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首页> 外文期刊>Physical review >Magnetic and structural phase transitions of multiferroic boracites M_3B_7O_(13)X (M = 3d transition metal Cr-Zn or Mg; X = halogen Cl, Br, I)
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Magnetic and structural phase transitions of multiferroic boracites M_3B_7O_(13)X (M = 3d transition metal Cr-Zn or Mg; X = halogen Cl, Br, I)

机译：多铁硼铁矿M_3B_7O_（13）X的磁性和结构相变（M = 3d过渡金属Cr-Zn或Mg; X =卤素Cl，Br，I）

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摘要

The specific heat capacity of mostly single-crystalline samples of 21 boracite compounds M_3B_7O_(13)X with M a 3d transition metal (Cr, Mn, Fe, Co, Ni, Cu, Zn) or Mg and X a halogen (Cl, Br, I) is determined. In combination with magnetic susceptibility data the magnetic ordering of the M~(2+) ions at T_N is investigated in detail. The fully ferroelectric/fully ferroelastic structural phase transitions at higher temperatures are measured by differential scanning calorimetry. In the Cr-Br, Cr-I, Cu-Cl, and Cu-Br compounds, previously unknown magnetic phases were found. Magnetic order in the boracites is characterized by the quantum and classical spin states of the M~(2+) ions, a variable degree of structural distortion, orbital effects, and competing exchange interactions. The Cu-Cl, Cu-Br, and Ni-Cl boracites exhibit broad maxima of magnetic specific heat and of magnetic susceptibility above T_N caused by low-dimensional or frustrated magnetic interactions. Co boracites display additional broad anomalies below T_N originating from continuous spin reorientations and effective S=1/2 ground states. Indications for spin reorientations are also observed for Fe boracites. New phases appear in high magnetic fields for some Co and Fe boracites, which is not the case for the Mn compounds. Stronger magnetic frustration is deduced for the cubic Cr compounds. For the latter compounds and Ni-I boracite magnetostructural phase transitions are observed.
机译：21种硼铁矿化合物M_3B_7O_（13）X与M为3d过渡金属（Cr，Mn，Fe，Co，Ni，Cu，Zn）或Mg和X为卤素（Cl，Br的大多数单晶样品的比热容，I）已确定。结合磁化率数据，详细研究了T_N处M〜（2+）离子的磁有序性。通过差示扫描量热法测量较高温度下的全铁电/全铁弹性结构相变。在Cr-Br，Cr-I，Cu-Cl和Cu-Br化合物中，发现了以前未知的磁相。硼铁矿中的磁序以M〜（2+）离子的量子和经典自旋态，可变程度的结构畸变，轨道效应和竞争性交换相互作用为特征。 Cu-Cl，Cu-Br和Ni-Cl硼铁矿的磁比热和T_N以上的磁化率表现出宽泛的最大值，这是由低维或受阻的磁相互作用引起的。硼铁矿还显示出T_N以下的其他广泛异常，这是由于连续自旋再取向和有效的S = 1/2基态引起的。铁硼铁矿也观察到自旋取向的迹象。对于某些钴硼铁矿和铁硼铁矿，在高磁场中会出现新相，而锰化合物并非如此。可以推断出立方Cr化合物的抗磁性更强。对于后一种化合物，观察到Ni-I硼铁矿的磁结构相变。

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