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Two isomeric Co(II) complexes with the same general molecular formula of [Co(napy)2(NO3)2] (napy = 1,8-naphthyridine) have been synthesized. X-ray single crystal structural determination demonstrates that the two compounds exhibit highly irregular six- (1) and seven-coordinate (2) geometries, respectively. The magnetic measurements, X-band EPR data and theoretical calculations were thoroughly investigated. Both complexes show field-induced slow magnetic relaxation, of which the slow magnetic relaxation in 2 is attributed to an easy-plane anisotropy. [ABSTRACT FROM AUTHOR]

In the present paper, we report the structural, electrical, and magnetic properties of Bi2-xDyxIr2O7 (x = 0, 0.5, 1.0, 1.5, 2.0) polycrystalline. Raman scattering spectra show the variation of active mode with doping induced by the changes of bond strength and the ionic masses. The resistivity behaviors show that the substitution of dysprosium significantly enhances the electrical resistance and presents a metal-insulator transition at about 60 K for the x = 1.5 samples. Fitted data of metallic regions indicate the importance of grain boundary effects while transport mechanism of insulating regions changes from thermal activation to variable range hopping model. Magnetic measurements suggest predominantly antiferromagnetic (AFM) interaction. With increasing content of Dy, the AFM interactions increase at first and then decrease, resulting from the competition among AFM Ir-Ir, AFM Ir-Dy, and ferromagnetic (FM) Dy-Dy interactions. [ABSTRACT FROM AUTHOR]

A mononuclear five‐coordinate Cu(II) complex [Cu(12‐TMC)Cl][B(C6H5)4] (1) (12‐TMC = 1,4,7,10‐tetramethyl‐1,4,7,10‐tetraazacyclododecane) with distorted square pyramidal geometry has been synthesized and characterized by single‐crystal X‐ray diffraction, direct‐current and alternating‐current magnetic measurements and electron paramagnetic resonance (EPR) spectroscopy. The complex displays slow magnetic relaxation under an external dc field. The analysis of the field‐ and temperature‐dependence of the relaxation rates suggests that the slow dynamics of the magnetization is dominated by the Raman‐like process in the temperature range of 1.8 K to 11 K under an applied dc field of 0.15 T. In addition, the results of magnetic dynamics for the diluted sample with diamagnetic Zn(II) ions confirms the molecular origin of slow magnetic relaxation. [ABSTRACT FROM AUTHOR]

Structural and magnetic properties of Bi0.5 Ca0.5-xBaxMnO3 (x = 0, 0.03, 0.05, 0.07 and 0.10) samples with charge ordering (CO) state and C-type antiferromagnetic (AFM) magnetic structure have been studied systematically. With increasing Ba-doping level, both CO and AFM are weakened. From the micro-magnetic analysis, we clarify the ambiguity about the Néel temperature TN in bismuth-based perovskite manganites. We find that the paramagnetic (PM)-CO/AFM transition temperature TCO at high temperature is the onset temperature of the PM-AFM transition, while customarily so-called TN at low temperature indicates the finish of the PM-AFM transition. Both the macro- and micro-magnetic data show that, in all the samples, only AFM state coexists with PM matrix below CO transition and above TN, while AFM state coexists with ferromagnetic (FM) state and PM state at lower temperature below TN. [ABSTRACT FROM AUTHOR]

We perform oxygen doping experiments in the CaFeAsF and CaFeCoAsF compounds. In the parent compound CaFeAsF, partial replacement of F by O leads to an increase of resistivity and a weakening of spin-density wave transition, indicating that the out-of-plane disorder strongly affects the electronic and magnetic properties of the system. In the CaFeCoAsFO system, the doping of oxygen leads to the suppression of superconductivity, reflecting the importance of Ca-F layer disorder in this system. [ABSTRACT FROM AUTHOR]

