. These results provide a route to synthesize pure YIG materials as the basic materials used in various spintronics applications.