Magnetic dipole interactions in crystals

Johnston, D. C.

doi:10.1103/physrevb.93.014421

Cited by 74 publications

(77 citation statements)

References 61 publications

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“…3 up to H = 800 Oe for all three compositions is χ c ≡ dM c /dH ≈ 0.077. This value is about the same as the value χ c = 1/4π ≈ 0.080 expected if M c /H in the absence of demagnetization effects is so large that the observed value is limited by the demagnetization factor [35]. Hence the magnetic response along the c axis is extremely soft for x = 0.19, 0.25 and 0.28, which may be expected if these compositions are in a crossover region in the magnetocrystalline anisotropy field from being parallel to perpendicular to the c axis.…”

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confidence: 99%

“…Finally, for x = 0.52, a PM behavior is observed. As a point of reference, the magnetic dipole interaction between local moments on a simple-tetragonal lattice with c/a ≈ 3.65 as in CaCo 2−y As 2 predicts that the ordered moments should lie in the ab plane [35].To clarify the origins of the behaviors in Fig. 1 and the magnetic ground state versus x, we carried out isothermal M (H) measurements on the same set of ten crystals at T = 2 K and the results are shown in Fig.…”

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Anomalous Composition-Induced Crossover in the Magnetic Properties of the Itinerant-Electron AntiferromagnetCa1−xSrxCo2−yAs2
Sangeetha¹,
Smetana²,
Mudring³
et al. 2017
Phys. Rev. Lett.
21
3
54
0
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The inference of Ying et al. [EPL 104, 67005 (2013)] of a composition-induced change from c-axis ordered-moment alignment in a collinear A-type AFM structure (AFMI) at small x to abplane alignment in an unknown AFM structure (AFMII) at larger x in Ca1−xSrxCo2−yAs2 with the body-centered tetragonal ThCr2Si2 structure is confirmed. Our major finding is an anomalous magnetic behavior in the crossover region 0.2 x 0.3 between these two phases. In this region the magnetic susceptibility versus temperature χ ab (T ) measured with magnetic fields H applied in the ab plane exhibit typical AFM behaviors with cusps at the Néel temperatures of ∼ 65 K, whereas χc(T ) and the low-temperature isothermal magnetization Mc(H) with H aligned along the c axis exhibit extremely soft ferromagnetic-like behaviors.Much research since 2008 has focused on studies of iron-based layered pnictides and chalcogenides due to their unique lattice, electronic, magnetic and superconducting properties [1][2][3][4][5][6]. An important family of these materials is comprised of doped and undoped bodycentered tetragonal parent compounds AFe 2 As 2 (A = Ca, Sr, Ba, Eu) with the ThCr 2 Si 2 -type structure (122-type compounds). The undoped and underdoped AFe 2 As 2 compounds exhibit a tetragonal to orthorhombic distortion of the crystal structure at T S 200 K. They also exhibit itinerant collinear antiferromagnetic (AFM) spindensity-wave ordering at a temperature T N the same or slightly lower than T S . The ordered moments in the stripe AFM structure of the orthorhombic phase are oriented in the ab plane. In 2014 a temperature Tinduced AFM spin-reorientation transition to a new AFM C 4 phase was discovered in the hole-underdoped Ba 1−x Na x Fe 2 As 2 system upon cooling below T N that can coexist with superconductivity [7]. A subsequent investigation by polarized and unpolarized neutron diffraction determined that the ordered moments in the new phase are aligned along the c axis instead of along the ab plane as in the stripe AFM structure [8]. The work on the Ba 1−x Na x Fe 2 As 2 system was followed by the observation of the same AFM C 4 phase in the Ba 1−x K x Fe 2 As 2 [9-11], Sr 1−x Na x Fe 2 As 2 [12, 13], and Ca 1−x Na x Fe 2 As 2 [14] systems. These results are important to understanding the mechanism of superconductivity and other aspects of the hole-doped iron arsenides [15][16][17][18][19][20][21].A similar but composition-induced moment realignment was suggested to occur in the isostructural CoAsbased system Ca 1−x Sr x Co 2−y As 2 [22]. CaCo 2−y As 2 has a so-called collapsed-tetragonal (cT) structure with AsAs bonding along the c axis between adjacent CoAs layers [23] and has ≈ 7% vacancies on the Co sites [24,25]. It exhibits itinerant A-type AFM ordering below T N = 52-77 K, depending on the sample, with the ordered moments of ≈ 0.3-0.4 µ B /Co (µ B is the Bohr magneton) within an ab-plane Co layer aligned ferromagnetically (FM) along the c axis and with AFM alignments between moments in adjacent Co planes [24][25][26][27][28]. The domi...

