Rare earth-based frustrated systems provide an excellent platform to study novel magnetic phenomena owing to their localized moment and unquenched orbital momentum. Here, we present a comprehensive investigation of crystallographic and thermodynamic properties of TbTaO4 and DyTaO4, wherein the magnetic ions form a distorted diamond structure. The former exhibits a crossover from short-ranged magnetic correlations to long-ranged antiferromagnetic ordering at ∼2.2 K, while the latter manifests only short-ranged magnetic correlations down to 1.8 K. Interestingly, a field-induced frequency dependence is observed in AC susceptibility in both cases, similar to that observed in spin ice systems. Analysis using the Casimir−duPre plot and Arrhenius law confirms that the origin behind this spin relaxation is thermal in nature, with activation energy close to the first excited crystal electric field gap. Our studies suggest that the observed frequency-dependent behavior is not only limited to spin ice materials, but it is a generic phenomenon in a broader class of rare earth-based frustrated magnetic systems.

J. Kumar et al, J. Am. Chem. Soc. 147, 14442–14454 (2025).

Frustrated magnetism, driven by competing exchange interactions, remains a pivotal topic in modern condensed-matter physics. In frustrated systems, observation of a partially disordered (PD) state where long range magnetic order coexists with disorder is a unique phenomenon. Here, we focus on the emergence of a PD state and its underlying mechanism in a Heusler alloy, Pd2DySn. Our findings reveal that this alloy crystallizes in a cubic structure and undergoes a partial transformation to tetragonal phase at low temperatures. The static magnetization and heat capacity studies reveal three successive long-ranged antiferromagnetic transitions at ∼16, 12, and 6 K, respectively, while dynamic magnetization studies provide clear evidence for multiple cluster glass transitions, concomitant with the long-range ordering temperatures. This study demonstrates the coexistence between antiferromagnetic and glassy magnetic states, which is a relatively rare phenomenon in Heusler alloys. We propose that the emergence of the PD state stems from magnetic frustration induced by the structural distortion rather than geometrical frustration associated with triangular networks of magnetic ions as observed in other PD magnetic systems.

Koushik P et al, Phys. Rev. B 111, 134435 (2025). 

Interplay between spin-orbit coupling and magnetic frustration can give rise to unique quantum phases with unusual excitations. Here, we report a comprehensive analysis of YbNbO4, where Yb3+ ions form a stretched diamond sublattice within the monoclinic crystal structure. Our bulk experimental investigations exclude the presence of magnetic ordering and spin freezing. Additionally, a low-energy effective spin-1/2 state is noted at lower temperatures. Our muon spin relaxation (μSR) measurements reveal the absence of static internal field. However, a critical slowing down of spins is observed below 2 K due to the development of strong magnetic correlations. The longitudinal field μSR investigations further suggest the strongly fluctuating nature of the spins and confirms the correlated dynamical ground state in YbNbO4 down to 300 mK. Our studies suggest that the titled system can be a potential candidate for hosting a spin liquid state.

J. Kumar et al, Phys. Rev. B 111, 014411 (2025)

Disordered materials often exhibit complex magnetic and electrical transport properties at low temperatures. Investigation of such phenomena is of current interest and is being actively pursued. Here, we have investigated the impact of carrier localization on the physical properties of a half-Heusler alloy, Ir0.9Mn0.95Sn1.15. Our studies reveal that this alloy exhibits Y-type chemical disorder and undergoes a cluster glass transition around 67 K. At low temperatures, the longitudinal resistivity exhibits a robust upturn arising due to electron-electron interaction. Along with this, below 100 K, an anomalous Hall effect driven by an intrinsic mechanism is also noted. Remarkably, the effect of localization manifests concurrently in magnetization, longitudinal resistivity, and all components of the Hall effect. Our observations are not in analogy with the existing theories that consider the skew scattering and side jump mechanisms of the anomalous Hall effect.

Koushik P et al, Phys. Rev. B 110, 174419 (2024)

Reentrant glassy systems are a class of disordered magnetic materials which can potentially host noncollinear spin state. Here, we focus on the role of site disorder on emergence of reentrant cluster glass state and the underlying mechanism for observation of anomalies in electrical transport properties of Ti2FeAl. Structural and magnetic studies reveal that this alloy hosts strong site disorder resulting in development of a reentrant cluster glass state (below10 K) along with a ferromagnetic ordering (around 30 K). Electrical resistivity in this alloy mimics a Kondo-like behavior along with the presence of weak localization effect at low temperatures. Remarkably, Hall resistivity measurements in glassy regime indicate a nontrivial, unconventional contribution which is attributed to the existence of noncollinear spin state. 

