Weak ferromagnetism in Fe1-xCoxSb2

Angewandte Chemie International Edition, 2010

Transition metal compounds exhibiting spontaneous drops in magnetization are being investigated for use as molecular switches, sensors, and data storage devices. This phenomenon of magnetization change is generally associated with spin transition or spin crossover (high spin to low spin) induced by temperature, pressure, or irradiation, and is generally found in insulating antiferromagnetic oxides and in transition metal complexes containing 3d n (4 n 7) ions, such as iron(II), iron(III), or cobalt(III), in octahedral or squareplanar coordination. Spontaneous loss of magnetization can also be induced by other mechanisms, such as the spin dimerization observed in CuIr 2 S 4 , the so-called spin-Peierls transition observed in CuGeO 3 , and the Verwey transition, which is commonly observed in mixed-valence transition metal oxides with the AB 2 X 4 spinel or inverse spinel structures such as magnetite (Fe 3 O 4 ). The loss of magnetization in Verwey compounds is accompanied by a metal-to-insulator transition, which is interpreted as resulting from long-range ordering of the mixed-valence ions within the B sites of the spinel structure. Herein we present the observation of room-temperature ferromagnetism, semiconductivity, and reversible, cooperative magnetic and semiconductor-to-insulator (SI) transitions in FeSb 2 Se 4 . To the best of our knowledge, the coexistence of these phenomena in a single transition metal chalcogenide compound has not been reported to date. Despite the analogy of stoichiometry between FeSb 2 Se 4 and CuIr 2 S 4 and the similarity in the formal distribution of charges between Fe 2+ (Sb 3+ ) 2 (Se 2À ) 4 and Fe 2+ (Fe 3+ ) 2 (O 2À ) 4 (magnetite), the crystal structures of these compounds are profoundly different and none of the mechanisms mentioned above is suitable for the interpretation of the phase transitions observed in the three-dimensional monoclinic structure of FeSb 2 Se 4 . Therefore, alternative mechanisms to explain the observed transitions must be explored. Because the nature of the phase transitions in FeSb 2 Se 4 can be rather complex, we have tackled the problem by performing systematic investigations of 1) the crystal structure above and below the transition temperature, 2) the thermal evolution of unit cell parameters using X-ray diffraction on powder and on single-crystal samples, 3) the electrical resistivity, and 4) the magnetic properties across the transition temperature.

The European Physical Journal B, 2006

We propose FeSb 2 to be a nearly ferromagnetic small gap semiconductor, hence a direct analog of FeSi. We find that despite different compositions and crystal structures, in the local density approximation with on-site Coulomb repulsion correction (LDA+U) method magnetic and semiconducting solutions for U =2.6 eV are energetically degenerate similar to the case of FeSi. For both FeSb 2 and FeSi (FeSi 1−x Ge x alloys) the underlying transition mechanism allows one to switch from a small gap semiconductor to a ferromagnetic metal with magnetic moment ≈ 1µ B per Fe ion with external magnetic field.

Proceedings of the National Academy of Sciences, 2021

Significance For many decades, it has been commonly believed that all electronic states of a collinear antiferromagnet (AF) are spin-degenerate, unless the underlying crystal structure lacks centrosymmetry and has spin–orbit coupling. This has been essentially definitional for antiferromagnetism and is widely used experimentally to distinguish ferromagnets from AFs. Recently, it was demonstrated that a new class of magnets, possessing antiferromagnetic order and without net magnetization but showing a typical ferromagnetic response in many aspects, is possible. We predict that F e S b 2 , which is well known but poorly understood magnetically, is an incipient unconventional magnet of this type and can be pushed to become one by Co or Cr doping. Moreover, the calculated magnetic anisotropy is favorable for exhibiting various anomalous properties.

Scientific Reports

Magnetic topological materials are promising for realizing novel quantum physical phenomena. Among these, bulk Mn-rich MnSb2Te4 is ferromagnetic due to MnSb antisites and has relatively high Curie temperatures (TC), which is attractive for technological applications. We have previously reported the growth of materials with the formula (Sb2Te3)1−x(MnSb2Te4)x, where x varies between 0 and 1. Here we report on their magnetic and transport properties. We show that the samples are divided into three groups based on the value of x (or the percent septuple layers within the crystals) and their corresponding TC values. Samples that contain x < 0.7 or x > 0.9 have a single TC value of 15–20 K and 20–30 K, respectively, while samples with 0.7 < x < 0.8 exhibit two TC values, one (TC1) at ~ 25 K and the second (TC2) reaching values above 80 K, almost twice as high as any reported value to date for these types of materials. Structural analysis shows that samples with 0.7 < x <...

