Canted Ferrimagnetic Structure Research Articles

TbMgNi4-xCox-(H,D)2 System. II: Correlation between Structural and Magnetic Properties.

The magnetic properties of TbMgNi4-xCox intermetallic compounds and selected hydrides and deuterides of this system have been studied by various techniques, including magnetic measurements, in situ X-ray and neutron powder diffraction. The intermetallic compounds crystallize in a SnMgCu4-type structure and magnetically order below a Curie temperature (TC), which increases exponentially with the Co content. This can be due to the ordering of the Co sublattice. On the other hand, the insertion of D or H in TbMgNiCo3 strongly decreases TC. The X-ray diffraction measurements versus temperature reveal cell volume minima at TC for the compounds with x = 1-3 without any hints of the structure change. The analysis of the neutron diffraction patterns for the intermetallics with x = 2 and 3 indicates a slightly canted ferrimagnetic structure below TC. The Tb moments refined at 16 K are 4.1(2) μB/Tb for x = 2, and 6.2(1) μB/Tb for x = 3, which are smaller than the free ion value (9.5 μB/Tb). This reduction can be due to the influence of temperature but also reveals the crystal field effect. As Ni and Co occupy statistically the same Wyckoff site, an average Ni/Co moment was refined, leading to 1.7(2) μB/atom for x = 2 and 1.8(1) μB/atom for x = 3 at 16 K. This moment is slightly canted compared to the Tb moment.

Magnetic and magnetothermal properties of the GdTi0.05Fe0.95-xMnxSi canted ferrimagnets

The GdTi0.05Fe0.95-xMnxSi, х = 0–0.95 intermetallic compounds with a tetragonal crystal structure of the CeFeSi type (space group P4/nmm, N 129, tP6) have been studied. The lattice parameter c and the Curie temperature TC increase quickly, whereas the lattice parameter a is almost unchanged in the system when the content of Mn increases. The saturation magnetization, magnetocaloric effect MCE and refrigerant capacity RC change non-monotonically with a dip at intermediate compositions that is presumably due to the canted ferrimagnetic structure of these compounds. The MCE and RC vary in a field changing to 17 kOe within the small ranges of 1.6–2.7 J/kgK and 60–117 J/kg around TC, respectively, while TC changes in a wide range around the room temperature from 160 to 360 K.

Partial substitution of cobalt by rare-earths (Gd or Sm) in cobalt ferrite: Effect on its microstructure and magnetic properties

Microstructure and magnetic properties of partially substituted cobalt ferrite, with small amounts of gadolinium or samarium, were investigated. Co1-xGdxFe2O4+δ (x = 0, 0.02, 0.04, 0.06, 0.08, 0.1, and 0.15) and Co1-xSmxFe2O4+δ (x = 0.04, and 0.08) were obtained through the citrate precursors route. X-ray powder diffraction patterns, of samples treated at temperatures between 400 and 1000 °C, are consistent with a cubic spinel-type structure. Substituted ferrites, with x = 0.04 and 0.08 (600 °C/2 h), show the combination of maximum enhancement of crystallinity and minimum change of the lattice parameters. At this temperature and composition range the crystallite size decreases up to a 41%. Rietveld analyses of Co1-x(Gd/Sm)xFe2O4+δ (x = 0, 0.04, and 0.08), carried out considering that Gd3+ (or Sm3+) occupies Co2+ positions, give rise to a good quality of refinement and cell parameters which are slightly smaller than those provided in the crystallographic database of CoFe2O4. Raman spectra of Gd3+ or Sm3+ substituted ferrites show the characteristic Raman modes expected in inverse spinel ferrites without additional signals. TEM micrographs reveal the presence of small agglomerates of nanoparticles. SAED patterns and HRTEM micrographs, are characteristic of polycrystalline powders while the interplanar distances well correspond to those of CoFe2O4. EDS analyses confirm the presence of Gd or Sm in substituted ferrites. Magnetic hysteresis loops of samples suggest a ferrimagnetic behavior and their squareness ratio values decrease up to 36% in Co1-xSmxFe2O4+δ (x = 0.04). Mössbauer studies reveal the presence of only Fe3+ ions, distributed in a proportion of 60 and 40% through octahedral and tetrahedral sites, respectively and a canted ferrimagnetic structure. Although the formation of the mixed spinel, rather than different substances (Sm or Gd oxide), fall in the sensitivity limits of the XRD technique all the results demonstrate that the replacement of Co2+ by Gd3+ or Sm3+ ions, in CoFe2O4, can tailor the crystal structure, microstructure, and magnetic properties of cobalt ferrite.

