Relief of frustration through spin disorder in multiferroicHo1−xYxMnO3

Abstract

The magnetic phase diagram of single crystalline Ho 1−x Y x MnO 3 below T N is determined by measuring the magnetic susceptibility ͑͒, specific heat ͑C p ͒, dielectric constant ͑͒, and thermal conductivity ͑͒. Y doping enhances the P6 គ 3 cm គ magnetic phase below T SR and therefore increases T SR ; only the P6 គ 3 cm គ phase exists below T N for x ജ 0.9 samples. Y doping also reduces the P6 3 cm phase below T 2. The anomaly around T SR appears in the dielectric constant but is absent in and C p for Ho 0.3 Y 0.7 MnO 3 and Ho 0.2 Y 0.8 MnO 3 samples, which indicates that the multiferroicity at T SR for HoMnO 3 is not necessarily related to the Ho 3+ spin ordering. Specific heat measurements show that the large electronic specific heat ͑␥͒ of HoMnO 3 is related to the disorder of Ho 3+ spins, and is correlated with the relief of frustration in the Mn sublattice. The thermal conductivity data support an enhanced spin-lattice interaction due to strong spin fluctuations in the geometrically frustrated Mn-spin system.

Hexagonal Manganites—(RMnO3): Class (I) Multiferroics with Strong Coupling of Magnetism and Ferroelectricity

“…The slope change (kink) of ( ) at happens within less than 0.7 K, the peak of the dielectric constant at SR is 0.5 K wide, and the sudden increase of ( ) at Ho has a width of 0.07 K [113,114]. The sharp dielectric anomalies of HoMnO 3 have been confirmed by different research groups [115][116][117][118][119][120]. The three magnetic transitions in HoMnO 3 are also reflected in sharp anomalies of other physical quantities [121].…”

“…The three sharp anomalies in ( ) have been verified by different groups [117,119,[123][124][125]. Near the Néel temperature, ( ) exhibits a -shaped peak characteristic for a second order phase transition.…”

Hyperfine and crystal field interactions in multiferroic HoCrO3

“…The most plausible explanation for the appearance of a linear term in the heat capacity in HoCrO 3 is due to disordered Ho 3+ as in the case of insulating Ho 1−x Y x MnO 3 . For this compound it was observed that with increasing Y content γ is reduced and drops to zero at x = 0.9, indicating the dependence of γ on the Ho content [49]. It was interpreted that the appearance of the linear term is due to high degeneracy of disordered Ho 3+ spins above the ordering temperature.…”

Directional growth and characterizations of orthorhombic HoMnO3 films

“…The typical HX structure occurs for RMnO 3 with R ¼ Y, Ho-Lu [3][4][5][6]. These HX manganites exhibit ferroelectric (FE) transitions well above room temperature (4600 1C), while their magnetic ordering takes place at much lower temperatures (antiferromagnetic transition, T N $70-100 K), suggesting weak interplay between the electric and magnetic degrees of freedom.…”