CVM study of FCC and BCC Ising magnets with generalised spin number

We have prepared a set of polycrystalline samples of La 0.8 Sr 0.2 Co 1 − x Al x O 3 ( 0 ≤ x ≤ 0.2 ), and have measured the magnetization as functions of temperature and magnetic field. We find that the average spin number per Co ion ( S Co ) evaluated from the room-temperature susceptibility is around 1.2–1.3 and independent of x. However, we further find that S Co evaluated from the saturation magnetization at 2 K is around 0.3–0.7, and decreases dramatically with x. This naturally indicates that a significant fraction of the Co 3 + ions experience a spin-state crossover from the intermediate- to low-spin state with decreasing temperature in the Al-substituted samples. This spin-state crossover also explains the resistivity and the thermopower consistently. In particular, we find that the thermopower is anomalously enhanced by the Al substitution, which can be consistently explained in terms of an extended Heikes formula.

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Novel Magnetic Orders and Ice Phases in Frustrated Kondo-Lattice Models

SPIN ◽

10.1142/s2010324715400068 ◽

2015 ◽

Vol 05 (02) ◽

pp. 1540006 ◽

Cited By ~ 3

Author(s):

Gia-Wei Chern

Keyword(s):

Berry Phase ◽

Magnetic Moments ◽

Lattice Models ◽

Magnetic Ordering ◽

Double Exchange ◽

Salient Feature ◽

Kondo Lattice ◽

Spin Ice ◽

Water Ice ◽

Ising Magnets

We review recent theoretical progress in our understanding of electron-driven novel magnetic phases on frustrated lattices. Our specific focus is on Kondo-lattice or double-exchange models assuming finite magnetic moments localized at the lattice sites. A salient feature of systems with SU(2) symmetric local moments is the emergence of noncoplanar magnetic ordering driven by the conduction electrons. The complex spin textures then endow the electrons a nontrivial Berry phase, often giving rise to a topologically nontrivial electronic state. The second part of the review is devoted to the discussion of metallic spin ice systems, which are essentially frustrated Ising magnets with local spin ordering governed by the so-called ice rules. These rules are similar to those that describe proton configurations in solid water ice, hence the name "spin ice". The nontrivial spin correlations in the ice phase give rise to unusual electron transport properties in metallic spin-ice systems.

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Nonclassicality of photon-modulated spin coherent states in the Holstein-Primakoff realization

Chinese Physics B ◽

10.1088/1674-1056/ac40f5 ◽

2021 ◽

Author(s):

Xiaoyan Zhang ◽

Jisuo Wang ◽

Lei Wang ◽

Xiangguo Meng ◽

Baolong Liang

Keyword(s):

Coherent States ◽

Wigner Distribution ◽

Hermite Polynomials ◽

Photon Number ◽

Spin Ladder ◽

Bernoulli Distribution ◽

Ladder Operators ◽

Spin Number ◽

Photon Number Distribution ◽

Spin Coherent States

Abstract Two new photon-modulated spin coherent states (SCSs) are introduced by operating the spin ladder operators J ± on the ordinary SCS in the Holstein-Primakoff realization and the nonclassicality is exhibited via their photon number distribution, second-order correlation function, photocount distribution and negativity of Wigner distribution. Analytical results show that the photocount distribution is a Bernoulli distribution and the Wigner functions are only associated with two-variable Hermite polynomials. Compared with the ordinary SCS, the photon-modulated SCSs exhibit more stronger nonclassicality in certain regions of the photon modulated number k and spin number j, which means that the nonclassicality can be enhanced by selecting suitable parameters.

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