Koushik P et al, Phys. Rev. B. 110, 054433 (2024) 

Realization of persistent discrete energy states in Co-based compounds due to unquenched orbital angular momentum remains an exciting perspective in systems which favour mixed state of Co2+ and Co3+ ions, without any chemical substitution. Structural investigations reveal the presence of anti-site disorder between V and Co results in Co3+ ions along with the expected Co2+ ions. A thorough investigation of AC susceptibility reveal the presence of cluster glass state below 3 K, strengthened by relaxation and memory effect measurements. The detailed analysis of the observed Schottky anomaly reveal the presence of persistent discrete energy state of Co3+ ions which appears due to octahedral distortion and spin-orbit coupling.

Dheeraj Ranaut  et  al,  Phys. Rev. B 107, 214413 (2023)

Our studies reveal that LuPd2Sn is a type II superconductor and undergoes superconducting transition below 2.5 K. Above 2.5 K, the temperature and field dependence of resistivity indicate to the presence of multiple bands and inter-band phonon assisted scattering. The upper critical field, HC2 exhibits linear behaviour and deviates from Werthamer, Helfand and Hohenberg model over the measured temperature range. Additionally, the Kadowaki–Woods ratio plot supports the unconventional superconductivity in this alloy. Moreover, a significant deviation from the s-wave behaviour is noted, which is studied using phases fluctuation analysis. It indicates the presence of spin triplet along with spin singlet component arising due to antisymmetric spin orbit coupling.  

Kavita Yadav  et  al,  J. Phys. Condens. Matter 35, 275601 (2023)

Novel quantum spin liquid (QSL) state is realised in HoVO4 via the means of experimental as well as computational techniques. Short-range correlations develop at low temperatures and the residual heat capacity follows quadratic dependence on temperature in the region of these correlations. This power law dependence matches very well with other 3D QSL materials. DFT calculation of magnetic interactions indicate towards the presence of strong magnetic frustration which results in the possible 3D QSL behavior.

Dheeraj Ranaut et al, J. Phys. Condens. Matter 34, 485803 (2022)

The presence of cluster glass (CG) phase is observed in the insulating perovskite CaHf1-xRuxO3 (0 ≤ x ≤ 0.50), confirmed through both static and dynamic susceptibility. Further, CG phase is characterized by non-equilibrium dynamical measurements such as magnetic relaxation, aging effect and memory effects. These studies indicate that the presence of competing short range interactions among randomly arranged Ru cations in CaHfO3.

Gurpreet Kaur  et  al, J. Phys. Condens. Matter 34, 415802 (2022)

Long-range antiferromagnetic (AFM) ordering is observed in Ba3GdRu2O9 around 14.8 K (TN) which splits in two transitions with applied magnetic field. Along with this, field-dependent magnetization at 2 K shows three metamagnetic transitions (MMT). From dielectric response, a maximum value of the magnetodielectric (MD) coupling is observed in the vicinity of metamagnetic transition (H2). In this system, Both Gd and Ru gets align at TN, whereas, above TN, short-range magnetic ordering is possibly responsible for MD coupling. This study highlights the importance of the investigation of metamagnetic transition’s effect on MD coupling.

Sonu Chhillar  et  al,  J. Phys. Condens. Matter 34, 145801 (2022)

A disorder driven non-Fermi liquid (NFL) behaviour is observed in Ce0.24La0.76Ge. In this work following queries are investigated: (1) whether the NFL state is associated with the local moment fluctuations (2) whether the observed new phase is due to the presence of biquadratic exchange coupling and (3) If yes, is the biquadratic exchange coupling related to fluctuations. Theoretical and computational study using DFT+DMFT indicate that at zero field, the presence of NFL state is associated with local moment fluctuations. The scaling of non-linear dc susceptibility suggests that the field induced phase originates due to establishment of partial order parameter associated with biquadratic exchange coupling.

Karan Singh et  al,  Phys. Rev. B 102, 235137 (2020)

Even after the absence of geometrical frustration and crystallographic disorder, Er5Pd2 undergoes a spin glass like transition below 17.2 K. Analysis of AC susceptibility data indicate that the dynamics in the system are due to the presence of strongly interacting superspins rather than individual spins. Non-linear dc susceptibility analysis suggests that the glassy behavior is introduced by random dipolar interaction among the group of spins.

Mohit K. Sharma et al, J. Phys.: Condens. Matter 30, 215803 (2018)