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One initial and essential question of magnetism is whether the magnetic properties of a material are governed by localized moments or itinerant electrons. Here, we expose the case for the weakly ferromagnetic system FeGa3-yGey, wherein these two opposite models are reconciled, such that the magnetic susceptibility is quantitatively explained by taking into account the effects of spin-spin correlation. With the electron doping introduced by Ge substitution, the diamagnetic insulating parent compound FeGa3 becomes a paramagnetic metal as early as at y = 0.01, and turns into a weakly ferromagnetic metal around the quantum critical point y = 0.15. Within the ferromagnetic regime of FeGa3-yGey, the magnetic properties are of a weakly itinerant ferromagnetic nature, located in the intermediate regime between the localized and the itinerant dominance. Our analysis implies a potential universality for all itinerant-electron ferromagnets. [ABSTRACT FROM AUTHOR]

We report on the anion substitution and pressure effects on the layered compound 1T-CrSe2 with unusual-valent chromium. Owing to the competition between the orbital degrees of freedom and the valence instability of Cr4+, the systems of Cr(Se1-xSx)2 and Cr(Se1-yTey)2 exhibit several types of phase transition. As well as the parent compound CrSe2, Te-substituted samples and slightly S-substituted samples of x = 0.025 show two phase transitions, which are likely to be related to both the valence change and orbital ordering of Cr4+. The highly S-substituted samples of x > 0.04 show one phase transition, which can be attributed to orbital ordering without a valence change. The intermediate Ssubstituted samples of 0:025 < x ≲ 0:04 exhibit the above three types of phase transition and, in addition, another type of transition. In contrast, the pressure effect on CrSe2 is qualitatively different from these anion substitution effects, which indicates that these anion substitution effects are not simply explained by a chemical pressure effect but also by the change of the stability in the Cr4+ state. [ABSTRACT FROM AUTHOR]

We synthesized single crystals of an itinerant ferromagnet LaCo2P2 with ThCr2Si2-type structure and studied their magnetism by magnetization and 31P NMR measurements. We measured Knight shift K and spin-lattice relaxation rate divided by temperature 1/T1T with the applied fields parallel to the a and c axes, and estimated spin fluctuations in the ab plane and c. In addition, we evaluated spin fluctuations from the result of magnetization data with a three-dimensional ferromagnetic model. There is little anisotropy in evaluated spin fluctuations in the ab plane and c. Spin fluctuations of LaCo2P2 have a three-dimensional character and can be understood in the framework of the self-consistent renormalization theory of spin fluctuations. [ABSTRACT FROM AUTHOR]

We took 31P NMR measurements of mainly paramagnetic phase Sr1-xCaxCo2P2 (0≤x≤0.5) to reveal the itinerant-electron metamagnetic transition, and of its magnetically ordered phase (0.7≤x≤1), and characterized their spin fluctuations by estimating the spin fluctuation parameter T0 corresponding to the width of the spin fluctuation in the spectrum in frequency space. SrCo2P2 has a quasi-two-dimensional uncollapsed tetragonal (ucT) cell without interlayer P-P bonds, whereas CaCo2P2 has a three-dimensional collapsed tetragonal (cT) cell with P-P bonds. The ab-in-plane component of T0 is much larger than the out-of-plane component in SrCo2P2. As x increases from 0 to 0.5, the in-plane component of T0 decreases proportionally with the metamagnetic transition field. In the antiferromagnetic cT phase (0.7≤x≤1), T0 is constant and spin fluctuations show an isotropic character in contrast to their behavior in the paramagnetic ucT phase (0≤x≤0.5). These results indicate that the in-plane spin fluctuations due to the quasi-two-dimensional crystal structure play a significant role in the metamagnetic transition of this system. [ABSTRACT FROM AUTHOR]

We synthesized the novel S=1/2Mo3 cluster magnet Li2ScMo3O8 as well as the isomorphic compound Li2InMo3O8, and investigated their macroscopic and microscopic physical properties. Li2InMo3O8 showed magnetic ordering at TN~12 K with a 120° structure, while no magnetic ordering is observed down to 0.5 K in Li2ScMo3O8 despite the strong antiferromagnetic interaction among clusters probed by the Weiss temperature. Results of the Li7 nuclear magnetic resonance spectra and the nuclear spin-lattice relaxation rate (1/T1) measurement show direct microscopic proof of the spin-disordered ground state. We discuss the difference in the ground state between Li2ScMo3O8 and Li2InMo3O8 using the description of localized magnetism based on spin frustration within the triangular lattice and that of inter- and intracluster charge fluctuations. [ABSTRACT FROM AUTHOR]

