Variation Of Magnetic Structure Research Articles

Effect of Zn2+ substitution on magnetic properties of the quasi-one-dimensional spin chain compound Ca3CoMnO6

The subtle variation of magnetic structure has large influence on the macroscopic magnetism of Ca3CoMnO6. As the isovalent nonmagnetic ions have no exchange interaction with the adjacent Co2+/Mn4+ and it could keep the valence states and spin states of the Co/Mn ions unchangeably. Introduction of isovalent nonmagnetic ions thus becomes an ideal selection for us to understand the relevant micromechanism. In this paper, a series of Zn2+ substituted Ca3Co1-xZnxMnO6 (0 ≤ x ≤ 0.2) samples were prepared, and the microstructure and magnetic properties were investigated in detail. The XRD results indicate that for low doped samples the larger radius of Zn2+ causes the lattice parameters and volume increase. While for high doped samples the Zn2+ ions enter the octahedral position, resulting in shrinkage of the lattice. The introduction of Zn2+ ions could also influence the magnetic structure of Ca3CoMnO6 effectively. A small amount of nonmagnetic Zn2+ ions well decrease the concentration of the intrinsic defects and help to form more short-range magnetic order. But as the Zn2+ doping concentration increases, the main effect of Zn2+ doping is to release the magnetic frustration of Ca3CoMnO6, and finally a more robust long range antiferromagnetic structure can be established in high doped samples. Simultaneously, the subtle variation of magnetic structure with Zn2+ substitution leads the Ca3Co1-xZnxMnO6 samples present different dynamic behaviors. This interesting finding could serve as a new reference for tuning the magnetic ordering of Ca3CoMnO6 and improving its multiferroic properties.

References regulating the BiMnxFe1-xO3 film conductivity upon cooling in magnetic and electric fields

The magnetic and electrical properties of the BiFe1-xMnxO3 (x = 0.05, 0.15) films in the temperature range of 80–600 K have been investigated. The Curie temperature (Tc) of the films has been determined. A decrease in the conductivity of the films with x = 0.05 upon cooling in an electric field from the temperatures T < Tc has been found. This effect has been described in the model of decreasing quantum well (domain wall) density and the tunneling coefficient drop. A decrease in the conductivity of the BiFe1-xMnxO3 film by more than an order of magnitude upon cooling from high temperatures in a magnetic field has been established. The experimental data are interpreted using the magnetic-field-induced magnetic structure variation and exchange splitting of the impurity subband.

Long-Time Variation of Magnetic Structure in (PrxLa1−x)Co2Si2: Coexistence of Slow and Fast Processes in Magnetic Phase Transition

Long-time variations of the magnetic structure in PrCo2Si2 and (Pr0.98La0.02)Co2Si2 were studied by magnetization and time-resolved neutron scattering measurements. The amplitudes of magnetic Bragg peaks showed marked time variations after cooling or heating across the magnetic transition temperature T1 between two different antiferromagnetic phases. However, the amplitude of the time variation decreased rapidly with increasing distance from T1. We analyzed the results on the basis of a phase transition model that includes the coexistence of fast and slow processes.

Pnictide-height dependent ferromagnetism in CuFeAs and CuFeSb

Electronic structures and magnetism properties of CuFeAs and CuFeSb are investigated by using first-principles calculations. We found that CuFeAs and CuFeSb share similar electronic structures and magnetic properties. Unlike the antiferromagnetic isostructure LiFeAs, the ground state of both compounds is ferromagnetic state driven by the Stoner ferromagnetic instability. Their ground state is very sensitive to the height of anion (As or Sb), translating from the ferromagnetic state to the stripe antiferromagnetic ordering when the anion height is smaller than a critical value. Such magnetic phase transition can be understood by the J1−J2 Heisenberg model. Reducing the anion height will decrease the nearest-neighbor interaction J1 but increase the next-nearest-neighbor interaction J2. The competing between the anion height dependent antiferromagnetic superexchange mediated by As(Sb) and the ferromagnetic direct exchange between Fe results the variations of magnetic structure with anion height.