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confidence: 68%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Anomalous Composition-Induced Crossover in the Magnetic Properties of the Itinerant-Electron AntiferromagnetCa1−xSrxCo2−yAs2
Sangeetha¹,
Smetana²,
Mudring³
et al. 2017
Phys. Rev. Lett.
21
3
54
0
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“…13(a). The T dependence of the anisotropy is too strong to arise from the conventional shape-, magneticdipole and single-ion anisotropies [68]. It may arise from c-axis FM correlations that grow with decreasing T faster than predicted by MFT and/or from interactions between the Eu and Mn spin sublattices.…”

Section: A Magnetization and Magnetic Susceptibilitymentioning

confidence: 89%

Metallic behavior induced by potassium doping of the trigonal antiferromagnetic insulatorEuMn2As2

Anand

Johnston

2016

Phys. Rev. B

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We report magnetic susceptibility χ, isothermal magnetization M , heat capacity Cp and electrical resistivity ρ measurements on undoped EuMn2As2 and K-doped Eu0.96K0.04Mn2As2 and Eu0.93K0.07Mn2As2 single crystals with the trigonal CaAl2Si2-type structure as a function of temperature T and magnetic field H. EuMn2As2 has an insulating ground state with an activation energy of 52 meV and exhibits antiferromagnetic (AFM) ordering of the Eu +2 spins S = 7/2 at TN1 = 15 K from Cp(T ) and χ(T ) data with a likely spin-reorientation transition at TN2 = 5.0 K. The Mn +2 3d 5 spins-5/2 exhibit AFM ordering at TN = 142 K from all three types of measurements. The M (H) isotherm and χ(T ) data indicate that the Eu AFM structure is both noncollinear and noncoplanar. The AFM structure of the Mn spins is also unclear. A 4% substitution of K for Eu in Eu0.96K0.04Mn2As2 is sufficient to induce a metallic ground state. Evidence is found for a difference in the AFM structure of the Eu moments in the metallic crystals from that of undoped EuMn2As2 versus both T and H. For metallic Eu0.96K0.04Mn2As2 and Eu0.93K0.07Mn2As2, an anomalous Sshape T dependence of ρ related to the Mn magnetism is found. Upon cooling from 200 K, ρ exhibits a strong negative curvature, reaches maximum positive slope at the Mn TN ≈ 150 K, and then continues to decrease but more slowly below TN. This suggests that dynamic short-range AFM order of the Mn spins above the Mn TN strongly suppresses the resistivity, contrary to the conventional decrease of ρ that is only observed upon cooling below TN of an antiferromagnet.

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“…[16] In fact, the application of spin models in the study of dielectric and magnetic properties of materials has a long history. [17][18][19][20][21][22][23][24][25][26][27][28][29] One particularly interesting result, found by Luttinger and Tisza, [19] is that the ground state of a simple cubic lattice of dipoles in the absence of an external field is two-site periodic along all three lattice axes and has no net polarization. Belobrov et al [23] later showed that in three dimensions such a lattice has an infinitely degenerate ground state, as we shall explain in more detail below.…”

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Order in the ground state of a simple cubic dipole lattice in an external field