We have studied the magnetic and magnetotransport properties of the perovskite LaMn[sub 1-x]Cu[sub x]O[sub 3] (x≤0.3). All of these compounds show ferromagnetism and cluster glass behavior at low temperatures. Though no metallic-insulating transition associated with the ferromagnetic-paramagnetic transition appears, a large magnetoresistance was observed in the ferromagnetic phase. Due to the fact that the Cu ion in these compounds is divalent, the ferromagnetism in LaMn[sub 1-x]Cu[sub x]O[sub 3] is believed to be consistent with the Mn[sup 3+]-O-Mn[sup 4+] double-exchange mechanism. These results suggest that double exchange and large magnetoresistance can be obtained by direct Mn-site doping. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The semiconductor-type EuMnSb 2 single crystal with an orthorhombic structure (space group Pnma , No.62) was synthesized using the Sn-flux method, and its physical properties were systematically investigated by magnetization, specific heat, and resistivity measurements. The magnetic and specific heat features reveal two successive antiferromagnetic (AFM) transitions exist separately at T N 1 ∼ 21 K and T N 2 ∼ 9 K, which have different responses to external magnetic field, and magnetic anisotropy is enhanced as the temperature is below T N 1. When the magnetic field is about 1.7 T and parallels the a -axis of the EuMnSb 2 crystal, a spin-flop transition of the AFM order appears. Electronic transport measurements show that the single crystal of EuMnSb 2 manifests semiconductor characteristic and magnetic field-induced semiconductor-to-metal transitions. In addition, we observe a colossal negative magnetoresistance for both in-plane and out-of-plane resistivity and two-fold period anisotropic magnetoresistance. Combining magnetic susceptibility, specific heat capacity and resistivity properties, we present a phase diagram which can be divided into AFM semiconductor, paramagnetic semiconductor and paramagnetic metal. These unique properties indicate that EuMnSb 2 can provide a platform for investigating the interplay between magnetic order, and charge transport. • Two successive AFM transitions of Eu moments were revealed by magnetic susceptibility and specific heat measurements. • Both in-plane and out-of-plane resistivity exhibit semiconductor-to-metal transition and colossal negative magnetoresistance. • Angle-dependent out-of-plane resistivity exhibits different behavior of anisotropic magnetoresistance above and below T N. • The magnetic phase diagrams help to understand the complex properties of semiconductor EuMnSb 2 crystals. [ABSTRACT FROM AUTHOR]

Abstract: The magnetic properties as well as the electronic transport behaviors of Mn-site electron-doped manganites CaMn1−x W x O3  have been studied. For low doping level , the system shows the coexistence of multi-magnetic phases which is tunable by the applied magnetic field. For , curve shows an obvious phase transition believed to be from paramagnetism (PM) to G-antiferromagnetism (AFM) at around 190 K. With further increase of tungsten concentration , besides a transition at 180 K, the system exhibits a peak at 350 K. According to the electron diffraction pattern, it is believed that the peak at is not a PM to charge ordering (CO) transition but a consequence of orbit ordering. The Jahn–Teller transition induced by the W doping should be responsible for the effect. [Copyright &y& Elsevier]

M-type Sr (SrM) hexaferrites have been widely applied in millimetre/microwave ferrite devices such as circulators and isolators. SrM hexaferrites must exhibit a high remanence ratio M r / M s , a high anisotropy field H a , and a low ferromagnetic resonance (FMR) linewidth Δ H to further develop millimetre/microwave equipment and devices with high frequencies, miniaturisation, and planarisation. However, it is difficult for M-type hexaferrite to simultaneously meet the requirements of high M r / M s , high H a , and low Δ H , which are key to realising high-frequency self-biased ferrite devices. In this work, Ca–La–Co-substituted SrM ferrite was prepared, and the influence of La substitution on the micromorphology, static magnetic properties, and Δ H values of SrM hexaferrites is discussed in detail. The results demonstrated that as the La substitution content x increased from 0.0 to 0.5, the saturation magnetisation 4π M s and coercivity H c initially increased, and then decreased. The H a values of all samples were higher than 18 kOe. The FMR linewidth Δ H initially increases, and then decreased after reaching a maximum value at x = 0.2. The independent grain approximation theory was used to analyse the changing trend of the FMR linewidth. The results showed that the crystalline anisotropy linewidth Δ H a accounted for a larger proportion of the FMR linewidth than the porosity linewidth Δ H p. The sample with a La substitution content x of 0.3, exhibited the best performance (4π M s = 3915 Gs, 4π M r = 3387 Gs, H c = 1818 Oe, M r / M s = 0.865, large H a = 23.99 kOe, and Δ H = 1548 Oe at 58.8 GHz). The materials prepared in this research have significant potential for application in high-frequency self-biased devices and microwave engineering. [ABSTRACT FROM AUTHOR]

