Spin dynamics in triangular-lattice antiferromagnets CuCr _{1− x} Mg _x O ₂

Abstract

Abstract. -The electron spin resonance (ESR) spectroscopy was employed to investigate the spin dynamics in triangular lattice antiferromagnets CuCr1−xMgxO2 with x = 0 and 0.02. All spectra can be well fitted by a single Lorentzian lineshape. The analysis of the g factor, the linewidth △H, and the ESR intensity I as a function of temperature suggests the development of significant antiferromagnetic (AFM) spin fluctuations at temperature well above TN in both samples. However, the evolution of the AFM spin fluctuations is different for each sample. For undoped sample the ESR intensity I is almost temperature independent between ∼ 100 K and 50 K and then drops rapidly below 50 K. But for x = 0.02, the I monotonously increases with cooling and reduces rapidly only below TN . These results indicate that the AFM spin fluctuations are extremely strong in the undoped sample and appear to be suppressed upon Mg doping.Introduction. -Triangular lattice antiferromagnets (TLAs) have attracted considerable interests because geometrical spin frustration inherent to these systems results in exceptionally rich physical properties ranging over spin liquid, [1, 2] quantum phase transition, [3] anomalous large thermoelectric response, [4] superconductivity, [5] and magnetoelectric properties. [6][7][8] A typical example of TLAs is CuCrO 2 ; it has a delafossite structure, which can be viewed as the alternate stacking of edge-shared CrO 6 octahedral layers and Cu layers along the [001] axis (see the inset to Fig. 1). Cr ions form an antiferromagnetic (AFM) triangular sublattice, and the compound enters a long range AFM ordered state below the Néel temperature T N ∼ 26 K.[9] Previous powder neutron diffraction study proposed that the ground state has an out-of-plane incommensurate spiral-spin structure with an in-plane wave vector q = (0.329, 0.329, 0) below T N .[10] In this spiral-spin ordered phase, the compound exhibits ferroelectricity driven by the magnetic order, [8] whose polarization P can be tuned by using both magnetic and electric fields. [11] In addition, for CuCrO 2 the temperature dependence of magnetization starts to devi-

Slight Ti‐Doping‐Induced Strong Time‐Dependent Electrical Transport Behavior in CuCr1−xTixO2

“…Figure (a) shows the temperature‐dependent magnetization M ( T ) under 0.5 T field from 2 to 400 K for CCTO series. For the undoped x = 0, a distinct peak occurs at T N = 26 K in M ( T ) curve associated with the paramagnetic (PM)‐AFM phase transition, which is consistent with the previous reports . Upon Ti substituting for Cr, the anomaly around T N becomes blurred while the T N shows little change, which should be attributed to the randomness or spin dilution introduced by the doping .…”

“…The ceramic polycrystalline samples of CuCr 1− x Ti x O 2 (abbreviated as CCTO) with x = 0, 0.0025 and 0.0050 were prepared with stoichiometric proportions of high purity CuO (99.995%), Cr 2 O 3 (99.97%), and TiO 2 (99.9%) by the conventional solid‐state reaction method as described in Refs. and . The structure and the phase purity of the samples were checked by powder X‐ray diffraction (XRD) at room temperature.…”

“…In delafossite CuCrO 2 , Cr 3+ ions ( S = 3/2) form spin‐frustrated triangular lattice planes stacked along the hexagonal [001] axis . Because of the inherent spin frustration in the system, it exhibits significant antiferromagnetic (AFM) spin fluctuations before entering a spiral AFM state at T N = 26 K . It displays a ferroelectric order driven by a spiral AFM spin order, in which the dielectric and magnetic properties can be modulated by applying either magnetic or electric field …”

“…Chemical doping on Cr site can also significantly tune the physical properties of CuCrO 2 . Substituting Cr 3+ ions by divalent ions such as Mg 2+ , Ca 2+ or introducing Cr deficiency leads to a drastic decrease in the resistivity and the Seebeck coefficient as well as a significant enhancement of the AFM transition .…”

Study of magnetic entropy and ESR in ferromagnet CuCr2Te4

“…5(b). This indicates that critical spin fluctuation [36,37] arises at T n , leading to the deviation from CW linear of 1/DIN-T (1/M-T). With further cooling below T C , the rapidly enhanced spinorbit coupling leads to the rapid increase of DH pp .…”