Neutron powder diffraction investigation of magnetic structure and spin reorientation transition of HoFe1-xCrxO3 solid solutions

Orthoferrite solid solution HoFe1−xCrxO3 (x=0, 0.2,…,1.0) was synthesized via solid state reaction methods. The crystal structure, magnetism and spin reorientation properties of this system were investigated by X-ray diffraction, neutron powder diffraction and magnetic measurements. For compositions of x≤0.6, the system exhibits similar magnetic properties to HoFeO3. With increasing Cr-doping, the system adopts a Γ4(GxAyFz) magnetic configuration with a decreased Neel temperature from 640K to 360K. A Γ42 spin reorientation of Fe(Cr)3+ was also observed in this system with an increase in transition temperature from 56K to about 200K due to competition between the Fe(Cr)–Fe(Cr) and Ho–Fe(Cr) interactions. For the x≥0.8, the system behaves more like HoCrO3 which adopts a Γ2(FxCyGz) configuration with no spin reorientation below the Neel temperature TN. Throughout the whole substitution range, we found that the saturated moment of Fe(Cr) was less than the ideal value for a free ion, which implies the existence of spin fluctuation in this system. A systematic magnetic structure variation with Cr-substitution is revealed by Rietveld refinement. A phase diagram combining the results of the magnetic measurements and neutron powder diffraction results was obtained.

Long-Time Variation in Magnetic Structure of CeIr3Si2: Observation of a Nucleation-and-Growth Process of Magnetic Domains

CeIr3Si2 is the first three-dimensional uniform magnet in which the long-time variation in magnetic structure was observed. To clarify the microscopic mechanism of this magnetic structural change, time-resolved neutron scattering measurements have been reinvestigated. Clear time variations in the line widths as well as the amplitudes of magnetic Bragg diffractions have been observed in this improved instrumentation. On the notion of this observation, a nucleation-and-growth model of magnetic structural change has been presented. The numerical calculation with this model reproduces well the observation.

Long-Time Variation in Magnetic Structure of Ce0.98La0.02Ir3Si2: Effect of Randomness on Time Variation

A long-time variation in the magnetic structure of Ce0.98La0.02Ir3Si2 has been studied by magnetization and time-resolved neutron scattering measurements. CeIr3Si2 is the first material in which the long-time variation in magnetic structure was observed in three-dimensional uniform magnets. Similar long-time variations in magnetic structure have been observed in several uniform materials. In order to clarify whether the long-time variations in the magnetic structure of these materials do not originate from randomness due to unexpected impurities or imperfections, the time variation behavior in a material with embedded randomness has been examined. The time variations observed in the magnetization and neutron scattering measurements of Ce0.98La0.02Ir3Si2 are basically the same as those observed in CeIr3Si2. Present results have shown that a peculiar long-time variation in the magnetic structure of CeIr3Si2 is not caused by inevitable randomness in a sample but is its intrinsic property.

Long-time variation of magnetic structure in multistep metamagnets Ca3(Co-M)2O6

A long-time variation of magnetic structure has been observed in a geometrically frustrated magnet Ca3Co2O6. In order to clarify that the long-time variation in this material does not originate in randomness due to impurities, magnetization measurements have been made on single crystals of diluted compounds Ca3(Co-M)2O6 (M=Ga, Mg and Al). The longtime variations of the magnetization were detected in these compounds and characteristics of the time variation behavior were not much modified by the introduction of disorder produced by the substitution of non-magnetic atoms. These results show that the long-time variation of the magnetic structure in Ca3Co2O6 is not caused by randomness or imperfections.

Magnetic structure variation in manganese-oxide clusters

Negative-ion photoelectron spectroscopy and ab initio simulations are used to study the variation in magnetic structure in Mn(x)O(y) (x = 3, 4[semicolon] y = 1, 2) clusters. The ferrimagnetic and antiferromagnetic ground-state structures of Mn(x)O(y) are 0.16-1.20 eV lower in energy than their ferromagnetic isomers. The presence of oxygen thus stabilizes low-spin isomers relative to the preferred high-spin ordering of bare Mn(3) and Mn(4). Each cluster has a preferred overall magnetic moment, and no evidence is seen of competing states with different spin multiplicities. However, non-degenerate isomags, which possess the same spin multiplicity but different arrangements of local moments, do contribute additional features and peak broadening in the photoelectron spectra. Proper accounting for all possible isomags is shown to be critical for accurate computational prediction of the spectra.