In the present paper, we report the structural, electrical, and magnetic properties of Bi2-xDyxIr2O7 (x = 0, 0.5, 1.0, 1.5, 2.0) polycrystalline. Raman scattering spectra show the variation of active mode with doping induced by the changes of bond strength and the ionic masses. The resistivity behaviors show that the substitution of dysprosium significantly enhances the electrical resistance and presents a metal-insulator transition at about 60 K for the x = 1.5 samples. Fitted data of metallic regions indicate the importance of grain boundary effects while transport mechanism of insulating regions changes from thermal activation to variable range hopping model. Magnetic measurements suggest predominantly antiferromagnetic (AFM) interaction. With increasing content of Dy, the AFM interactions increase at first and then decrease, resulting from the competition among AFM Ir-Ir, AFM Ir-Dy, and ferromagnetic (FM) Dy-Dy interactions. [ABSTRACT FROM AUTHOR]

The electric and magnetic properties of doped iridates Y 2 Ir 2- x Cu x O 7 have been studied in the present paper. It is found that the magnetic properties show an enhanced ferromagnetism with doping, which comes from Cu spins and doping-broken Ir networks. The M–T data of all the doped compounds show a magnetic order around 150 K, which should be rooted in antiferromagnetic (AFM) order of Ir spins. However, there is also another transition below 20 K for x ≥ 0.2 samples, which should be originated from AFM Cu-Ir interactions. The result of bulk magnetization can be further proved by Electron spin resonance (ESR) measurements which suggest ferromagnetic (FM) interactions of Cu ions and the occurrence of magnetic order below 20 K. From the data of M – H curves, we found that there is a metamagnetic-like transition at 20 kOe for all the doped samples, which is considered as reconstruction of the Ir electrons. While another metamagnetic-like transition at 60 kOe for x = 0.4 sample is observed and considered as a spin-reorientation Cu spins. Resistivity data indicate that all the doped samples can be fitted by Mott's variable-range hopping (VRH) model at low temperatures. This is the consequence of localization due to disorder on the Ir/Cu site. • Magnetic properties show an enhanced ferromagnetism with doping. • There is another transition below 20 K with doping due to AFM Cu-Ir interactions. • The two metamagnetic-like transitions are due to a spin-reorientation of Ir and Cu. • The conduction of the doped samples is explained with VRH mechanism due to disorder. [ABSTRACT FROM AUTHOR]

We present an investigation of Griffiths singularity in La 0.5 Sr 0.5 MnO 3 nanocrystalline by means of magnetic susceptibility and electron paramagnetic resonance (EPR). An unusual platform was found in paramagnetic region. Based on the analysis of EPR spectrum and magnetization variation across the whole temperature range of phase transition, we confirm it is due to the presence of Griffiths singularity rather than a superparamagnetic state in the nanocrystalline system. Such a singularity phase is constituted with some correlated ferromagnetic clusters which embed in paramagnetic matrix. Although they form ferromagnetic spin correlation, the system do not yield any spontaneous magnetization. According to core–shell model, the emergence of Griffiths singularity can be considered due to the presence of local ferromagnetic fluctuations originated from surface spin disorder as the sample size is confined to nanoscale. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fe 2.71 Se 4 (dien) 2 was obtained by assembly of FeSe 2 chains and Fe(dien) 2 complexes. • High Fe vacancies induce the long-range ferrimagnetic order in Fe 2.71 Se 4 (dien) 2. • Magnetic properties are tuned by varying x from 0.86 to 1.23 in Fe 2x+1 Se 4 (dien) 2. Challenges still remain in producing room-temperature ferromagnetism/ferrimagnetism in inorganic–organic hybrid compounds. Here, we report the Fe vacancy-doped inorganic–organic (Fe x Se 2) 2 Fe(dien) 2 (dien = diethylenetriamine, x = 0.86) hybrid cuboids by self-assemble of finite one-dimensional (1D) FeSe 2 chains and Fe(dien) 2 complexes. A growth model is proposed by kinetically controllable syntheses of novel Fe 2x+1 Se 4 (dien) 2 hybrids. The Rietveld refinement reveals that Fe vacancies in the Fe 2.71 Se 4 (dien) 2 hybrid cuboids induce large distortions of the FeSe 2 chains and the room-temperature lattice parameters are a = 9.225(4) Å, b = 18.021(8) Å and c = 11.609(6) Å. Magnetic measurements and electron spin resonance spectra of the Fe 2.71 Se 4 (dien) 2 hybrid cuboids show the ferrimagnetism with the Curie temperature (T C) of 600 K and the spin glass state with the freezing temperature (T f) of 108 K. Impressive room-temperature ferrimagnetic properties of the Fe 2.71 Se 4 (dien) 2 hybrid cuboids were ascribed to the high concentration of Fe3+ vacancies (0.29 per cell) in the hybrid cuboids, which is supported by the 57Fe Mössbauer spectrum fitting based on the ferrimagnetic model. [ABSTRACT FROM AUTHOR]

