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Register a new userEffects of Uniaxial Stress on Antiferromagnetic Moment in the Heavy Electron Compound URu_2Si_2
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We have performed the elastic neutron scattering experiments under uniaxial stress sigma along the tetragonal [100], [110] and [001] directions for URu2Si2. For sigma // [100] and [110], the antiferromagnetic moment mu_o is strongly enhanced from 0.02 mu_B (sigma=0) to 0.22 mu_B (sigma=2.5 kbar) at 1.5 K. The rate of increase dmu_o/dsigma is roughly estimated to be ~ 0.1 mu_B/kbar, which is much larger than that for the hydrostatic pressure (~ 0.025 mu_B/kbar). Above 2.5 kbar, mu_o shows a tendency to saturate similar to the behavior in the hydrostatic pressure. For sigma // [001], on the other hand, mu_o shows only a slight increase to 0.028 mu_B (sigma = 4.6 kbar) with a rate of ~ 0.002 mu_B/kbar. The observed anisotropy suggests that the competition between the hidden order and the antiferromagnetic state in URu2Si2 is strongly coupled with the tetragonal four-fold symmetry and the c/a ratio, or both.
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We have investigated the nature of the antiferromagnetic (AF) phase induced by uniaxial stress sigma in URu2Si2, by performing elastic neutron scattering measurements up to 0.4 GPa. We have found that the AF Bragg-peak intensity shows a clear hysteresis loop with sigma under the zero-stress cooling condition. The result strongly suggests that the sigma-induced AF phase is metastable and separated from the coexisting hidden ordered phase by a first-order phase transition. We also present the analyses of the crystalline strain effects, and suggest that the c/a ratio plays an important role in the competition between these two phases.
We have performed elastic neutron scattering experiments under uniaxial stress sigma applied along the tetragonal [100], [110] and [001] directions for the heavy electron compound URu2Si2. We found that antiferromagnetic (AF) order with large moment is developed with sigma along the [100] and [110] directions. If the order is assumed to be homogeneous, the staggered ordered moment mu_o continuously increases from 0.02 mu_B (sigma=0) to 0.22 mu_B (0.25 GPa). The rate of increase partial mu_o/partial sigma is ~ 1.0 mu_B/GPa, which is four times larger than that for the hydrostatic pressure (partial mu_o/partial P sim 0.25 mu_B/GPa). Above 0.25 GPa, mu_o shows a tendency to saturate, similar to the hydrostatic pressure behavior. For sigma||[001], mu_o shows only a slight increase to 0.028 mu_B (sigma = 0.46 GPa) with a rate of ~ 0.02 mu_B/GPa, indicating that the development of the AF state highly depends on the direction of sigma. We have also found a clear hysteresis loop in the isothermal mu_o(sigma) curve obtained for sigma||[110] under the zero-stress-cooled condition at 1.4 K. This strongly suggests that the sigma-induced AF phase is metastable, and separated from the hidden order phase by a first-order phase transition. We discuss these experimental results on the basis of crystalline strain effects and elastic energy calculations, and show that the c/a ratio plays a key role in the competition between these two phases.
The nature of competition between incommensurate (IC) and commensurate (C) antiferromagnetic (AF) orders in UPd2Si2 was investigated by performing elastic neutron scattering experiments under uniaxial stress sigma. It is found that applying sigma along tetragonal [010] direction reduces the IC-AF order, and then stabilizes the C-AF order. The transition temperature from IC- to C-AF phases T_Nl is enhanced from 109 K (sigma=0) to 112.5 K (0.8 GPa), while the onset of IC-AF transition T_Nh is unchanged from 132 K under sigma. In addition, c-axis component q_z of the IC-AF modulation at 115 K also increases from 0.736 (sigma=0) to 0.747 (0.8 GPa). The magnitude of C-AF moment at 5 K is estimated to be 2.2 mu_B/U in the entire sigma range presently investigated (sigma <= 0.8 GPa). These features are similar to those obtained from the investigations using hydrostatic pressure p, indicating that applications of p and sigma||[010] commonly induce the crystal strains which inherently affect a delicate balance of frustrated magnetic interactions between uranium 5f moments.
We present results of measurements of resistivity of CAS{} under the combination of $c$-axis magnetic field and in-plane uniaxial stress. In unstressed CAS{} there are two magnetic phases. The low-field A phase is a single-component spin-density wave (SDW), with $mathbf{q} = (eta, pm eta, 1/2)$, and the high-field B phase consists of microscopically coexisting $(eta, eta, 1/2)$ and $(eta, -eta, 1/2)$ spin-density waves. Pressure along a $langle 100 rangle$ lattice direction is a transverse field to both of these phases, and so initially has little effect, however eventually induces new low- and high-field phases in which the principal axes of the SDW components appear to have rotated to the $langle 100 rangle$ directions. Under this strong $langle 100 rangle$ compression, the field evolution of the resistivity is much smoother than at zero strain: In zero strain, there is a strong first-order transition, while under strong $langle 100 rangle$ it becomes much broader. We hypothesize that this is a consequence of the uniaxial stress lifting the degeneracy between the (100) and (010) directions.
The spin ice materials Ho2Ti2O7 and Dy2Ti2O7 are experimental and theoretical exemplars of highly frustrated magnetic materials. However, the effects of an applied uniaxial pressure are not well studied, and here we report magnetization measurements of Ho2Ti2O7 under uniaxial pressure applied in the [001], [111] and [110] crystalline directions. The basic features are captured by an extension of the dipolar spin ice model. We find a good match between our model and measurements with pressures applied along two of the three directions, and extend the framework to discuss the influence of crystal misalignment for the third direction. The parameters determined from the magnetization measurements reproduce neutron scattering measurements we perform under uniaxial pressure applied along the [110] crystalline direction. In the detailed analysis we include the recently verified susceptibility dependence of the demagnetizing factor. Our work demonstrates the application of a moderate applied pressure to modify the magnetic interaction parameters. The knowledge can be used to predict critical pressures needed to induce new phases and transitions in frustrated materials, and in the case of Ho2Ti2O7 we expect a transition to a ferromagnetic ground state for uniaxial pressures above 3.3 GPa.
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