Spin order in FeV2O4 determined by single crystal Mössbauer spectroscopy in applied magnetic field

In order to clarify the spin order of FeV2O4, 57Fe Mössbauer spectroscopy has been conducted by using a single crystal specimen. A measurement in applied magnetic field has been also conducted. By applying a slight compression in the sample plane, almost single domain state was achieved in the low temperature phases. The spectra consist of Fe2+ spectra (~ 85%) and Fe2.5+ spectra (~ 15%), corresponding to the A- and B-site Fe ions, respectively. The B-site spectrum well represents the local structure and the magnetic structure of V3+ ion on the B-site. Notable changes in the Mössbauer parameters are recognized at 140, 110, and 65K, where the successive phase transitions take place. The feature well represents the orbital and spin order. In the orthorhombic phase below 110K, Fe2+ and V3+ spins form a collinear ferrimagnetic order along the a-axis. Below 65K in the low temperature tetragonal phase, however, both spins incline from the c-axis to form a canted ferrimagnetic structure. The canting angles are about 17° and 52° at 4.2K for Fe2+ and V3+ spins, respectively.

Metamagnetic transitions in RFe2(H,D)4.2 compounds (R=Y,Tb)

The Tb for Y substitution in YFe2D4.2 leads to an increase of cell volume, a canted ferrimagnetic structure at low temperature, and a shift of the magnetovolumic transition temperature to higher value. The study of the structural and magnetic properties of TbFe2H4.2 and TbFe2D4.2 indicates a significant (H,D) isotope effect implying a larger cell volume and a higher transition temperature for the hydride compared to the deuteride.

High magnetic field properties of yttrium-substituted Ho6Fe23 alloys and deuterides

The magnetic properties of the Ho6−xYxFe23Dz (x=0, 0.5, 1 and z=0, 16) deuterides and of the parent alloys are studied under high dc magnetic field (230kOe) on samples oriented parallel and perpendicular to the external field in the 4.2–300K temperature range. All compounds that retain the cubic Fm3m crystallographic structure present canted ferrimagnetic structure. For most of the samples, field-induced transitions characterized by a linear variation of M above the transition field are found. Upon deuteration drastic changes of the magnetic properties are observed and the main “magnetic parameters” are then determined. In the alloys the exchange interaction Ho–Fe increases when the yttrium content increases but decreases in the deuterides. For all alloys the Curie temperature remains close to 510K.

Magnetic structural characterization of Mg–Co–Cr ferrite by neutron diffraction

Temperature-dependent neutron diffraction studies were done on the spinel oxide system Mg x Co 1− x Cr x Fe 2− x O 4 ( x=0.0, 0.25, 0.50, 0.75 and 1.0). Neutron diffraction data recorded in the temperature range 10–810 K were analyzed in the Rietveld method. Ordered sublattice magnetic moments of the five compositions of the spinel series at various temperatures were deduced from the analysis. A decreasing ordered moment with increasing substitution ( x) was found indicating a gradual weakening of ferrimagnetic order. Huge diffuse signals around the 1 1 1 Bragg diffraction peak were found in the neutron patterns of the composition x=1.0 below the Curie temperature manifesting a build-up of short-range magnetic spin clusters. The observed features suggest a canted ferrimagnetic structure in the composition range x⩽0.75 and a semi-spin glass-like transition at x=1.0.

Hidden ferrimagnetism in pniktides (Fe–Mn)1.95As

The results of experimental investigations of the magnetic properties of the antiferromagnetic alloy Fe0.765Mn1.185As are presented. They show that at atmospheric pressure and temperatures below 65 K the antiferromagnetic state is not the only stable state, since the imposition of a magnetic field in this temperature range makes it possible to observe irreversible induced transitions into a state with a canted ferrimagnetic structure. This is a second stable state for the experimental sample. As the temperature increases, this state vanishes via a first-order phase transformation at 65 K. Above 65 K reversible induced first-order transitions from the antiferromagnetic into a canted ferrimagnetic structure are observed. The results are discussed on the basis of a phenomenological expression for the free energy of a system with two interacting magnetic-order parameters. It is shown that a simple phenomenological model qualitatively describes the behavior of the system investigated. A single-band Hubbard model is used to give a microscopic substantiation of the phenomenological approach.

