Transition from a hysteresis-like to an exchange-bias-like response of an uncompensated antiferromagnet

Abstract

Highly Co-doped ZnO shows uncompensated antiferromagnetic order and a vertical exchange bias shift even in the absence of a ferromagnet. Therefore, it is an ideal model system to study the behavior of uncompensated antiferromagnetic moments, which play a crucial role in the description of conventional exchange bias. Temperature-and cooling-field-dependent magnetometry measurements provide further information on the compensated and uncompensated antiferromagnetic configurations in Co-doped ZnO, revealing that observed effects of both vertical exchange shift and open hysteresis stem from similar magnetic configurations. This transition is evidenced by the increase of the vertical exchange shift on the expense of the hysteresis opening by lowering the temperature.

Direct Imaging of the ac Component of Pumped Spin Polarization with Element Specificity

“…For better comparability all resulting magnetization values (M ) were further divided by the magnetization value recorded at T = 2 K and H = 5 T [M (2 K, 5 T)] for the respective sample. The M (H ) curve at 2 K exhibits for both samples the typical, narrowly opened and vertically shifted hysteresis that is indicative of uncompensated antiferromagnetism [20,26]. More importantly, for STXM-FMR measurements, which are conducted at room temperature only, the M (T) measurements recorded at 10 mT under field heated (FH), field cooled (FC), and zero field cooled (ZFC) conditions reveal that the magnetic order is restricted to below 25 K and no evidence of the formation of Co metallic clusters can be derived by SQUID magnetometry.…”

“…Single films of Py, 50% Co:ZnO, and heterostructures thereof are fabricated on c-plane sapphire substrates as well as SiN membranes on highly insulating Si substrates by using reactive magnetron sputtering at a process pressure of 4 × 10 −3 mbar in the same ultrahigh vacuum chamber with a base pressure of 2 × 10 −9 mbar. For the 50% Co:ZnO layer, a metallic composite target is used, an Ar:O 2 ratio of 10:1 standard cubic centimeters per minute (sccm) is used as a process gas, and the substrate temperature is kept at 294 • C, which are optimized growth conditions for 50% Co:ZnO [19,20]. Py with a typical thickness of 20 nm is fabricated at room temperature using 10 sccm of only Ar as a process gas.…”

Spin Wave Propagation through Antiferromagnet/Ferromagnet Interface

“…However, in some problems such as transmission of the spin current through a thin AFM insulator by means of evanescent AFM SWs, it has been recently assumed that the AFM could be partially noncompensated at the interface [41]. Moreover, it has been pointed out that the effective magnetic moment can be a complex arrangement of not fully compensated moments along compensated AFM structures [42]. Considering the compensated or noncompensated limiting cases significantly simplifies the description of underlying AFM physics, but does not cover the entire spectrum of the AFMs, and furthermore, requires perfectly flat AFM interfaces.…”

Direct imaging of the ac component of the pumped spin polarization with element specificity

“…Single films of Py, 50% Co:ZnO, and heterostructures thereof were fabricated on c-plane sapphire substrates as well as SiN-membranes using reactive magnetron sputtering (RMS) at a process pressure of 4 × 10 −3 mbar in the same ultrahigh vacuum chamber with a base pressure of 2 × 10 −9 mbar. For the 50% Co:ZnO layer a metallic composite target is used, an Ar:O 2 ratio of 10:1 standard cubic centimeters per minute (sccm) is used as process gas, and the substrate temperature is kept at 294 • C, which are optimized growth conditions for 50% Co:ZnO [14,15]. Py with a typical thickness of 20 nm is fabricated at room temperature using 10 sccm of only Ar as a process gas.…”

“…Figure 2(b) shows superconducting quantum interference device (SQUID) magnetometry measurements following a standard protocol, see [21]. The M (H) curve at 2 K exhibits for both samples the typical, narrowly opened and vertically shifted hysteresis which is indicative of uncompensated antiferromagnetism [15,21]. More important for the STXM-FMR measurements, which are conducted at room temperature only, the M (T ) measurements under field heated (FH), field cooled (FC), and zero field cooled (ZFC) conditions reveal that the magnetic order is restricted to below 25 K and no evidence of the formation of Co metallic clusters can be derived by SQUID.…”