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Register a new userMagnetic structure, magnetoelastic coupling, and thermal properties of EuCrO$_3$ nano-powders
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We carried out detailed studies of the magnetic structure, magnetoelastic coupling, and thermal properties of EuCrO$_3$ nano-powders from room temperature to liquid helium temperature. Our neutron powder diffraction and X-ray powder diffraction measurements provide precise atomic positions of all atoms in the cell, especially for the light oxygen atoms. The low-temperature neutron powder diffraction data revealed extra Bragg peaks of magnetic origin which can be attributed to a $G_x$ antiferromagnetic structure with an ordered moment of $sim$ 2.4 $mu_{rm B}$ consistent with the $3d^3$ electronic configuration of the Cr$^{3+}$ cations. Apart from previously reported antiferromagnetic and ferromagnetic transitions in EuCrO$_3$ at low temperatures, we also observed an anomaly at about 100 K. This anomaly was observed in temperature dependence of samples, lattice parameters, thermal expansion, Raman spectroscopy, permittivity and conductance measurements. This anomaly is attributed to the magnetoelastic distortion in the EuCrO$_3$ crystal.
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The series of intermetallic compounds $R$NiSi$_3$ ($R$ = rare earth) shows interesting magnetic properties evolving with $R$ and metamagnetic transitions under applied magnetic field for some of the compounds. The microscopic magnetic structures must be determined to rationalize such rich behavior. Here, resonant x-ray magnetic diffraction experiments are performed on single crystals of GdNiSi$_{3}$ and TbNiSi$_{3}$ at zero field. The primitive magnetic unit cell matches the chemical cell below the Neel temperatures $T_{N}$ = 22.2 and 33.2 K, respectively. The magnetic structure is determined to be the same for both compounds (magnetic space group $Cmmm$). It features ferromagnetic {it ac} planes that are stacked in an antiferromagnetic $+-+-$ pattern, with the rare-earth magnetic moments pointing along the $vec{a}$ direction, which contrasts with the $+--+$ stacking and moment direction along the $vec{b}$ axis previously reported for YbNiSi$_3$. This indicates a sign reversal of the coupling constant between second-neighbor $R$ planes as $R$ is varied from Gd and Tb to Yb. The long {it b} lattice parameter of GdNiSi$_{3}$ and TbNiSi$_{3}$ shows a magnetoelastic expansion upon cooling below $T_N$, pointing to the conclusion that the $+-+-$ stacking is stabilized under lattice expansion. A competition between distinct magnetic stacking patterns with similar exchange energies tuned by the size of $R$ sets the stage for the magnetic ground state instability observed along this series.
High-quality single crystals of CoTiO$_3$ are grown and used to elucidate in detail structural and magnetostructural effects by means of high-resolution capacitance dilatometry studies in fields up to 15 T which are complemented by specific heat and magnetization measurements. In addition, we refine the single-crystal structure of the ilmenite ($Rbar{3}$) phase. At the antiferromagnetic ordering temperature $T_mathrm{N}$, pronounced $lambda$-shaped anomaly in the thermal expansion coefficients signals shrinking of both the $c$ and $b$ axes, indicating strong magnetoelastic coupling with uniaxial pressure along $c$ yielding six times larger effect on $T_mathrm{N}$ than the pressure applied in-plane. The hydrostatic pressure dependency derived by means of Gruneisen analysis amounts to $partial T_mathrm{N}/ partial papprox 2.7(4)$~K/GPa. The high-field magnetization studies in static and pulsed magnetic fields up to 60~T along with high-field thermal expansion measurements facilitate in constructing the complete anisotropic magnetic phase diagram of CoTiO$_3$. While the results confirm the presence of significant magnetodielectric coupling, our data show that magnetism drives the observed structural, dielectric, and magnetic changes both in the short-range ordered regime well-above $T_mathrm{N}$ as well as in the long-range magnetically ordered phase.
The Co2V2O7 is recently reported to exhibit amazing magnetic field-induced magnetization plateaus and ferroelectricity, but its magnetic ground state remains ambiguous due to its structural complexity. Magnetometry measurements, and time-of-flight neutron powder diffraction (NPD) have been employed to study the structural and magnetic properties of Co2V2O7, which consists of two non-equivalent Co sites. Upon cooling below the Neel temperature TN = 6.3 K, we observe magnetic Bragg peaks at 2K in NPD which indicated the formation of long range magnetic order of Co2+ moments. After symmetry analysis and magnetic structure refinement, we demonstrate that Co2V2O7 possesses a complicated non-collinear magnetic ground state with Co moments mainly located in b-c plane and forming a non-collinear spin-chain-like structure along the c-axis. The ab initio calculations demonstrate that the non-collinear magnetic structure is more stable than various ferromagnetic states at low temperature. The non-collinear magnetic structure with canted up-up-down-down spin configuration is considered as the origin of magnetoelectric coupling in Co2V2O7 because the inequivalent exchange striction induced by the spin-exchange interaction between the neighboring spins is the driving force of ferroelectricity. Besides, it is found that the deviation of lattice parameters a and b is opposite below TN, while the lattice parameter c and stay almost constant below TN, evidencing the anisotropic magnetoelastic coupling in Co2V2O7.
We have investigated the effect of Cd substitution on the archetypal heavy fermion antiferromagnet CeIn$_3$ via magnetic susceptibility, specific heat and resistivity measurements. The suppression of the Neel temperature, T$_{N}$, with Cd doping is more pronounced than with Sn. Nevertheless, a doping induced quantum critical point does not appear to be achievable in this system. The magnetic entropy at $T_N$ and the temperature of the maximum in resistivity are also systematically suppressed with Cd, while the effective moment and the Curie-Weiss temperature in the paramagnetic state are not affected. These results suggest that Cd locally disrupts the AFM order on its neighboring Ce moments, without affecting the valence of Ce. Moreover, the temperature dependence of the specific heat below $T_N$ is not consistent with 3D magnons in pure as well as in Cd-doped CeIn$_3$, a point that has been missed in previous investigations of CeIn$_3$ and that has bearing on the type of quantum criticality in this system.
We present high-resolution measurements of the thermal expansion and the magnetostriction of TlCuCl$_{3}$ which shows field-induced antiferromagnetic order. We find pronounced anomalies in the field and temperature dependence of different directions of the lattice signaling a large magnetoelastic coupling. The phase boundary is extremely sensitive to pressure, e.g. the transition field would change by about +/- 185$%/GPa under uniaxial pressure applied along certain directions. This drastic effect can unambiguously be traced back to changes of the intradimer coupling under uniaxial pressure. The interdimer couplings remain essentially unchanged under pressure, but strongly change when Tl is replaced by K.
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