2019

Richardson. A very special thank you to Renee Hilgendorf for all her support and guidance during my entire doctoral journey. Thank you for all you do. To Kim Elliott, Andria Rose, Shira Washington, and Tiffany Porties for help during my time at Michigan. A very special thank you to my cohort of 2013. We started the doctorate journey together and their support and camaraderie have been greatly appreciated. A warm thank you to Elizabeth Kwamboka Gichana for your friendship and support during the thesis writing process. Lastly, I would like to thank my family; my mamá Maria "Imilla", my papá Miguel "K'aspikunka", and my brother Juanvi "Yasa Siki" for their love and support throughout my entire journey at the University of Michigan.

Physical Review B, 2011

We analyze the thermodynamic, magnetic, and transport properties of the narrow band-gap semiconductor FeSb 2 using density functional theory calculations corroborated by nuclear inelastic spectroscopy and ultrasound experiments. The vibrational properties (phonon spectrum, density of states, heat capacity) and elastic constants are computed through response function calculations and are in good agreements with the measurements. The electron-phonon coupling effects are also studied. The estimations of linewidth broadening due to electron-phonon coupling along the high-symmetry directions in the first Brillouin zone are given. The linewidth broadening reaches the largest value for Fe optical modes in the vicinity of the X[0.5,0,0] point. The broadening, when compared to those obtained at the other symmetry points, differs by up to two orders of magnitude. From the Boltzmann theory applied to our electronic band structure, we investigate the electrical transport properties. It is found that a purely electronic structure description is incompatible with the record value of the Seebeck coefficient experimentally observed at T ≈ 12 K. The diamagnetic to paramagnetic crossover at a temperature around 100 K is also described from the calculation of the magnetic susceptibility, and results compare well with experiment.

Physical Review B, 2011

We report inelastic neutron scattering measurements aimed at investigating the origin of the temperature-induced paramagnetism in the narrow-gap semiconductor FeSb2. We find that inelastic response for energies up to 60 meV and at temperatures ≈ 4.2 K, ≈ 300 K and ≈ 550 K is essentially consistent with the scattering by lattice phonon excitations. We observe no evidence for a welldefined magnetic peak corresponding to the excitation from the non-magnetic S = 0 singlet ground state to a state of magnetic multiplet in the localized spin picture. However, a broad magnetic scattering continuum in the 15 meV to 35 meV energy range is not ruled out by our data. Our findings make description in terms of the localized Fe spins unlikely and suggest that paramagnetic susceptibility of itinerant electrons is at the origin of the temperature-induced magnetism in FeSb2.

Physical Review B, 2021

Neutron diffraction and x-ray pair distribution function experiments were performed to investigate the magnetic and local crystal structures of ${\mathrm{Ba}}_{2}\mathrm{FeSb}{\mathrm{Se}}_{5}$ and to compare them with the average (i.e., long range) structural model previously obtained by single-crystal x-ray diffraction. Changes in the local crystal structure (i.e., in the second coordination sphere) are observed upon cooling from 295 to 95 K, resulting in deviations from the average (i.e., long range) crystal structure. In this paper, we demonstrate that these observations cannot be explained by local or long-range magnetoelastic effects involving Fe-Fe correlations. Instead, we found that the observed differences between local and average crystal structure can be explained by Sb-$5s$ lone pair dynamics. We also find that, below the N\'eel temperature $({T}_{N}=58\phantom{\rule{0.16em}{0ex}}\mathrm{K})$, the two distinct magnetic ${\mathrm{Fe}}^{3+}$ sites order collinearly, s...

2009

Research Square (Research Square), 2023

Magnetic topological materials are promising for realizing novel quantum physical phenomena. Among these, bulk Mn-rich MnSb 2 Te 4 is ferromagnetic due to Mn Sb antisites and has relatively high Curie temperatures (T C), which is attractive for technological applications. We have previously reported the growth of materials with the formula (Sb 2 Te 3) 1−x (MnSb 2 Te 4) x. Here we report their magnetic and transport properties. We show that the samples are divided into three groups based on the percent septuple layers (SLs) within the crystals and their corresponding T C values. Samples that contain less than 70% or more than 90% SLs have a single T C value of 15-20K and 30-40K, respectively, while samples with between 70-80% SLs exhibit two T C values, one at ~ 30-40K and the second (T C2) reaching values above 80K, almost twice as high as any reported value to date for these type of materials. Structural analysis shows that samples with 70-80% SLs have large regions of only SLs, which should give rise to a T C of ~ 30-40K, while other regions have isolated QLs embedded within the SL lattice. We propose that the latter regions are responsible for the higher T C2 values. Our results have important implications for the design of magnetic topological materials having optimum properties.