Abstract
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, DyVO
4
. Magnetic susceptibility and heat capacity indicate to the presence of a long-range second order antiferromagnetic transition at
T
N
~ 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 − d
M
/d
T
, 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 d
M
/d
T
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.
Abstract
Study of quantum magnetism in rare earth orthovanadates (RVO
4
, 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 TbVO
4
, at low temperatures. The structural transition reported around 31 K, results in the formation of pseudospin—
$${\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 2}}\right.\kern-0pt} \!\lower0.7ex\hbox{$2$}}$$
1
/
2
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.
Abstract
Recent investigation on weak ferromagnets Fe
2-x
Mn
x
CrAl (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 (
T
C
), respectively (2019)
Sci. Rep.
9
15888. In this work, the influence of these inhomogeneous phases on the critical behaviour (around
T
C
) of the above-mentioned series of alloys has been investigated in detail. For the parent alloy Fe
2
CrAl, 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 β ~ 0.273 does not belong to any universality class. With increment in Mn concentration, both exponents γ and β increase, where γ and β 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 β 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 Fe
2-x
Mn
x
CrAl (0 ≤ x < 1) alloys possibly belong to a separate class, which is not described within the framework of any existing universal model.
Pyrochlores offer an ideal playground to investigate the magnetic ground state of frustrated magnetic systems. In this class of materials, competition between various magnetic interactions remains ...frustrated and prevents an ordered magnetic state at low temperatures. Tb2Sn2O7 has recently attracted significant attention due to its ordered spin-ice state. Additionally, in such systems, application of external magnetic field might result in exotic magnetic states. Our current investigation on Tb2Sn2O7 reveal the presence of a new phase associated with fifth order susceptibility at low temperatures and high magnetic fields. In this compound, at zero fields, for a stabilized spin-ice state, the singlet–singlet state separated by δ play an imperative role. Under magnetic fields, δ increases and the Zeeman energy associated with the magnetic anisotropy is believed to get enhanced; which can be the key ingredient for evolution of higher-order moments, above 10 kOe, in this compound.
The 4f6 systems were hypothesized to possess non-magnetic (J=0) ground state. However, all such systems have distinctly shown the presence of non-zero effective moment at low temperatures. In this ...context, a rare earth orthovanadate EuVO4, which in spite of having J=0 ground state, possess non-zero magnetic moment. Our studies on EuVO4 reveal three different regions, having different features in magnetic susceptibility. The high temperature susceptibility exhibits linear dependence on temperature which arises due to inter-mixing of ground and excited states, followed by a temperature independent plateau-like region, ascribed to Van Vleck paramagnetism. At low temperatures, Curie-Weiss like behaviour is observed, which arise due to magnetic Eu2+ ions and results in non-zero effective moment. Our analysis reveals that the separation (λ) between the J=0 and 1 states decreases on increasing the external magnetic field which leads to an enhanced effective moment at higher fields.
•Magnetic susceptibility in EuVO4 is manifested by three different features.•Inter-mixing of ground and excited states at high temperatures results in linear susceptibility.•Van Vleck PM at intermediate temperatures; solely dependent on J=0 ground state.•Non-zero effective moment at low temperatures in J = 0 state due to magnetic Eu2+ ions.•Decreased separation between J=0 and 1 states at high fields results in enhanced effective moment.
•Random arrangement of Li and Ni ions reduces magnetic frustration.•Additional anti-site disorder induces an inter-sublattice magnetic interaction.•Short-range ordering is developed below ...30 K.•Canted antiferromagnetism is observed at low temperatures.•Competing magnetic interactions and reduced frustration stabilize these orderings.
Frustration driven short-range magnetic correlations/fluctuations in quantum materials usually host exotic ground states like spin glass, low dimensional magnetism and quantum spin liquid. In this context, different members of spinel (both normal and inverse) family have gained enormous interest and an inverse spinel vanadate, LiNiVO4, seems to be an interesting candidate. Structural investigations reveal that unlike usual cation ordering, Ni and Li ions are randomly distributed at octahedral sites and results in reduced magnetic frustration. Further, an additional anti-site disorder is present, as a small fraction of Ni ions occupies tetrahedral sites. Magnetic susceptibility and heat capacity studies show that short-range magnetic correlations develop below 30 K, followed by a canted antiferromagnetism below 2.2 K. Different competing magnetic interactions due to the presence of disorder and reduced magnetic frustration result in the short-range ordering as well as canted antiferromagnetism in LiNiVO4.
Study of quantum magnetism in rare earth orthovanadates (RVO
, 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 TbVO
, 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.
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, DyVO
. Magnetic susceptibility and heat capacity indicate to the presence of a long-range second order antiferromagnetic transition at T
~ 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.
Abstract
Pyrochlores offer an ideal playground to investigate the magnetic ground state of frustrated magnetic systems. In this class of materials, competition between various magnetic interactions ...remains frustrated and prevents an ordered magnetic state at low temperatures. Tb
2
Sn
2
O
7
has recently attracted significant attention due to its ordered spin-ice state. Additionally, in such systems, application of external magnetic field might result in exotic magnetic states. Our current investigation on Tb
2
Sn
2
O
7
reveal the presence of a new phase associated with fifth order susceptibility at low temperatures and high magnetic fields. In this compound, at zero fields, for a stabilized spin-ice state, the singlet–singlet state separated by
δ
play an imperative role. Under magnetic fields,
δ
increases and the Zeeman energy associated with the magnetic anisotropy is believed to get enhanced; which can be the key ingredient for evolution of higher-order moments, above 10 kOe, in this compound.
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