Optimization of spontaneous exchange bias in Mn-rich Heusler alloys
Optimization of spontaneous exchange bias in Mn-rich Heusler alloys
复制标题
富锰霍斯勒合金自发交换偏压的优化
DOI：
10.1039/d1cp01797g
复制
发表时间：
2021
影响因子：
3.3
通讯作者：
Hu Yong
中科院分区：
文献类型：
--
作者：
Ma Yitian;Yang Yayi;Gao Yuan;Hu Yong
NiMn基Heusler合金在低温下可产生自发的（零场冷却）和传统的（场冷却）交换偏置效应，且交换偏置效应对合金元素和成分敏感，但其机制仍不清楚。因此，富Mn的Heusler合金的SEB铁磁和反铁磁交换相互作用共存的数值研究进行了修改的Monte Carlo模拟。本征磁晶各向异性（KAF），交换相互作用（JFM-AF和JAF-AF），和占领概率（xFM）直接调谐，以建立其依赖性的零场冷却/场冷却的热磁曲线和零场冷却的磁化磁滞回线。结果表明，凝固温度随KAF的增加而单调增加，随其它参数的增加而非单调变化，在5 K时，即使不存在自旋玻璃态，反铁磁成分的不可逆性也足以触发SEB. SEB与KAF、JFM-AF、JAF-AF和xFM是非单调的，其最大值将在KAF = 4.5 × 106 J m−3、JFM-AF = 5 meV、JAF-AF = −5 meV或xFM = 0.3时获得。相反，KAF和JFM-AF的相干度也是非单调的，而JAF-AF和xFM的相干度是单调的。SEB场的值比双折射率的值小近一个数量级，与实验数据一致。计算磁弛豫特性以提出两个因素，即，铁磁和反铁磁成分之间的铁磁状域和衰减速率，以确定最终的SEB。这项工作证明了机制，以优化SEB富锰Heusler合金，物理上所获得的结果也适用于其他材料系统的自发铁磁/反铁磁相分离。
At low temperature, spontaneous (zero-field-cooled, SEB) and traditional (field-cooled) exchange bias effects may be induced in a series of NiMn-based Heusler alloys, and the exchange bias is commonly sensitive to alloying elements and compositions, while the mechanisms especially for SEB are still elusive. Therefore, the SEB in Mn-rich Heusler alloys with coexistence of ferromagnetic and antiferromagnetic exchange interactions is numerically studied by performing a modified Monte Carlo simulation. The intrinsic magnetocrystalline anisotropies (KAF), exchange interactions (JFM–AF and JAF–AF), and occupation probabilities (xFM) are directly tuned to establish their dependencies of zero-field-cooled/field-cooled thermomagnetic curves and zero-field-cooled magnetization hysteresis loops. The results indicate that the freezing temperature is monotonically enhanced with increasing KAF and varies nonmonotonically with other parameters, and at 5 K, the irreversibility arising from antiferromagnetic components becomes high enough to trigger SEB even though no spin glass state exists. The SEB is nonmonotonic with KAF, JFM–AF, JAF–AF, and xFM, and its maximum value will be obtained at KAF = 4.5 × 106 J m−3, JFM–AF = 5 meV, JAF–AF = −5 meV, or xFM = 0.3. On the contrary, the coercivity is also nonmonotonic with KAF and JFM–AF while monotonic with JAF–AF and xFM. The values of the SEB field are nearly one order of magnitude smaller than those of coercivity, consistent with experimental data. The magnetic relaxation properties are calculated to propose two factors, i.e., ferromagnetic-like domain between ferromagnetic and antiferromagnetic components and decay rate, to determine the final SEB. This work demonstrates the mechanisms to optimize SEB in Mn-rich Heusler alloys, and physically the results obtained are also suitable for other material systems with spontaneous ferromagnet/antiferromagnet phase separations.