Abstract Topological materials have gained remarkable attention due to their exotic properties and potential applications in advanced devices. The Ln3MPn5 (Ln = lanthanide, M = transition metal, Pn = pnictide) family, which hosts hypervalent Bi chains, has been identified as a promising platform to study magnetic topological materials. Herein, we present single-crystal growth of new compounds Ln3TiBi5 (Ln = Pr, Nd, and Gd) and their property characterization. Magnetic measurements on Pr3TiBi5 show no apparent indications of magnetic ordering down to 2 K, whereas both Nd3TiBi5 and Gd3TiBi5 show antiferromagnetic ordering at 6.2 and ∼18 K, respectively. Gd3TiBi5 exhibits antiferromagnetic transitions at 17.1 K (H ∥ c) and 18.8 K (H ⊥ c), respectively, suggesting competing ground states of this compound. Heat capacity measurements on the samples confirm the presence of magnetic ordering. DFT calculations reveal band crossings that are located above the Fermi level in Pr3TiBi5 and Nd3TiBi5, while the band structure of Gd3TiBi5 exhibits topologically nontrivial states near the Fermi level. In the presence of SOC, the electronic structure of Gd3TiBi5 changes dramatically. In particular, a local gap opens at the band crossing along M–K, and the band crossing along Γ–A moves above the Fermi level. The crystal orbital Hamilton population (COHP) calculations illustrate the bonding character of Ln-Bi6g, Ln-Bi4d, Ti–Bi6g, Bi4d-Bi4d, and Ti–Ti in Ln3TiBi5 (Ln = Pr, Nd, Gd). Ln forms the strongest bonds with Bi6g, followed by Ti–Bi6g and Ln-Bi4d. Bi4d–Bi4d in 1D Bi2– chains forms hypervalent bonding, with both bonding and antibonding states below the Fermi level. Ti–Ti interactions are relatively weak compared with the other bonding interactions. This work fills the gap in the Ln3TiBi5 family with the synthesis of Pr3TiBi5 and Nd3TiBi5 and also extends it to Gd3TiBi5, the first Gd-containing compound in the anti-Hf5Sn3Cu-type series.

The tetragonal BaAl_4 (I4/mmm) parent structure underpins a diverse family of materials exhibiting novel phenomena, including nematic superconductivity, topological semimetallicity, and heavy fermion behavior. The recent growth of ternary R-Zn-Ga compounds, such as the previously reported CeZn_2Ga_2, has explored some of the members exhibiting rare-earth magnetism within this family. In this paper, we report on the structural and magnetic properties of single crystals of CeZn_2-xGa_2+x, a Ga-rich analogue of CeZn_2Ga_2. Our CeZn_2-xGa_2+x samples exhibit magnetic properties distinct from the paramagnetic behavior previously reported for CeZn_2Ga_2. We observe a magnetic transition around 4 K, pronounced metamagnetic states at low temperatures, and strong magnetic anisotropy. Though there are batch-to-batch variations that suggest a strong sensitivity to local structural imperfections, we consistently see the presence of magnetic transitions and metamagnetic states in our crystals. To investigate the local structural sensitivity hypothesis, we performed Reverse Monte Carlo analysis of collected powder neutron diffraction data, revealing the presence of significant local crystallographic disorder of the magnetic Ce site. Our findings demonstrate that the positional disorder drives competing ferromagnetic and antiferromagnetic correlations that lead to the observed spin glass behavior and complex anisotropic magnetism. This study illustrates that tuning the local crystallographic disorder enables engineering frustrated magnetic states in BaAl_4-type and similar intermetallic structures.

We report a comprehensive investigation of the anisotropic magnetism and magnetic field-induced transitions in single crystals of the orthorhombic system TbAlGe, a member of the topological RAlGe (where R denotes rare earth) family with the highest ordering temeprature in the RAlX (X = Si,Ge) series. With a single rare-earth site with triangular coordination in its Cmcm orthorhombic unit cell, TbAlGe harbors complex magnetic interactions that yield two antiferromagnetic transitions at 40 and 8 K in zero field, and a rich cascade of metamagnetic transitions that only appear for fields directed along the crystallographic a-axis. Combining electrical resistivity, magnetization, and heat capacity measurements with magnetotransport experiments performed up to 41.5 T, we construct a magnetic phase diagram mapping the multiple magnetic phases of TbAlGe, and we discuss the complex interplay between localized 4 f magnetism and itinerant electronic topology, establishing TbAlGe as a compelling platform for exploring tunable magnetic semimetal physics.