Influence of thermal history on crystal structure, microstructure and magnetic properties of TbFe 6Ge 6 (II)

The relation between crystal structure, microstructure and magnetic structure in TbFe 6Ge 6 is derived on the basis of neutron powder diffraction for samples annealed at 925, 800 (part I) and 650°C. All samples display a density modulation of only the guest subsystem (Tb/Tb* and Ge5/Ge5*) described by the wave vector q=( 1 2 , 1 2 , 0) of the orthohexagonal YCo 6Ge 6 structure. The occupancy of the Tb site is 1 for the sample with T an=925°C and decreases to 0.830(6) for the sample with T an=650°C. At high temperatures (HT) T 1< T< T N ( T N≈450 K, T 1=9.5 K) the Fe moments order with the wave vector q 1=(0 1 0) and have an antiferromagnetic collinear arrangement (+−+−··) along the x-axis. The Tb magnetic order sets in at T 1=9.5 K and is associated with two wave vectors q 1=(0 1 0) (antiferromagnetic, AF) and q 2=(0 0 0) (ferromagnetic, F). The Tb F-component is parallel to x, while the Tb AF-component is confined to the ( x 0 z)-plane. However, their relative amount depends strongly on the thermal history and this in turn influences the Fe ordering. The largest Tb F-component is observed for the sample with T an=925°C and it induces a reorientation of the Fe moments below T 1 which at 1.4 K are tilted away from the x-axis by an angle φ xy =25.0(6)°. The 1.4 K ordered moment values are 2.22(4) μ B/Fe and 8.0(1) μ B/Tb. The coupling within the Tb[1 0 0]-layers stacked along x is F. The canted ferrimagnetic structure has moments in general directions and comprises four sublattices, two Fe AF and two Tb ferrimagnetic. For sample with T an=650°C the Tb AF-component is dominant, leading to a braking of the F coupling within the Tb[1 0 0]-layers. The Fe moments preserve the HT arrangement below T 1. The 1.4 K ordered moment values are 2.29(6) μ B/Fe, 9.5(2) μ B/Tb ( x=0) and 4.1(2) μ B/Tb ( x=0.5). The canted magnetic structure comprises six sublattices, two Fe AF and four Tb ferrimagnetic, all within the ( x 0 z) plane. The change of the Tb atoms distribution and coherency of the guest subsystem (peak broadening) are coupled in two ways with the magnetic ordering. They change the total magnetic structure and determine the correlation length of the long-range order of the Tb moments.

Magnetic properties in intermetallic compounds DyMn 2(Si 1− xGe x) 2(0 ≤ x≤ 1)

Magnetic measurements have been performed in order to investigate magnetic properties of pseudo-ternary compounds DyMn 2(Si 1 - x Ge x ) 2(0 ≤ x≤1). As x increases, lattice parameters increase from a = 3.904 A ̊ and c = 10.41 A ̊ at x = 0 to a = 3.975 A ̊ and c = 10.79 A ̊ at x = 1 , and the Néel temperature decreases from 523 to 430 K. In all the compounds, magnetic transitions are observed at low temperatures where Dy moments start to order magnetically. DyMn 2Si 2 has three magnetic phases below 38 K whose magnetic structures are long-periodic, and it is supposed that there occurs a magnetic short-range order of Dy moments between 38 and 83 K. The compounds with 0.1 ≤ x≤ 0.6 have a magnetic phase below about 25 K with a canted-ferrimagnetic structure. This phase exists up to x = 0.9, although DyMn 2Ge 2 has a collinear-ferrimagnetic phase. For 0.7 ≤ x≤ 1.0, there exists an intermediate-temperature phase which may have a ferrimagnetic structure with a long-periodic arrangement.

The 3d Mn magnetism instability in TbMn 2

The magnetic structure of the compound Tb(Mn 0.96Fe 0.04) 2 has been determined by neutron diffraction studies. It is generated by two magnetic components leading to a canted ferrimagnetic structure. A huge rhombohedral distortion with unusual thermal variation is observed below T c. A strong magnetic anisotropy of Mn atoms with axial symmetry is found.

Magnetization and neutron-diffraction studies of magnetic properties of single-crystal DyMn2Ge2.

Magnetic properties of single-crystal ${\mathrm{DyMn}}_{2}$${\mathrm{Ge}}_{2}$ have been studied by magnetization measurement in high fields up to 150 kOe and by neutron diffraction. Four magnetically ordered phases have been observed. In low magnetic fields parallel to the [001] direction, collinear antiferromagnetism is observed in the temperature range from 37.5 to 431 K with the Mn moments ferromagnetically coupled on the (001) layers, and with antiferromagnetic coupling between the adjacent (001) Mn layers. Below 33 K, there is a collinear ferrimagnetic structure with the Dy and Mn moments antiparallel to each other along the c axis. A new magnetic phase is observed in the temperature range between 33 and 37.5 K, where its magnetic structure is not uniquely determined but the averaged moments at the Dy and the Mn atoms are evaluated to be about 6${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ and 1${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$, respectively. Another new magnetic phase is observed in high magnetic fields along the [001] directions below 65 K. The magnetic structure of this phase, which has been deduced from the magnetization measurement, is a canted ferrimagnetic structure, with the Dy moments oriented along the c axis, and the Mn moments canted away from the c axis.

