arXiv subjects

Gina Angelo

Publications and source records attributed to Gina Angelo.

5 recordsLinked to original sources

arXiv2025

Site Preference and Possible Coexistence of Antiferromagnetic Order and Magnetic Frustration in (Co1-xMgx)10Ge3O16 (0 <= x <= 30%)

Geometrically frustrated magnetism has attracted tremendous attention while chemical doping has been utilized as an important tool to probe frustrated magnetism in various systems. Here we perform a systematic study by doping non-magnetic Mg2+ into a magnetically complicated system, Co10Ge3O16, which contains three frustrated sublattices of Co2+, e.g., triangular Co1, Kagome Co2 and Co3 sublattices. By growing crystals for (Co1-xMgx)10Ge3O16 (0 < x <= 30%), we observed obvious site preference of Mg2+ on Co1 and Co3 sites over the Co2 site. Powder X-ray diffraction (XRD) patterns confirm the high purity of the samples and indicate systematic peak shift, consistent with the loading compositions. Although previously investigated, the magnetic structure and expected magnetic frustration in this system are not fully uncovered. Our temperature-dependent magnetic susceptibility measurements suggest that the high-temperature magnetostructural phase transition with antiferromagnetic ordering and a low-temperature broad peak are suppressed with Mg2+ doping, while two new magnetic features emerge at high Mg2+ level. Moreover, the structural phase transition from high-temperature R-3m to low-temperature C2/m space group is absent at the antiferromagnetic ordering temperature, as confirmed by single-crystal XRD. By analyzing the heat capacity and neutron powder diffraction results of the highest doped sample, (Co0.7Mg0.3)10Ge3O16, we speculate that the Co1 site is responsible for the long-range antiferromagnetic ordering, while the other two sites are short-range correlated in addition to a Mg2+-induced spin-glass state. This study provides more insights into the complex magnetism in Co10Ge3O16 by using the non-magnetic Mg2+ as a probe. However, detailed magnetic structure requires further efforts on growing large single crystals.

cond-mat.str-el↗

arXiv2024

ASb3Mn9O19 (A = K or Rb): New Mn-Based Two-Dimensional Magnetoplumbites with Geometric and Magnetic Frustration

Magnetoplumbites are one of the most broadly studied families of hexagonal ferrites, typically with high magnetic ordering temperatures, making them excellent candidates for permanent magnets. However, magnetic frustration was rarely observed in magnetoplumbites. Herein, we report the discovery, synthesis and characterization of the first Mn-based magnetoplumbite, as well as the first magnetoplumbite involving pnictogens (Sb), ASb3Mn9O19 (A = K or Rb). The Mn3+ (S = 2) cations, further confirmed by DC magnetic susceptibility and X-ray photoelectron spectroscopy, construct three geometrically frustrated sublattices, including Kagome, triangular and puckered honeycomb lattices. Magnetic properties measurements revealed strong antiferromagnetic spin-spin coupling as well as multiple low-temperature magnetic features. Heat capacity data did not show any prominent lambda-anomaly, suggesting minimal associated magnetic entropy. Moreover, neutron powder diffraction implied the absence of long-range magnetic ordering in KSb3Mn9O19 down to 3 K. However, several magnetic peaks were observed in RbSb3Mn9O19 at 3 K, corresponding to an incommensurate magnetic structure. Interestingly, strong diffuse scattering was seen in the neutron powder diffraction patterns of both compounds at low angles, and was analyzed by reverse Monte Carlo refinements, indicating short-range spin ordering related to frustrated magnetism as well as two-dimensional magnetic correlations in ASb3Mn9O19 (A = K or Rb).

cond-mat.mtrl-sci↗

arXiv2024

Evolution of Ferromagnetism and Electrical Resistivity in Sb-Doped Cr4PtGa17

We describe the doping effects on a metallic breathing pyrochlore compound, Cr4PtGa17. Upon doping with Sb, i.e., Cr4Pt(Ga1-xSbx)17, it was found that a selective doping on one of the seven Ga sites occurs. With increasing dopant level, the ferromagnetism in the parent compound is gradually suppressed, along with a decrease in fitted Curie-Weiss temperature (from 61 (1) K to -1.8 (1) K) and effective moment (from ~2.26 muB/f.u. to ~0.68 muB/f.u.). Low-temperature heat capacity measurements confirm the absence of magnetic ordering above 0.4 K for the three most doped samples. Meanwhile, electrical resistivity measurements display a metal-semiconductor transition with increasing Sb contents, which is attributed to an increase of Fermi energy based on the calculations of electronic band structure and density of states. Moreover, we have speculated that the ferromagnetism in Cr4PtGa17 is governed by itinerant electrons according to our observations. This study of Sb-doping effect on Cr4PtGa17 provides deeper understanding of magnetism of this system and possibilities for future modifications.

cond-mat.mtrl-sci↗

arXiv2024

Absence of Long-Range Magnetic Ordering in a Trirutile High-Entropy Oxide (Mn$_{0.2}$Fe$_{0.2}$Co$_{0.2}$Ni$_{0.2}$Cu$_{0.2}$)Ta$_{1.92}$O$_{6-\delta}$

Functionalities of solid-state materials are usually considered to be dependent on their crystal structures. The limited structural types observed in the emerged high-entropy oxides put constraints on exploration of their physical properties and potential applications. Herein, we synthesized the first high-entropy oxide in a trirutile structure, (Mn$_{0.2}$Fe$_{0.2}$Co$_{0.2}$Ni$_{0.2}$Cu$_{0.2}$)Ta$_{1.92}$O$_{6-\delta}$, and investigated its magnetism. The phase purity and high-entropy nature were confirmed by powder X-ray diffraction and energy-dispersive spectroscopy, respectively. X-ray photoelectron spectroscopy indicated divalent Mn, Co, Ni and Cu along with trivalent Fe. Magnetic properties measurements showed antiferromagnetic coupling and potential short-range magnetic ordering below ~ 4 K. The temperature-dependent heat capacity data measured under zero and high magnetic field confirmed the lack of long-range magnetic ordering and a possible low-temperature phonon excitation. The discovery of the first trirutile high-entropy oxide opens a new way for studying the relationship between the highly disordered atomic arrangement and their magnetic interaction. Furthermore, it provides a new direction for exploring functionalities of high-entropy oxides.

cond-mat.mtrl-sci↗

arXiv2023

Magnetic Order in A Quenched-High-Temperature-Phase of Cu-Doped MnBi

Permanent magnets are of great importance due to their vast applications. MnBi has been proposed to be a potential permanent magnet that can be widely used while past efforts have been focused on optimizing the ferromagnetic low-temperature phase of MnBi. Herein, we report a series of new materials, CuxMn1-xBi, crystallizing in a quenched high-temperature-phase (QHTP) MnBi-related structure. We synthesized single crystals of CuxMn1-xBi and found that they crystallize in an unreported trigonal structure (P -31c). Magnetic properties measurements imply high-temperature antiferromagnetic (AFM) ordering and low-temperature ferromagnetic or ferrimagnetic (FM/FiM) ordering. By analyzing the doping effect on crystal structure and magnetic properties, we established a magnetic phase diagram for Cu-doped MnBi and attributed the AFM and FM/FiM to two different atomic sites of Mn.

cond-mat.mtrl-sci↗