The Magnetic Susceptibility Bifurcation in the Ni-Doped Sb2Te3 Topological Insulator with Antiferromagnetic Order Accompanied by Weak Ferromagnetic Alignment

The magnetic susceptibility reveals a discontinuity at Néel temperature and a hysteresis loop with low coercive field was observed below Néel temperature. The magnetic susceptibility of zero field cool and field cool processes coincide at a temperature above the discontinuity, and they split at temperature blow the discontinuity. The magnetic susceptibility splitting is larger at lower external magnetic fields. No more magnetic susceptibility splitting was observed at a magnetic field above 7000 Oe which is consistent with the magnetic anisotropy energy. Our study supports that these magnetic susceptibility characteristics originate from an antiferromagnetic order accompanied by weak ferromagnetism.

The Influence of Annealing Temperature on the Structure and Magnetic Properties of Nanocrystalline BiFeO3 Prepared by Sol–Gel Method

In this work, BiFeO3 powders were synthesized by a sol–gel method. The influence of annealing temperature on the structure and magnetic properties of the samples has been discussed. X-ray diffraction studies showed that the purest phase was formed in the temperature range of 400 °C to 550 °C and the samples annealed at a temperature below 550 °C were of nanocrystalline character. Mössbauer spectroscopy and magnetization measurements were used as complementary methods to investigate the magnetic state of the samples. In particular, the appearance of weak ferromagnetic properties, significant growth of magnetization, and spin-glass-like behavior were observed along with the drop of average grain size. Mössbauer spectra were fitted by the model assuming cycloidal modulation of spins arrangement and properties of the spin cycloid were determined and analyzed. Most importantly, it was proved that the spin cycloid does not disappear even in the case of the samples with a particle size well below the cycloid modulation period λ = 62 nm. Furthermore, the cycloid becomes more anharmonic as the grain size decreases. The possible origination of weak ferromagnetism of the nanocrystalline samples has also been discussed.

Theory of Itinerant Electron Magnetism, 2nd Edition

The book, in the broadest sense, is an application of quantum mechanics and statistical mechanics to the field of magnetism. Under certain well-described conditions, an immensely large number of electrons moving in the solid will collectively produce permanent magnetism. Permanent magnets are of fundamental interest, and magnetic materials are of great practical importance as they provide a large field of technological applications. The physical details describing the many-electron problem of magnetism are presented in this book on the basis of the density-functional approximation. The emphasis is on realistic magnets, for which the equations describing properties of the many-electron problem can only be solved by using computers. The great recent and continuing improvements are, to a very large extent, responsible for the progress in this field. Along with an introduction to the density-functional theory, the book describes representative computational methods and detailed formulas for physical properties of magnets, which include among other things the computation of magnetic ordering temperatures, the giant magnetoresistance, magneto-optical effects, weak ferromagnetism, the anomalous Hall and Nernst effects, and novel quasiparticles, such as Weyl fermions and magnetic skyrmions.

Structural Investigation into Magnetic Spin Orders of a Manganese Phosphatic Oxyhydroxide, Mn5[(PO4)2(PO3(OH))2](HOH)4

The ferri- and antiferromagnetic structures of a hureaulite-type synthetic compound, Mn2+5(PO4)2(PO3(OH))2(HOH)4, were elucidated by high-resolution neutron powder diffraction in combination with magnetic susceptibility and heat capacity measurements. At 6.17 K, the paramagnetic phase (space group: C2/c) transforms to inherit a ferrimagnetic order (magnetic space group: C2′/c′), followed at 1.86 K by an incommensurately modulated antiferromagnetic order (magnetic superspace group: P21/c.1′(α0γ)00s with the propagation vector k(0.523(2), 0, 0.055(1)). In the ferrimagnetic state, antiferromagnetic interactions are dominant for both intra and inter pentamers of Mn2+(O, HOH)6 octahedra. Differently aligned spin-canting sublattices seen in the ferrimagnetic models at 3.4, 4.5, and 6.1 K explain a weak ferromagnetism in the title compound. The observation of magnetic moments vigorously changing in a small temperature range of 6.1–1.5 K adumbrates a high complexity of interplaying structural and magnetic orders in this manganese phosphatic oxyhydroxide.

SPS Temperature Influence on the Composition, Structure and Magnetic Properties of Hematite Ceramics

Spark Plasma Sintering (SPS), also known as pulsed electric current sintering (PECS) or field assisted sintering technology (FAST), belongs to a class of powder metallurgy methods. Investigations of the effect of thermal, electric and electromagnetic fields arising under the conditions of spark plasma sintering of ceramic materials on their final characteristics are of important fundamental scientific significance. In this regard, the work investigated the effect of the IPA temperature on the structure, composition and magnetic properties of hematite α-Fe2O3 of high purity 99.995%. Changes in the structure and composition of ceramic specimens under SPS conditions in the temperature range 800-1000°C are described by scanning electron microscopy and X-ray phase analysis. The magnetic properties are studied and the regularities of changes of the magnetization (Ms) and coercive force (Hc) under the influence of an external magnetic field for ceramic samples are determined depending on the temperature of the SPS. These results can be considered as initial study of the process of consolidation of materials with weak ferromagnetism under conditions of spark plasma sintering.

Unusual cation coordination in nanostructured mullites

Nanocrystalline mullite-type bismuth-bearing complex oxides Bi2(M0.5Al0.5)4O9 (M=Fe3+, Ga3+) are prepared by high-energy ball milling of the corresponding microcrystalline counterparts. An unusual five-fold coordination of metal cations is revealed in nanostructured Bi2(M0.5Al0.5)4O9 by means of 27Al magic angle spinning nuclear magnetic resonance and 57Fe Mössbauer spectroscopies. The concentration of five-fold coordinated cations increases with decreasing crystallite size of a material at the expense of octahedrally coordinated ones. In addition to the nuclear spectroscopic methods, Rietveld analyses of the X-ray diffraction data of the as-prepared nanooxides show that the constituent tetrahedra, octahedra, and the newly formed structural units with five-fold cation coordination are strongly distorted. With decreasing crystallite size of mullites, the average volume of their octahedra increases whereas this parameter decreases for tetrahedra. The macroscopic behaviour of the non-equilibrium nanomullites is characterised by SQUID magnetometry. The Fe-containing mullites exhibit a superposition of a dominant antiferromagnetism and a weak ferromagnetism. The increase in both the remanent magnetization and the coercive field with decreasing crystallite size is attributed to the effect of spin canting. The latter is confined to the interfacial and surface regions of the nanomaterials, and arises due to both the mechanically induced deformation of constituent structural units and the formation of cation sites with the unusual five-fold coordination.