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Magnetic properties of copper pyrazi...

Clark University.

Magnetic properties of copper pyrazine bridged quasi two dimensional quantum Heisenberg antiferromagnetic (QHAF) compounds.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Magnetic properties of copper pyrazine bridged quasi two dimensional quantum Heisenberg antiferromagnetic (QHAF) compounds.
作者:	Xiao, Fan.
面頁冊數:	88 p.
附註:	Source: Dissertation Abstracts International, Volume: 72-07, Section: B, page: .
附註:	Adviser: Christopher Landee.
Contained By:	Dissertation Abstracts International72-07B.
標題:	Physics, Quantum.
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3455151
ISBN:	9781124623689

Magnetic properties of copper pyrazine bridged quasi two dimensional quantum Heisenberg antiferromagnetic (QHAF) compounds.
Xiao, Fan.

Magnetic properties of copper pyrazine bridged quasi two dimensional quantum Heisenberg antiferromagnetic (QHAF) compounds. - 88 p.

Source: Dissertation Abstracts International, Volume: 72-07, Section: B, page: .

Thesis (Ph.D.)--Clark University, 2011.

The magnetic properties of a family of molecular-based quasi-two-dimensional S=1/2 Heisenberg antiferromagnets (2D QHAF) are studied. Three compounds, Cu(pz)2 (ClO4)2, Cu(pz)2(BF 4)2, and [Cu(pz)2(NO3)](PF6) contain similar planes of Cu2+ ions linked into magnetically square lattices by bridging pyrazine molecules (pz =C4H4N 2). The anions provide charge balance as well as isolation between the layers. Low field single crystal measurements of susceptibility and magnetization reveal low ratios of Neel temperatures to exchange strengths (4.25/17.5 = 0.243, 3.80/15.3 = 0.248, and 3.05/10.8 = 0.282, respectively) while the ratio of the anisotropy fields HA(kOe) to the saturation field HSAT(kOe) are small (2.6/490 = 5.3x10-3, 2.4/430 = 5.5x10-3, and 0.07/300 = 2.3x10-4, respectively), demonstrating close approximations to a two-dimensional Heisenberg model.

ISBN: 9781124623689Subjects--Topical Terms:

530960
Physics, Quantum.

Magnetic properties of copper pyrazine bridged quasi two dimensional quantum Heisenberg antiferromagnetic (QHAF) compounds.
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245 1 0 $a Magnetic properties of copper pyrazine bridged quasi two dimensional quantum Heisenberg antiferromagnetic (QHAF) compounds.
300 $a 88 p.
500 $a Source: Dissertation Abstracts International, Volume: 72-07, Section: B, page: .
500 $a Adviser: Christopher Landee.
502 $a Thesis (Ph.D.)--Clark University, 2011.
520 $a The magnetic properties of a family of molecular-based quasi-two-dimensional S=1/2 Heisenberg antiferromagnets (2D QHAF) are studied. Three compounds, Cu(pz)2 (ClO4)2, Cu(pz)2(BF 4)2, and [Cu(pz)2(NO3)](PF6) contain similar planes of Cu2+ ions linked into magnetically square lattices by bridging pyrazine molecules (pz =C4H4N 2). The anions provide charge balance as well as isolation between the layers. Low field single crystal measurements of susceptibility and magnetization reveal low ratios of Neel temperatures to exchange strengths (4.25/17.5 = 0.243, 3.80/15.3 = 0.248, and 3.05/10.8 = 0.282, respectively) while the ratio of the anisotropy fields HA(kOe) to the saturation field HSAT(kOe) are small (2.6/490 = 5.3x10-3, 2.4/430 = 5.5x10-3, and 0.07/300 = 2.3x10-4, respectively), demonstrating close approximations to a two-dimensional Heisenberg model.
520 $a The susceptibilities of Cu(pz)2(ClO4)2 and Cu(pz)2(BF4)2 show evidence of a spin crossover (Heisenberg to XY) at low temperatures; their zero-field ordering transitions are primarily driven by the XY behavior with the ultimate three-dimensional transition appearing parasitically. The [Cu(pz)2(NO 3)](PF6) compound remains Heisenberg-like at all temperatures, with its transition to the Neel state due to the inter- layer interactions.
520 $a High field single crystal measurements of Cu(pz)2(ClO 4)2 indicates that both spin crossover transition temperature and ordering temperature increase as the external field increases up to 5 T. The results suggests a field-induced XY anisotropy is produced by the external field and the ordering temperature vs field follows a Berezinskii-Kosterlitz-Thouless (BKT)-like transition trend predicted by quantum Monte Carlo simulation.
520 $a Calorimetry measurements were performed to verify the hypothesis with external fields up to 33 T. The results successfully confirmed our prediction. The transition temperature shows a rounded maximum at 16 T and starts dropping as the field gets stronger. The ordering temperature is raised by as much as 41% (6 K) at 16 T and drops down to around 4.5 K at 33 T.
520 $a These three compounds serve as very good examples of 2D QHAF for testing the theoretical predictions, and they have shown the unique magnetic behavior that only exists at extreme conditions, such as a spin Heisenberg to XY crossover and BKT-like transition.
590 $a School code: 0048.
650 4 $a Physics, Quantum. $3 530960
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