The magnetic phase diagram of Sr 1 - x Ca x Co 2 P 2 as a function of hydrostatic pressure and temperature is investigated by means of high pressure muon spin rotation, relaxation and resonance ( μ + SR). The weak pressure dependence for the x ≠ 1 compounds suggests that the rich phase diagram of Sr 1 - x Ca x Co 2 P 2 as a function of x at ambient pressure may not solely be attributed to chemical pressure effects. The x = 1 compound on the other hand reveals a high pressure dependence, where the long range magnetic order is fully suppressed at p c 2 ≈ 9.8 kbar, which seem to be a first order transition. In addition, an intermediate phase consisting of magnetic domains is formed above p c 1 ≈ 8 kbar where they co-exist with a magnetically disordered state. These domains are likely to be ferromagnetic islands (FMI) and consist of an high- (FMI- 1 ) and low-temperature (FMI- 2 ) region, respectively, separated by a phase boundary at T i ≈ 20 K. This kind of co-existence is unusual and is originating from a coupling between lattice and magnetic degrees of freedoms. [ABSTRACT FROM AUTHOR]

Novel amorphous iron hydrides (AIHs) are synthesized for the first time under ambient conditions by employing novel "quiescent reaction", without stirring for mixing solutions, during a conventional aqueous reduction-precipitation process. The kind and morphology of AIHs are dependent on the processing condition, where two types are found, with one form consisting of a tangle of uniform nanowires and the other being granular in nature. Both AIHs undergo transformation to crystalline α-Fe by heat treatment at 600 °C. The nanowire AIH exhibits the hydrogen content of 0.10 wt%, while the granular AIH of 0.22 wt%. Their magnetic and thermal properties are accordingly different, and the non-diffusive hydrogen contributes to stability of AIHs. It is strongly suggested that, by use of quiescent reaction, iron-hydrogen clusters are formed and preserved at an early stage of precipitation reaction, and subsequently aggregated into novel AIHs, preventing α-Fe crystallization. Hence, the AIHs would be categorized as metastable hydrides stabilized with iron-hydrogen clusters. In addition, newly discovered quiescent reaction in aqueous solution, from which unprecedented AIHs are derived, sheds new light on fundamental and essential aqueous reaction. [ABSTRACT FROM AUTHOR]

The brief history of itinerant-electron magnetism has been reviewed in terms of spin fluctuations. In the research field of itinerant-electron magnetism, the effects of spin fluctuations are very important to understand the experimental results. Among itinerant-electron theories, the self-consistent renormalization theory of spin fluctuations (the SCR theory) has developed since 1973 by Moriya’s group. Now, we can use the SCR theory in order to analyze our experimental data quantitatively by means of 4 spin fluctuation parameters, ps, F1, T0, TA, by which we can calculate Curie temperature TC, inverse magnetic susceptibility 1/χ, nuclear spin-lattice relaxation rate 1/T1, specific heats C, etc. quantitatively. In fact, the quantitative discussion is very important to characterize itinerant-electron magnets which distribute from weak-itinerant to localized-moment regimes. Furthermore, Takahashi’s theory of spin fluctuations has been developed since 1986 by setting up two hypotheses in order to solve some serious problems existing in previous itinerant theories including the SCR theory. One is that total amplitudes of spin fluctuations should be conserved (TAC). The second is global consistency (GC), implying that the continuity of magnetization and inverse magnetic susceptibility should be preserved through TC. These two assumptions result in two equations among these 4 spin-fluctuation parameters, by which we can estimate 4 parameters quite easily only by using static magnetic measurements like magnetization and magnetic susceptibility. At the same time, the assumption TAC may result in the unified picture of itinerant ferromagnetism. The effects of spin fluctuations are also important to understand the exotic superconductors of which mechanism is not of BCS-type but of magnetic origin. The superconducting transition temperatures TC of those exotic superconductors can be explained universally by T0 which is the energy width of the spin-fluctuation spectrum. Here, the effects of spin fluctuations are explained quantitatively in itinerant-electron magnetism as well as exotic superconductivity in the review. [ABSTRACT FROM AUTHOR]

The Curie temperature TC of the weakly ferromagnetic system FeGa3−yGey is investigated by means of isothermal magnetization experiments. The critical temperature of the ferromagnetic phase transition is estimated by the so-called M4 plots rather than the Arrott plots technique. The M4 plots are exploited from the sixth power term of the expanded free energy, which is neglected by the Arrott plots. The magnetic properties are analyzed by taking into account the effects of spin fluctuations in terms of related spin-fluctuation theories. [ABSTRACT FROM AUTHOR]

One initial and essential question of magnetism is whether the magnetic properties of a material are governed by localized moments or itinerant electrons. Here, we expose the case for the weakly ferromagnetic system FeGa3-yGey, wherein these two opposite models are reconciled, such that the magnetic susceptibility is quantitatively explained by taking into account the effects of spin-spin correlation. With the electron doping introduced by Ge substitution, the diamagnetic insulating parent compound FeGa3 becomes a paramagnetic metal as early as at y = 0.01, and turns into a weakly ferromagnetic metal around the quantum critical point y = 0.15. Within the ferromagnetic regime of FeGa3-yGey, the magnetic properties are of a weakly itinerant ferromagnetic nature, located in the intermediate regime between the localized and the itinerant dominance. Our analysis implies a potential universality for all itinerant-electron ferromagnets. [ABSTRACT FROM AUTHOR]

