Evolution of field induced magnetic phase attributed to higher order magnetic moments in TbVO4.

Study of quantum magnetism in rare earth orthovanadates (RVO4, R = rare earth) is a topic which is currently being investigated by the condensed matter physicists. In this work, through both experimental and theoretical tools, we report the presence of field induced magnetic phase, attributed to fifth order susceptibility, in TbVO4, at low temperatures. The structural transition reported around 31 K, results in the formation of pseudospin-[Formula: see text] doublet ground state separated by an energy δ. Temperature dependent heat capacity indicates toward an increment in δ, on application of magnetic fields. Above 10 kOe, the Zeeman energy associated with magnetic anisotropy strengthens, resulting in an enhanced splitting of the pseudo-doublet ground state. This increased splitting stabilizes the magnetic phase associated with higher order moments. These observations are further supported by our theoretical model to evaluate δ, as a function of applied field. Our study provides a platform to study the possible presence of higher order moments in other Jahn-Teller systems.

A plausible investigation of low dimensional magnetism in a 3D spin system PrVO4.

3D spin systems provide an important platform to investigate the novel magnetic behaviors, which arise due to the complex network of spins in such materials. In this context, we have studied a rare-earth orthovanadate PrVO4, in which the distorted PrO8 polyhedral results in complex spin geometries made by the near neighbor Pr atoms. The fourth near neighbor Pr atoms form linear chains, which are separated by non-magnetic VO4 tetrahedra. DC magnetic susceptibility reveals a broad maximum and its position remains unaltered under applied magnetic field. The magnetic heat capacity shows a broad maximum with almost zero value at low temperatures. This indicates the presence of spin gap in the excitation spectra and hints toward the possibility of low dimensional magnetism. Our investigations reveal that PrVO4 can be a potential candidate to study low dimensional magnetism in rare-earth-based systems.

Possible realization of three-dimensional quantum spin liquid behavior in HoVO4.

The study of geometrically frustrated magnetic systems with unusual crystal field ground states offers a possibility of realizing the new aspects of physics of disordered systems. In this study, we report our results of structural, magnetic susceptibility, heat capacity measurements, along with density functional theory (DFT) calculations on HoVO4; a compound in which the presence of a distorted kind of HoO8polyhedral leads to multiple magnetic interaction paths. The observed broad maximum below 10 K in the temperature response of DC susceptibility curves implies the presence of short-range correlations. AC susceptibility rules out the possibility of any kind of spin freezing. Temperature dependent heat capacity measurement at zero field indicate towards the absence of long-range ordering, along with the presence of a broad maximum centered around 14 K. The residual heat capacity exhibits a characteristic power-law (Tα) behavior with the exponentαnearly equal to 2, which is analogous to that observed for other three-dimensional (3D) quantum spin liquid (QSL) systems. The DFT calculations signify the presence of dominant second and third nearest neighbor interactions, which in turn lead to magnetic frustration in our system. Our investigations suggest that HoVO4can be a candidate for realizing a 3D QSL state.

Unravelling the signatures of effective spin1/2moments in CeVO4: magnetization and heat capacity study.

The realization of an effective spin (Jeff) ½ state at low temperatures offers a platform to study the enthralling physics behind the disordered states in certain systems. Here, we report the signatures of magnetic ground state associated withJeff= ½ in CeVO4. Our studies confirm the absence of any ordering or freezing down to 1.8 K. In the low temperature region, the Curie-Weiss fit of the inverse DC susceptibility indicate towards the presence of antiferromagnetic correlations among the Ce3+spins. The calculated value of effective moment (∼1.16µB) corresponds toJ= ½ withgJ∼ 1.20. Further, the field dependent magnetization curve at 2 K follows a behaviour corresponding toJ= ½ Brillouin function withgJ∼ 1.13. Magnetic field dependent heat capacity fits very well with two-level Schottky scheme. Our investigations suggest that CeVO4can be a promising candidate to realiseJeff= ½ properties among 3D spin systems.

Entropic topography associated with field-induced quantum criticality in a magnetic insulator DyVO4.

Exploration of low temperature phase transitions associated with quantum critical point is one of the most mystifying fields of research which is under intensive focus in recent times. In this work, through comprehensive experimental evidences, we report the possibility of achieving quantum criticality in the neighborhood of a magnetic field-tuned tricritical point separating paramagnetic, antiferromagnetic and metamagnetic phases in a magnetic insulator, DyVO4. Magnetic susceptibility and heat capacity indicate to the presence of a long-range second order antiferromagnetic transition at TN ~ 3.2 K. Field variation of Magnetic susceptibility and heat capacity, along with differential magnetic susceptibility and DC field dependent AC susceptibility gives evidence of the modification of the antiferromagnetic structure below the tricritical point; implying the presence of a field-induced first order metamagnetic transition which persists down to 1.8 K. Further, the magnetic field dependence of the thermodynamic quantity - dM/dT, which is related to magnetic Gruneisen parameter, approaches a minimum, followed by a crossover near 5 kOe to a maximum; along with a hyperbolic divergence in temperature response of dM/dT in the critical field regime. Temperature response of heat capacity at 5 kOe also shows a deviation from the conventional behavior. Entropic topography phase diagram allows tracking of the variation of the entropy, which indicates towards the emergence of the peak at quantum critical point into a V-shaped region at high temperatures. Our studies yield an inimitable phase diagram describing a tricritical point at which the second-order antiferromagnetic phase line terminates followed by a first order line of metamagnetic transition, as the temperature is lowered, leading to metamagnetic quantum critical end point.

Unconventional critical behaviour in weak ferromagnets Fe2-xMnxCrAl (0 ≤ x < 1).

Recent investigation on weak ferromagnets Fe2-xMnxCrAl (0 ≤ x < 1) reveal the existence of a cluster glass phase (CGP) and a Griffiths-like phase (GP) below and above the ferromagnetic transition temperature (TC), respectively [(2019) Sci. Rep. 9 15888]. In this work, the influence of these inhomogeneous phases on the critical behaviour (around TC) of the above-mentioned series of alloys has been investigated in detail. For the parent alloy Fe2CrAl, the critical exponent γ is estimated as ~ 1.34, which lies near to the ordered 3D Heisenberg class, whereas the obtained value of the critical exponent ß ~ 0.273 does not belong to any universality class. With increment in Mn concentration, both exponents γ and ß increase, where γ and ß approach the disordered and ordered 3D Heisenberg class, respectively. The observed deviation of γ and unconventional value of δ can be ascribed to the increment of GP with Mn-concentration. The trend noted for ß can be attributed to the increment in CGP regime with an increase in Mn-content. The estimated critical exponents are consistent and reliable as corroborated using the scaling law and equations of state. Our studies indicate that the critical phenomenon of Fe2-xMnxCrAl (0 ≤ x < 1) alloys possibly belong to a separate class, which is not described within the framework of any existing universal model.