Magnetic Structure and Its Long-Time Variation in the Multistep Metamagnet CeIr3Si2

Neutron scattering measurements have been made on a single crystal of CeIr 3 Si 2 which shows successive magnetic transitions at T N1 =4.1 K and T N2 =3.3 K. A long-time variation in magnetic structure has been observed. After rapidly cooling the sample below T N2 , the intensity of the Bragg peaks corresponding to a magnetic phase at T N2 < T < T N1 remains and decreases with time. Instead, the Bragg peak intensity corresponding to a magnetic phase at T < T N2 increases with time. The characteristic time for this variation follows the Arrhenius law with an activation energy E a / k B =4 K. Magnetic structure models in two magnetic phases with a ×8 b ×8 c and a ×3 b ×3 c structures are presented. On the basis of these models, the mechanism of long-time variation of magnetic structure is discussed.

Incommensurate Magnetic Structure and Its Long-Time Variation in a Geometrically Frustrated Magnet Ca3Co2O6

Magnetization and neutron scattering measurements have been performed on a single crystal of the magnetically frustrated compound Ca 3 Co 2 O 6 . This compound has no random magnetic interactions, but has frustrating magnetic interactions arising from its crystal structure. In this material, a long-time variation in magnetic structure has been observed. After cooling the sample below the transition temperature T c2 =13 K, the magnetic Bragg peaks at (1, 0, ±δ) corresponding to an incommensurate antiferromagnetic structure move toward (1, 0, 0) with time. The characteristic time for this variation follows the Arrhenius law with an activation energy E a / k B ∼53 K. A new magnetic structure model of this material is also presented.

Long-time variation of magnetic structure in a geometrically frustrated magnet Ca3Co2O6

Magnetization and neutron scattering measurements have been made on a single crystal of geometrically frustrated compound Ca3Co2O6 which shows successive magnetic transitions at Tc1~25 K and Tc2~13 K and multi-step metamagnetic transitions in low magnetic field. In this compound without random magnetic interactions, a long-time variation of magnetic structure has been detected. The magnetic Bragg peaks corresponding to an incommensurate antiferromagnetic structure observed at (1 0 ± 6) reciprocal lattice positions after cooled below Tc2 move toward (1 0 0) with time. The characteristic time for these variations follows the Arrhenius law with an activation energy Ea/kB=57 K.

Long-time variation of magnetic structure in rare-earth intermetallic compounds

Long-time variations of magnetic structure have been studied by means of time-resolved neutron scattering measurements in two kinds of non-diluted uniform magnets, PrCo2Si2 and TbNi2Si2. These materials show commensurate (C) to incommensurate (IC) magnetic transitions below Néel temperature. When a sample is cooled to the low temperature C-phase, magnetic Bragg scattering signals from the C and the IC phases coexist and then their intensity vary with time. These characteristics are similar to those of the previously studied material CeIr3Si2. However, the temperature ranges in which clear time variations exist are much narrower in the present materials.

Real-time observation of magnetic structural change in the multistep metamagnet CeIr3Si2

A ternary intermetallic compound CeIr3Si2 shows successive magnetic transitions at TN1=4.1 K and TN2=3.3 K. At T < TN2 it shows three-step metamagnetic transitions below H=1.43 T. In this non-diluted compound a long-time variation of magnetic structure has been detected by means of time-resolved neutron scattering measurements. When a sample is rapidly cooled below TN2, the magnetic Bragg peaks corresponding to the intermediate temperature phase (TN2 < T < TN1) are observed. The amplitude of these Bragg peaks gradually decreases with time. On the other hand, another group of Bragg peaks corresponding to the low temperature phase (T < TN2) gradually grow with time. The characteristic time for these variations follows the Arrhenius law with an activation energy Ea/kB =4 K.

Long-time variation of magnetic structure in CeIr3Si2

CeIr3Si2 shows successive magnetic transitions at TN1=4.1 K and TN2=3.3 K. At T < TN2 it shows three-step metamagnetic transitions below H=1.43 T. In this non-diluted compound a long-time variation of magnetic structure has been detected by means of magnetc susceptibility and time-resolved neutron scattering measurements. When a sample is rapidly cooled below TN2, the magnetic Bragg peaks corresponding to the intermediate temperature phase (TN2 < T < TN1) are observed. The amplitude of these Bragg peaks gradually decreases with time. On the other hand, another group of Bragg peaks corresponding to the low temperature phase (T < TN2) gradually grow with time. The characteristic time for these variations follows the Arrhenius law with an activation energy Ea/kB =4 K. This is the first observation of long-time variation of magnetic structure in non-diluted uniform magnets.