We have systematically investigated the magnetic properties of La- and Co-substituted SrFe12O19 using single crystals. By utilizing the traveling solvent floating zone technique, we have grown single crystals over a wide range of substitution content, and examined their saturation moments and magnetocrystalline anisotropy. With increasing content of La and Co, the saturation moment at 300K monotonically increases. The increment of magnetocrystalline anisotropy is almost proportional to the content of Co. In addition, further La substitution also enhances magnetocrystalline anisotropy, which demonstrates that Fe2+ plays an important role to enhance magnetocrystalline anisotropy. We have analyzed magnetocrystalline anisotropy energy as a function of substitution content, and elucidate the effects of Co2+ and Fe2+. [ABSTRACT FROM AUTHOR]

We have investigated crystal structure and magnetic properties of three S=1V3+ Ising-like anisotropic kagome lattice antiferromagnets, Cs2KV3F12,Cs2NaV3F12, and Rb2NaV3F12, using single crystals. Each compound crystallizes in a monoclinic system and has a slightly distorted kagome lattice. Although the magnetic properties are similar, the details depend on the magnitude of magnetic anisotropy. The magnetization and magnetic susceptibility are highly anisotropic owing to anisotropic g factors and Ising-like single ion anisotropy originating from partially unquenched orbital moments of V3+, and the easy axis of Ising-like anisotropy is perpendicular to the kagome plane. In contrast to disordered ground states in the isostructural Ti3+ (S=1/2) compounds, the V3+ (S=1) compounds exhibit antiferromagnetic ordering with distorted 120° structure or other nearly coplanar magnetic structure whose basal spin plane includes the easy axis, which is mainly due to large magnetic anisotropy and decrease of quantum fluctuation. Moreover, when magnetic fields are applied perpendicular to the kagome plane, magnetization curves of them show distinct 1/3 and 2/3 magnetization plateaus, which are stabilized by Ising-like single ion anisotropy. In particular, the 2/3 magnetization plateaus are notable magnetic phenomena in kagome lattice antiferromagnets and are due to the combination of spin frustration, Ising-like single ion anisotropy, and the small monoclinic distortion of kagome lattices. [ABSTRACT FROM AUTHOR]

The physical properties of novel cluster-based triangular lattice antiferromagnets Na3A2(MoO4)2Mo3O8 (A=In, Sc), synthesized through a topochemical Na-intercalation to nonmagnetic Na2A2(MoO4)2Mo3O8, are reported. The S=1/2 [Mo3]11+ clusters form a regular triangular lattice, which gives the magnetic system a strong geometrical spin frustration effect. Despite the strong antiferromagnetic couplings among [Mo3]11+ clusters, they show no long-range magnetic orderings down to 0.5 K with the finite residual magnetic entropy. The ground states of Na3A2(MoO4)2Mo3O8 have been characterized as a quantum spin liquid, owing to the strong spin frustration of cluster spins on the triangular lattice. [ABSTRACT FROM AUTHOR]

We have investigated the crystal structure and magnetic properties of three kagome lattice antiferromagnets, Rb2NaTi3F12, Cs2NaTi3F12, and Cs2KTi3F12, using single crystals. These compounds represent a S=1/2 kagome system consisting of magnetic Ti3+ ions, which is expected to have negligibly small Dzyaloshinsky-Moriya interaction. The structural analyses revealed that each of the three compounds has a slightly distorted kagome lattice. The distortion of the kagome lattice becomes small as the ionic radii of constituent alkali metals increase. All three compounds have nearly the same Weiss temperature of -45 K, and the ground states are disordered and strongly depend on the distortion. The ground states of Rb2NaTi3F12, Cs2NaTi3F12, and Cs2KTi3F12 are found to be a two-component state including approximately 1/3 nearly free spins, a gapless disordered state, and a gapped disordered state, respectively. Our experimental results suggest that the ground state of the ideal S=1/2 Heisenberg kagome lattice antiferromagnet is gapped. In addition, the magnetization curves of Cs2NaTi3F12 and Cs2KTi3F12 show anomalies at approximately 1/3 of the full magnetic moment of Ti3+, which are a notable observation of signs of the theoretically proposed 1/3 magnetization plateau in S=1/2 kagome antiferromagnets. [ABSTRACT FROM AUTHOR]

The magnetic nature of a metallic two-dimensional triangular compound, CrSe2, has been investigated by muon spin rotation and relaxation (µSR+) measurements using both powder and single crystal samples. It is found that CrSe2 enters into a static antiferromagnetic (AF) ordered state below 157 K (=TN). Furthermore, the AF state is slightly changed below around 20 K (=TN2). Based on the analysis of the internal magnetic fields at the muon sites predicted with DFT calculations, collinear AF and helical 120° AF are clearly eliminated for the ground state of CrSe2. The most probable one is an incommensurate spin density wave order. [ABSTRACT FROM AUTHOR]