A very fundamental property of both weakly and strongly interacting materials is the nature of their magnetic response. In this work, we detail the growth of crystals of the quasicrystal approximant Fe4Al13 with an Al flux solvent method. We characterize our samples using electrical transport and heat capacity, yielding results consistent with a simple non-magnetic metal. However, magnetization measurements portray an extremely unusual response for a dilute paramagnet and do not exhibit the characteristic Curie behavior expected for a weakly interacting material at high temperature. Electronic structure calculations confirm metallic behavior but also indicate that each isolated band near the Fermi energy hosts non-trivial topologies, including strong, weak, and nodal components, with resultant topological surface states distinguishable from bulk states on the (001) surface. With half-filled flat bands apparent in the calculation, but an absence of long-range magnetic order, the unusual quasi-paramagnetic response suggests the dilute paramagnetic behavior in this quasicrystal approximant is surprising and may serve as a test of the fundamental assumptions that are taken for granted for the magnetic response of weakly interacting systems.

We present a detailed investigation of single-crystal samples of the magnetic compound Gd2AlSi3, which crystallizes in the alpha-ThSi2-type tetragonal structure. We report the temperature and magnetic field dependence of the magnetic susceptibility, magnetization, heat capacity, electrical resistivity, and magnetoresistance for magnetic fields applied along both the tetragonal c-axis and in the basal ab plane. X-ray diffraction measurements confirm a centrosymmetric, I41/amd space group of the crystal structure. Despite single-site occupancy of the Gd position in this tetragonal structure, we identify two successive antiferromagnetic phase transitions at Ne & eacute;l temperatures 32 K and 23 K via magnetic susceptibility, heat capacity, and transport measurements, as well as a complex magnetic interaction with a magnetic anisotropy that plays an important role in the direction-dependent transport response. Our identification of multiple magnetic phases in Gd2AlSi3, where Gd is the only magnetic species, helps to elucidate the field-induced skyrmionic behavior in the Gd-based intermetallic compounds.

The chemical pressure-induced magneto-structural changes were investigated in Nd _1-x Eu _x CrO _3 with 0.2 ≤ x ≤ 1.0 compounds. The magnetic study shows the decrease of antiferromagnetic transition temperature ( T_N ) ∼ 220.7 K ( x = 0.2) to 182.5 K ( x = 1.0) due to the modification of Cr-Cr interaction. The spin-reorientation transition ( T _SR ) exhibits for all samples except x = 1.0 with a decrease from ∼ 40.1 K ( x = 0.2) to 13.3 K ( x = 0.9). We observed the exchange bias (EB) effect and the EB field decreases with increasing Eu content. The chemical pressure boundary at x = 0.5 is marked and the lattice softens on both sides of this substitution. The magnetoelastic coupling below T_N is revealed by the temperature dependence of the lattice parameters, Cr-O lengths, Cr-O-Cr angles, and Nd/Eu positions for x < 0.5 samples. We have reported the electron density distribution using the maximum entropy method for the first time in the Nd _1-x Eu _x CrO _3 compound. Interestingly, we found a structural reorientation around ∼ 80 K between T_N and T _SR from a centrosymmetric structure ( Pnma ) with unstable electron density to a stable noncentrosymmetric (Pna2_1) structure.

We report a detailed investigation of the superconducting properties of the kagome-honeycomb lattice compound LaRu3Si2 by systematically tuning the spin-orbit coupling (SOC) via doping of heavier elements Rh and Ir at the Ru site. All doped samples (for a doping level of 10 at. %) preserve the pristine hexagonal crystal structure in the space group P63/mmc, though a marginal lattice compression was noted for Rh doping. Based on the results of dc magnetization, resistivity, and heat capacity measurements, we derived the normal and superconducting state electronic and thermodynamic properties of the pristine and doped samples. Substitution of Ir/Rh at the Ru site of LaRu3Si2 resulted in a rather slow but linear suppression of superconducting transition temperature (Tc), which may be related to the decrease in the density of states. As manifested by the estimated electron-phonon (el-ph) coupling constant (lambda el-ph -0.58-0.66) and the normalized specific heat jump at Tc (AC/gamma Tc -1.5), the observed superconductivity in LaRu3Si2 and the doped variants is moderately coupled. We observed a nonmonotonous variation of the upper critical field [mu 0Hc2(0)] with respect to the doping concentration, as it is influenced by the effective SOC and the coherence length. Most strikingly, we found an enhancement of the superconducting gap parameter (40/kBTc) with doping concentration even though lambda el-ph remains essentially unchanged. Moreover, we also notice a nonzero residual electronic specific heat coefficient (gamma r) in the limit T -> 0 for all compositions. Interestingly, the evolution of the gamma r with the magnetic field can be well described by a root H dependence, which was attributed to multiband superconductivity.