Magnetic characteristics of TbMn 2Si 2

Magnetic structures in TbMn 2Si 2 were determined by measurements of magnetization and neutron diffraction. The compound has a canted ferrimagnetic structure at T < 53 K and a collinear Mn antiferromagnetic one at 65 K < T < 550 K ( t= T N ). Coexistence of ferromagnetic Tb sublattice and antiferromagnetic Mn sublattice is observed at 53 K < T < 65 K.

Magnetic Characteristics of Laves Phase RMn2 Compounds (R=Gd, Tb, Dy, Ho and Er)

Measurements of magnetization, susceptibility, thermal expansion and electrical resistivity have been carried out on the RMn 2 compounds with R=Gd, Tb, Dy, Ho and Er. Magnetization measurements were made on the single crystals for all the compounds. A simple ferrimagnetic structure is observed at 4.2 K for GdMn 2 , HoMn 2 and ErMn 2 , and an antiferromagnetic one in TbMn 2 . While, a canted ferrimagnetic structure appears at 4.2 K in DyMn 2 . The Mn moment deduced from saturation magnetization decreases rapidly from 1.6 µ B for GdMn 2 to 0.2 µ B for HoMn 2 with increasing the atomic number of rare earth in the C15 compounds. While, the Mn moment is almost zero in ErMn 2 with the C14 structure. Anomalous discontinuities in the thermal expansion and resistivity for GdMn 2 and TbMn 2 are observed at the magnetic transition temperature where Mn moments lose a long range ordering. It seems likely that the discontinuity is associated with the onset of the Mn moment.

The canted ferrimagnetic structure of Nd 5Ge 4 by neutron diffraction

The chemical and magnetic structures of the intermetallic compound Nd 5Ge 4 were determined from neutron diffraction powder data. In contrast to the isomorphous heavy rare-earth compounds, Nd 5Ge 4 orders with a canted ferrimagnetic arrangement below T c = 52 K. The ordered Nd moments are 2.6, 3.1 and 2.4 μ B for the three sites respectively. The magnetic space group is Pnm'a' and the plane of easy magnetization (010).

Magnetic Studies on Basic Salts of Copper, Dicopper Arsenate Hydroxide, Dicopper Hydroxide Phosphate, and Dicopper Oxide Sulfate

Abstract Magnetic susceptibilities, χ, of Cu2AsO4(OH), Cu2(OH)PO4, and Cu2OSO4 have been measured from 4.2 to 360 K to establish the role of the OH− and O2− ions in the magnetic superexchange interaction. The former two compounds showed a broad maximum for χ at 118 and 110 K, respectively. Although the crystal structure is three-dimensional, only a tetramer model with two parameters can explain the temperature dependence of χ, since the hydroxide anion causes a strong magnetic interaction which is limited to four copper atoms between which the anion is intermediary. The magnetic susceptibility of Cu2OSO4 obeyed the Curie-Weiss law above 140 K with a Weiss constant of −56 K. At 16 K the compound transformed into a ferrimagnetic phase, the effective megneton number of which is 0.11 at 4.2 K. A canted ferrimagnetic structure has been proposed and the canting angle estimated. In the superexchange interaction, only hydroxide and oxide anions are significant and both anions behave similarly.

Magnetic structures of iron germanides

The structures of phases in the Fe-Ge system were studied by means of neutron and X-ray diffraction. The Fe 1 + y Ge phase of the hexagonal B8 2 type has a canted ferrimagnetic structure with magnetic unit cell identical to the chemical one. The Fe atoms in 2( a) sites form one sublattice, Fe I, with parallel spin directions, while those, Fe II, in 2( d) sites form Fe II-Ge-Fe II chains with spin directions canted 28° from the Fe I spin direction and 56° from adjacent Fe II chains. The spin directions lie in the basal plane. Magnetic moments at 25°C were μ I = 1.30 μβ and μ II = 1.10 μβ. No long-range antiferromagnetic structure was found for the phase FeGe with hexagonal B35-type crystal structure according to neutron diffraction patterns down to 80°K. The FeGe 2 phase was found to be antiferromagnetic. The limits of the phase field for Fe 1 + y Ge were established.