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Register a new userNeutron Scattering Study on Commensurate and Incommensurate Antiferromagnetic Phases in UPd2Si2 under Uniaxial Stress
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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.
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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.
Polarized neutron scattering experiments were performed on mixed compound CeRh0.6Co0.4In5 to clarify the nature of the low-temperature ordered states. Three nonequivalent Bragg peaks, characterized by the wave vectors of q_h ~ (1/2,1/2,0.3), q_1 ~ (1/2,1/2,0.4) and q_c=(1/2,1/2,1/2), were observed at 1.4 K. These Bragg peaks are found to occur entirely in spin-flip channel. This indicates that these Bragg peaks originate from the magnetic scattering, i.e., the antiferromagnetic orders with three different modulations appear in this compound.
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.
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.
We present a method for measuring thermal expansion under tunable uniaxial stresses, and show measurements of the thermal expansion of Mn$_3$Sn, a room temperature antiferromagnet that exhibits a spontaneous Hall effect, under uniaxial stresses of up to 1.51 GPa compression. Measurement of thermal expansion provides thermodynamic data about the nature of phase transitions, and uniaxial stress provides a powerful tuning method that does not introduce disorder. Mn$_3$Sn exhibits an anomaly in its thermal expansion near $sim$270 K, associated with a first-order change in its magnetic structure. We show this transition temperature is suppressed by 54.6 K by 1.51 GPa compression along [0001]. We find the associated entropy change at the transition to be $sim$ 0.1 J mol$^{-1}$ K$^{-1}$ and to vary only weakly with applied stress.
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