We report the electronic properties of R4PtAl (R = Ho, and Er), which contains three sites for R, by the measurements of magnetization (ac and dc), heat-capacity, transport, and magnetoresistance (MR). Dc magnetization data reveal antiferromagnetic order below 19 K and 12 K in Ho and Er compounds, respectively. Additional features observed at lower temperatures (12 K for Ho4PtAl and 5 K for Er4PtAl) are akin to the cluster spin-glass phase. Resistivity data exhibit a weak minimum at a temperature marginally higher than their respective Néel temperature (TN), which is unusual for such rare-earths with well-localized 4f states. Isothermal magnetization and magnetoresistance data well below TN exhibit signatures of a subtle field-induced magnetic transition for a small magnetic field (<10 kOe). Notably, the isothermal entropy change at TN has the largest peak value within this rare-earth family; for a field change from zero to 50 kOe, the entropy change is ~14.5 J/kg K (Ho4PtAl) and ~21.5 J/kg K (Er4PtAl) suggesting a role of anisotropy of 4f orbital in determining this large value. The results provide some clues for the advancement of the field of magnetocaloric effect. The magnetocaloric property of Er4PtAl is nonhysteretic, meeting a challenge to find materials with reversible magnetocaloric effect.

Partially disordered antiferro (PDA) magnetism (in which one of the three magnetic ions in a triangular network remains magnetically disordered), has been known commonly among geometrically frustrated insulating materials. The one-third plateau in isothermal magnetization (M) of such materials has been of great theoretical interest. Here, we report these properties in a AlB2-structure derived metallic material, Er2RhSi3 in which Er sublattice has triangular networks. The presence of a well-defined lamda anomaly in the temperature (T) dependence of heat capacity and its magnetic-field (H) dependence, and the loss of spin-disorder contribution in electrical resistivity (rho) confirm antiferromagnetic order below (TN=) 5 K. On the other hand, the separation of zero-field-cooled and field-cooled dc magnetic susceptibility (chi) curves, decay of isothermal remnant magnetization and the frequency dependence of real and imaginary components of ac chi suggest the onset of spin-glass freezing concomitant with the antiferromagnetic order. In addition, interestingly, we observe one-third plateau in M(H) below 20 kOe for T less than TN. The change in rho as a function of H at a given temperature well below TN is also revealing, with this compound exhibiting a plateau below 20 kOe, with complexities at higher fields. Therefore, this compound serves as a prototype for theoretical understanding of transport behavior across one-third plateau due to PDA magnetism in a metal without any interference from the 4f delocalization phenomena.

The Haldane-spin chain compound, Tb2BaNiO5, has been known to be an exotic multiferroic system, exhibiting antiferromagnetic anomalies at T_N1= 63 K and T_N2= 25 K, with ferroelectricity appearing below T_N2 only. Previous reports in addition established that, interestingly, Tb ions play a direct and decisive role to lead to multiferroic properties with a critical canting angle of magnetic moments, unlike other well-known multiferroics. Here, we report the results of temperature dependent neutron powder diffraction studies on Tb_2-x Y_x BaNiO_5, to get an insight into the critical canting angle for multiferroic behavior. While multiferroic transition temperature decreases linearly with Y concentration, there is an abrupt drop of relative canting angle (of Tb and Ni magnetic moments) with respect to that in parent compound for an initial substitution ofx = 0.5 in the multiferroic region, without any notable change thereafter. We therefore infer that this critical canting angle is made up of two components - cooperative (long-range) and local (short-range) contributions.

