Structural and magnetic phase transitions inEuTi1−xNbxO3

Abstract

We have investigated the structural and magnetic phase transitions in EuTi1−xNbxO3 (0 ≤ x ≤ 0.3) with synchrotron powder X-ray diffraction (XRD), resonant ultrasound spectroscopy (RUS), and magnetization measurements. Upon Nb-doping, the P m3m ↔ I4/mcm structural transition shifts to higher temperatures and the room temperature lattice parameter increases while the magnitude of the octahedral tilting decreases. In addition, Nb substitution for Ti destabilizes the antiferromagnetic ground state of the parent compound and long range ferromagnetic order is observed in the samples with x ≥ 0.1. The structural transition in pure and doped compounds is marked by a dramatic step-like softening of the elastic moduli near TS, which resembles that of SrTiO3 and can be adequately modeled using the Landau free energy model employing the same coupling between strain and octahedral tilting order parameter as previously used to model SrTiO3.

Giant low-field magnetocaloric effect in single-crystalline EuTi0.85Nb0.15O3

“…We would like to mention that Li et al also observed similar value of the saturation moment. 13,14 The inset of the figure shows a five segment magnetization curve at 5 K without any visible hysteresis loop. To explore the nature of the magnetic transition, we have transformed the M(H) curves into the well known Belov-Arrott plots and observed a positive slope for these M 2 versus H/M (not shown) curves which indicates that the FM transition is continuous in nature.…”

“…27 The latter involves a fast heat exchange, i.e., the material should possess a high thermal diffusivity, which is the ratio of thermal conductivity to the thermal capacity per unit volume. From the zero-field specific heat and thermal conductivity data for the present sample and using the density 14 Another very important parameter related to the magnetocaloric effect is the adiabatic temperature change (∆T ad ), which can be calculated from the field-dependent magnetization and zero-field heat capacity data. The total entropy S(0,T) in absence of magnetic field is given by S(0,T) =  T 0 C p (0,T)/T dT and then S(H,T) may be evaluated by subtracting the corresponding ∆S m (H,T) determined using Equation (1) from this calculated value of S(0,T).…”

“…It has been shown that a small amount of Nb substitution at the Ti site drives the system into a FM metallic state. [12][13][14] However, the magnetocaloric effect and the detailed magnetic properties of Nb-doped EuTiO 3 have not been studied so far. In this regard, we have studied the field and temperature dependence of magnetization and heat capacity of an EuTi 0.85 Nb 0.15 O 3 single crystal and calculated several magnetocaloric parameters in order to test whether this material is suitable for low temperature magnetic refrigeration.…”

“…With decreasing temperature, χ increases down to the FM transition point T C = 9.5 K. Below T C , χ exhibits a saturation-like behavior similar to that reported earlier. 13,14 The FM transition temperature was determined from the position of the minimum of the dM/dT versus T curve. In EuTiO 3 , the Eu spin orders antiferromagnetically around 5.5 K. However, the Curie-Weiss fitting of the susceptibility, χ = C/(T − θ CW ), reveals a positive value for the Curie-Weiss temperature θ CW .…”

“…10 When a small amount of Nb is doped at the Ti site, the AFM ordering collapses and the system becomes an itinerant FM. [12][13][14] The FM ordering of the localized Eu 2+ spin is mediated by the itinerant electrons of the dopant Nb 4+ (4d 1 ). It is evident from the figure that χ(T) obeys the Curie-Weiss law over a wide temperature range above T C .…”