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Motivated by the multiferroic effects and quantum magnetization plateaus in the skew chain antiferromagnets T 2 V 2 O 7 (T = Ni, Co), we have conducted a detailed density function theoretical study on Co 2 V 2 O 7. The results show that the nearest-neighbor interchain interaction (J 3 / k B = − 35.57 K) is not much greater than the intrachain interactions (J 1 / k B = − 19.54 K and J 2 / k B = 27.55 K), showing the absence of interchain dimerization of the Co ions. This indicates that the "dimer+monomer" model used for Ni 2 V 2 O 7 [Cao et al., Phys. Rev. B 106, 184409 (2022)] is no longer applicable to Co 2 V 2 O 7. Finally, the exact diagonalization of spin Hamiltonian, including anisotropic exchanges, produces the experimentally observed 1/2 and 3/4 magnetization plateaus. [ABSTRACT FROM AUTHOR]

We report the decoupling of Gd–Cr magnetism and the resulting giant magnetocaloric effect in honeycomb-lattice tellurate GdCrTeO6. This compound adopts the hexagonal structure with the space group P-3. The susceptibility curve presents a paramagnetic behavior from room temperature to 2 K. Very intriguingly, however, the heat capacity measurement probes a λ-like peak at TN = 10 K, characterizing the long-range antiferromagnetic order. This suggests that the Gd and Cr sublattices are magnetically independent, i.e., the Gd ions are paramagnetic and the strong paramagnetism nearly masks the antiferromagnetic order of Cr ions, which is further evidenced by our ESR data. The maximum magnetic entropy change at 2 K is 41.8 J kg−1 K−1 in a field range of 0–7 T and 30.3 J kg−1 K−1 for 0–3 T, larger than those of most of the Gd oxides reported. The observed giant magnetocaloric effect is due to strong paramagnetism of Gd ions. [ABSTRACT FROM AUTHOR]

The nature of 4f-3d magnetic interaction in oxides as well as its influence on the magnetocaloric effect (MCE) is an interesting topic. Here, we report the weak magnetic interaction and large MCE in a new triangular lattice GdFeTeO6 synthesized by the solid state reaction method. The weak exchange, which was seldom observed in 4f-3d oxides, is supported by the low ordering temperature (TC ≤ 3 K) and a positive but small Curie-Weiss temperature (θp = 3 K). Under an external magnetic field, the magnetization process yields a large magnetic entropy change of 38.5 J kg−1 K−1 at 5 K for 0-7 T and 23.6 J kg−1 K−1 at 3 K for 0-3 T. Finally, our first-principles calculations demonstrate a ferrimagnetic spin model with the Gd(↑)-Gd(↑)-Fe(↓)-Fe(↓) configuration. The weak magnetic interaction is an average effect of ferromagnetic (4f-4f and 3d-3d) and antiferromagnetic (4f-3d) interactions. The antiferromagnetic 4f-3d interaction is a reason for the reduction of MCE. [ABSTRACT FROM AUTHOR]

Mossbauer spectrometric analysis of metaloxides with the composition of MgFe2O4 shows that the materials are made of magnesioferrite particles having anisotropy constant similar to magnetocrystalline anisotropy. Annealing increases the particle size and the formation of the oxide, alpha-Fe2O3. Heat treatment increases the value of anisotropy constant.

High-field electron spin resonance (ESR) has been employed to study the antiferromagnetic (AFM) ordering state (TN=55 K) of spin-chain multiferroic Gd2BaNiO5. The spin reorientation at TSR=24K is well characterized by the temperature-dependent ESR spectra. The magnetization data evidence a field-induced spin-flop transition at 2K. The frequency-field relationship of the ESR data can be explained by conventional AFM resonance theory with uniaxial anisotropy, in good agreement with magnetization data. Related discussion on zero-field spin gap is presented. [ABSTRACT FROM AUTHOR]

NaZn13-type La(Fe0.94Co0.06)11.8Si1.2 alloys were manufactured to investigate the influence of their microstructural change on magnetic refrigeration performance during magnetic field cycling. The magnetic refrigeration performance measurements indicate that both the large magnetic entropy change value (ΔS=14.1 J kg-1 K-1) and maximum adiabatic temperature change (Δ=2.2K) are favorable for the alloys to be superior candidate of magnetic refrigerants. However, the alloys exhibit nearly 10% decrease of ΔS and ΔT when they performed cycling ten-thousand times. More than thousand times of cycles induce local stress and grain cleavages presented by the accumulation of irreversible microstructure changes such as micro-cracks and sub-boundaries. According to the domain observation for the alloys with different field cycles, these microstructure characteristics accompany with the reconfiguration of the local magnetic domains and increase of domain wall energy, which are considered to be the reason of the decrease of ΔS. [ABSTRACT FROM AUTHOR]