We report the results of magnetic, heat-capacity, electrical and magnetoresistance measurements on Ho4RhAl and Er4RhAl, characterized by 3 sites for rare-earths (R). Antiferromagnetic ordering sets in at (T_N =) about 8.8 and 4.0 K respectively. While Ho compound appears to enter into a complex spin-glass phase at T less thanT_N (at nearly 5 K), spin-glass component appears to set in essentially almost at T_N for the Er case. The loss of the spin-disorder contribution in the magnetically ordered state is not pronounced, mimicking that in Gd2PdSi3, a compound which now attracts interest in the area of topological Hall effect and magnetic skyrmions, indicating complex Fermi surface. There is a minimum in the temperature dependence of electrical resistivity in the case of only Ho above T_N, but significant negative magnetoresistance is observed over a wide temperature range in the paramagnetic state increasing with decreasing temperature for both the cases. This finding establishes that these compounds belong to a select group of intermetallics in which spin-disorder contribution apparently increases gradually as one approaches respective TN with decreasing temperature. This could be an experimental signature for the effect due to classical spin-liquid above T_N. In view of these properties analogous to those of Gd2PdSi3, it is of interest to investigate these 4:1:1 compounds further to understand possible unconventional roles of itinerant electrons, not only in the magnetically ordered state but also in the paramagnetic state, predicted by some theories in recent years for which this Gd compound is considered to be a classic example.Besides, magnetoresistance and isothermal entropy change (magnetocaloric effect) track each other.

We report complex magnetic, magnetoresistance (MR) and magnetocaloric properties of Gd4RhAl and Tb4RhAl forming in the Gd4RhIn type cubic structure. Though the synthesis of the compounds was reported long ago, to our knowledge, no attempt was made to investigate the properties of these compounds. The present results of ac and dc magnetization, electrical resistivity and heat-capacity measurements down to 1.8 K establish that these compounds undergo antiferromagnetic order initially, followed by complex spin-glass features with decreasing temperature. These characteristic temperatures are: For Gd case, TN is about 46K and TG is about 21 K, and for Tb, about 32 and 28 K respectively. Additionally, there are field induced magnetic effects, interestingly leading to non-monotonic variations in MR. There is a significant MR over a wide temperature range above TN, similar to the behavior of magnetocaloric effect (MCE) as measured by isothermal entropy change (DeltaS). An intriguing finding we made is that DeltaS at the onset of magnetic order is significantly larger for the Tb compound than that observed for the Gd analogue near its TN. On the basis of this observation in a cubic material, we raise a question whether aspherical nature of the 4f orbital can play a role to enhance MCE under favorable circumstances, a clue that could be useful to find materials for magnetocaloric applications.

We have studied the influence of external pressure up to 1 GPa on the magnetic transitions of the orthorhombic Haldane-spin chain compound Tb2BaNiO5 an exotic multiferroic material. This parent compound is known to undergo N\'eel ordering at TN1= 63 K and another magnetic transition at TN2= 25K at which ferroelectricity sets in, however, without any change in the magnetic symmetry, but with only a sharp change in the canting angle of Tb 4f and Ni 3d magnetic moments. There is a subtle difference in the antiferromagnetic state above and below TN2, which is supported by the fact that there is a metamagnetic transition below TN2only (for 5 K, at about 60 kOe). We report here that, with the application of external pressure, there is an upward shift of TN1, while TN2 shifts towards lower temperatures. It is interesting that the two magnetic transitions in the same compound behave differently under pressure and the opposite behavior at TN2 is attributed to local distortion leading to ferroelectricity. The results are augmented by temperature dependent x-ray diffraction and positive chemical pressure studies. The chemical pressure caused by the isoelectronic doping at Ba site by Sr reduces both the transition temperatures. Clearly, the external pressure favors antiferromagnetic coupling (that is, leading to TN1 enhancement), whereas the chemical pressure reduces TN1, suggesting important role of the changes in local hybridization induced by doping on magnetism in this material.

The compound Dy4PtAl, belonging to a recently reported rare-earth family forming in Gd4RhIn-type cubic crystal structure, is studied by various bulk measurements down to 1.8 K for its magnetic and transport behavior. We emphasize on the fact that the onset of magnetic order is of a ferromagnetic type, unlike in Gd and Tb analogues. The ferromagnetism that sets in at 32 K transforms to spin-glass phase, predominantly around 20 K as the temperature is lowered, as suggested by ac and dc magnetization data. It appears that there is another spin-glass-like magnetic feature around 10 K. There is an evidence for a disorder-broadened field-induced ferromagnetic transition at low temperatures. As a result, there are many fascinating findings in the isothermal magnetoresistance (MR) data including evidence for magnetic phase co-existence and for complex butterfly-shaped hysteresis loops with varying temperature. There are sign reversals with varying temperature and magnetic field, which are associated with the complexity of the transport process. There is a resistivity minimum before long range order sets.

