The primary goal of this review is to present a clear chemical perspective of borates in order to stimulate and facilitate the discovery of new borate-based optical materials. These materials, whic...

Borates: A Rich Source for Optical Materials.

Second-harmonic generation (SHG) in magnetically ordered crystals is reviewed. The symmetry of such crystals is determined by the arrangement of both the charges and the spins, so their contributions to the crystallographic and the magnetic structures, respectively, must be distinguished. Magnetic SHG is introduced as a probe for magnetic structures and sublattice interactions. The specific degrees of optical experiments - including spectral, spatial, and temporal resolution - lead to the observation of novel physical effects that cannot be revealed by other techniques of probing magnetism. These include local or hidden phase transitions, interacting magnetized and polarized sublattices and domain walls, and magnetic interfaces. SHG in various centrosymmetric and noncentrosymmetric crystal classes of antiferromagnetic oxides such as Cr2O3, hexagonal RMnO3(R=Sc,Y,In,Ho-Lu), magnetic garnet films, CuB2O4, CoO, and NiO, is discussed.

/pdf/second-harmonic-generation-as-a-tool-for-studying-electronic-2jobylwfik.pdf

Second-harmonic generation as a tool for studying electronic and magnetic structures of crystals: review

The metal sulfides exhibit a great diversity of electrical and magnetic properties with both scientific interest and practical applications. These properties apply major constraints on models of the electronic structure (or chemical bonding) in sulfides (Vaughan and Rosso 2006, this volume). The pure and doped synthetic equivalents of certain sulfide minerals have actual or potential applications in the electronics industries (optical devices, photovoltaics, photodiodes and magnetic recording devices). Sulfides are also components of many thin film devices and have been extensively investigated as part of the nanotechnology revolution. Certain electrical and magnetic properties of sulfide minerals mean they contribute to geomagnetism and paleo-magnetism, and provide the geophysical prospector with exploration tools for metalliferous ore deposits. To the mineral technologist, these same properties provide methods for the separation of the metal-bearing sulfides from associated waste minerals after mining and milling and before extraction of the metal by pyrometallurgical or hydrometallurgical treatment.

In this chapter, the theory and measurement of electrical and magnetic properties are outlined along with spectroscopic and diffraction studies that can provide insights into magnetic behavior are discussed. A brief review of electrical and magnetic studies of major sulfide minerals includes some examples of the applications of sulfide electrical and magnetic properties, including special consideration of the properties of sulfide nanoparticles. Most of the available data presented are for pure synthetic binary and ternary sulfides, as very small concentrations of impurities can dramatically affect electrical properties leading to problems of interpreting data from natural samples. Although data for several of the commonly found sulfides are discussed in this chapter, no attempt is made at a comprehensive coverage.

The section below on theory and measurement of electrical and magnetic properties draws on the account given in Vaughan and Craig (1978) to which readers are referred for further details. It …

Electrical and magnetic properties of sulfides

The magnetic, electric, magnetoelectric, and magnetoelastic properties of rare-earth ferroborates RFe3(BO3)4 (R=Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er) as well as yttrium ferroborate YFe3(BO3)4 have been studied comprehensively. A strong dependence not only of the magnetic but also magnetoelectric properties on the type of rare-earth ion, specifically, on its anisotropy, which determines the magnetic structure and the large contribution to the electric polarization, has been found. This is manifested in the strong temperature dependence of the polarization below the Neel point TN and its specific field dependence, which is determined by the competition between the external and exchange f-d fields. A close correlation has been found between the magnetoelastic properties of ferroborates and the magnetoelastic and magnetic anomalies at magnetic-field induced phase transitions. It is found that in easy-plane ferroborates, together with magnetic-field induced electric polarization spontaneous polarization also ari...

Magnetoelectric and magnetoelastic properties of rare-earth ferroborates

The bismuth borates Bi2ZnB2O7 and CaBiGaB2O7 have been synthesized by solid-state reactions at temperatures in the 650−825 °C range at 1 atm pressure. These compounds are the only synthetic diborate members of the melilite family, A2XZ2O7, in which layers of A cations alternate with XZ2O7 tetrahedral layers. Except for CdBiGaB2O7, the synthesis of other substituted bismuth borate melilites has been unsuccessful. The crystal structures of Bi2ZnB2O7 and CaBiGaB2O7 have been determined by powder X-ray diffraction and refined by the Rietveld method using powder neutron diffraction data. CaBiGaB2O7 adopts the regular tetragonal melilite structure (P421m space group, Z = 2) containing B2O7 tetrahedral dimers. The refinement of split eight-coordinated sites for the Ca2+ and Bi3+ interlayer cations suggests the presence of additional disorder. Bi2ZnB2O7 adopts a unique orthorhombic melilite superstructure (Pba2 space group, Z = 4) containing both tetrahedral B2O7 and triangular B2O5 dimers. The Bi3+ cations occu...