Carignano

Madjet

2019

Int J of Quantum Chemistry

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Motivated by the presence of a lattice of rotating molecular dipoles in the high temperature phase of methylammonium lead iodide, we investigate the ground state of a simple cubic lattice of dipoles interacting with each other via the dipole-dipole interaction and with an external field via the standard, linear dipole-field interaction. In the absence of an external field, the ground state is infinitely degenerate, and all the configurations in the ground state manifold are periodic along the three lattice axes with a period of two lattice sites. Using a 1000-dipole lattice as a unit cell in numerical simulations of an infinite simple cubic lattice, we determine the ground state dipole configurations in the presence of an external field. We then analyze the polarization, dipole orientation statistics and correlations in these configurations. Our calculations show that for some special directions of the external field the two-site periodicity in the dipole configurations is preserved, while in the general case this periodicity is lost and complex dipole configurations form under the influence of the external field. More specifically, for a general field direction, a sudden transition from two-site-periodic configurations to irregular configurations occurs at a finite value of the applied field strength.Spin models are ubiquitous in theoretical physics in the study of a variety of physical systems, and they can be used to understand a wide range of phenomena such as ordered states of matter, domain boundaries and phase transitions. [1] Recently, they have also served as natural models to investigate entanglement and related properties in the study of condensed matter systems from the viewpoint of quantum information. [2,3] In the field of light harvesting devices, the recently emerging hybrid organic-inorganic lead-halide perovskites have opened a novel application for spin models, because the organic component often has a net dipole moment. The most representative perovskite material in this area is methylammonium lead iodide (CH 3 NH 3 PbI 3 ), which in its high-temperature phase contains a simple cubic lattice of dipoles from the polar molecule CH 3 NH 3 that occupies the A site in the perovskite crystal structure. [4,5] Spin models have been used to explore the possible origin of hysteresis observed in solar cells, [6,7] to understand the dynamics of cation rotation [8] and to explain the enhancement of carrier conductivity at the interface between domains. [9] More recently, spin models have been used to explore the long-range order in perovskites [10] and the structure of the interface between domains with different ordering patterns across the interface. [11] Spin models apply more generally to other systems in nature, some examples being the ordering of the electric dipoles of water molecules in ice [12] and the dipolar ordering of small molecules trapped in regular cage structures. [13][14][15] Artificially fabricated magnetic superstructures can also

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Magnetic dipole interactions in crystals

Cited by 74 publications

References 61 publications

Anomalous Composition-Induced Crossover in the Magnetic Properties of the Itinerant-Electron AntiferromagnetCa1−xSrxCo2−yAs2
Sangeetha¹,
Smetana²,
Mudring³
et al. 2017
Phys. Rev. Lett.
21
3
54
0
View full text Add to dashboard Cite

Anomalous Composition-Induced Crossover in the Magnetic Properties of the Itinerant-Electron AntiferromagnetCa1−xSrxCo2−yAs2
Sangeetha¹,
Smetana²,
Mudring³
et al. 2017
Phys. Rev. Lett.
21
3
54
0
View full text Add to dashboard Cite

Metallic behavior induced by potassium doping of the trigonal antiferromagnetic insulatorEuMn2As2

Order in the ground state of a simple cubic dipole lattice in an external field

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Magnetic dipole interactions in crystals

Cited by 74 publications

References 61 publications

Anomalous Composition-Induced Crossover in the Magnetic Properties of the Itinerant-Electron AntiferromagnetCa1−xSrxCo2−yAs2Sangeetha1, Smetana2, Mudring3 et al. 2017Phys. Rev. Lett.213540View full textAdd to dashboardCite

Anomalous Composition-Induced Crossover in the Magnetic Properties of the Itinerant-Electron AntiferromagnetCa1−xSrxCo2−yAs2Sangeetha1, Smetana2, Mudring3 et al. 2017Phys. Rev. Lett.213540View full textAdd to dashboardCite

Metallic behavior induced by potassium doping of the trigonal antiferromagnetic insulatorEuMn2As2

Order in the ground state of a simple cubic dipole lattice in an external field

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Anomalous Composition-Induced Crossover in the Magnetic Properties of the Itinerant-Electron AntiferromagnetCa1−xSrxCo2−yAs2
Sangeetha¹,
Smetana²,
Mudring³
et al. 2017
Phys. Rev. Lett.
21
3
54
0
View full text Add to dashboard Cite

Anomalous Composition-Induced Crossover in the Magnetic Properties of the Itinerant-Electron AntiferromagnetCa1−xSrxCo2−yAs2
Sangeetha¹,
Smetana²,
Mudring³
et al. 2017
Phys. Rev. Lett.
21
3
54
0
View full text Add to dashboard Cite