The phase separation and dendritic growth characteristics of undercooled liquid Fe62.5Cu27.5Sn10 alloy have been investigated by glass fluxing and drop tube techniques. Three critical bulk undercoolings of microstructure evolution are experimentally determined as 7, 65, and 142 K. Equilibrium peritectic solidification proceeds in the small undercooling regime below 7K. Metastable liquid phase separation takes place if bulk undercooling increases above 65 K. Remarkable macroscopic phase separation is induced providing that bulk undercooling overtakes the third threshold of 142 K. With the continuous increase of bulk undercooling, the solidified microstructure initially appears as well-branched dendrites, then displays microscale segregation morphology, and finally evolves into macrosegregation patterns. If alloy undercooling is smaller than 142 K, the dendritic growth velocity of γFe phase varies with undercooling according to a power function relationship. Once bulk undercooling exceeds 142 K, its dendritic growth velocity increases exponentially with undercooling, which reaches 30.4 m/s at the maximum undercooling of 360K (0.21TL). As a comparative study, the liquid phase separation of Fe62.5Cu27.5Sn10 alloy droplets is also explored under the free fall condition. Theoretical calculations reveal that the thermal and solutal Marangoni migrations are the dynamic mechanisms responsible for the development of core-shell structure. [ABSTRACT FROM AUTHOR]

We have illustrated the presence of spin-glass-like freezing in the Mn-doped spin-chain compounds Ca3Co2-xMnxO6, which was not reported previously. With increasing Mn composition, the magnetic relaxation due to spin freezing is gradually suppressed. Interestingly, the magnetization in the intermediate Mn compositions relaxes more slowly (characteristic time is significantly enhanced) than those in x = 0.0 and 1.0. This could be understood within the framework of disorder with randomness or imperfections, which plays an important role in the formation of spin-glass-like feature in intermediate Mn compositions, quite different from the cases in x = 0.0 with strong spin frustration and in x ∼ 1.0 with perfect Co/Mn ionic order. [ABSTRACT FROM AUTHOR]

We investigated the structure and magnetic properties of the multiferroic hexagonal manganite Y1-xTbxMnO3 (x = 0, 0.1, 0.2) single crystals. At 23 K, a Mn spin reorientation transition, which is not reported in the parent compound YMnO3, is observed in Y0.8Tb0.2MnO3. At a lower temperature, another new transition is observed in the doping system, which is attributed to the formation of long range antiferromagntic order of the doped Tb3+ moments. Based on the experimental results, we suggest that the effect of Tb doping is to bring about the increase of the Mn-O-Mn bond angle and the relief of the magnetic frustration. With increasing the doping level, for x = 0.2, when a magnetic field is applied parallel to the c axis, the field induced spin-flop transition is appeared, which indicates the reorientation of the Mn3+ moments along with the field-induced ferromagnetic ordering of the Tb3+ moments. These results suggest that the possibility of the Tb doping can change the magnetic structure and ferroelectricity properties of YMnO3. [ABSTRACT FROM AUTHOR]

We have demonstrated that in Ca3Co2-xScxO6, substitution of nonmagnetic Sc3+ (S = 0) for high-spin Cotrig, even up to the solid solubility limit of x = 0.5-0.6, does not dramatically modify the intrachain ferromagnetic (FM) interaction. This is quite different from the cases of Ir- and Rh-doping, which much enhance the intrachain FM interaction, and the cases of Mn-, Fe-, and Cr-doping, which gradually reduce the intrachain FM interaction, simultaneously introducing antiferromagnetic interaction. The results of band-structure calculations of x = 0.5 are qualitatively consistent with our magnetization data. [ABSTRACT FROM AUTHOR]

Various types of anomalies of inverse dc susceptibility (H/M) have been observed in spin-chain compounds Ca3Co2-xMnxO6. For x = 1.0, the H/M curve exhibits a field-dependent downturn from the paramagnetic Curie-Weiss behavior, signaling the presence of a Griffiths-like cluster phase. A slight decrease of x leads to a rapid suppression of the Griffiths-like singularity, followed by an appearance of field-independent, non-Griffiths-like behavior at x = 0.92. This feature persists until x = 0.33, at and below which the H/M curve presents an unambiguous, field-independent upturn from the Curie-Weiss law. These Mn-doping-dependent anomalies of H/M curves are associated with complex competing magnetic interactions. [ABSTRACT FROM AUTHOR]

Measurements of isothermal magnetization and electrical transport on Pr0.5Ca0.5Mn0.97Ga0.03O3 have been performed in a magnetic field up to 15 T. Two distinct metamagnetic transitions, which may relate to the collapse of the pseudo-CE-type and CE-type antiferromagnetic phases (CE, a composite antiferromagnetic structure composed of a chequeboard of alternating C and E type), have been observed in the temperature region of 2.5-140 K. Different from the traditional magnetization steps, the two metamagnetic transitions are not dependent on the field sweep rate. These peculiar features are sensitive to the microstructure of the sample. A temperature-field phase diagram has been constructed and found to exhibit a minimum critical field, similar to other phase-separated systems. [ABSTRACT FROM AUTHOR]