Melilite-type borates Bi2ZnB2O7 and CaBiGaB2O7

Magnetization, susceptibility and neutron scattering measurements were performed on the terbium iron borate TbFe3(BO3)4. Structural and magnetic phase transitions were obtained as a function of external magnetic field and temperature. A metamagnetic transition of the terbium spins and a spin-flop transition of the iron sublattice are obtained at an external magnetic field 35?kOe<Ht<60?kOe. The values of the effective exchange HE and the anisotropy HA fields are evaluated. Temperature dependent neutron diffraction studies reveal the magnetic structure of TbFe3(BO3)4 and the thermal evolution of the two magnetic sublattices. An antiferromagnetic coupling along the helicoidal chains of Fe atoms sets in at 40?K with a propagation vector . The magnetic ordering of the Tb sublattice sets in at the same temperature and leads to an anti-parallel alignment of the Fe and Tb moments within the a?b-planes with ?Fe = 4.4??B and ?Tb = 8.6??B at 2?K.

https://iopscience.iop.org/article/10.1088/0953-8984/19/19/196227/pdf

Magnetic structure, magnetic interactions and metamagnetism in terbium iron borate TbFe3(BO3)4: a?neutron diffraction and magnetization study

Neutron diffraction, susceptibility and magnetization measurements (for R = Er only) were performed on iron borates RFe(3)(BO(3))(4) (R = Pr, Er) to investigate details of the crystallographic structure, the low temperature magnetic structures and transitions and to study the role of the rare earth anisotropy. PrFe(3)(BO(3))(4), which crystallizes in the spacegroup R32, becomes antiferromagnetic at T(N) = 32 K, with τ = [0 0 3/2], while ErFe(3)(BO(3))(4), which keeps the P3(1)21 symmetry over the whole studied temperature range 1.5 K < T < 520 K, becomes antiferromagnetic below T(N) = 40 K, with τ = [0 0 1/2]. Both magnetic propagation vectors lead to a doubling of the crystallographic unit cell in the c-direction. Due to the strong polarization of the Fe-sublattice, the magnetic ordering of the rare earth sublattices appears simultaneously at T(N). The moment directions are determined by the rare earth anisotropy: easy-axis along c for PrFe(3)(BO(3))(4) and easy-plane a-b for ErFe(3)(BO(3))(4). There are no spin reorientations present in either of the two compounds but there is the appearance below 10 K of a minority phase in the Er-compound adopting a 120° arrangement of the Er-moments.

http://iopscience.iop.org/article/10.1088/0953-8984/20/36/365209/pdf

Magnetic structure in iron borates RFe3(BO3)4(R = Y,Ho): a neutron diffraction and magnetization study

Powders of undoped ferrihydrite nanoparticles and ferrihydrite nanoparticles doped with cobalt in the ratio of 5: 1 have been prepared by hydrolysis of 3d-metal salts. It has been shown using Mossbauer spectroscopy that cobalt is uniformly distributed over characteristic crystal-chemical positions of iron ions. The blocking temperatures of ferrihydrite nanoparticles have been determined. The nanoparticle sizes, magnetizations, surface anisotropy constants, and bulk anisotropy constants have been estimated. The doping of ferrihydrite nanoparticles with cobalt leads to a significant increase in the anisotropy constant of a nanoparticle and to the formation of surface rotational anisotropy with the surface anisotropy constant K
 u = 1.6 × 10–3 erg/cm2.

/pdf/magnetic-and-resonance-properties-of-ferrihydrite-bl1gjqa7h5.pdf

Magnetic and resonance properties of ferrihydrite nanoparticles doped with cobalt

The temperature dependence of resistivity, magnetization, and electron-spin resonance of the $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Mn}\mathrm{S}$ single crystal were measured in temperature range of $5\phantom{\rule{0.3em}{0ex}}\mathrm{K}lTl550\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Magnetization hysteresis in an applied magnetic field up to $0.7\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ at $T=5$, 77, and $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, irreversible temperature behavior of magnetization, and resistivity were found. The obtained data were explained in terms of a degenerate tight binding model using random phase approximation. The contribution of holes in ${t}_{2g}$ and ${e}_{g}$ bands of manganese ions to the conductivity, optical absorbtion spectra, and charge instability in $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Mn}\mathrm{S}$ were studied. Charge susceptibility maxima resulted from the competition of the on-site Coulomb interaction between the holes in different orbitals and small hybridization of subbands were calculated at $T=160$, 250, and $475\phantom{\rule{0.3em}{0ex}}\mathrm{K}$.

Conductivity, weak ferromagnetism, and charge instability in an α − Mn S single crystal

An experimental study is reported regarding the temperature dependence of the magnetic susceptibility of a CuB2O4 tetragonal single crystal within the 4.2–200-K range. It has been established that the magnetic susceptibility exhibits anomalies at 21 and 10 K and depends strongly on crystal orientation in the magnetic field. A study has been carried out of the field dependences of the magnetization of CuB2O4 at various temperatures and crystal orientations. It is shown that for T>21 K, the crystal is in a paramagnetic state determined by Cu2+ copper ions with an effective magnetic moment of 1.77 µB. Within the 10–21 K interval, the field dependence of the magnetization is typical of a weak ferromagnet with magnetic moments of the two antiferromagnetically coupled sublattices lying in the tetragonal plane of the crystal. The spontaneous weakly-ferromagnetic moment is 0.56 emu/g at 10 K. The canting angle of the sublattice magnetic moments, determined by the Dzyaloshinski-Moriya interaction, is 0.49°. It is believed that below 10 K, the CuB2O4 crystal retains its easy-plane magnetic structure, but with a zero spontaneous magnetic moment.

A. M. Vorotynov

Papers

Magnetic structure, magnetic interactions and metamagnetism in terbium iron borate TbFe3(BO3)4: a?neutron diffraction and magnetization study

Magnetic structure in iron borates RFe3(BO3)4(R = Y,Ho): a neutron diffraction and magnetization study

Magnetic and resonance properties of ferrihydrite nanoparticles doped with cobalt

Conductivity, weak ferromagnetism, and charge instability in an α − Mn S single crystal

Magnetic susceptibility and magnetic-field behavior of CuB 2 O 4 copper metaborate