The compound, HfMnMo3O12, the synthesis of which was reported recently, has been shown to exhibit a structural phase transition from a monoclinic to an orthorhombic form above room temperature (T). It was also reported that this compound exhibits negative thermal expansion (NTE) coefficient in the orthorhombic phase, despite the fact that HfMgMo3O12 does not show this behavior. Here, we report the results of magnetic investigations in the temperature interval 1.8 - 360 K. The results establish that this compound undergoes antiferromagnetic ordering below (T-N=) 7.3 K, presumably from divalent Mn and it is of interest to focus future studies to understand possible role of the magnetism on Mn on NTE. It is to be remarked that heat-capacity deviates from T-3 form in the Neel ordered state. Finally, low-field (100 Oe) magnetic susceptibility shows a jump around 348 K, as a consequence of possible structural transition, as though there is a magnetoelastic coupling. This feature is washed out in 5 kOe, thereby suggesting sensitivity of a such coupling for small applications of magnetic fields - an observation relevant to applications.

We have carried out magnetization, heat capacity, electrical and magnetoresistance measurements (2-300 K) for the polycrystalline form of intermetallic compounds, R2RhSi3 (R= Gd, Tb, and Dy), forming in a AlB2 derived hexagonal structure with a triangular R network. This work was primarily motivated by a revival of interest on Gd2PdSi3 after about two decades in the field of Toplogical Hall Effect due to magnetic skyrmions. We report here that these compounds are characterized by double antiferromagnetic transitions (T_N= 13.5 and 12 K for Gd, 13.5 and 6.5 K for Tb; 6.5 and 2.5 for Dy), but antiferromagnerism seems to be complex. The most notable observations common to all these compounds are: (i) There are many features in the data mimicking those seen for Gd2PdSi3, including the two field-induced changes in isothermal magnetization as though there are two metamagnetic transitions well below T_N. In view of such a resemblance of the properties, we speculate that these Rh-based materials offer a good playground to study toplogical Hall effect in a centrosymmetric structure, with its origin lying in triangular lattice of magnetic R ions; (ii) There is an increasing contribution of electronic scattering with decreasing temperature towards T_N in all cases, similar to Gd2PdSi3, thereby serving as examples for a theoretical prediction for a classical spin-liquid phase in metallic systems due to geometrical frustration.

We report temperature (T) dependence (2-330 K) of DC and AC magnetization (M), isothermal remnant magnetization (M_IRM), heat capacity (C), electrical resistivity (rho), and magnetoresistance (MR) of a ternary intermetallic compound, Gd4PtAl, crystallizing in a cubic (space group F-43m) structure. In this structure, there are three sites for the rare-earth. The magnetization data reveal that, in addition to a magnetic transition at 64 K, there is another magnetic feature below 20 K. The C(T) data reveal an upturn below 64 K, shifting to a lower temperature with increasing field, which establishes that the onset of magnetic order is of an antiferromagnetic type. However, there is no worthwhile feature near 20 K in the C(T) curve. AC susceptibility peak undergoes an observable change with frequency and, in particular, the peak around 20 K gets suppressed with the application of a dc magnetic field; in addition, M_IRM undergoes a slow decay with time and isothermal M exhibits low-field hysteresis below 20 K only, which is typical of spin-glasses. The results overall suggest that this compound is a reentrant spin-glass in zero-field. There are experimental signatures pointing to the existence of both antiferromagnetic and ferromagnetic components, competing with the variation of temperature and magnetic field, as a result of which electrical and magnetoresistance behaviors are peculiar. The results overall suggest this compound exhibits interesting magnetic and transport properties.

We report an unusual canted magnetism due to 3d and 4f electrons, occupying two different crystallographic sites, with its consequence to electric dipole order. This is based on neutron powder diffraction measurements on Tb2BaNiO5 (orthorhombic, Immm centrosymmetric space group), exhibiting Neel order below (TN) 63 K, to understand multiferroic behavior below 25 K. The magnetic structure is made up of Ni and Tb magnetic moments, which are found to be mutually canted in the entire temperature range below TN, though collinearity is seen within each sublattice, as known in the past. First-principles density functional theory calculations (GCA plus SO and GCA plus U plus SO approximations) support such a canted ground state. The intriguing finding, being reported here, is that there is a sudden increase in this Tb-Ni relative cantingle angle at the temperature (that is, at 25 K) at which spontaneous electric polarization sets in, with bond distance and bong angle anomalies. This finding emphasizes the need for a new spin-driven polarization mechanism, that is, a critical canting angle coupled with exchangestriction, to induce multiferroicity in magnetic insulators with canted spins.