Specific heat of delafossite oxideCuCr1−xMgxO2

Abstract

Specific heat, magnetization, resistivity, and structure of delafossite oxide CuCr 1−x A x O 2 ͑A =Mg 2+ ,Ca 2+ ,Al 3+ ͒ have been investigated. With the substitution of nonmagnetic Mg 2+ for Cr 3+ ͑S =3/ 2͒, the peak of specific heat upon antiferromagnetic ͑AF͒ transition becomes sharper and the transition temperature increases. The peak is much affected by a magnetic field of 9 T when Cr 3+ is substituted by Mg 2+ . Comparing the substitution effect of Mg 2+ to those of other nonmagnetic Ca 2+ and Al 3+ , magnetization around the AF transition does not seem to correlate with randomness and lattice parameter but with itinerancy of the doped holes. These results suggest that the residual magnetic frustration stemming from a modulated triangular 120°s pin structure is partially broken by spin fluctuations, which are enhanced through the interaction between the hole introduced by Mg doping and the localized spin at the Cr site.

Lattice dynamics and thermal transport in multiferroicCuCrO2

“…For the point-defect scattering, we have not considered the perturbation in force-constants and nearest-neighbor distances. A Debye temperature θ D = 850 ± 50 K was estimated by Okuda et al from heat capacity measurements [13]. We have calculated the Debye temperature from the first moment of the measured phonon DOS, as θ D = 4⟨E⟩ 3k B , where ⟨E⟩ = ∫ g(E)E dE and k B is Boltzmann's constant.…”

“…Thus, it presents an opportunity to study the direct coupling between the magnetic and ferroelectric order parameters [3,4]. A number of studies have investigated the crystal structure, magnetic excitations, magnetization, and electric polarization in CuCrO 2 [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], but little is known about the phonons and their coupling or response to the magnetic/ferroelectric ordering.…”

Spin dynamics in triangular-lattice antiferromagnets CuCr 1− x Mg x O 2

“…the Ca, Al doping in CuCrO 2 . [12,13] But the Mg substitution for Cr leads to the sharpen of the AFM transition and the large enhancement of magnetization around T N , which means that the magnetic order is enhanced by Mg doping. [9,12] This is thought to stem from the partially lifted residual magnetic frustration due to spin fluctuations, which are enhanced through the interaction between the hole introduced by Mg doping and the localized Cr spins.…”

“…[12,13] But the Mg substitution for Cr leads to the sharpen of the AFM transition and the large enhancement of magnetization around T N , which means that the magnetic order is enhanced by Mg doping. [9,12] This is thought to stem from the partially lifted residual magnetic frustration due to spin fluctuations, which are enhanced through the interaction between the hole introduced by Mg doping and the localized Cr spins. [9,12] All these behaviors hint that there is a close relation between the magnetic and transport behaviors even at temperatures much higher than T N and the spin fluctuations might play an important role.…”

“…[9,12] This is thought to stem from the partially lifted residual magnetic frustration due to spin fluctuations, which are enhanced through the interaction between the hole introduced by Mg doping and the localized Cr spins. [9,12] All these behaviors hint that there is a close relation between the magnetic and transport behaviors even at temperatures much higher than T N and the spin fluctuations might play an important role. Previous powder neutron diffraction probes observable intensity of (000) magnetic peak below ∼ 70 K, which is attributed to the occurrence of appreciable short-range magnetic interactions [10].…”