We have performed magnetization measurements of Gd5Ge4 with little or no ferromagnetic (FM) impurities under a pulsed magnetic field up to 40 T. The results reveal previously undetected transitions between 85 and 105 K, that is, a distinct second-order antiferromagnetic (AFM)-paramagnetic (PM) transition, followed by a first-order PM-ferromagnetic (FM) transition. The distinct variation of the slope of the M(H) curves is observed around the AFM-PM transition. Combining our high-field data and those reported earlier, a new magnetic field-temperature phase diagram, in which the AFM, PM, and FM states are well separated, is constructed. [ABSTRACT FROM AUTHOR]

Unusual magnetization process has been observed in Gd5Ge4 prepared with commercial Gd of 99.9 wt %. First, the zero-field-cooled M(H) curves below 25 K contain a significant low-field ferromagnetic (FM) component followed by an unusually broadened field-induced antiferromagnetic (AFM)-FM transition, which was not observed in previous reports no matter if the sample owns a residual FM component or not. Second, the M(H) curves at 4.2 K collected using pulsed magnetic fields reveal some unusual dynamics on the low-field FM state and the following AFM-FM transition. Thus, the present sample of Gd5Ge4 is a new example showing complexity of the influence from impurities of Gd upon the magnetization process. [ABSTRACT FROM AUTHOR]

(Mn, N)-codoped ZnO films have been achieved by oxidative annealing of sputtered Zn2N3:Mn films at different temperatures in flowing O2 ambient. X-ray diffraction measurements and x-ray photoelectron spectroscopy studies indicate that both divalent Mn2+ and trivalent N3- ions are incorporated into ZnO lattice. Ferromagnetism with Curie temperature above 300 K was observed in the (Mn, N)-codoped ZnO films and found to be sensitive to the oxidative annealing temperature due to its strong effect on the carrier type and concentration. The strongest ferromagnetism has been found in the (Mn, N)-codoped ZnO films with the highest hole concentration in this study. The results indicate that holes are favorable for ferromagnetic ordering of doped Mn2+ ions in ZnO in agreement with the recent theoretical studies. The mechanism of ferromagnetic coupling in (Mn, N)-codoped ZnO is discussed. [ABSTRACT FROM AUTHOR]

Field-induced unidirectional anisotropy of Co-based amorphous ribbons was discussed by magnetization measurement. The shifted hysteresis loops of Co58Fe5Ni10Si11B16 amorphous ribbons were obtained by annealing the samples in longitudinal magnetic field. Here, the feasibility of employing the longitudinal pulse field to tailor the anisotropy characteristic is demonstrated. It is found that the shifted loops can be technically controlled by enhancing the pulse field to modulate the magnetic anisotropy from unidirectional to uniaxial, and even back to unidirectional. The surface domains scan gives strong evidence that the pulse field can be one of the skillful methods to navigate the unidirectional anisotropy in the amorphous ribbons for potential applications. [ABSTRACT FROM AUTHOR]

Motivated by the multiferroic effects and quantum magnetization plateaus in the skew chain antiferromagnets T 2 V 2 O 7 (T = Ni, Co), we have conducted a detailed density function theoretical study on Co 2 V 2 O 7. The results show that the nearest-neighbor interchain interaction (J 3 / k B = − 35.57 K) is not much greater than the intrachain interactions (J 1 / k B = − 19.54 K and J 2 / k B = 27.55 K), showing the absence of interchain dimerization of the Co ions. This indicates that the "dimer+monomer" model used for Ni 2 V 2 O 7 [Cao et al., Phys. Rev. B 106, 184409 (2022)] is no longer applicable to Co 2 V 2 O 7. Finally, the exact diagonalization of spin Hamiltonian, including anisotropic exchanges, produces the experimentally observed 1/2 and 3/4 magnetization plateaus. [ABSTRACT FROM AUTHOR]

The performance of Halbach magnetized brushless motors equipped with air-cored and iron-cored rotors is investigated theoretically and experimentally. It is shown that an optimal combination of magnet thickness and pole number exists for maximum air-gap flux density. By employing a rotor back iron, the air-gap field and hence the output torque can be enhanced significantly if the ratio of the radial thickness of the magnet to the pole pitch is small. [ABSTRACT FROM AUTHOR]

The nature of 4f-3d magnetic interaction in oxides as well as its influence on the magnetocaloric effect (MCE) is an interesting topic. Here, we report the weak magnetic interaction and large MCE in a new triangular lattice GdFeTeO6 synthesized by the solid state reaction method. The weak exchange, which was seldom observed in 4f-3d oxides, is supported by the low ordering temperature (TC ≤ 3 K) and a positive but small Curie-Weiss temperature (θp = 3 K). Under an external magnetic field, the magnetization process yields a large magnetic entropy change of 38.5 J kg−1 K−1 at 5 K for 0-7 T and 23.6 J kg−1 K−1 at 3 K for 0-3 T. Finally, our first-principles calculations demonstrate a ferrimagnetic spin model with the Gd(↑)-Gd(↑)-Fe(↓)-Fe(↓) configuration. The weak magnetic interaction is an average effect of ferromagnetic (4f-4f and 3d-3d) and antiferromagnetic (4f-3d) interactions. The antiferromagnetic 4f-3d interaction is a reason for the reduction of MCE. [ABSTRACT FROM AUTHOR]