Theoretical calculation of magnetic structure variation in Pr5Ni2Si3

The variation of magnetization with temperature of the Pr5Ni2Si3 compound was calculated using a nearest neighbor exchange interaction approximation. Pr atoms, which are the only element in this compound with a net magnetic moment, were classified into three types based on the number of nearest neighbor exchange interactions. The expected magnetization versus temperature curve for each type of Pr atom was calculated using the Brillouin function, as well as the average magnetization versus temperature curve for the entire unit cell. The results show that the “corner” atoms exhibit very different behavior from that of the other types of Pr atoms on the “center” or “edge” sites. This is due to the broken symmetry in exchange interaction at the corner site due to interactions with atoms from outside the unit cell that are in closer proximity than atoms within the unit cell. This is considered to be the cause of a second magnetic phase transition observed at a lower temperature than the Curie temperature.

The influence of Sm doping at A site on the magnetic,electrical properties in La0.67Sr0.33MnO3

In this paper, the M_T curves, ESR, Infrared and Raman spectra, ρ_T cu rves and MR_T curves of La067-xSmxSr033MnO 3 (x=000, 010, 020, 030) are studied. The experimental results ind icate that with increasing Sm content, the compound undergoes a transition from long_range ferromagnetic order to the cluster_spin glass state, and further to a ntiferromagnetic order. The variation in magnetic structure and extra magnetic c oupling caused by Sm doping lead to colossal magnetoresistance effect.

Thermopower peak in phase transition region of (1−x)La2/3Ca1/3MnO3/(x)yttria-stabilized zirconia

The thermoelectric power (TEP) and the electrical resistivity of the intergranular magnetoresistance composite (1−x)La2/3Ca1/3MnO3/(x)yttria-stabilized zirconia (YSZ) (LCMO/YSZ) with x=0%, 0.75%, 1.25%, 4.5%, 13%, 15%, and 80% of YSZ have been measured from 300 down to 77 K. A pronounced TEP peak appears during phase transition for samples with x&amp;gt;0, while it is not observed for x=0. We suggest that this is due to the magnetic structure variation induced by lattice strain which is a result of the LCMO/YSZ boundary layers. The transition width in the temperature derived from dχ/dT, with χ the ac magnetic susceptibility, supports this interpretation.

The influence of Gd doping at A site on the magnetic and electrical properties i n La0.7Sr0.3MnO3

The M-T curves， M-H curves, infrared spectra, Raman spectra，ρ-T curves and MR -T curves of La0.7-xGdxSr0.3MnO3 (x= 0.00, 0.10, 0.15, 0.20, 0.30 , 0.40, 0.50, 0.60, and 0.70) are studied. The experimental results indicate tha t with increasing Gd doping, the system undergoes a transition from long-range f erromagnetic order to the cluster-spin glass state and further to an antiferroma gnetic order. With heavily doping content, the transport property exhibits an ab normal behavior under magnetic background. The variation in magnetic structure a nd extra magnetic coupling caused by Gd doping lead to colossal magnetoresista nce.

Variation of magnetic structure with order in the Ni3Mn superlattice

Abstract The magnetic domain structure has been studied extensively by transmission electron microscopy techniques in the Ni3Mn alloy, which becomes strongly magnetic with increasing atomic order. It has been found that the configurations of intermediate equilibrium long-range order consist of a mosaic structure of long-range ordered single non-contiguous magnetic domain rods in a disordered non-magnetic matrix, similar to that observed in the Alnico V structure. Magnetic domain walls are therefore not observed in these alloys. The fully ordered alloy, on the other hand, as well as alloys possessing homogeneous configurations of imperfect long-range order, show a well-defined magnetic domain wall structure. In addition some complex magnetic domain wall configurations in the vicinity of grain and twin boundaries have been observed and analysed. Long tails which are exhibited by the magnetization—temperature curves for alloys possessing imperfect order, and which are eliminated as the order becomes perfect,...