• Magnetic properties of SrM hexaferrites are regulated by changing Bi 2 O 3 additive. • All samples showed strong uniaxial anisotropy as Bi 2 O 3 additive amount increased. • When Bi 2 O 3 additive x = 1.0 wt%, the overall performance of sample is the best. • Theory of independent grain approximation was adopted to divide the FMR linewidth. Considering the improvement of electronics regarding high frequency and miniaturization, SrM hexaferrites need to exhibit high anisotropy field H a , high remanence ratio M r / M s , and low ferromagnetic resonance linewidth Δ H to create microwave devices and equipment with planarisation, miniaturisation, and high frequencies. The key to achieving self-biased microwave devices with high-frequency is to simultaneously achieve high H a , high M r / M s , and low Δ H. However, it is hard to meet these requirements. In this study, Sr 0.4 La 0.3 Ca 0.3 Fe 11.85 Al 1.0 Co 0.15 O 19 was used to study the effect of different doping amounts of Bi 2 O 3 on its magnetic characteristics, micromorphology and FMR linewidth. With the increase of Bi 2 O 3 doping, the grain size of the sample gradually increased, and the uniformity of the grain size gradually decreased. When the Bi 2 O 3 doping amount x increased from 0 to 1.2 wt%, the 4π M s and 4π M r values increased and the coercivity displayed the opposite tendency. The samples showed great uniaxial anisotropy. The magnetocrystalline anisotropy field H a shows a trend of initially decreased and then increased. When x = 1.0 wt%, H a reaches the maximum value of 28.9 kOe. At this time, the ferromagnetic resonance linewidth Δ H of the sample is 1578 Oe. The theory of IGA was adopted to divide the FMR linewidth into two parts Δ H a and Δ H p. Accroding to the results, Δ H a takes the bigger proportion of linewidth. However, the change in Δ H p is not negligible. When x = 1.0 wt%, the sample showed its best performance (4π M s = 3412 Gs, 4π M r = 2905 Gs, H c = 2649 Oe, M r / M s = 85.1%, large H a = 28.864 kOe, and Δ H = 1578 Oe). The SrM ferrite materials provided in this study can potentially be used in the microwave engineering, high-frequency, and self-biased devices. [ABSTRACT FROM AUTHOR]

• La 0.7 Ca 0.3 MnO 3 films sputtered from He-treated target surface. • He+ ion penetration in the cathode target is the crucial step for the He treatment. • He treatment increased the films' transition temperature and c-axis lattice parameter. • Direct film exposition to He plasma was more effective than He target treatment. We previously reported that out-of-plane lattice of in-plane tensile strained (001) La 0.7 Ca 0.3 MnO 3 thin films can be stretched by He treatment of the films via adding helium gas in an Ar/O 2 mixed sputtering atmosphere. To gain more insight into the He treatment process, in this study, we carried out He plasma treatment on a target and He atom adsorption on a substrate surface respectively before/between sputtering deposition of La 0.7 Ca 0.3 MnO 3 films. The films deposited after the target pre-treatment show remarkable changes in the out-of-plane lattice and magnetotransport properties, while the films deposited through the latter method changes only slightly, suggesting that the He+ ion penetration in the cathode target plays a key role in the He treatment of the manganite films. Furthermore, we placed the as-grown films at the cathode position and exposed them directly to He discharge plasma. After the He plasma post-treatment, the out-of-plane lattice parameter increases from 3.823 to 3.851Å, accompanied by an increase in the metal-insulator transition temperature from 260 to 290 K. The results demonstrate that the He plasma treatment is a simple strategy for the single-axis control of epitaxial thin films. [ABSTRACT FROM AUTHOR]